Merging upstream version 1.35.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

33 files changed, 2727 insertions, 699 deletions

diff --git a/database/KolmogorovSmirnovDist.c b/database/KolmogorovSmirnovDist.c
new file mode 100644
index 00000000..1486abc7
--- /dev/null
+++ b/database/KolmogorovSmirnovDist.c
@@ -0,0 +1,788 @@
+// SPDX-License-Identifier: GPL-3.0
+
+/********************************************************************
+ *
+ * File:          KolmogorovSmirnovDist.c
+ * Environment:   ISO C99 or ANSI C89
+ * Author:        Richard Simard
+ * Organization:  DIRO, Université de Montréal
+ * Date:          1 February 2012
+ * Version        1.1
+
+ * Copyright 1 march 2010 by Université de Montréal,
+                             Richard Simard and Pierre L'Ecuyer
+ =====================================================================
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, version 3 of the License.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+ =====================================================================*/
+
+#include "KolmogorovSmirnovDist.h"
+#include <math.h>
+#include <stdlib.h>
+
+#define num_Pi     3.14159265358979323846 /* PI */
+#define num_Ln2    0.69314718055994530941 /* log(2) */
+
+/* For x close to 0 or 1, we use the exact formulae of Ruben-Gambino in all
+   cases. For n <= NEXACT, we use exact algorithms: the Durbin matrix and
+   the Pomeranz algorithms. For n > NEXACT, we use asymptotic methods
+   except for x close to 0 where we still use the method of Durbin
+   for n <= NKOLMO. For n > NKOLMO, we use asymptotic methods only and
+   so the precision is less for x close to 0.
+   We could increase the limit NKOLMO to 10^6 to get better precision
+   for x close to 0, but at the price of a slower speed. */
+#define NEXACT 500
+#define NKOLMO 100000
+
+/* The Durbin matrix algorithm for the Kolmogorov-Smirnov distribution */
+static double DurbinMatrix (int n, double d);
+
+
+/*========================================================================*/
+#if 0
+
+/* For ANSI C89 only, not for ISO C99 */
+#define MAXI 50
+#define EPSILON 1.0e-15
+
+double log1p (double x)
+{
+   /* returns a value equivalent to log(1 + x) accurate also for small x. */
+   if (fabs (x) > 0.1) {
+      return log (1.0 + x);
+   } else {
+      double term = x;
+      double sum = x;
+      int s = 2;
+      while ((fabs (term) > EPSILON * fabs (sum)) && (s < MAXI)) {
+         term *= -x;
+         sum += term / s;
+         s++;
+      }
+      return sum;
+   }
+}
+
+#undef MAXI
+#undef EPSILON
+
+#endif
+
+/*========================================================================*/
+#define MFACT 30
+
+/* The natural logarithm of factorial n! for  0 <= n <= MFACT */
+static double LnFactorial[MFACT + 1] = {
+   0.,
+   0.,
+   0.6931471805599453,
+   1.791759469228055,
+   3.178053830347946,
+   4.787491742782046,
+   6.579251212010101,
+   8.525161361065415,
+   10.60460290274525,
+   12.80182748008147,
+   15.10441257307552,
+   17.50230784587389,
+   19.98721449566188,
+   22.55216385312342,
+   25.19122118273868,
+   27.89927138384088,
+   30.67186010608066,
+   33.50507345013688,
+   36.39544520803305,
+   39.33988418719949,
+   42.33561646075348,
+   45.3801388984769,
+   48.47118135183522,
+   51.60667556776437,
+   54.7847293981123,
+   58.00360522298051,
+   61.26170176100199,
+   64.55753862700632,
+   67.88974313718154,
+   71.257038967168,
+   74.65823634883016
+};
+
+/*------------------------------------------------------------------------*/
+
+static double getLogFactorial (int n)
+{
+   /* Returns the natural logarithm of factorial n! */
+   if (n <= MFACT) {
+      return LnFactorial[n];
+
+   } else {
+      double x = (double) (n + 1);
+      double y = 1.0 / (x * x);
+      double z = ((-(5.95238095238E-4 * y) + 7.936500793651E-4) * y -
+         2.7777777777778E-3) * y + 8.3333333333333E-2;
+      z = ((x - 0.5) * log (x) - x) + 9.1893853320467E-1 + z / x;
+      return z;
+   }
+}
+
+/*------------------------------------------------------------------------*/
+
+static double rapfac (int n)
+{
+   /* Computes n! / n^n */
+   int i;
+   double res = 1.0 / n;
+   for (i = 2; i <= n; i++) {
+      res *= (double) i / n;
+   }
+   return res;
+}
+
+
+/*========================================================================*/
+
+static double **CreateMatrixD (int N, int M)
+{
+   int i;
+   double **T2;
+
+   T2 = (double **) malloc (N * sizeof (double *));
+   T2[0] = (double *) malloc ((size_t) N * M * sizeof (double));
+   for (i = 1; i < N; i++)
+      T2[i] = T2[0] + i * M;
+   return T2;
+}
+
+
+static void DeleteMatrixD (double **T)
+{
+   free (T[0]);
+   free (T);
+}
+
+
+/*========================================================================*/
+
+static double KSPlusbarAsymp (int n, double x)
+{
+   /* Compute the probability of the KS+ distribution using an asymptotic
+      formula */
+   double t = (6.0 * n * x + 1);
+   double z = t * t / (18.0 * n);
+   double v = 1.0 - (2.0 * z * z - 4.0 * z - 1.0) / (18.0 * n);
+   if (v <= 0.0)
+      return 0.0;
+   v = v * exp (-z);
+   if (v >= 1.0)
+      return 1.0;
+   return v;
+}
+
+
+/*-------------------------------------------------------------------------*/
+
+static double KSPlusbarUpper (int n, double x)
+{
+   /* Compute the probability of the KS+ distribution in the upper tail using
+      Smirnov's stable formula */
+   const double EPSILON = 1.0E-12;
+   double q;
+   double Sum = 0.0;
+   double term;
+   double t;
+   double LogCom;
+   double LOGJMAX;
+   int j;
+   int jdiv;
+   int jmax = (int) (n * (1.0 - x));
+
+   if (n > 200000)
+      return KSPlusbarAsymp (n, x);
+
+   /* Avoid log(0) for j = jmax and q ~ 1.0 */
+   if ((1.0 - x - (double) jmax / n) <= 0.0)
+      jmax--;
+
+   if (n > 3000)
+      jdiv = 2;
+   else
+      jdiv = 3;
+
+   j = jmax / jdiv + 1;
+   LogCom = getLogFactorial (n) - getLogFactorial (j) -
+            getLogFactorial (n - j);
+   LOGJMAX = LogCom;
+
+   while (j <= jmax) {
+      q = (double) j / n + x;
+      term = LogCom + (j - 1) * log (q) + (n - j) * log1p (-q);
+      t = exp (term);
+      Sum += t;
+      LogCom += log ((double) (n - j) / (j + 1));
+      if (t <= Sum * EPSILON)
+         break;
+      j++;
+   }
+
+   j = jmax / jdiv;
+   LogCom = LOGJMAX + log ((double) (j + 1) / (n - j));
+
+   while (j > 0) {
+      q = (double) j / n + x;
+      term = LogCom + (j - 1) * log (q) + (n - j) * log1p (-q);
+      t = exp (term);
+      Sum += t;
+      LogCom += log ((double) j / (n - j + 1));
+      if (t <= Sum * EPSILON)
+         break;
+      j--;
+   }
+
+   Sum *= x;
+   /* add the term j = 0 */
+   Sum += exp (n * log1p (-x));
+   return Sum;
+}
+
+
+/*========================================================================*/
+
+static double Pelz (int n, double x)
+{
+   /* Approximating the Lower Tail-Areas of the Kolmogorov-Smirnov One-Sample
+      Statistic,
+      Wolfgang Pelz and I. J. Good,
+      Journal of the Royal Statistical Society, Series B.
+      Vol. 38, No. 2 (1976), pp. 152-156
+   */
+
+   const int JMAX = 20;
+   const double EPS = 1.0e-10;
+   const double C = 2.506628274631001;         /* sqrt(2*Pi) */
+   const double C2 = 1.2533141373155001;       /* sqrt(Pi/2) */
+   const double PI2 = num_Pi * num_Pi;
+   const double PI4 = PI2 * PI2;
+   const double RACN = sqrt ((double) n);
+   const double z = RACN * x;
+   const double z2 = z * z;
+   const double z4 = z2 * z2;
+   const double z6 = z4 * z2;
+   const double w = PI2 / (2.0 * z * z);
+   double ti, term, tom;
+   double sum;
+   int j;
+
+   term = 1;
+   j = 0;
+   sum = 0;
+   while (j <= JMAX && term > EPS * sum) {
+      ti = j + 0.5;
+      term = exp (-ti * ti * w);
+      sum += term;
+      j++;
+   }
+   sum *= C / z;
+
+   term = 1;
+   tom = 0;
+   j = 0;
+   while (j <= JMAX && fabs (term) > EPS * fabs (tom)) {
+      ti = j + 0.5;
+      term = (PI2 * ti * ti - z2) * exp (-ti * ti * w);
+      tom += term;
+      j++;
+   }
+   sum += tom * C2 / (RACN * 3.0 * z4);
+
+   term = 1;
+   tom = 0;
+   j = 0;
+   while (j <= JMAX && fabs (term) > EPS * fabs (tom)) {
+      ti = j + 0.5;
+      term = 6 * z6 + 2 * z4 + PI2 * (2 * z4 - 5 * z2) * ti * ti +
+         PI4 * (1 - 2 * z2) * ti * ti * ti * ti;
+      term *= exp (-ti * ti * w);
+      tom += term;
+      j++;
+   }
+   sum += tom * C2 / (n * 36.0 * z * z6);
+
+   term = 1;
+   tom = 0;
+   j = 1;
+   while (j <= JMAX && term > EPS * tom) {
+      ti = j;
+      term = PI2 * ti * ti * exp (-ti * ti * w);
+      tom += term;
+      j++;
+   }
+   sum -= tom * C2 / (n * 18.0 * z * z2);
+
+   term = 1;
+   tom = 0;
+   j = 0;
+   while (j <= JMAX && fabs (term) > EPS * fabs (tom)) {
+      ti = j + 0.5;
+      ti = ti * ti;
+      term = -30 * z6 - 90 * z6 * z2 + PI2 * (135 * z4 - 96 * z6) * ti +
+         PI4 * (212 * z4 - 60 * z2) * ti * ti + PI2 * PI4 * ti * ti * ti * (5 -
+         30 * z2);
+      term *= exp (-ti * w);
+      tom += term;
+      j++;
+   }
+   sum += tom * C2 / (RACN * n * 3240.0 * z4 * z6);
+
+   term = 1;
+   tom = 0;
+   j = 1;
+   while (j <= JMAX && fabs (term) > EPS * fabs (tom)) {
+      ti = j * j;
+      term = (3 * PI2 * ti * z2 - PI4 * ti * ti) * exp (-ti * w);
+      tom += term;
+      j++;
+   }
+   sum += tom * C2 / (RACN * n * 108.0 * z6);
+
+   return sum;
+}
+
+
+/*=========================================================================*/
+
+static void CalcFloorCeil (
+   int n,                         /* sample size */
+   double t,                      /* = nx */
+   double *A,                     /* A_i */
+   double *Atflo,                 /* floor (A_i - t) */
+   double *Atcei                  /* ceiling (A_i + t) */
+   )
+{
+   /* Precompute A_i, floors, and ceilings for limits of sums in the Pomeranz
+      algorithm */
+   int i;
+   int ell = (int) t;             /* floor (t) */
+   double z = t - ell;            /* t - floor (t) */
+   double w = ceil (t) - t;
+
+   if (z > 0.5) {
+      for (i = 2; i <= 2 * n + 2; i += 2)
+         Atflo[i] = i / 2 - 2 - ell;
+      for (i = 1; i <= 2 * n + 2; i += 2)
+         Atflo[i] = i / 2 - 1 - ell;
+
+      for (i = 2; i <= 2 * n + 2; i += 2)
+         Atcei[i] = i / 2 + ell;
+      for (i = 1; i <= 2 * n + 2; i += 2)
+         Atcei[i] = i / 2 + 1 + ell;
+
+   } else if (z > 0.0) {
+      for (i = 1; i <= 2 * n + 2; i++)
+         Atflo[i] = i / 2 - 1 - ell;
+
+      for (i = 2; i <= 2 * n + 2; i++)
+         Atcei[i] = i / 2 + ell;
+      Atcei[1] = 1 + ell;
+
+   } else {                       /* z == 0 */
+      for (i = 2; i <= 2 * n + 2; i += 2)
+         Atflo[i] = i / 2 - 1 - ell;
+      for (i = 1; i <= 2 * n + 2; i += 2)
+         Atflo[i] = i / 2 - ell;
+
+      for (i = 2; i <= 2 * n + 2; i += 2)
+         Atcei[i] = i / 2 - 1 + ell;
+      for (i = 1; i <= 2 * n + 2; i += 2)
+         Atcei[i] = i / 2 + ell;
+   }
+
+   if (w < z)
+      z = w;
+   A[0] = A[1] = 0;
+   A[2] = z;
+   A[3] = 1 - A[2];
+   for (i = 4; i <= 2 * n + 1; i++)
+      A[i] = A[i - 2] + 1;
+   A[2 * n + 2] = n;
+}
+
+
+/*========================================================================*/
+
+static double Pomeranz (int n, double x)
+{
+   /* The Pomeranz algorithm to compute the KS distribution */
+   const double EPS = 1.0e-15;
+   const int ENO = 350;
+   const double RENO = ldexp (1.0, ENO); /* for renormalization of V */
+   int coreno;                    /* counter: how many renormalizations */
+   const double t = n * x;
+   double w, sum, minsum;
+   int i, j, k, s;
+   int r1, r2;                    /* Indices i and i-1 for V[i][] */
+   int jlow, jup, klow, kup, kup0;
+   double *A;
+   double *Atflo;
+   double *Atcei;
+   double **V;
+   double **H;                    /* = pow(w, j) / Factorial(j) */
+
+   A = (double *) calloc ((size_t) (2 * n + 3), sizeof (double));
+   Atflo = (double *) calloc ((size_t) (2 * n + 3), sizeof (double));
+   Atcei = (double *) calloc ((size_t) (2 * n + 3), sizeof (double));
+   V = (double **) CreateMatrixD (2, n + 2);
+   H = (double **) CreateMatrixD (4, n + 2);
+
+   CalcFloorCeil (n, t, A, Atflo, Atcei);
+
+   for (j = 1; j <= n + 1; j++)
+      V[0][j] = 0;
+   for (j = 2; j <= n + 1; j++)
+      V[1][j] = 0;
+   V[1][1] = RENO;
+   coreno = 1;
+
+   /* Precompute H[][] = (A[j] - A[j-1]^k / k! for speed */
+   H[0][0] = 1;
+   w = 2.0 * A[2] / n;
+   for (j = 1; j <= n + 1; j++)
+      H[0][j] = w * H[0][j - 1] / j;
+
+   H[1][0] = 1;
+   w = (1.0 - 2.0 * A[2]) / n;
+   for (j = 1; j <= n + 1; j++)
+      H[1][j] = w * H[1][j - 1] / j;
+
+   H[2][0] = 1;
+   w = A[2] / n;
+   for (j = 1; j <= n + 1; j++)
+      H[2][j] = w * H[2][j - 1] / j;
+
+   H[3][0] = 1;
+   for (j = 1; j <= n + 1; j++)
+      H[3][j] = 0;
+
+   r1 = 0;
+   r2 = 1;
+   for (i = 2; i <= 2 * n + 2; i++) {
+      jlow = 2 + (int) Atflo[i];
+      if (jlow < 1)
+         jlow = 1;
+      jup = (int) Atcei[i];
+      if (jup > n + 1)
+         jup = n + 1;
+
+      klow = 2 + (int) Atflo[i - 1];
+      if (klow < 1)
+         klow = 1;
+      kup0 = (int) Atcei[i - 1];
+
+      /* Find to which case it corresponds */
+      w = (A[i] - A[i - 1]) / n;
+      s = -1;
+      for (j = 0; j < 4; j++) {
+         if (fabs (w - H[j][1]) <= EPS) {
+            s = j;
+            break;
+         }
+      }
+      /* assert (s >= 0, "Pomeranz: s < 0"); */
+
+      minsum = RENO;
+      r1 = (r1 + 1) & 1;          /* i - 1 */
+      r2 = (r2 + 1) & 1;          /* i */
+
+      for (j = jlow; j <= jup; j++) {
+         kup = kup0;
+         if (kup > j)
+            kup = j;
+         sum = 0;
+         for (k = kup; k >= klow; k--)
+            sum += V[r1][k] * H[s][j - k];
+         V[r2][j] = sum;
+         if (sum < minsum)
+            minsum = sum;
+      }
+
+      if (minsum < 1.0e-280) {
+         /* V is too small: renormalize to avoid underflow of probabilities */
+         for (j = jlow; j <= jup; j++)
+            V[r2][j] *= RENO;
+         coreno++;                /* keep track of log of RENO */
+      }
+   }
+
+   sum = V[r2][n + 1];
+   free (A);
+   free (Atflo);
+   free (Atcei);
+   DeleteMatrixD (H);
+   DeleteMatrixD (V);
+   w = getLogFactorial (n) - coreno * ENO * num_Ln2 + log (sum);
+   if (w >= 0.)
+      return 1.;
+   return exp (w);
+}
+
+
+/*========================================================================*/
+
+static double cdfSpecial (int n, double x)
+{
+   /* The KS distribution is known exactly for these cases */
+
+   /* For nx^2 > 18, KSfbar(n, x) is smaller than 5e-16 */
+   if ((n * x * x >= 18.0) || (x >= 1.0))
+      return 1.0;
+
+   if (x <= 0.5 / n)
+      return 0.0;
+
+   if (n == 1)
+      return 2.0 * x - 1.0;
+
+   if (x <= 1.0 / n) {
+      double t = 2.0 * x * n - 1.0;
+      double w;
+      if (n <= NEXACT) {
+         w = rapfac (n);
+         return w * pow (t, (double) n);
+      }
+      w = getLogFactorial (n) + n * log (t / n);
+      return exp (w);
+   }
+
+   if (x >= 1.0 - 1.0 / n) {
+      return 1.0 - 2.0 * pow (1.0 - x, (double) n);
+   }
+
+   return -1.0;
+}
+
+
+/*========================================================================*/
+
+double KScdf (int n, double x)
+{
+   const double w = n * x * x;
+   double u = cdfSpecial (n, x);
+   if (u >= 0.0)
+      return u;
+
+   if (n <= NEXACT) {
+      if (w < 0.754693)
+         return DurbinMatrix (n, x);
+      if (w < 4.0)
+         return Pomeranz (n, x);
+      return 1.0 - KSfbar (n, x);
+   }
+
+   if ((w * x * n <= 7.0) && (n <= NKOLMO))
+      return DurbinMatrix (n, x);
+
+   return Pelz (n, x);
+}
+
+
+/*=========================================================================*/
+
+static double fbarSpecial (int n, double x)
+{
+   const double w = n * x * x;
+
+   if ((w >= 370.0) || (x >= 1.0))
+      return 0.0;
+   if ((w <= 0.0274) || (x <= 0.5 / n))
+      return 1.0;
+   if (n == 1)
+      return 2.0 - 2.0 * x;
+
+   if (x <= 1.0 / n) {
+      double z;
+      double t = 2.0 * x * n - 1.0;
+      if (n <= NEXACT) {
+         z = rapfac (n);
+         return 1.0 - z * pow (t, (double) n);
+      }
+      z = getLogFactorial (n) + n * log (t / n);
+      return 1.0 - exp (z);
+   }
+
+   if (x >= 1.0 - 1.0 / n) {
+      return 2.0 * pow (1.0 - x, (double) n);
+   }
+   return -1.0;
+}
+
+
+/*========================================================================*/
+
+double KSfbar (int n, double x)
+{
+   const double w = n * x * x;
+   double v = fbarSpecial (n, x);
+   if (v >= 0.0)
+      return v;
+
+   if (n <= NEXACT) {
+      if (w < 4.0)
+         return 1.0 - KScdf (n, x);
+      else
+         return 2.0 * KSPlusbarUpper (n, x);
+   }
+
+   if (w >= 2.65)
+      return 2.0 * KSPlusbarUpper (n, x);
+
+   return 1.0 - KScdf (n, x);
+}
+
+
+/*=========================================================================
+
+The following implements the Durbin matrix algorithm and was programmed by
+G. Marsaglia, Wai Wan Tsang and Jingbo Wong.
+
+I have made small modifications in their program. (Richard Simard)
+
+
+
+=========================================================================*/
+
+/*
+ The C program to compute Kolmogorov's distribution
+
+             K(n,d) = Prob(D_n < d),         where
+
+      D_n = max(x_1-0/n,x_2-1/n...,x_n-(n-1)/n,1/n-x_1,2/n-x_2,...,n/n-x_n)
+
+    with  x_1<x_2,...<x_n  a purported set of n independent uniform [0,1)
+    random variables sorted into increasing order.
+    See G. Marsaglia, Wai Wan Tsang and Jingbo Wong,
+       J.Stat.Software, 8, 18, pp 1--4, (2003).
+*/
+
+#define NORM 1.0e140
+#define INORM 1.0e-140
+#define LOGNORM 140
+
+
+/* Matrix product */
+static void mMultiply (double *A, double *B, double *C, int m);
+
+/* Matrix power */
+static void mPower (double *A, int eA, double *V, int *eV, int m, int n);
+
+
+static double DurbinMatrix (int n, double d)
+{
+   int k, m, i, j, g, eH, eQ;
+   double h, s, *H, *Q;
+   /* OMIT NEXT TWO LINES IF YOU REQUIRE >7 DIGIT ACCURACY IN THE RIGHT TAIL */
+#if 0
+   s = d * d * n;
+   if (s > 7.24 || (s > 3.76 && n > 99))
+      return 1 - 2 * exp (-(2.000071 + .331 / sqrt (n) + 1.409 / n) * s);
+#endif
+   k = (int) (n * d) + 1;
+   m = 2 * k - 1;
+   h = k - n * d;
+   H = (double *) malloc ((m * m) * sizeof (double));
+   Q = (double *) malloc ((m * m) * sizeof (double));
+   for (i = 0; i < m; i++)
+      for (j = 0; j < m; j++)
+         if (i - j + 1 < 0)
+            H[i * m + j] = 0;
+         else
+            H[i * m + j] = 1;
+   for (i = 0; i < m; i++) {
+      H[i * m] -= pow (h, (double) (i + 1));
+      H[(m - 1) * m + i] -= pow (h, (double) (m - i));
+   }
+   H[(m - 1) * m] += (2 * h - 1 > 0 ? pow (2 * h - 1, (double) m) : 0);
+   for (i = 0; i < m; i++)
+      for (j = 0; j < m; j++)
+         if (i - j + 1 > 0)
+            for (g = 1; g <= i - j + 1; g++)
+               H[i * m + j] /= g;
+   eH = 0;
+   mPower (H, eH, Q, &eQ, m, n);
+   s = Q[(k - 1) * m + k - 1];
+
+   for (i = 1; i <= n; i++) {
+      s = s * (double) i / n;
+      if (s < INORM) {
+         s *= NORM;
+         eQ -= LOGNORM;
+      }
+   }
+   s *= pow (10., (double) eQ);
+   free (H);
+   free (Q);
+   return s;
+}
+
+
+static void mMultiply (double *A, double *B, double *C, int m)
+{
+   int i, j, k;
+   double s;
+   for (i = 0; i < m; i++)
+      for (j = 0; j < m; j++) {
+         s = 0.;
+         for (k = 0; k < m; k++)
+            s += A[i * m + k] * B[k * m + j];
+         C[i * m + j] = s;
+      }
+}
+
+
+static void renormalize (double *V, int m, int *p)
+{
+   int i;
+   for (i = 0; i < m * m; i++)
+      V[i] *= INORM;
+   *p += LOGNORM;
+}
+
+
+static void mPower (double *A, int eA, double *V, int *eV, int m, int n)
+{
+   double *B;
+   int eB, i;
+   if (n == 1) {
+      for (i = 0; i < m * m; i++)
+         V[i] = A[i];
+      *eV = eA;
+      return;
+   }
+   mPower (A, eA, V, eV, m, n / 2);
+   B = (double *) malloc ((m * m) * sizeof (double));
+   mMultiply (V, V, B, m);
+   eB = 2 * (*eV);
+   if (B[(m / 2) * m + (m / 2)] > NORM)
+      renormalize (B, m, &eB);
+
+   if (n % 2 == 0) {
+      for (i = 0; i < m * m; i++)
+         V[i] = B[i];
+      *eV = eB;
+   } else {
+      mMultiply (A, B, V, m);
+      *eV = eA + eB;
+   }
+
+   if (V[(m / 2) * m + (m / 2)] > NORM)
+      renormalize (V, m, eV);
+   free (B);
+}
diff --git a/database/KolmogorovSmirnovDist.h b/database/KolmogorovSmirnovDist.h
new file mode 100644
index 00000000..cf455042
--- /dev/null
+++ b/database/KolmogorovSmirnovDist.h
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-3.0
+
+#ifndef KOLMOGOROVSMIRNOVDIST_H
+#define KOLMOGOROVSMIRNOVDIST_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/********************************************************************
+ *
+ * File:          KolmogorovSmirnovDist.h
+ * Environment:   ISO C99 or ANSI C89
+ * Author:        Richard Simard
+ * Organization:  DIRO, Université de Montréal
+ * Date:          1 February 2012
+ * Version        1.1
+ *
+ * Copyright March 2010 by Université de Montréal,
+                           Richard Simard and Pierre L'Ecuyer
+ =====================================================================
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, version 3 of the License.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+ =====================================================================*/
+/*
+ *
+ * The Kolmogorov-Smirnov test statistic D_n is defined by
+ *
+ *        D_n = sup_x |F(x) - S_n(x)|
+ *
+ * where n is the sample size, F(x) is a completely specified theoretical
+ * distribution, and S_n(x) is an empirical distribution function.
+ *
+ *
+ * The function
+ *
+ *        double KScdf (int n, double x);
+ *
+ * computes the cumulative probability P[D_n <= x] of the 2-sided 1-sample
+ * Kolmogorov-Smirnov distribution with sample size n at x.
+ * It returns at least 13 decimal digits of precision for n <= 500,
+ * at least 7 decimal digits of precision for 500 < n <= 100000,
+ * and a few correct decimal digits for n > 100000.
+ *
+ */
+
+double KScdf (int n, double x);
+
+
+/*
+ * The function
+ *
+ *        double KSfbar (int n, double x);
+ *
+ * computes the complementary cumulative probability P[D_n >= x] of the
+ * 2-sided 1-sample Kolmogorov-Smirnov distribution with sample size n at x.
+ * It returns at least 10 decimal digits of precision for n <= 500,
+ * at least 6 decimal digits of precision for 500 < n <= 200000,
+ * and a few correct decimal digits for n > 200000.
+ *
+ */
+
+double KSfbar (int n, double x);
+
+
+/*
+ * NOTE:
+ * The ISO C99 function log1p of the standard math library does not exist in
+ * ANSI C89. Here, it is programmed explicitly in KolmogorovSmirnovDist.c.
+
+ * For ANSI C89 compilers, change the preprocessor condition to make it
+ * available.
+ */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/database/engine/journalfile.c b/database/engine/journalfile.c
index 1541eb10..0b3d3eeb 100644
--- a/database/engine/journalfile.c
+++ b/database/engine/journalfile.c
@@ -84,6 +84,7 @@ void * wal_get_transaction_buffer(struct rrdengine_worker_config* wc, unsigned s
         if (unlikely(ret)) {
             fatal("posix_memalign:%s", strerror(ret));
         }
+        memset(ctx->commit_log.buf, 0, buf_size);
         buf_pos = ctx->commit_log.buf_pos = 0;
         ctx->commit_log.buf_size =  buf_size;
     }
diff --git a/database/engine/metadata_log/logfile.c b/database/engine/metadata_log/logfile.c
index f5bd9b2d..07eb9b6f 100644
--- a/database/engine/metadata_log/logfile.c
+++ b/database/engine/metadata_log/logfile.c
@@ -375,19 +375,15 @@ static int scan_metalog_files(struct metalog_instance *ctx)
     struct metalog_pluginsd_state metalog_parser_state;
     metalog_pluginsd_state_init(&metalog_parser_state, ctx);
 
-    PARSER_USER_OBJECT metalog_parser_object;
-    metalog_parser_object.enabled = cd.enabled;
-    metalog_parser_object.host = ctx->rrdeng_ctx->host;
-    metalog_parser_object.cd = &cd;
-    metalog_parser_object.trust_durations = 0;
-    metalog_parser_object.private = &metalog_parser_state;
+    PARSER_USER_OBJECT metalog_parser_object = {
+        .enabled = cd.enabled,
+        .host = ctx->rrdeng_ctx->host,
+        .cd = &cd,
+        .trust_durations = 0,
+        .private = &metalog_parser_state
+    };
 
     PARSER *parser = parser_init(metalog_parser_object.host, &metalog_parser_object, NULL, PARSER_INPUT_SPLIT);
-    if (unlikely(!parser)) {
-        error("Failed to initialize metadata log parser.");
-        failed_to_load = matched_files;
-        goto after_failed_to_parse;
-    }
     parser_add_keyword(parser, PLUGINSD_KEYWORD_HOST, metalog_pluginsd_host);
     parser_add_keyword(parser, PLUGINSD_KEYWORD_GUID, pluginsd_guid);
     parser_add_keyword(parser, PLUGINSD_KEYWORD_CONTEXT, pluginsd_context);
@@ -428,10 +424,8 @@ static int scan_metalog_files(struct metalog_instance *ctx)
     size_t count __maybe_unused = metalog_parser_object.count;
 
     debug(D_METADATALOG, "Parsing count=%u", (unsigned)count);
-after_failed_to_parse:
 
     freez(metalogfiles);
-
     return matched_files;
 }
 
diff --git a/database/engine/pagecache.c b/database/engine/pagecache.c
index 40e24b32..cddbf9e1 100644
--- a/database/engine/pagecache.c
+++ b/database/engine/pagecache.c
@@ -356,7 +356,7 @@ static void pg_cache_evict_unsafe(struct rrdengine_instance *ctx, struct rrdeng_
 {
     struct page_cache_descr *pg_cache_descr = descr->pg_cache_descr;
 
-    freez(pg_cache_descr->page);
+    dbengine_page_free(pg_cache_descr->page);
     pg_cache_descr->page = NULL;
     pg_cache_descr->flags &= ~RRD_PAGE_POPULATED;
     pg_cache_release_pages_unsafe(ctx, 1);
@@ -437,7 +437,6 @@ uint8_t pg_cache_punch_hole(struct rrdengine_instance *ctx, struct rrdeng_page_d
     ret = JudyLDel(&page_index->JudyL_array, (Word_t)(descr->start_time / USEC_PER_SEC), PJE0);
     if (unlikely(0 == ret)) {
         uv_rwlock_wrunlock(&page_index->lock);
-        error("Page under deletion was not in index.");
         if (unlikely(debug_flags & D_RRDENGINE)) {
             print_page_descr(descr);
         }
@@ -1067,10 +1066,13 @@ pg_cache_lookup_next(struct rrdengine_instance *ctx, struct pg_cache_page_index
 
     page_not_in_cache = 0;
     uv_rwlock_rdlock(&page_index->lock);
+    int retry_count = 0;
     while (1) {
         descr = find_first_page_in_time_range(page_index, start_time, end_time);
-        if (NULL == descr || 0 == descr->page_length) {
+        if (NULL == descr || 0 == descr->page_length || retry_count == MAX_PAGE_CACHE_RETRY_WAIT) {
             /* non-empty page not found */
+            if (retry_count == MAX_PAGE_CACHE_RETRY_WAIT)
+                error_report("Page cache timeout while waiting for page %p : returning FAIL", descr);
             uv_rwlock_rdunlock(&page_index->lock);
 
             pg_cache_release_pages(ctx, 1);
@@ -1114,7 +1116,11 @@ pg_cache_lookup_next(struct rrdengine_instance *ctx, struct pg_cache_page_index
             print_page_cache_descr(descr);
         if (!(flags & RRD_PAGE_POPULATED))
             page_not_in_cache = 1;
-        pg_cache_wait_event_unsafe(descr);
+
+        if (pg_cache_timedwait_event_unsafe(descr, 1) == UV_ETIMEDOUT) {
+            error_report("Page cache timeout while waiting for page %p : retry count = %d", descr, retry_count);
+            ++retry_count;
+        }
         rrdeng_page_descr_mutex_unlock(ctx, descr);
 
         /* reset scan to find again */
@@ -1222,7 +1228,7 @@ void free_page_cache(struct rrdengine_instance *ctx)
                 /* Check rrdenglocking.c */
                 pg_cache_descr = descr->pg_cache_descr;
                 if (pg_cache_descr->flags & RRD_PAGE_POPULATED) {
-                    freez(pg_cache_descr->page);
+                    dbengine_page_free(pg_cache_descr->page);
                     bytes_freed += RRDENG_BLOCK_SIZE;
                 }
                 rrdeng_destroy_pg_cache_descr(ctx, pg_cache_descr);
diff --git a/database/engine/pagecache.h b/database/engine/pagecache.h
index d5350ef5..0ba4639c 100644
--- a/database/engine/pagecache.h
+++ b/database/engine/pagecache.h
@@ -11,6 +11,7 @@ struct extent_info;
 struct rrdeng_page_descr;
 
 #define INVALID_TIME (0)
+#define MAX_PAGE_CACHE_RETRY_WAIT (3)
 
 /* Page flags */
 #define RRD_PAGE_DIRTY          (1LU << 0)
diff --git a/database/engine/rrdengine.c b/database/engine/rrdengine.c
index a975cfa6..9f43f445 100644
--- a/database/engine/rrdengine.c
+++ b/database/engine/rrdengine.c
@@ -11,8 +11,24 @@ rrdeng_stats_t global_flushing_pressure_page_deletions = 0;
 
 static unsigned pages_per_extent = MAX_PAGES_PER_EXTENT;
 
+#if WORKER_UTILIZATION_MAX_JOB_TYPES < (RRDENG_MAX_OPCODE + 2)
+#error Please increase WORKER_UTILIZATION_MAX_JOB_TYPES to at least (RRDENG_MAX_OPCODE + 2)
+#endif
+
+void *dbengine_page_alloc() {
+    void *page = netdata_mmap(NULL, RRDENG_BLOCK_SIZE, MAP_PRIVATE, enable_ksm);
+    if(!page) fatal("Cannot allocate dbengine page cache page, with mmap()");
+    return page;
+}
+
+void dbengine_page_free(void *page) {
+    munmap(page, RRDENG_BLOCK_SIZE);
+}
+
 static void sanity_check(void)
 {
+    BUILD_BUG_ON(WORKER_UTILIZATION_MAX_JOB_TYPES < (RRDENG_MAX_OPCODE + 2));
+
     /* Magic numbers must fit in the super-blocks */
     BUILD_BUG_ON(strlen(RRDENG_DF_MAGIC) > RRDENG_MAGIC_SZ);
     BUILD_BUG_ON(strlen(RRDENG_JF_MAGIC) > RRDENG_MAGIC_SZ);
@@ -176,7 +192,7 @@ void read_cached_extent_cb(struct rrdengine_worker_config* wc, unsigned idx, str
     struct extent_info *extent = xt_io_descr->descr_array[0]->extent;
 
     for (i = 0 ; i < xt_io_descr->descr_count; ++i) {
-        page = mallocz(RRDENG_BLOCK_SIZE);
+        page = dbengine_page_alloc();
         descr = xt_io_descr->descr_array[i];
         for (j = 0, page_offset = 0 ; j < extent->number_of_pages ; ++j) {
             /* care, we don't hold the descriptor mutex */
@@ -331,7 +347,7 @@ after_crc_check:
                 continue; /* Failed to reserve a suitable page */
             is_prefetched_page = 1;
         }
-        page = mallocz(RRDENG_BLOCK_SIZE);
+        page = dbengine_page_alloc();
 
         /* care, we don't hold the descriptor mutex */
         if (have_read_error) {
@@ -735,6 +751,7 @@ static int do_flush_pages(struct rrdengine_worker_config* wc, int force, struct
         fatal("posix_memalign:%s", strerror(ret));
         /* freez(xt_io_descr);*/
     }
+    memset(xt_io_descr->buf, 0, ALIGN_BYTES_CEILING(size_bytes));
     (void) memcpy(xt_io_descr->descr_array, eligible_pages, sizeof(struct rrdeng_page_descr *) * count);
     xt_io_descr->descr_count = count;
 
@@ -1074,13 +1091,17 @@ void async_cb(uv_async_t *handle)
 
 void timer_cb(uv_timer_t* handle)
 {
+    worker_is_busy(RRDENG_MAX_OPCODE + 1);
+
     struct rrdengine_worker_config* wc = handle->data;
     struct rrdengine_instance *ctx = wc->ctx;
 
     uv_stop(handle->loop);
     uv_update_time(handle->loop);
-    if (unlikely(!ctx->metalog_ctx->initialized))
+    if (unlikely(!ctx->metalog_ctx->initialized)) {
+        worker_is_idle();
         return; /* Wait for the metadata log to initialize */
+    }
     rrdeng_test_quota(wc);
     debug(D_RRDENGINE, "%s: timeout reached.", __func__);
     if (likely(!wc->now_deleting_files && !wc->now_invalidating_dirty_pages)) {
@@ -1122,12 +1143,26 @@ void timer_cb(uv_timer_t* handle)
         debug(D_RRDENGINE, "%s", get_rrdeng_statistics(wc->ctx, buf, sizeof(buf)));
     }
 #endif
+
+    worker_is_idle();
 }
 
 #define MAX_CMD_BATCH_SIZE (256)
 
 void rrdeng_worker(void* arg)
 {
+    worker_register("DBENGINE");
+    worker_register_job_name(RRDENG_NOOP,                          "noop");
+    worker_register_job_name(RRDENG_READ_PAGE,                     "page read");
+    worker_register_job_name(RRDENG_READ_EXTENT,                   "extent read");
+    worker_register_job_name(RRDENG_COMMIT_PAGE,                   "commit");
+    worker_register_job_name(RRDENG_FLUSH_PAGES,                   "flush");
+    worker_register_job_name(RRDENG_SHUTDOWN,                      "shutdown");
+    worker_register_job_name(RRDENG_INVALIDATE_OLDEST_MEMORY_PAGE, "page lru");
+    worker_register_job_name(RRDENG_QUIESCE,                       "quiesce");
+    worker_register_job_name(RRDENG_MAX_OPCODE,                    "cleanup");
+    worker_register_job_name(RRDENG_MAX_OPCODE + 1,                "timer");
+
     struct rrdengine_worker_config* wc = arg;
     struct rrdengine_instance *ctx = wc->ctx;
     uv_loop_t* loop;
@@ -1175,8 +1210,11 @@ void rrdeng_worker(void* arg)
 
     fatal_assert(0 == uv_timer_start(&timer_req, timer_cb, TIMER_PERIOD_MS, TIMER_PERIOD_MS));
     shutdown = 0;
+    int set_name = 0;
     while (likely(shutdown == 0 || rrdeng_threads_alive(wc))) {
+        worker_is_idle();
         uv_run(loop, UV_RUN_DEFAULT);
+        worker_is_busy(RRDENG_MAX_OPCODE);
         rrdeng_cleanup_finished_threads(wc);
 
         /* wait for commands */
@@ -1193,6 +1231,9 @@ void rrdeng_worker(void* arg)
             opcode = cmd.opcode;
             ++cmd_batch_size;
 
+            if(likely(opcode != RRDENG_NOOP))
+                worker_is_busy(opcode);
+
             switch (opcode) {
             case RRDENG_NOOP:
                 /* the command queue was empty, do nothing */
@@ -1219,6 +1260,10 @@ void rrdeng_worker(void* arg)
                 break;
             case RRDENG_READ_EXTENT:
                 do_read_extent(wc, cmd.read_extent.page_cache_descr, cmd.read_extent.page_count, 1);
+                if (unlikely(!set_name)) {
+                    set_name = 1;
+                    uv_thread_set_name_np(ctx->worker_config.thread, "DBENGINE");
+                }
                 break;
             case RRDENG_COMMIT_PAGE:
                 do_commit_transaction(wc, STORE_DATA, NULL);
@@ -1265,6 +1310,7 @@ void rrdeng_worker(void* arg)
     fatal_assert(0 == uv_loop_close(loop));
     freez(loop);
 
+    worker_unregister();
     return;
 
 error_after_timer_init:
@@ -1277,6 +1323,7 @@ error_after_loop_init:
     wc->error = UV_EAGAIN;
     /* wake up initialization thread */
     completion_mark_complete(&ctx->rrdengine_completion);
+    worker_unregister();
 }
 
 /* C entry point for development purposes
diff --git a/database/engine/rrdengine.h b/database/engine/rrdengine.h
index b0c8e4d0..c6f89a37 100644
--- a/database/engine/rrdengine.h
+++ b/database/engine/rrdengine.h
@@ -34,6 +34,28 @@ struct rrdengine_instance;
 #define RRDENG_FILE_NUMBER_SCAN_TMPL "%1u-%10u"
 #define RRDENG_FILE_NUMBER_PRINT_TMPL "%1.1u-%10.10u"
 
+struct rrdeng_collect_handle {
+    struct rrdeng_page_descr *descr, *prev_descr;
+    unsigned long page_correlation_id;
+    struct rrdengine_instance *ctx;
+    // set to 1 when this dimension is not page aligned with the other dimensions in the chart
+    uint8_t unaligned_page;
+};
+
+struct rrdeng_query_handle {
+    struct rrdeng_page_descr *descr;
+    struct rrdengine_instance *ctx;
+    struct pg_cache_page_index *page_index;
+    time_t next_page_time;
+    time_t now;
+    unsigned position;
+    unsigned entries;
+    storage_number *page;
+    usec_t page_end_time;
+    uint32_t page_length;
+    usec_t dt;
+    time_t dt_sec;
+};
 
 typedef enum {
     RRDENGINE_STATUS_UNINITIALIZED = 0,
@@ -227,6 +249,9 @@ struct rrdengine_instance {
     struct rrdengine_statistics stats;
 };
 
+extern void *dbengine_page_alloc(void);
+extern void dbengine_page_free(void *page);
+
 extern int init_rrd_files(struct rrdengine_instance *ctx);
 extern void finalize_rrd_files(struct rrdengine_instance *ctx);
 extern void rrdeng_test_quota(struct rrdengine_worker_config* wc);
diff --git a/database/engine/rrdengineapi.c b/database/engine/rrdengineapi.c
index 6ebee145..76010a7c 100755
--- a/database/engine/rrdengineapi.c
+++ b/database/engine/rrdengineapi.c
@@ -126,12 +126,13 @@ void rrdeng_store_metric_init(RRDDIM *rd)
     struct pg_cache_page_index *page_index;
 
     ctx = get_rrdeng_ctx_from_host(rd->rrdset->rrdhost);
-    handle = &rd->state->handle.rrdeng;
-    handle->ctx = ctx;
 
+    handle = callocz(1, sizeof(struct rrdeng_collect_handle));
+    handle->ctx = ctx;
     handle->descr = NULL;
     handle->prev_descr = NULL;
     handle->unaligned_page = 0;
+    rd->state->handle = (STORAGE_COLLECT_HANDLE *)handle;
 
     page_index = rd->state->page_index;
     uv_rwlock_wrlock(&page_index->lock);
@@ -162,7 +163,7 @@ void rrdeng_store_metric_flush_current_page(RRDDIM *rd)
     struct rrdengine_instance *ctx;
     struct rrdeng_page_descr *descr;
 
-    handle = &rd->state->handle.rrdeng;
+    handle = (struct rrdeng_collect_handle *)rd->state->handle;
     ctx = handle->ctx;
     if (unlikely(!ctx))
         return;
@@ -202,7 +203,7 @@ void rrdeng_store_metric_flush_current_page(RRDDIM *rd)
             /* handle->prev_descr = descr;*/
         }
     } else {
-        freez(descr->pg_cache_descr->page);
+        dbengine_page_free(descr->pg_cache_descr->page);
         rrdeng_destroy_pg_cache_descr(ctx, descr->pg_cache_descr);
         freez(descr);
     }
@@ -211,14 +212,13 @@ void rrdeng_store_metric_flush_current_page(RRDDIM *rd)
 
 void rrdeng_store_metric_next(RRDDIM *rd, usec_t point_in_time, storage_number number)
 {
-    struct rrdeng_collect_handle *handle;
+    struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)rd->state->handle;
     struct rrdengine_instance *ctx;
     struct page_cache *pg_cache;
     struct rrdeng_page_descr *descr;
     storage_number *page;
     uint8_t must_flush_unaligned_page = 0, perfect_page_alignment = 0;
 
-    handle = &rd->state->handle.rrdeng;
     ctx = handle->ctx;
     pg_cache = &ctx->pg_cache;
     descr = handle->descr;
@@ -301,7 +301,7 @@ int rrdeng_store_metric_finalize(RRDDIM *rd)
     struct pg_cache_page_index *page_index;
     uint8_t can_delete_metric = 0;
 
-    handle = &rd->state->handle.rrdeng;
+    handle = (struct rrdeng_collect_handle *)rd->state->handle;
     ctx = handle->ctx;
     page_index = rd->state->page_index;
     rrdeng_store_metric_flush_current_page(rd);
@@ -314,6 +314,7 @@ int rrdeng_store_metric_finalize(RRDDIM *rd)
         can_delete_metric = 1;
     }
     uv_rwlock_wrunlock(&page_index->lock);
+    freez(handle);
 
    return can_delete_metric;
 }
@@ -406,6 +407,7 @@ unsigned rrdeng_variable_step_boundaries(RRDSET *st, time_t start_time, time_t e
     is_first_region_initialized = 0;
     region_points = 0;
 
+    int is_out_of_order_reported = 0;
     /* pages loop */
     for (i = 0, curr = NULL, prev = NULL ; i < pages_nr ; ++i) {
         old_prev = prev;
@@ -446,7 +448,7 @@ unsigned rrdeng_variable_step_boundaries(RRDSET *st, time_t start_time, time_t e
                 is_metric_out_of_order = 1;
             if (is_metric_earlier_than_range || unlikely(is_metric_out_of_order)) {
                 if (unlikely(is_metric_out_of_order))
-                    info("Ignoring metric with out of order timestamp.");
+                    is_out_of_order_reported++;
                 continue; /* next entry */
             }
             /* here is a valid metric */
@@ -519,6 +521,8 @@ unsigned rrdeng_variable_step_boundaries(RRDSET *st, time_t start_time, time_t e
             freez(region_info_array);
         }
     }
+    if (is_out_of_order_reported)
+        info("Ignored %d metrics with out of order timestamp in %u regions.", is_out_of_order_reported, regions);
     return regions;
 }
 
@@ -535,12 +539,14 @@ void rrdeng_load_metric_init(RRDDIM *rd, struct rrddim_query_handle *rrdimm_hand
     ctx = get_rrdeng_ctx_from_host(rd->rrdset->rrdhost);
     rrdimm_handle->start_time = start_time;
     rrdimm_handle->end_time = end_time;
-    handle = &rrdimm_handle->rrdeng;
+
+    handle = callocz(1, sizeof(struct rrdeng_query_handle));
     handle->next_page_time = start_time;
     handle->now = start_time;
     handle->position = 0;
     handle->ctx = ctx;
     handle->descr = NULL;
+    rrdimm_handle->handle = (STORAGE_QUERY_HANDLE *)handle;
     pages_nr = pg_cache_preload(ctx, rd->state->rrdeng_uuid, start_time * USEC_PER_SEC, end_time * USEC_PER_SEC,
                                 NULL, &handle->page_index);
     if (unlikely(NULL == handle->page_index || 0 == pages_nr))
@@ -548,102 +554,109 @@ void rrdeng_load_metric_init(RRDDIM *rd, struct rrddim_query_handle *rrdimm_hand
         handle->next_page_time = INVALID_TIME;
 }
 
-/* Returns the metric and sets its timestamp into current_time */
-storage_number rrdeng_load_metric_next(struct rrddim_query_handle *rrdimm_handle, time_t *current_time)
-{
-    struct rrdeng_query_handle *handle;
-    struct rrdengine_instance *ctx;
-    struct rrdeng_page_descr *descr;
-    storage_number *page, ret;
-    unsigned position, entries;
-    usec_t next_page_time = 0, current_position_time, page_end_time = 0;
+static int rrdeng_load_page_next(struct rrddim_query_handle *rrdimm_handle) {
+    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrdimm_handle->handle;
+
+    struct rrdengine_instance *ctx = handle->ctx;
+    struct rrdeng_page_descr *descr = handle->descr;
+
     uint32_t page_length;
+    usec_t page_end_time;
+    unsigned position;
 
-    handle = &rrdimm_handle->rrdeng;
-    if (unlikely(INVALID_TIME == handle->next_page_time)) {
-        return SN_EMPTY_SLOT;
-    }
-    ctx = handle->ctx;
-    if (unlikely(NULL == (descr = handle->descr))) {
-        /* it's the first call */
-        next_page_time = handle->next_page_time * USEC_PER_SEC;
-    } else {
-        pg_cache_atomic_get_pg_info(descr, &page_end_time, &page_length);
-    }
-    position = handle->position + 1;
+    if (likely(descr)) {
+        // Drop old page's reference
 
-    if (unlikely(NULL == descr ||
-                 position >= (page_length / sizeof(storage_number)))) {
-        /* We need to get a new page */
-        if (descr) {
-            /* Drop old page's reference */
 #ifdef NETDATA_INTERNAL_CHECKS
-            rrd_stat_atomic_add(&ctx->stats.metric_API_consumers, -1);
+        rrd_stat_atomic_add(&ctx->stats.metric_API_consumers, -1);
 #endif
-            pg_cache_put(ctx, descr);
-            handle->descr = NULL;
-            handle->next_page_time = (page_end_time / USEC_PER_SEC) + 1;
-            if (unlikely(handle->next_page_time > rrdimm_handle->end_time)) {
-                goto no_more_metrics;
-            }
-            next_page_time = handle->next_page_time * USEC_PER_SEC;
-        }
 
-        descr = pg_cache_lookup_next(ctx, handle->page_index, &handle->page_index->id,
-                                     next_page_time, rrdimm_handle->end_time * USEC_PER_SEC);
-        if (NULL == descr) {
-            goto no_more_metrics;
-        }
+        pg_cache_put(ctx, descr);
+        handle->descr = NULL;
+        handle->next_page_time = (handle->page_end_time / USEC_PER_SEC) + 1;
+
+        if (unlikely(handle->next_page_time > rrdimm_handle->end_time))
+            return 1;
+    }
+
+    usec_t next_page_time = handle->next_page_time * USEC_PER_SEC;
+    descr = pg_cache_lookup_next(ctx, handle->page_index, &handle->page_index->id, next_page_time, rrdimm_handle->end_time * USEC_PER_SEC);
+    if (NULL == descr)
+        return 1;
+
 #ifdef NETDATA_INTERNAL_CHECKS
-        rrd_stat_atomic_add(&ctx->stats.metric_API_consumers, 1);
+    rrd_stat_atomic_add(&ctx->stats.metric_API_consumers, 1);
 #endif
-        handle->descr = descr;
-        pg_cache_atomic_get_pg_info(descr, &page_end_time, &page_length);
-        if (unlikely(INVALID_TIME == descr->start_time ||
-                     INVALID_TIME == page_end_time)) {
-            goto no_more_metrics;
-        }
-        if (unlikely(descr->start_time != page_end_time && next_page_time > descr->start_time)) {
-            /* we're in the middle of the page somewhere */
-            entries = page_length / sizeof(storage_number);
-            position = ((uint64_t)(next_page_time - descr->start_time)) * (entries - 1) /
-                       (page_end_time - descr->start_time);
-        } else {
-            position = 0;
-        }
+
+    handle->descr = descr;
+    pg_cache_atomic_get_pg_info(descr, &page_end_time, &page_length);
+    if (unlikely(INVALID_TIME == descr->start_time || INVALID_TIME == page_end_time))
+        return 1;
+
+    if (unlikely(descr->start_time != page_end_time && next_page_time > descr->start_time)) {
+        // we're in the middle of the page somewhere
+        unsigned entries = page_length / sizeof(storage_number);
+        position = ((uint64_t)(next_page_time - descr->start_time)) * (entries - 1) /
+                   (page_end_time - descr->start_time);
     }
-    page = descr->pg_cache_descr->page;
-    ret = page[position];
-    entries = page_length / sizeof(storage_number);
-    if (entries > 1) {
-        usec_t dt;
+    else
+        position = 0;
+
+    handle->page_end_time = page_end_time;
+    handle->page_length = page_length;
+    handle->page = descr->pg_cache_descr->page;
+    usec_t entries = handle->entries = page_length / sizeof(storage_number);
+    if (likely(entries > 1))
+        handle->dt = (page_end_time - descr->start_time) / (entries - 1);
+    else
+        handle->dt = 0;
 
-        dt = (page_end_time - descr->start_time) / (entries - 1);
-        current_position_time = descr->start_time + position * dt;
-    } else {
-        current_position_time = descr->start_time;
+    handle->dt_sec = handle->dt / USEC_PER_SEC;
+    handle->position = position;
+
+    return 0;
+}
+
+/* Returns the metric and sets its timestamp into current_time */
+storage_number rrdeng_load_metric_next(struct rrddim_query_handle *rrdimm_handle, time_t *current_time) {
+    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrdimm_handle->handle;
+
+    if (unlikely(INVALID_TIME == handle->next_page_time))
+        return SN_EMPTY_SLOT;
+
+    struct rrdeng_page_descr *descr = handle->descr;
+    unsigned position = handle->position + 1;
+    time_t now = handle->now + handle->dt_sec;
+
+    if (unlikely(!descr || position >= handle->entries)) {
+        // We need to get a new page
+        if(rrdeng_load_page_next(rrdimm_handle)) {
+            // next calls will not load any more metrics
+            handle->next_page_time = INVALID_TIME;
+            return SN_EMPTY_SLOT;
+        }
+
+        descr = handle->descr;
+        position = handle->position;
+        now = (descr->start_time + position * handle->dt) / USEC_PER_SEC;
     }
+
+    storage_number ret = handle->page[position];
     handle->position = position;
-    handle->now = current_position_time / USEC_PER_SEC;
-/*  fatal_assert(handle->now >= rrdimm_handle->start_time && handle->now <= rrdimm_handle->end_time);
-    The above assertion is an approximation and needs to take update_every into account */
-    if (unlikely(handle->now >= rrdimm_handle->end_time)) {
-        /* next calls will not load any more metrics */
+    handle->now = now;
+
+    if (unlikely(now >= rrdimm_handle->end_time)) {
+        // next calls will not load any more metrics
         handle->next_page_time = INVALID_TIME;
     }
-    *current_time = handle->now;
-    return ret;
 
-no_more_metrics:
-    handle->next_page_time = INVALID_TIME;
-    return SN_EMPTY_SLOT;
+    *current_time = now;
+    return ret;
 }
 
 int rrdeng_load_metric_is_finished(struct rrddim_query_handle *rrdimm_handle)
 {
-    struct rrdeng_query_handle *handle;
-
-    handle = &rrdimm_handle->rrdeng;
+    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrdimm_handle->handle;
     return (INVALID_TIME == handle->next_page_time);
 }
 
@@ -652,19 +665,20 @@ int rrdeng_load_metric_is_finished(struct rrddim_query_handle *rrdimm_handle)
  */
 void rrdeng_load_metric_finalize(struct rrddim_query_handle *rrdimm_handle)
 {
-    struct rrdeng_query_handle *handle;
-    struct rrdengine_instance *ctx;
-    struct rrdeng_page_descr *descr;
+    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrdimm_handle->handle;
+    struct rrdengine_instance *ctx = handle->ctx;
+    struct rrdeng_page_descr *descr = handle->descr;
 
-    handle = &rrdimm_handle->rrdeng;
-    ctx = handle->ctx;
-    descr = handle->descr;
     if (descr) {
 #ifdef NETDATA_INTERNAL_CHECKS
         rrd_stat_atomic_add(&ctx->stats.metric_API_consumers, -1);
 #endif
         pg_cache_put(ctx, descr);
     }
+
+    // whatever is allocated at rrdeng_load_metric_init() should be freed here
+    freez(handle);
+    rrdimm_handle->handle = NULL;
 }
 
 time_t rrdeng_metric_latest_time(RRDDIM *rd)
@@ -724,7 +738,7 @@ void *rrdeng_create_page(struct rrdengine_instance *ctx, uuid_t *id, struct rrde
 
     descr = pg_cache_create_descr();
     descr->id = id; /* TODO: add page type: metric, log, something? */
-    page = mallocz(RRDENG_BLOCK_SIZE); /*TODO: add page size */
+    page = dbengine_page_alloc(); /*TODO: add page size */
     rrdeng_page_descr_mutex_lock(ctx, descr);
     pg_cache_descr = descr->pg_cache_descr;
     pg_cache_descr->page = page;
@@ -949,7 +963,7 @@ int rrdeng_init(RRDHOST *host, struct rrdengine_instance **ctxp, char *dbfiles_p
     /* wait for worker thread to initialize */
     completion_wait_for(&ctx->rrdengine_completion);
     completion_destroy(&ctx->rrdengine_completion);
-    uv_thread_set_name_np(ctx->worker_config.thread, "DBENGINE");
+    uv_thread_set_name_np(ctx->worker_config.thread, "LIBUV_WORKER");
     if (ctx->worker_config.error) {
         goto error_after_rrdeng_worker;
     }
diff --git a/database/metric_correlations.c b/database/metric_correlations.c
new file mode 100644
index 00000000..3b8968c9
--- /dev/null
+++ b/database/metric_correlations.c
@@ -0,0 +1,300 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "daemon/common.h"
+#include "KolmogorovSmirnovDist.h"
+
+#define MAX_POINTS 10000
+int enable_metric_correlations = CONFIG_BOOLEAN_NO;
+int metric_correlations_version = 1;
+
+struct charts {
+    RRDSET *st;
+    struct charts *next;
+};
+
+struct per_dim {
+    char *dimension;
+    calculated_number baseline[MAX_POINTS];
+    calculated_number highlight[MAX_POINTS];
+
+    double baseline_diffs[MAX_POINTS];
+    double highlight_diffs[MAX_POINTS];
+};
+
+int find_index(double arr[], long int n, double K, long int start)
+{
+    for (long int i = start; i < n; i++) {
+        if (K<arr[i]){
+            return i;
+        }
+    }
+    return n;
+}
+
+int compare(const void *left, const void *right) {
+    double lt = *(double *)left;
+    double rt = *(double *)right;
+
+    if(unlikely(lt < rt)) return -1;
+    if(unlikely(lt > rt)) return 1;
+    return 0;
+}
+
+void kstwo(double data1[], long int n1, double data2[], long int n2, double *d, double *prob)
+{
+	double en1, en2, en, data_all[MAX_POINTS*2], cdf1[MAX_POINTS], cdf2[MAX_POINTS], cddiffs[MAX_POINTS];
+    double min = 0.0, max = 0.0;
+    qsort(data1, n1, sizeof(double), compare);
+    qsort(data2, n2, sizeof(double), compare);
+
+    for (int i = 0; i < n1; i++)
+        data_all[i] = data1[i];
+    for (int i = 0; i < n2; i++)
+        data_all[n1 + i] = data2[i];
+
+    en1 = (double)n1;
+	en2 = (double)n2;
+    *d = 0.0;
+    cddiffs[0]=0; //for uninitialized warning
+
+    for (int i=0; i<n1+n2;i++)
+        cdf1[i] = find_index(data1, n1, data_all[i], 0) / en1; //TODO, use the start to reduce loops
+
+    for (int i=0; i<n1+n2;i++)
+        cdf2[i] = find_index(data2, n2, data_all[i], 0) / en2;
+
+    for ( int i=0;i<n2+n1;i++)
+        cddiffs[i] = cdf1[i] - cdf2[i];
+
+    min = cddiffs[0];
+    for ( int i=0;i<n2+n1;i++) {
+        if (cddiffs[i] < min)
+            min = cddiffs[i];
+    }
+
+    //clip min
+    if (fabs(min) < 0) min = 0;
+    else if (fabs(min) > 1) min = 1;
+
+    max = fabs(cddiffs[0]);
+    for ( int i=0;i<n2+n1;i++)
+        if (cddiffs[i] >= max) max = cddiffs[i];
+
+    if (fabs(min) < max)
+        *d = max;
+    else
+        *d = fabs(min);
+
+    
+    
+    en = (en1*en2 / (en1 + en2));
+    *prob = KSfbar(round(en), *d);
+}
+
+void fill_nan (struct per_dim *d, long int hp, long int bp)
+{
+    int k;
+
+    for (k = 0; k < bp; k++) {
+        if (isnan(d->baseline[k])) {
+            d->baseline[k] = 0.0;
+        }
+    }
+
+    for (k = 0; k < hp; k++) {
+        if (isnan(d->highlight[k])) {
+            d->highlight[k] = 0.0;
+        }
+    }
+}
+
+//TODO check counters
+void run_diffs_and_rev (struct per_dim *d, long int hp, long int bp)
+{
+    int k, j;
+
+    for (k = 0, j = bp; k < bp - 1; k++, j--)
+        d->baseline_diffs[k] = (double)d->baseline[j - 2] - (double)d->baseline[j - 1];
+    for (k = 0, j = hp; k < hp - 1; k++, j--) {
+        d->highlight_diffs[k] = (double)d->highlight[j - 2] - (double)d->highlight[j - 1];
+    }
+}
+
+int run_metric_correlations (BUFFER *wb, RRDSET *st, long long baseline_after, long long baseline_before, long long highlight_after, long long highlight_before, long long max_points)
+{
+    uint32_t options = 0x00000000;
+    int group_method = RRDR_GROUPING_AVERAGE;
+    long group_time = 0;
+    struct context_param  *context_param_list = NULL;
+    long c;
+    int i=0, j=0;
+    int b_dims = 0;
+    long int baseline_points = 0, highlight_points = 0;
+
+    struct per_dim *pd = NULL;
+
+    //TODO get everything in one go, when baseline is right before highlight
+    //get baseline
+    ONEWAYALLOC *owa = onewayalloc_create(0);
+    RRDR *rb = rrd2rrdr(owa, st, max_points, baseline_after, baseline_before, group_method, group_time, options, NULL, context_param_list, 0);
+    if(!rb) {
+        info("Cannot generate metric correlations output with these parameters on this chart.");
+        onewayalloc_destroy(owa);
+        return 0;
+    } else {
+        baseline_points = rrdr_rows(rb);
+        pd = mallocz(sizeof(struct per_dim) * rb->d);
+        b_dims = rb->d;
+        for (c = 0; c != rrdr_rows(rb) ; ++c) {
+            RRDDIM *d;
+            for (j = 0, d = rb->st->dimensions ; d && j < rb->d ; ++j, d = d->next) {
+                calculated_number *cn = &rb->v[ c * rb->d ];
+                if (!c) {
+                    //TODO use points from query
+                    pd[j].dimension = strdupz (d->name);
+                    pd[j].baseline[c] = cn[j];
+                } else {
+                    pd[j].baseline[c] = cn[j];
+                }
+            }
+        }
+    }
+    rrdr_free(owa, rb);
+    onewayalloc_destroy(owa);
+    if (!pd)
+        return 0;
+
+    //get highlight
+    owa = onewayalloc_create(0);
+    RRDR *rh = rrd2rrdr(owa, st, max_points, highlight_after, highlight_before, group_method, group_time, options, NULL, context_param_list, 0);
+    if(!rh) {
+        info("Cannot generate metric correlations output with these parameters on this chart.");
+        freez(pd);
+        onewayalloc_destroy(owa);
+        return 0;
+    } else {
+        if (rh->d != b_dims) {
+            //TODO handle different dims
+            rrdr_free(owa, rh);
+            onewayalloc_destroy(owa);
+            freez(pd);
+            return 0;
+        }
+        highlight_points = rrdr_rows(rh);
+        for (c = 0; c != rrdr_rows(rh) ; ++c) {
+            RRDDIM *d;
+            for (j = 0, d = rh->st->dimensions ; d && j < rh->d ; ++j, d = d->next) {
+                calculated_number *cn = &rh->v[ c * rh->d ];
+                    pd[j].highlight[c] = cn[j];
+            }
+        }
+    }
+    rrdr_free(owa, rh);
+    onewayalloc_destroy(owa);
+
+    for (i = 0; i < b_dims; i++) {
+        fill_nan(&pd[i], highlight_points, baseline_points);
+    }
+
+    for (i = 0; i < b_dims; i++) {
+        run_diffs_and_rev(&pd[i], highlight_points, baseline_points);
+    }
+
+    double d=0, prob=0;
+    for (i=0;i < j ;i++) {
+        if (baseline_points && highlight_points) {
+            kstwo(pd[i].baseline_diffs, baseline_points-1, pd[i].highlight_diffs, highlight_points-1, &d, &prob);
+            buffer_sprintf(wb, "\t\t\t\t\"%s\": %f", pd[i].dimension, prob);
+            if (i != j-1)
+                buffer_sprintf(wb, ",\n");
+            else
+                buffer_sprintf(wb, "\n");
+        }
+    }
+
+    freez(pd);
+    return j;
+}
+
+void metric_correlations (RRDHOST *host, BUFFER *wb, long long baseline_after, long long baseline_before, long long highlight_after, long long highlight_before, long long max_points)
+{
+    info ("Running metric correlations, highlight_after: %lld, highlight_before: %lld, baseline_after: %lld, baseline_before: %lld, max_points: %lld", highlight_after, highlight_before, baseline_after, baseline_before, max_points);
+
+    if (!enable_metric_correlations) {
+        error("Metric correlations functionality is not enabled.");
+        buffer_strcat(wb, "{\"error\": \"Metric correlations functionality is not enabled.\" }");
+        return;
+    }
+
+    if (highlight_before <= highlight_after || baseline_before <= baseline_after) {
+        error("Invalid baseline or highlight ranges.");
+        buffer_strcat(wb, "{\"error\": \"Invalid baseline or highlight ranges.\" }");
+        return;
+    }
+
+    long long dims = 0, total_dims = 0;
+    RRDSET *st;
+    size_t c = 0;
+    BUFFER *wdims = buffer_create(1000);
+
+    if (!max_points || max_points > MAX_POINTS)
+        max_points = MAX_POINTS;
+
+    //dont lock here and wait for results
+    //get the charts and run mc after
+    //should not be a problem for the query
+    struct charts *charts = NULL;
+    rrdhost_rdlock(host);
+    rrdset_foreach_read(st, host) {
+        if (rrdset_is_available_for_viewers(st)) {
+            rrdset_rdlock(st);
+            struct charts *chart = callocz(1, sizeof(struct charts));
+            chart->st = st;
+            chart->next = NULL;
+            if (charts) {
+                chart->next = charts;
+            }
+            charts = chart;
+        }
+    }
+    rrdhost_unlock(host);
+
+    buffer_strcat(wb, "{\n\t\"correlated_charts\": {");
+
+    for (struct charts *ch = charts; ch; ch = ch->next) {
+        buffer_flush(wdims);
+        dims = run_metric_correlations(wdims, ch->st, baseline_after, baseline_before, highlight_after, highlight_before, max_points);
+        if (dims) {
+            if (c)
+                buffer_strcat(wb, "\t\t},");
+            buffer_strcat(wb, "\n\t\t\"");
+            buffer_strcat(wb, ch->st->id);
+            buffer_strcat(wb, "\": {\n");
+            buffer_strcat(wb, "\t\t\t\"context\": \"");
+            buffer_strcat(wb, ch->st->context);
+            buffer_strcat(wb, "\",\n\t\t\t\"dimensions\": {\n");
+            buffer_sprintf(wb, "%s", buffer_tostring(wdims));
+            buffer_strcat(wb, "\t\t\t}\n");
+            total_dims += dims;
+            c++;
+        }
+    }
+    buffer_strcat(wb, "\t\t}\n");
+    buffer_sprintf(wb, "\t},\n\t\"total_dimensions_count\": %lld\n}", total_dims);
+
+    if (!total_dims) {
+        buffer_flush(wb);
+        buffer_strcat(wb, "{\"error\": \"No results from metric correlations.\" }");
+    }
+
+    struct charts* ch;
+    while(charts){
+        ch = charts;
+        charts = charts->next;
+        rrdset_unlock(ch->st);
+        free(ch);
+    }
+
+    buffer_free(wdims);
+    info ("Done running metric correlations");
+}
diff --git a/database/metric_correlations.h b/database/metric_correlations.h
new file mode 100644
index 00000000..83ea9b74
--- /dev/null
+++ b/database/metric_correlations.h
@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#ifndef NETDATA_METRIC_CORRELATIONS_H
+#define NETDATA_METRIC_CORRELATIONS_H 1
+
+extern int enable_metric_correlations;
+extern int metric_correlations_version;
+
+void metric_correlations (RRDHOST *host, BUFFER *wb, long long selected_after, long long selected_before, long long reference_after, long long reference_before, long long max_points);
+
+#endif //NETDATA_METRIC_CORRELATIONS_H
diff --git a/database/ram/rrddim_mem.c b/database/ram/rrddim_mem.c
new file mode 100644
index 00000000..b17f03ca
--- /dev/null
+++ b/database/ram/rrddim_mem.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "rrddim_mem.h"
+
+// ----------------------------------------------------------------------------
+// RRDDIM legacy data collection functions
+
+void rrddim_collect_init(RRDDIM *rd) {
+    rd->values[rd->rrdset->current_entry] = SN_EMPTY_SLOT;
+    rd->state->handle = calloc(1, sizeof(struct mem_collect_handle));
+}
+void rrddim_collect_store_metric(RRDDIM *rd, usec_t point_in_time, storage_number number) {
+    (void)point_in_time;
+    rd->values[rd->rrdset->current_entry] = number;
+}
+int rrddim_collect_finalize(RRDDIM *rd) {
+    free((struct mem_collect_handle*)rd->state->handle);
+    return 0;
+}
+
+// ----------------------------------------------------------------------------
+// RRDDIM legacy database query functions
+
+void rrddim_query_init(RRDDIM *rd, struct rrddim_query_handle *handle, time_t start_time, time_t end_time) {
+    handle->rd = rd;
+    handle->start_time = start_time;
+    handle->end_time = end_time;
+    struct mem_query_handle* h = calloc(1, sizeof(struct mem_query_handle));
+    h->slot = rrdset_time2slot(rd->rrdset, start_time);
+    h->last_slot = rrdset_time2slot(rd->rrdset, end_time);
+    h->finished = 0;
+    handle->handle = (STORAGE_QUERY_HANDLE *)h;
+}
+
+storage_number rrddim_query_next_metric(struct rrddim_query_handle *handle, time_t *current_time) {
+    RRDDIM *rd = handle->rd;
+    struct mem_query_handle* h = (struct mem_query_handle*)handle->handle;
+    long entries = rd->rrdset->entries;
+    long slot = h->slot;
+
+    (void)current_time;
+    if (unlikely(h->slot == h->last_slot))
+        h->finished = 1;
+    storage_number n = rd->values[slot++];
+
+    if(unlikely(slot >= entries)) slot = 0;
+    h->slot = slot;
+
+    return n;
+}
+
+int rrddim_query_is_finished(struct rrddim_query_handle *handle) {
+    struct mem_query_handle* h = (struct mem_query_handle*)handle->handle;
+    return h->finished;
+}
+
+void rrddim_query_finalize(struct rrddim_query_handle *handle) {
+    freez(handle->handle);
+}
+
+time_t rrddim_query_latest_time(RRDDIM *rd) {
+    return rrdset_last_entry_t_nolock(rd->rrdset);
+}
+
+time_t rrddim_query_oldest_time(RRDDIM *rd) {
+    return rrdset_first_entry_t_nolock(rd->rrdset);
+}
diff --git a/database/ram/rrddim_mem.h b/database/ram/rrddim_mem.h
new file mode 100644
index 00000000..9a215387
--- /dev/null
+++ b/database/ram/rrddim_mem.h
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#ifndef NETDATA_RRDDIMMEM_H
+#define NETDATA_RRDDIMMEM_H
+
+#include "database/rrd.h"
+
+struct mem_collect_handle {
+    long slot;
+    long entries;
+};
+struct mem_query_handle {
+    long slot;
+    long last_slot;
+    uint8_t finished;
+};
+
+extern void rrddim_collect_init(RRDDIM *rd);
+extern void rrddim_collect_store_metric(RRDDIM *rd, usec_t point_in_time, storage_number number);
+extern int rrddim_collect_finalize(RRDDIM *rd);
+
+extern void rrddim_query_init(RRDDIM *rd, struct rrddim_query_handle *handle, time_t start_time, time_t end_time);
+extern storage_number rrddim_query_next_metric(struct rrddim_query_handle *handle, time_t *current_time);
+extern int rrddim_query_is_finished(struct rrddim_query_handle *handle);
+extern void rrddim_query_finalize(struct rrddim_query_handle *handle);
+extern time_t rrddim_query_latest_time(RRDDIM *rd);
+extern time_t rrddim_query_oldest_time(RRDDIM *rd);
+
+#endif
diff --git a/database/rrd.c b/database/rrd.c
index 321d3561..f91039ea 100644
--- a/database/rrd.c
+++ b/database/rrd.c
@@ -2,6 +2,7 @@
 #define NETDATA_RRD_INTERNALS 1
 
 #include "rrd.h"
+#include "storage_engine.h"
 
 // ----------------------------------------------------------------------------
 // globals
@@ -47,24 +48,19 @@ inline const char *rrd_memory_mode_name(RRD_MEMORY_MODE id) {
             return RRD_MEMORY_MODE_DBENGINE_NAME;
     }
 
+    STORAGE_ENGINE* eng = storage_engine_get(id);
+    if (eng) {
+        return eng->name;
+    }
+
     return RRD_MEMORY_MODE_SAVE_NAME;
 }
 
 RRD_MEMORY_MODE rrd_memory_mode_id(const char *name) {
-    if(unlikely(!strcmp(name, RRD_MEMORY_MODE_RAM_NAME)))
-        return RRD_MEMORY_MODE_RAM;
-
-    else if(unlikely(!strcmp(name, RRD_MEMORY_MODE_MAP_NAME)))
-        return RRD_MEMORY_MODE_MAP;
-
-    else if(unlikely(!strcmp(name, RRD_MEMORY_MODE_NONE_NAME)))
-        return RRD_MEMORY_MODE_NONE;
-
-    else if(unlikely(!strcmp(name, RRD_MEMORY_MODE_ALLOC_NAME)))
-        return RRD_MEMORY_MODE_ALLOC;
-
-    else if(unlikely(!strcmp(name, RRD_MEMORY_MODE_DBENGINE_NAME)))
-        return RRD_MEMORY_MODE_DBENGINE;
+    STORAGE_ENGINE* eng = storage_engine_find(name);
+    if (eng) {
+        return eng->id;
+    }
 
     return RRD_MEMORY_MODE_SAVE;
 }
@@ -139,8 +135,7 @@ const char *rrdset_type_name(RRDSET_TYPE chart_type) {
 // ----------------------------------------------------------------------------
 // RRD - cache directory
 
-char *rrdset_cache_dir(RRDHOST *host, const char *id, const char *config_section) {
-    UNUSED(config_section);
+char *rrdset_cache_dir(RRDHOST *host, const char *id) {
     char *ret = NULL;
 
     char b[FILENAME_MAX + 1];
diff --git a/database/rrd.h b/database/rrd.h
index 071e1d03..dc32b2a2 100644
--- a/database/rrd.h
+++ b/database/rrd.h
@@ -170,17 +170,12 @@ typedef enum rrddim_flags {
     RRDDIM_FLAG_ACLK                            = (1 << 4),
 
     RRDDIM_FLAG_PENDING_FOREACH_ALARM           = (1 << 5), // set when foreach alarm has not been initialized yet
+    RRDDIM_FLAG_META_HIDDEN                     = (1 << 6), // Status of hidden option in the metadata database
 } RRDDIM_FLAGS;
 
-#ifdef HAVE_C___ATOMIC
 #define rrddim_flag_check(rd, flag) (__atomic_load_n(&((rd)->flags), __ATOMIC_SEQ_CST) & (flag))
 #define rrddim_flag_set(rd, flag)   __atomic_or_fetch(&((rd)->flags), (flag), __ATOMIC_SEQ_CST)
 #define rrddim_flag_clear(rd, flag) __atomic_and_fetch(&((rd)->flags), ~(flag), __ATOMIC_SEQ_CST)
-#else
-#define rrddim_flag_check(rd, flag) ((rd)->flags & (flag))
-#define rrddim_flag_set(rd, flag)   (rd)->flags |= (flag)
-#define rrddim_flag_clear(rd, flag) (rd)->flags &= ~(flag)
-#endif
 
 typedef enum label_source {
     LABEL_SOURCE_AUTO             = 0,
@@ -332,53 +327,56 @@ struct rrddim {
 };
 
 // ----------------------------------------------------------------------------
-// iterator state for RRD dimension data collection
-union rrddim_collect_handle {
-    struct {
-        long slot;
-        long entries;
-    } slotted;                           // state the legacy code uses
-#ifdef ENABLE_DBENGINE
-    struct rrdeng_collect_handle {
-        struct rrdeng_page_descr *descr, *prev_descr;
-        unsigned long page_correlation_id;
-        struct rrdengine_instance *ctx;
-        // set to 1 when this dimension is not page aligned with the other dimensions in the chart
-        uint8_t unaligned_page;
-    } rrdeng; // state the database engine uses
-#endif
-};
+// engine-specific iterator state for dimension data collection
+typedef struct storage_collect_handle STORAGE_COLLECT_HANDLE;
 
 // ----------------------------------------------------------------------------
-// iterator state for RRD dimension data queries
-
-#ifdef ENABLE_DBENGINE
-struct rrdeng_query_handle {
-    struct rrdeng_page_descr *descr;
-    struct rrdengine_instance *ctx;
-    struct pg_cache_page_index *page_index;
-    time_t next_page_time;
-    time_t now;
-    unsigned position;
-};
-#endif
+// engine-specific iterator state for dimension data queries
+typedef struct storage_query_handle STORAGE_QUERY_HANDLE;
 
+// ----------------------------------------------------------------------------
+// iterator state for RRD dimension data queries
 struct rrddim_query_handle {
     RRDDIM *rd;
     time_t start_time;
     time_t end_time;
-    union {
-        struct {
-            long slot;
-            long last_slot;
-            uint8_t finished;
-        } slotted;                         // state the legacy code uses
-#ifdef ENABLE_DBENGINE
-        struct rrdeng_query_handle rrdeng; // state the database engine uses
-#endif
-    };
+    STORAGE_QUERY_HANDLE* handle;
 };
 
+// ------------------------------------------------------------------------
+// function pointers that handle data collection
+struct rrddim_collect_ops {
+    // an initialization function to run before starting collection
+    void (*init)(RRDDIM *rd);
+
+    // run this to store each metric into the database
+    void (*store_metric)(RRDDIM *rd, usec_t point_in_time, storage_number number);
+
+    // an finalization function to run after collection is over
+    // returns 1 if it's safe to delete the dimension
+    int (*finalize)(RRDDIM *rd);
+};
+
+// function pointers that handle database queries
+struct rrddim_query_ops {
+    // run this before starting a series of next_metric() database queries
+    void (*init)(RRDDIM *rd, struct rrddim_query_handle *handle, time_t start_time, time_t end_time);
+
+    // run this to load each metric number from the database
+    storage_number (*next_metric)(struct rrddim_query_handle *handle, time_t *current_time);
+
+    // run this to test if the series of next_metric() database queries is finished
+    int (*is_finished)(struct rrddim_query_handle *handle);
+
+    // run this after finishing a series of load_metric() database queries
+    void (*finalize)(struct rrddim_query_handle *handle);
+
+    // get the timestamp of the last entry of this metric
+    time_t (*latest_time)(RRDDIM *rd);
+
+    // get the timestamp of the first entry of this metric
+    time_t (*oldest_time)(RRDDIM *rd);
+};
 
 // ----------------------------------------------------------------------------
 // volatile state per RRD dimension
@@ -391,42 +389,9 @@ struct rrddim_volatile {
     int aclk_live_status;
 #endif
     uuid_t metric_uuid;                 // global UUID for this metric (unique_across hosts)
-    union rrddim_collect_handle handle;
-    // ------------------------------------------------------------------------
-    // function pointers that handle data collection
-    struct rrddim_collect_ops {
-        // an initialization function to run before starting collection
-        void (*init)(RRDDIM *rd);
-
-        // run this to store each metric into the database
-        void (*store_metric)(RRDDIM *rd, usec_t point_in_time, storage_number number);
-
-        // an finalization function to run after collection is over
-        // returns 1 if it's safe to delete the dimension
-        int (*finalize)(RRDDIM *rd);
-    } collect_ops;
-
-    // function pointers that handle database queries
-    struct rrddim_query_ops {
-        // run this before starting a series of next_metric() database queries
-        void (*init)(RRDDIM *rd, struct rrddim_query_handle *handle, time_t start_time, time_t end_time);
-
-        // run this to load each metric number from the database
-        storage_number (*next_metric)(struct rrddim_query_handle *handle, time_t *current_time);
-
-        // run this to test if the series of next_metric() database queries is finished
-        int (*is_finished)(struct rrddim_query_handle *handle);
-
-        // run this after finishing a series of load_metric() database queries
-        void (*finalize)(struct rrddim_query_handle *handle);
-
-        // get the timestamp of the last entry of this metric
-        time_t (*latest_time)(RRDDIM *rd);
-
-        // get the timestamp of the first entry of this metric
-        time_t (*oldest_time)(RRDDIM *rd);
-    } query_ops;
-
+    STORAGE_COLLECT_HANDLE* handle;
+    struct rrddim_collect_ops collect_ops;
+    struct rrddim_query_ops query_ops;
     ml_dimension_t ml_dimension;
 };
 
@@ -434,6 +399,7 @@ struct rrddim_volatile {
 // volatile state per chart
 struct rrdset_volatile {
     char *old_title;
+    char *old_units;
     char *old_context;
     uuid_t hash_id;
     struct label *new_labels;
@@ -459,7 +425,6 @@ struct rrdset_volatile {
 // and may lead to missing information.
 
 typedef enum rrdset_flags {
-    RRDSET_FLAG_ENABLED             = 1 << 0, // enables or disables a chart
     RRDSET_FLAG_DETAIL              = 1 << 1, // if set, the data set should be considered as a detail of another
                                               // (the master data set should be the one that has the same family and is not detail)
     RRDSET_FLAG_DEBUG               = 1 << 2, // enables or disables debugging for a chart
@@ -483,16 +448,9 @@ typedef enum rrdset_flags {
     RRDSET_FLAG_ANOMALY_DETECTION   = 1 << 18 // flag to identify anomaly detection charts.
 } RRDSET_FLAGS;
 
-#ifdef HAVE_C___ATOMIC
 #define rrdset_flag_check(st, flag) (__atomic_load_n(&((st)->flags), __ATOMIC_SEQ_CST) & (flag))
 #define rrdset_flag_set(st, flag)   __atomic_or_fetch(&((st)->flags), flag, __ATOMIC_SEQ_CST)
 #define rrdset_flag_clear(st, flag) __atomic_and_fetch(&((st)->flags), ~flag, __ATOMIC_SEQ_CST)
-#else
-#define rrdset_flag_check(st, flag) ((st)->flags & (flag))
-#define rrdset_flag_set(st, flag)   (st)->flags |= (flag)
-#define rrdset_flag_clear(st, flag) (st)->flags &= ~(flag)
-#endif
-#define rrdset_flag_check_noatomic(st, flag) ((st)->flags & (flag))
 
 struct rrdset {
     // ------------------------------------------------------------------------
@@ -511,7 +469,7 @@ struct rrdset {
                                                     // since the config always has a higher priority
                                                     // (the user overwrites the name of the charts)
 
-    char *config_section;                           // the config section for the chart
+    void *unused_ptr;                               // Unused field (previously it held the config section of the chart)
 
     char *type;                                     // the type of graph RRD_TYPE_* (a category, for determining graphing options)
     char *family;                                   // grouping sets under the same family
@@ -642,15 +600,9 @@ typedef enum rrdhost_flags {
     RRDHOST_FLAG_PENDING_FOREACH_ALARMS  = 1 << 7, // contains dims with uninitialized foreach alarms
 } RRDHOST_FLAGS;
 
-#ifdef HAVE_C___ATOMIC
 #define rrdhost_flag_check(host, flag) (__atomic_load_n(&((host)->flags), __ATOMIC_SEQ_CST) & (flag))
 #define rrdhost_flag_set(host, flag)   __atomic_or_fetch(&((host)->flags), flag, __ATOMIC_SEQ_CST)
 #define rrdhost_flag_clear(host, flag) __atomic_and_fetch(&((host)->flags), ~flag, __ATOMIC_SEQ_CST)
-#else
-#define rrdhost_flag_check(host, flag) ((host)->flags & (flag))
-#define rrdhost_flag_set(host, flag)   (host)->flags |= (flag)
-#define rrdhost_flag_clear(host, flag) (host)->flags &= ~(flag)
-#endif
 
 #ifdef NETDATA_INTERNAL_CHECKS
 #define rrdset_debug(st, fmt, args...) do { if(unlikely(debug_flags & D_RRD_STATS && rrdset_flag_check(st, RRDSET_FLAG_DEBUG))) \
@@ -767,6 +719,7 @@ struct rrdhost_system_info {
     char *install_type;
     char *prebuilt_arch;
     char *prebuilt_dist;
+    int mc_version;
 };
 
 struct rrdhost {
@@ -815,6 +768,8 @@ struct rrdhost {
     unsigned int rrdpush_send_enabled;            // 1 when this host sends metrics to another netdata
     char *rrdpush_send_destination;                 // where to send metrics to
     char *rrdpush_send_api_key;                     // the api key at the receiving netdata
+    struct rrdpush_destinations *destinations;      // a linked list of possible destinations
+    struct rrdpush_destinations *destination;       // the current destination from the above list
 
     // the following are state information for the threading
     // streaming metrics from this netdata to an upstream netdata
@@ -842,10 +797,14 @@ struct rrdhost {
     volatile size_t connected_senders;              // when remote hosts are streaming to this
                                                     // host, this is the counter of connected clients
 
+    time_t senders_connect_time;                    // the time the last sender was connected
+    time_t senders_last_chart_command;              // the time of the last CHART streaming command
     time_t senders_disconnected_time;               // the time the last sender was disconnected
 
     struct receiver_state *receiver;
     netdata_mutex_t receiver_lock;
+    int trigger_chart_obsoletion_check;             // set when child connects, will instruct parent to
+                                                    // trigger a check for obsoleted charts since previous connect
 
     // ------------------------------------------------------------------------
     // health monitoring options
@@ -1120,8 +1079,8 @@ extern void rrdset_is_obsolete(RRDSET *st);
 extern void rrdset_isnot_obsolete(RRDSET *st);
 
 // checks if the RRDSET should be offered to viewers
-#define rrdset_is_available_for_viewers(st) (rrdset_flag_check(st, RRDSET_FLAG_ENABLED) && !rrdset_flag_check(st, RRDSET_FLAG_HIDDEN) && !rrdset_flag_check(st, RRDSET_FLAG_OBSOLETE) && !rrdset_flag_check(st, RRDSET_FLAG_ARCHIVED) && (st)->dimensions && (st)->rrd_memory_mode != RRD_MEMORY_MODE_NONE)
-#define rrdset_is_available_for_exporting_and_alarms(st) (rrdset_flag_check(st, RRDSET_FLAG_ENABLED) && !rrdset_flag_check(st, RRDSET_FLAG_OBSOLETE) && !rrdset_flag_check(st, RRDSET_FLAG_ARCHIVED) && (st)->dimensions)
+#define rrdset_is_available_for_viewers(st) (!rrdset_flag_check(st, RRDSET_FLAG_HIDDEN) && !rrdset_flag_check(st, RRDSET_FLAG_OBSOLETE) && !rrdset_flag_check(st, RRDSET_FLAG_ARCHIVED) && (st)->dimensions && (st)->rrd_memory_mode != RRD_MEMORY_MODE_NONE)
+#define rrdset_is_available_for_exporting_and_alarms(st) (!rrdset_flag_check(st, RRDSET_FLAG_OBSOLETE) && !rrdset_flag_check(st, RRDSET_FLAG_ARCHIVED) && (st)->dimensions)
 #define rrdset_is_archived(st) (rrdset_flag_check(st, RRDSET_FLAG_ARCHIVED) && (st)->dimensions)
 
 // get the total duration in seconds of the round robin database
@@ -1322,7 +1281,9 @@ extern void rrddim_isnot_obsolete(RRDSET *st, RRDDIM *rd);
 
 extern collected_number rrddim_set_by_pointer(RRDSET *st, RRDDIM *rd, collected_number value);
 extern collected_number rrddim_set(RRDSET *st, const char *id, collected_number value);
-
+#if defined(ENABLE_ACLK) && defined(ENABLE_NEW_CLOUD_PROTOCOL)
+extern time_t calc_dimension_liveness(RRDDIM *rd, time_t now);
+#endif
 extern long align_entries_to_pagesize(RRD_MEMORY_MODE mode, long entries);
 
 // ----------------------------------------------------------------------------
@@ -1339,10 +1300,9 @@ extern int alarm_compare_name(void *a, void *b);
 extern avl_tree_lock rrdhost_root_index;
 
 extern char *rrdset_strncpyz_name(char *to, const char *from, size_t length);
-extern char *rrdset_cache_dir(RRDHOST *host, const char *id, const char *config_section);
+extern char *rrdset_cache_dir(RRDHOST *host, const char *id);
 
-#define rrddim_free(st, rd) rrddim_free_custom(st, rd, 0)
-extern void rrddim_free_custom(RRDSET *st, RRDDIM *rd, int db_rotated);
+extern void rrddim_free(RRDSET *st, RRDDIM *rd);
 
 extern int rrddim_compare(void* a, void* b);
 extern int rrdset_compare(void* a, void* b);
diff --git a/database/rrdcalc.c b/database/rrdcalc.c
index 1b1a1496..b29a0ffc 100644
--- a/database/rrdcalc.c
+++ b/database/rrdcalc.c
@@ -81,35 +81,32 @@ static void rrdsetcalc_link(RRDSET *st, RRDCALC *rc) {
 
     if(!rc->units) rc->units = strdupz(st->units);
 
-    if(!rrdcalc_isrepeating(rc)) {
-        time_t now = now_realtime_sec();
-        ALARM_ENTRY *ae = health_create_alarm_entry(
-                host,
-                rc->id,
-                rc->next_event_id++,
-                rc->config_hash_id,
-                now,
-                rc->name,
-                rc->rrdset->id,
-                rc->rrdset->family,
-                rc->classification,
-                rc->component,
-                rc->type,
-                rc->exec,
-                rc->recipient,
-                now - rc->last_status_change,
-                rc->old_value,
-                rc->value,
-                rc->status,
-                RRDCALC_STATUS_UNINITIALIZED,
-                rc->source,
-                rc->units,
-                rc->info,
-                0,
-                0
-        );
-        health_alarm_log(host, ae);
-    }
+    time_t now = now_realtime_sec();
+    ALARM_ENTRY *ae = health_create_alarm_entry(
+        host,
+        rc->id,
+        rc->next_event_id++,
+        rc->config_hash_id,
+        now,
+        rc->name,
+        rc->rrdset->id,
+        rc->rrdset->family,
+        rc->classification,
+        rc->component,
+        rc->type,
+        rc->exec,
+        rc->recipient,
+        now - rc->last_status_change,
+        rc->old_value,
+        rc->value,
+        rc->status,
+        RRDCALC_STATUS_UNINITIALIZED,
+        rc->source,
+        rc->units,
+        rc->info,
+        0,
+        0);
+    health_alarm_log(host, ae);
 }
 
 static inline int rrdcalc_test_additional_restriction(RRDCALC *rc, RRDSET *st){
@@ -119,6 +116,31 @@ static inline int rrdcalc_test_additional_restriction(RRDCALC *rc, RRDSET *st){
     if (rc->plugin_match && !simple_pattern_matches(rc->plugin_pattern, st->plugin_name))
         return 0;
 
+    if (rc->labels) {
+        int labels_count=1;
+        int labels_match=0;
+        char *s = rc->labels;
+        while (*s) {
+            if (*s==' ')
+                labels_count++;
+            s++;
+        }
+        RRDHOST *host = st->rrdhost;
+        char cmp[CONFIG_FILE_LINE_MAX+1];
+        struct label *move = host->labels.head;
+        while(move) {
+            snprintf(cmp, CONFIG_FILE_LINE_MAX, "%s=%s", move->key, move->value);
+            if (simple_pattern_matches(rc->splabels, move->key) ||
+                simple_pattern_matches(rc->splabels, cmp)) {
+                labels_match++;
+            }
+            move = move->next;
+        }
+
+        if (labels_match != labels_count)
+            return 0;
+    }
+
     return 1;
 }
 
@@ -159,35 +181,32 @@ inline void rrdsetcalc_unlink(RRDCALC *rc) {
 
     RRDHOST *host = st->rrdhost;
 
-    if(!rrdcalc_isrepeating(rc)) {
-        time_t now = now_realtime_sec();
-        ALARM_ENTRY *ae = health_create_alarm_entry(
-                host,
-                rc->id,
-                rc->next_event_id++,
-                rc->config_hash_id,
-                now,
-                rc->name,
-                rc->rrdset->id,
-                rc->rrdset->family,
-                rc->classification,
-                rc->component,
-                rc->type,
-                rc->exec,
-                rc->recipient,
-                now - rc->last_status_change,
-                rc->old_value,
-                rc->value,
-                rc->status,
-                RRDCALC_STATUS_REMOVED,
-                rc->source,
-                rc->units,
-                rc->info,
-                0,
-                0
-        );
-        health_alarm_log(host, ae);
-    }
+    time_t now = now_realtime_sec();
+    ALARM_ENTRY *ae = health_create_alarm_entry(
+        host,
+        rc->id,
+        rc->next_event_id++,
+        rc->config_hash_id,
+        now,
+        rc->name,
+        rc->rrdset->id,
+        rc->rrdset->family,
+        rc->classification,
+        rc->component,
+        rc->type,
+        rc->exec,
+        rc->recipient,
+        now - rc->last_status_change,
+        rc->old_value,
+        rc->value,
+        rc->status,
+        RRDCALC_STATUS_REMOVED,
+        rc->source,
+        rc->units,
+        rc->info,
+        0,
+        0);
+    health_alarm_log(host, ae);
 
     debug(D_HEALTH, "Health unlinking alarm '%s.%s' from chart '%s' of host '%s'", rc->chart?rc->chart:"NOCHART", rc->name, st->id, host->hostname);
 
@@ -293,19 +312,15 @@ inline uint32_t rrdcalc_get_unique_id(RRDHOST *host, const char *chart, const ch
 char *alarm_name_with_dim(char *name, size_t namelen, const char *dim, size_t dimlen) {
     char *newname,*move;
 
-    newname = malloc(namelen + dimlen + 2);
-    if(newname) {
-        move = newname;
-        memcpy(move, name, namelen);
-        move += namelen;
+    newname = mallocz(namelen + dimlen + 2);
+    move = newname;
+    memcpy(move, name, namelen);
+    move += namelen;
 
-        *move++ = '_';
-        memcpy(move, dim, dimlen);
-        move += dimlen;
-        *move = '\0';
-    } else {
-        newname = name;
-    }
+    *move++ = '_';
+    memcpy(move, dim, dimlen);
+    move += dimlen;
+    *move = '\0';
 
     return newname;
 }
@@ -422,6 +437,7 @@ inline RRDCALC *rrdcalc_create_from_template(RRDHOST *host, RRDCALCTEMPLATE *rt,
     rc->delay_multiplier = rt->delay_multiplier;
 
     rc->last_repeat = 0;
+    rc->times_repeat = 0;
     rc->warn_repeat_every = rt->warn_repeat_every;
     rc->crit_repeat_every = rt->crit_repeat_every;
 
@@ -534,6 +550,7 @@ inline RRDCALC *rrdcalc_create_from_rrdcalc(RRDCALC *rc, RRDHOST *host, const ch
     newrc->delay_multiplier = rc->delay_multiplier;
 
     newrc->last_repeat = 0;
+    newrc->times_repeat = 0;
     newrc->warn_repeat_every = rc->warn_repeat_every;
     newrc->crit_repeat_every = rc->crit_repeat_every;
 
diff --git a/database/rrdcalc.h b/database/rrdcalc.h
index d7446f63..2ae47788 100644
--- a/database/rrdcalc.h
+++ b/database/rrdcalc.h
@@ -121,6 +121,7 @@ struct rrdcalc {
     time_t next_update;             // the next update timestamp of the alarm
     time_t last_status_change;      // the timestamp of the last time this alarm changed status
     time_t last_repeat; // the last time the alarm got repeated
+    uint32_t times_repeat;          // number of times the alarm got repeated
 
     time_t db_after;                // the first timestamp evaluated by the db lookup
     time_t db_before;               // the last timestamp evaluated by the db lookup
diff --git a/database/rrddim.c b/database/rrddim.c
index df45363b..e488d8b0 100644
--- a/database/rrddim.c
+++ b/database/rrddim.c
@@ -2,6 +2,10 @@
 
 #define NETDATA_RRD_INTERNALS
 #include "rrd.h"
+#ifdef ENABLE_DBENGINE
+#include "database/engine/rrdengineapi.h"
+#endif
+#include "storage_engine.h"
 
 // ----------------------------------------------------------------------------
 // RRDDIM index
@@ -38,14 +42,15 @@ inline RRDDIM *rrddim_find(RRDSET *st, const char *id) {
 // RRDDIM rename a dimension
 
 inline int rrddim_set_name(RRDSET *st, RRDDIM *rd, const char *name) {
-    if(unlikely(!name || !*name || !strcmp(rd->name, name)))
+    if(unlikely(!name || !*name || (rd->name && !strcmp(rd->name, name))))
         return 0;
 
     debug(D_RRD_CALLS, "rrddim_set_name() from %s.%s to %s.%s", st->name, rd->name, st->name, name);
 
-    char varname[CONFIG_MAX_NAME + 1];
-    snprintfz(varname, CONFIG_MAX_NAME, "dim %s name", rd->id);
-    rd->name = config_set_default(st->config_section, varname, name);
+    if (rd->name)
+        freez((void *) rd->name);
+
+    rd->name = strdupz(name);
     rd->hash_name = simple_hash(rd->name);
 
     if (!st->state->is_ar_chart)
@@ -96,113 +101,65 @@ inline int rrddim_set_divisor(RRDSET *st, RRDDIM *rd, collected_number divisor)
 }
 
 // ----------------------------------------------------------------------------
-// RRDDIM legacy data collection functions
-
-static void rrddim_collect_init(RRDDIM *rd) {
-    rd->values[rd->rrdset->current_entry] = SN_EMPTY_SLOT;
-}
-static void rrddim_collect_store_metric(RRDDIM *rd, usec_t point_in_time, storage_number number) {
-    (void)point_in_time;
-
-    rd->values[rd->rrdset->current_entry] = number;
-}
-static int rrddim_collect_finalize(RRDDIM *rd) {
-    (void)rd;
-
-    return 0;
-}
-
-// ----------------------------------------------------------------------------
-// RRDDIM legacy database query functions
-
-static void rrddim_query_init(RRDDIM *rd, struct rrddim_query_handle *handle, time_t start_time, time_t end_time) {
-    handle->rd = rd;
-    handle->start_time = start_time;
-    handle->end_time = end_time;
-    handle->slotted.slot = rrdset_time2slot(rd->rrdset, start_time);
-    handle->slotted.last_slot = rrdset_time2slot(rd->rrdset, end_time);
-    handle->slotted.finished = 0;
-}
-
-static storage_number rrddim_query_next_metric(struct rrddim_query_handle *handle, time_t *current_time) {
-    RRDDIM *rd = handle->rd;
-    long entries = rd->rrdset->entries;
-    long slot = handle->slotted.slot;
-
-    (void)current_time;
-    if (unlikely(handle->slotted.slot == handle->slotted.last_slot))
-        handle->slotted.finished = 1;
-    storage_number n = rd->values[slot++];
-
-    if(unlikely(slot >= entries)) slot = 0;
-    handle->slotted.slot = slot;
-
-    return n;
-}
-
-static int rrddim_query_is_finished(struct rrddim_query_handle *handle) {
-    return handle->slotted.finished;
-}
-
-static void rrddim_query_finalize(struct rrddim_query_handle *handle) {
-    (void)handle;
-
-    return;
-}
-
-static time_t rrddim_query_latest_time(RRDDIM *rd) {
-    return rrdset_last_entry_t_nolock(rd->rrdset);
-}
-
-static time_t rrddim_query_oldest_time(RRDDIM *rd) {
-    return rrdset_first_entry_t_nolock(rd->rrdset);
-}
-
-
-// ----------------------------------------------------------------------------
 // RRDDIM create a dimension
 
 void rrdcalc_link_to_rrddim(RRDDIM *rd, RRDSET *st, RRDHOST *host) {
     RRDCALC *rrdc;
+    
     for (rrdc = host->alarms_with_foreach; rrdc ; rrdc = rrdc->next) {
         if (simple_pattern_matches(rrdc->spdim, rd->id) || simple_pattern_matches(rrdc->spdim, rd->name)) {
             if (rrdc->hash_chart == st->hash_name || !strcmp(rrdc->chart, st->name) || !strcmp(rrdc->chart, st->id)) {
                 char *name = alarm_name_with_dim(rrdc->name, strlen(rrdc->name), rd->name, strlen(rd->name));
-                if (name) {
-                    if(rrdcalc_exists(host, st->name, name, 0, 0)){
-                        freez(name);
-                        continue;
-                    }
+                if(rrdcalc_exists(host, st->name, name, 0, 0)) {
+                    freez(name);
+                    continue;
+                }
+
+                netdata_rwlock_wrlock(&host->health_log.alarm_log_rwlock);
+                RRDCALC *child = rrdcalc_create_from_rrdcalc(rrdc, host, name, rd->name);
+                netdata_rwlock_unlock(&host->health_log.alarm_log_rwlock);
 
-                    RRDCALC *child = rrdcalc_create_from_rrdcalc(rrdc, host, name, rd->name);
-                    if (child) {
-                        rrdcalc_add_to_host(host, child);
-                        RRDCALC *rdcmp  = (RRDCALC *) avl_insert_lock(&(host)->alarms_idx_health_log,(avl_t *)child);
-                        if (rdcmp != child) {
-                            error("Cannot insert the alarm index ID %s",child->name);
-                        }
-                    } else {
-                        error("Cannot allocate a new alarm.");
-                        rrdc->foreachcounter--;
+                if (child) {
+                    rrdcalc_add_to_host(host, child);
+                    RRDCALC *rdcmp  = (RRDCALC *) avl_insert_lock(&(host)->alarms_idx_health_log,(avl_t *)child);
+                    if (rdcmp != child) {
+                        error("Cannot insert the alarm index ID %s",child->name);
                     }
                 }
+                else {
+                    error("Cannot allocate a new alarm.");
+                    rrdc->foreachcounter--;
+                }
             }
         }
     }
-#ifdef ENABLE_ACLK
-    rrdset_flag_clear(st, RRDSET_FLAG_ACLK);
-#endif
 }
 
+// Return either
+//   0 : Dimension is live
+//   last collected time : Dimension is not live
+
+#if defined(ENABLE_ACLK) && defined(ENABLE_NEW_CLOUD_PROTOCOL)
+time_t calc_dimension_liveness(RRDDIM *rd, time_t now)
+{
+    time_t last_updated = rd->last_collected_time.tv_sec;
+    int live;
+    if (rd->state->aclk_live_status == 1)
+        live =
+            ((now - last_updated) <
+             MIN(rrdset_free_obsolete_time, RRDSET_MINIMUM_DIM_OFFLINE_MULTIPLIER * rd->update_every));
+    else
+        live = ((now - last_updated) < RRDSET_MINIMUM_DIM_LIVE_MULTIPLIER * rd->update_every);
+    return live ? 0 : last_updated;
+}
+#endif
+
 RRDDIM *rrddim_add_custom(RRDSET *st, const char *id, const char *name, collected_number multiplier,
                           collected_number divisor, RRD_ALGORITHM algorithm, RRD_MEMORY_MODE memory_mode)
 {
     RRDHOST *host = st->rrdhost;
     rrdset_wrlock(st);
 
-    rrdset_flag_set(st, RRDSET_FLAG_SYNC_CLOCK);
-    rrdset_flag_clear(st, RRDSET_FLAG_UPSTREAM_EXPOSED);
-
     RRDDIM *rd = rrddim_find(st, id);
     if(unlikely(rd)) {
         debug(D_RRD_CALLS, "Cannot create rrd dimension '%s/%s', it already exists.", st->id, name?name:"<NONAME>");
@@ -227,11 +184,19 @@ RRDDIM *rrddim_add_custom(RRDSET *st, const char *id, const char *name, collecte
             debug(D_METADATALOG, "DIMENSION [%s] metadata updated", rd->id);
             (void)sql_store_dimension(&rd->state->metric_uuid, rd->rrdset->chart_uuid, rd->id, rd->name, rd->multiplier, rd->divisor,
                                       rd->algorithm);
+#if defined(ENABLE_ACLK) && defined(ENABLE_NEW_CLOUD_PROTOCOL)
+            queue_dimension_to_aclk(rd, calc_dimension_liveness(rd, now_realtime_sec()));
+#endif
+            rrdset_flag_set(st, RRDSET_FLAG_SYNC_CLOCK);
+            rrdset_flag_clear(st, RRDSET_FLAG_UPSTREAM_EXPOSED);
         }
         rrdset_unlock(st);
         return rd;
     }
 
+    rrdset_flag_set(st, RRDSET_FLAG_SYNC_CLOCK);
+    rrdset_flag_clear(st, RRDSET_FLAG_UPSTREAM_EXPOSED);
+
     char filename[FILENAME_MAX + 1];
     char fullfilename[FILENAME_MAX + 1];
 
@@ -244,12 +209,11 @@ RRDDIM *rrddim_add_custom(RRDSET *st, const char *id, const char *name, collecte
 
     if(memory_mode == RRD_MEMORY_MODE_SAVE || memory_mode == RRD_MEMORY_MODE_MAP ||
        memory_mode == RRD_MEMORY_MODE_RAM) {
-        rd = (RRDDIM *)mymmap(
-                  (memory_mode == RRD_MEMORY_MODE_RAM) ? NULL : fullfilename
-                , size
-                , ((memory_mode == RRD_MEMORY_MODE_MAP) ? MAP_SHARED : MAP_PRIVATE)
-                , 1
-        );
+        rd = (RRDDIM *)netdata_mmap(
+            (memory_mode == RRD_MEMORY_MODE_RAM) ? NULL : fullfilename,
+            size,
+            ((memory_mode == RRD_MEMORY_MODE_MAP) ? MAP_SHARED : MAP_PRIVATE),
+            1);
 
         if(likely(rd)) {
             // we have a file mapped for rd
@@ -369,30 +333,16 @@ RRDDIM *rrddim_add_custom(RRDSET *st, const char *id, const char *name, collecte
     rd->state->aclk_live_status = -1;
 #endif
     (void) find_dimension_uuid(st, rd, &(rd->state->metric_uuid));
-    if(memory_mode == RRD_MEMORY_MODE_DBENGINE) {
+
+    STORAGE_ENGINE* eng = storage_engine_get(memory_mode);
+    rd->state->collect_ops = eng->api.collect_ops;
+    rd->state->query_ops = eng->api.query_ops;
+
 #ifdef ENABLE_DBENGINE
+    if(memory_mode == RRD_MEMORY_MODE_DBENGINE) {
         rrdeng_metric_init(rd);
-        rd->state->collect_ops.init = rrdeng_store_metric_init;
-        rd->state->collect_ops.store_metric = rrdeng_store_metric_next;
-        rd->state->collect_ops.finalize = rrdeng_store_metric_finalize;
-        rd->state->query_ops.init = rrdeng_load_metric_init;
-        rd->state->query_ops.next_metric = rrdeng_load_metric_next;
-        rd->state->query_ops.is_finished = rrdeng_load_metric_is_finished;
-        rd->state->query_ops.finalize = rrdeng_load_metric_finalize;
-        rd->state->query_ops.latest_time = rrdeng_metric_latest_time;
-        rd->state->query_ops.oldest_time = rrdeng_metric_oldest_time;
-#endif
-    } else {
-        rd->state->collect_ops.init         = rrddim_collect_init;
-        rd->state->collect_ops.store_metric = rrddim_collect_store_metric;
-        rd->state->collect_ops.finalize     = rrddim_collect_finalize;
-        rd->state->query_ops.init           = rrddim_query_init;
-        rd->state->query_ops.next_metric    = rrddim_query_next_metric;
-        rd->state->query_ops.is_finished    = rrddim_query_is_finished;
-        rd->state->query_ops.finalize       = rrddim_query_finalize;
-        rd->state->query_ops.latest_time    = rrddim_query_latest_time;
-        rd->state->query_ops.oldest_time    = rrddim_query_oldest_time;
     }
+#endif
     store_active_dimension(&rd->state->metric_uuid);
     rd->state->collect_ops.init(rd);
     // append this dimension
@@ -437,22 +387,16 @@ RRDDIM *rrddim_add_custom(RRDSET *st, const char *id, const char *name, collecte
     ml_new_dimension(rd);
 
     rrdset_unlock(st);
-#ifdef ENABLE_ACLK
-    rrdset_flag_clear(st, RRDSET_FLAG_ACLK);
-#endif
     return(rd);
 }
 
 // ----------------------------------------------------------------------------
 // RRDDIM remove / free a dimension
 
-void rrddim_free_custom(RRDSET *st, RRDDIM *rd, int db_rotated)
+void rrddim_free(RRDSET *st, RRDDIM *rd)
 {
     ml_delete_dimension(rd);
-
-#ifndef ENABLE_ACLK
-    UNUSED(db_rotated);
-#endif
+    
     debug(D_RRD_CALLS, "rrddim_free() %s.%s", st->name, rd->name);
 
     if (!rrddim_flag_check(rd, RRDDIM_FLAG_ARCHIVED)) {
@@ -483,10 +427,10 @@ void rrddim_free_custom(RRDSET *st, RRDDIM *rd, int db_rotated)
         error("RRDDIM: INTERNAL ERROR: attempt to remove from index dimension '%s' on chart '%s', removed a different dimension.", rd->id, st->id);
 
     // free(rd->annotations);
-#if defined(ENABLE_ACLK) && defined(ENABLE_NEW_CLOUD_PROTOCOL)
-    if (!netdata_exit)
-        aclk_send_dimension_update(rd);
-#endif
+//#if defined(ENABLE_ACLK) && defined(ENABLE_NEW_CLOUD_PROTOCOL)
+//    if (!netdata_exit)
+//        aclk_send_dimension_update(rd);
+//#endif
 
     RRD_MEMORY_MODE rrd_memory_mode = rd->rrd_memory_mode;
     switch(rrd_memory_mode) {
@@ -512,10 +456,6 @@ void rrddim_free_custom(RRDSET *st, RRDDIM *rd, int db_rotated)
             freez(rd);
             break;
     }
-#ifdef ENABLE_ACLK
-    if (db_rotated || RRD_MEMORY_MODE_DBENGINE != rrd_memory_mode)
-        rrdset_flag_clear(st, RRDSET_FLAG_ACLK);
-#endif
 }
 
 
@@ -532,12 +472,11 @@ int rrddim_hide(RRDSET *st, const char *id) {
         error("Cannot find dimension with id '%s' on stats '%s' (%s) on host '%s'.", id, st->name, st->id, host->hostname);
         return 1;
     }
-    (void) sql_set_dimension_option(&rd->state->metric_uuid, "hidden");
+    if (!rrddim_flag_check(rd, RRDDIM_FLAG_META_HIDDEN))
+        (void)sql_set_dimension_option(&rd->state->metric_uuid, "hidden");
 
     rrddim_flag_set(rd, RRDDIM_FLAG_HIDDEN);
-#ifdef ENABLE_ACLK
-    rrdset_flag_clear(st, RRDSET_FLAG_ACLK);
-#endif
+    rrddim_flag_set(rd, RRDDIM_FLAG_META_HIDDEN);
     return 0;
 }
 
@@ -550,12 +489,11 @@ int rrddim_unhide(RRDSET *st, const char *id) {
         error("Cannot find dimension with id '%s' on stats '%s' (%s) on host '%s'.", id, st->name, st->id, host->hostname);
         return 1;
     }
-    (void) sql_set_dimension_option(&rd->state->metric_uuid, NULL);
+    if (rrddim_flag_check(rd, RRDDIM_FLAG_META_HIDDEN))
+        (void)sql_set_dimension_option(&rd->state->metric_uuid, NULL);
 
     rrddim_flag_clear(rd, RRDDIM_FLAG_HIDDEN);
-#ifdef ENABLE_ACLK
-    rrdset_flag_clear(st, RRDSET_FLAG_ACLK);
-#endif
+    rrddim_flag_clear(rd, RRDDIM_FLAG_META_HIDDEN);
     return 0;
 }
 
@@ -568,18 +506,12 @@ inline void rrddim_is_obsolete(RRDSET *st, RRDDIM *rd) {
     }
     rrddim_flag_set(rd, RRDDIM_FLAG_OBSOLETE);
     rrdset_flag_set(st, RRDSET_FLAG_OBSOLETE_DIMENSIONS);
-#ifdef ENABLE_ACLK
-    rrdset_flag_clear(st, RRDSET_FLAG_ACLK);
-#endif
 }
 
 inline void rrddim_isnot_obsolete(RRDSET *st __maybe_unused, RRDDIM *rd) {
     debug(D_RRD_CALLS, "rrddim_isnot_obsolete() for chart %s, dimension %s", st->name, rd->name);
 
     rrddim_flag_clear(rd, RRDDIM_FLAG_OBSOLETE);
-#ifdef ENABLE_ACLK
-    rrdset_flag_clear(st, RRDSET_FLAG_ACLK);
-#endif
 }
 
 // ----------------------------------------------------------------------------
diff --git a/database/rrdhost.c b/database/rrdhost.c
index 649736ca..cb56bf35 100644
--- a/database/rrdhost.c
+++ b/database/rrdhost.c
@@ -181,6 +181,8 @@ RRDHOST *rrdhost_create(const char *hostname,
 
     host->rrdpush_send_enabled     = (rrdpush_enabled && rrdpush_destination && *rrdpush_destination && rrdpush_api_key && *rrdpush_api_key) ? 1 : 0;
     host->rrdpush_send_destination = (host->rrdpush_send_enabled)?strdupz(rrdpush_destination):NULL;
+    if (host->rrdpush_send_destination)
+        host->destinations = destinations_init(host->rrdpush_send_destination);
     host->rrdpush_send_api_key     = (host->rrdpush_send_enabled)?strdupz(rrdpush_api_key):NULL;
     host->rrdpush_send_charts_matching = simple_pattern_create(rrdpush_send_charts_matching, NULL, SIMPLE_PATTERN_EXACT);
 
@@ -390,6 +392,7 @@ RRDHOST *rrdhost_create(const char *hostname,
     if (is_localhost && host->system_info) {
         host->system_info->ml_capable = ml_capable();
         host->system_info->ml_enabled = ml_enabled(host);
+        host->system_info->mc_version = enable_metric_correlations ? metric_correlations_version : 0;
     }
 
     ml_new_host(host);
@@ -698,7 +701,7 @@ int rrd_init(char *hostname, struct rrdhost_system_info *system_info) {
     if (gap_when_lost_iterations_above < 1)
         gap_when_lost_iterations_above = 1;
 
-    if (unlikely(sql_init_database(DB_CHECK_NONE))) {
+    if (unlikely(sql_init_database(DB_CHECK_NONE, 0))) {
         if (default_rrd_memory_mode == RRD_MEMORY_MODE_DBENGINE)
             fatal("Failed to initialize SQLite");
         info("Skipping SQLITE metadata initialization since memory mode is not db engine");
@@ -1488,9 +1491,8 @@ restart_after_removal:
                             continue;
                         }
 #if defined(ENABLE_ACLK) && defined(ENABLE_NEW_CLOUD_PROTOCOL)
-                        else {
-                            aclk_send_dimension_update(rd);
-                        }
+                        else
+                            queue_dimension_to_aclk(rd, rd->last_collected_time.tv_sec);
 #endif
                     }
                     last = rd;
@@ -1528,6 +1530,18 @@ restart_after_removal:
     }
 }
 
+void rrdset_check_obsoletion(RRDHOST *host)
+{
+    RRDSET *st;
+    time_t last_entry_t;
+    rrdset_foreach_read(st, host) {
+        last_entry_t = rrdset_last_entry_t(st);
+        if (last_entry_t && last_entry_t < host->senders_connect_time) {
+            rrdset_is_obsolete(st);
+        }
+    }
+}
+
 void rrd_cleanup_obsolete_charts()
 {
     rrd_rdlock();
@@ -1547,6 +1561,16 @@ void rrd_cleanup_obsolete_charts()
 #endif
             rrdhost_unlock(host);
         }
+
+        if (host != localhost &&
+            host->trigger_chart_obsoletion_check &&
+            host->senders_last_chart_command &&
+            host->senders_last_chart_command + 120 < now_realtime_sec()) {
+            rrdhost_rdlock(host);
+            rrdset_check_obsoletion(host);
+            rrdhost_unlock(host);
+            host->trigger_chart_obsoletion_check = 0;
+        }
     }
 
     rrd_unlock();
diff --git a/database/rrdset.c b/database/rrdset.c
index f8e471be..e7cb89df 100644
--- a/database/rrdset.c
+++ b/database/rrdset.c
@@ -125,7 +125,7 @@ char *rrdset_strncpyz_name(char *to, const char *from, size_t length) {
     char c, *p = to;
 
     while (length-- && (c = *from++)) {
-        if(c != '.' && !isalnum(c))
+        if(c != '.' && c != '-' && !isalnum(c))
             c = '_';
 
         *p++ = c;
@@ -366,11 +366,6 @@ void rrdset_free(RRDSET *st) {
     rrdvar_free_remaining_variables(host, &st->rrdvar_root_index);
 
     // ------------------------------------------------------------------------
-    // remove it from the configuration
-
-    appconfig_section_destroy_non_loaded(&netdata_config, st->config_section);
-
-    // ------------------------------------------------------------------------
     // unlink it from the host
 
     if(st == host->rrdset_root) {
@@ -402,10 +397,10 @@ void rrdset_free(RRDSET *st) {
     freez(st->units);
     freez(st->context);
     freez(st->cache_dir);
-    freez(st->config_section);
     freez(st->plugin_name);
     freez(st->module_name);
     freez(st->state->old_title);
+    freez(st->state->old_units);
     freez(st->state->old_context);
     free_label_list(st->state->labels.head);
     freez(st->state);
@@ -557,6 +552,10 @@ RRDSET *rrdset_create_custom(
         return NULL;
     }
 
+    if (host != localhost) {
+        host->senders_last_chart_command = now_realtime_sec();
+    }
+
     // ------------------------------------------------------------------------
     // check if it already exists
 
@@ -567,15 +566,13 @@ RRDSET *rrdset_create_custom(
     RRDSET *st = rrdset_find_on_create(host, fullid);
     if (st) {
         int mark_rebuild = 0;
-        rrdset_flag_set(st, RRDSET_FLAG_SYNC_CLOCK);
-        rrdset_flag_clear(st, RRDSET_FLAG_UPSTREAM_EXPOSED);
         if (rrdset_flag_check(st, RRDSET_FLAG_ARCHIVED)) {
             rrdset_flag_clear(st, RRDSET_FLAG_ARCHIVED);
             changed_from_archived_to_active = 1;
             mark_rebuild |= META_CHART_ACTIVATED;
         }
         char *old_plugin = NULL, *old_module = NULL, *old_title = NULL, *old_context = NULL,
-             *old_title_v = NULL, *old_context_v = NULL;
+             *old_title_v = NULL, *old_context_v = NULL, *old_units_v = NULL, *old_units = NULL;
         int rc;
 
         if(unlikely(name))
@@ -635,6 +632,17 @@ RRDSET *rrdset_create_custom(
             mark_rebuild |= META_CHART_UPDATED;
         }
 
+        if (unlikely(units && st->state->old_units && strcmp(st->state->old_units, units))) {
+            char *new_units = strdupz(units);
+            old_units_v = st->state->old_units;
+            st->state->old_units = strdupz(units);
+            json_fix_string(new_units);
+            old_units= st->units;
+            st->units = new_units;
+            mark_rebuild |= META_CHART_UPDATED;
+        }
+
+
         if (st->chart_type != chart_type) {
             st->chart_type = chart_type;
             mark_rebuild |= META_CHART_UPDATED;
@@ -671,8 +679,10 @@ RRDSET *rrdset_create_custom(
             freez(old_plugin);
             freez(old_module);
             freez(old_title);
+            freez(old_units);
             freez(old_context);
             freez(old_title_v);
+            freez(old_units_v);
             freez(old_context_v);
             if (mark_rebuild != META_CHART_ACTIVATED) {
                 info("Collector updated metadata for chart %s", st->id);
@@ -684,6 +694,11 @@ RRDSET *rrdset_create_custom(
             int rc = update_chart_metadata(st->chart_uuid, st, id, name);
             if (unlikely(rc))
                 error_report("Failed to update chart metadata in the database");
+
+            if (!changed_from_archived_to_active) {
+                rrdset_flag_set(st, RRDSET_FLAG_SYNC_CLOCK);
+                rrdset_flag_clear(st, RRDSET_FLAG_UPSTREAM_EXPOSED);
+            }
         }
         /* Fall-through during switch from archived to active so that the host lock is taken and health is linked */
         if (!changed_from_archived_to_active)
@@ -713,26 +728,14 @@ RRDSET *rrdset_create_custom(
     char fullfilename[FILENAME_MAX + 1];
 
     // ------------------------------------------------------------------------
-    // compose the config_section for this chart
-
-    char config_section[RRD_ID_LENGTH_MAX + GUID_LEN + 2];
-    if(host == localhost)
-        strcpy(config_section, fullid);
-    else
-        snprintfz(config_section, RRD_ID_LENGTH_MAX + GUID_LEN + 1, "%s/%s", host->machine_guid, fullid);
-
-    // ------------------------------------------------------------------------
     // get the options from the config, we need to create it
 
-    long entries;
-    int enabled = config_get_boolean(config_section, "enabled", 1);
-    if(!enabled || memory_mode == RRD_MEMORY_MODE_DBENGINE)
-        entries = 5;
-    else
+    long entries = 5;
+    if (memory_mode != RRD_MEMORY_MODE_DBENGINE)
         entries = align_entries_to_pagesize(memory_mode, history_entries);
 
     unsigned long size = sizeof(RRDSET);
-    char *cache_dir = rrdset_cache_dir(host, fullid, config_section);
+    char *cache_dir = rrdset_cache_dir(host, fullid);
 
     time_t now = now_realtime_sec();
 
@@ -744,12 +747,11 @@ RRDSET *rrdset_create_custom(
     snprintfz(fullfilename, FILENAME_MAX, "%s/main.db", cache_dir);
     if(memory_mode == RRD_MEMORY_MODE_SAVE || memory_mode == RRD_MEMORY_MODE_MAP ||
        memory_mode == RRD_MEMORY_MODE_RAM) {
-        st = (RRDSET *) mymmap(
-                  (memory_mode == RRD_MEMORY_MODE_RAM) ? NULL : fullfilename
-                , size
-                , ((memory_mode == RRD_MEMORY_MODE_MAP) ? MAP_SHARED : MAP_PRIVATE)
-                , 0
-        );
+        st = (RRDSET *)netdata_mmap(
+            (memory_mode == RRD_MEMORY_MODE_RAM) ? NULL : fullfilename,
+            size,
+            ((memory_mode == RRD_MEMORY_MODE_MAP) ? MAP_SHARED : MAP_PRIVATE),
+            0);
 
         if(st) {
             memset(&st->avl, 0, sizeof(avl_t));
@@ -759,7 +761,6 @@ RRDSET *rrdset_create_custom(
             memset(&st->rrdset_rwlock, 0, sizeof(netdata_rwlock_t));
 
             st->name = NULL;
-            st->config_section = NULL;
             st->type = NULL;
             st->family = NULL;
             st->title = NULL;
@@ -832,7 +833,6 @@ RRDSET *rrdset_create_custom(
     st->plugin_name = plugin?strdupz(plugin):NULL;
     st->module_name = module?strdupz(module):NULL;
 
-    st->config_section = strdupz(config_section);
     st->rrdhost = host;
     st->memsize = size;
     st->entries = entries;
@@ -859,6 +859,7 @@ RRDSET *rrdset_create_custom(
     st->state->is_ar_chart = strcmp(st->id, ML_ANOMALY_RATES_CHART_ID) == 0;
 
     st->units = units ? strdupz(units) : strdupz("");
+    st->state->old_units = strdupz(st->units);
     json_fix_string(st->units);
 
     st->context = context ? strdupz(context) : strdupz(st->id);
@@ -867,27 +868,9 @@ RRDSET *rrdset_create_custom(
     st->hash_context = simple_hash(st->context);
 
     st->priority = priority;
-    if(enabled)
-        rrdset_flag_set(st, RRDSET_FLAG_ENABLED);
-    else
-        rrdset_flag_clear(st, RRDSET_FLAG_ENABLED);
 
-    rrdset_flag_clear(st, RRDSET_FLAG_DETAIL);
-    rrdset_flag_clear(st, RRDSET_FLAG_DEBUG);
-    rrdset_flag_clear(st, RRDSET_FLAG_OBSOLETE);
-    rrdset_flag_clear(st, RRDSET_FLAG_EXPORTING_SEND);
-    rrdset_flag_clear(st, RRDSET_FLAG_EXPORTING_IGNORE);
-    rrdset_flag_clear(st, RRDSET_FLAG_UPSTREAM_SEND);
-    rrdset_flag_clear(st, RRDSET_FLAG_UPSTREAM_IGNORE);
-    rrdset_flag_clear(st, RRDSET_FLAG_UPSTREAM_EXPOSED);
     rrdset_flag_set(st, RRDSET_FLAG_SYNC_CLOCK);
 
-    // if(!strcmp(st->id, "disk_util.dm-0")) {
-    //     st->debug = 1;
-    //     error("enabled debugging for '%s'", st->id);
-    // }
-    // else error("not enabled debugging for '%s'", st->id);
-
     st->green = NAN;
     st->red = NAN;
 
@@ -960,7 +943,7 @@ RRDSET *rrdset_create_custom(
 // RRDSET - data collection iteration control
 
 inline void rrdset_next_usec_unfiltered(RRDSET *st, usec_t microseconds) {
-    if(unlikely(!st->last_collected_time.tv_sec || !microseconds || (rrdset_flag_check_noatomic(st, RRDSET_FLAG_SYNC_CLOCK)))) {
+    if(unlikely(!st->last_collected_time.tv_sec || !microseconds || (rrdset_flag_check(st, RRDSET_FLAG_SYNC_CLOCK)))) {
         // call the full next_usec() function
         rrdset_next_usec(st, microseconds);
         return;
@@ -978,7 +961,7 @@ inline void rrdset_next_usec(RRDSET *st, usec_t microseconds) {
     usec_t discarded = microseconds;
     #endif
 
-    if(unlikely(rrdset_flag_check_noatomic(st, RRDSET_FLAG_SYNC_CLOCK))) {
+    if(unlikely(rrdset_flag_check(st, RRDSET_FLAG_SYNC_CLOCK))) {
         // the chart needs to be re-synced to current time
         rrdset_flag_clear(st, RRDSET_FLAG_SYNC_CLOCK);
 
@@ -1010,7 +993,9 @@ inline void rrdset_next_usec(RRDSET *st, usec_t microseconds) {
 
         if(unlikely(since_last_usec < 0)) {
             // oops! the database is in the future
+            #ifdef NETDATA_INTERNAL_CHECKS
             info("RRD database for chart '%s' on host '%s' is %0.5" LONG_DOUBLE_MODIFIER " secs in the future (counter #%zu, update #%zu). Adjusting it to current time.", st->id, st->rrdhost->hostname, (LONG_DOUBLE)-since_last_usec / USEC_PER_SEC, st->counter, st->counter_done);
+            #endif
 
             st->last_collected_time.tv_sec  = now.tv_sec - st->update_every;
             st->last_collected_time.tv_usec = now.tv_usec;
@@ -1027,7 +1012,9 @@ inline void rrdset_next_usec(RRDSET *st, usec_t microseconds) {
         }
         else if(unlikely((usec_t)since_last_usec > (usec_t)(st->update_every * 5 * USEC_PER_SEC))) {
             // oops! the database is too far behind
+            #ifdef NETDATA_INTERNAL_CHECKS
             info("RRD database for chart '%s' on host '%s' is %0.5" LONG_DOUBLE_MODIFIER " secs in the past (counter #%zu, update #%zu). Adjusting it to current time.", st->id, st->rrdhost->hostname, (LONG_DOUBLE)since_last_usec / USEC_PER_SEC, st->counter, st->counter_done);
+            #endif
 
             microseconds = (usec_t)since_last_usec;
             #ifdef NETDATA_INTERNAL_CHECKS
@@ -1403,8 +1390,9 @@ void rrdset_done(RRDSET *st) {
 #ifdef ENABLE_ACLK
     if (likely(!st->state->is_ar_chart)) {
         if (unlikely(!rrdset_flag_check(st, RRDSET_FLAG_ACLK))) {
-            if (likely(st->dimensions && st->counter_done && !queue_chart_to_aclk(st)))
+            if (likely(st->dimensions && st->counter_done && !queue_chart_to_aclk(st))) {
                 rrdset_flag_set(st, RRDSET_FLAG_ACLK);
+            }
         }
     }
 #endif
@@ -1823,7 +1811,7 @@ after_first_database_work:
 after_second_database_work:
     st->last_collected_total  = st->collected_total;
 
-#ifdef ENABLE_NEW_CLOUD_PROTOCOL
+#if defined(ENABLE_ACLK) && defined(ENABLE_NEW_CLOUD_PROTOCOL)
     time_t mark = now_realtime_sec();
 #endif
     rrddim_foreach_read(rd, st) {
@@ -1831,20 +1819,10 @@ after_second_database_work:
             continue;
 
 #if defined(ENABLE_ACLK) && defined(ENABLE_NEW_CLOUD_PROTOCOL)
-    if (likely(!st->state->is_ar_chart)) {
-        if (!rrddim_flag_check(rd, RRDDIM_FLAG_HIDDEN)) {
-            int live =
-                ((mark - rd->last_collected_time.tv_sec) < RRDSET_MINIMUM_DIM_LIVE_MULTIPLIER * rd->update_every);
-            if (unlikely(live != rd->state->aclk_live_status)) {
-                if (likely(rrdset_flag_check(st, RRDSET_FLAG_ACLK))) {
-                    if (likely(!queue_dimension_to_aclk(rd))) {
-                        rd->state->aclk_live_status = live;
-                        rrddim_flag_set(rd, RRDDIM_FLAG_ACLK);
-                    }
-                }
-            }
+        if (likely(!st->state->is_ar_chart)) {
+            if (!rrddim_flag_check(rd, RRDDIM_FLAG_HIDDEN) && likely(rrdset_flag_check(st, RRDSET_FLAG_ACLK)))
+                queue_dimension_to_aclk(rd, calc_dimension_liveness(rd, mark));
         }
-    }
 #endif
         if(unlikely(!rd->updated))
             continue;
@@ -1946,7 +1924,7 @@ after_second_database_work:
                         } else {
                             /* Do not delete this dimension */
 #if defined(ENABLE_ACLK) && defined(ENABLE_NEW_CLOUD_PROTOCOL)
-                            aclk_send_dimension_update(rd);
+                            queue_dimension_to_aclk(rd, calc_dimension_liveness(rd, mark));
 #endif
                             last = rd;
                             rd = rd->next;
@@ -1996,7 +1974,7 @@ void rrdset_finalize_labels(RRDSET *st)
         replace_label_list(labels, new_labels);
     }
 
-    netdata_rwlock_wrlock(&labels->labels_rwlock);
+    netdata_rwlock_rdlock(&labels->labels_rwlock);
     struct label *lbl = labels->head;
     while (lbl) {
         sql_store_chart_label(st->chart_uuid, (int)lbl->label_source, lbl->key, lbl->value);
diff --git a/database/sqlite/sqlite_aclk.c b/database/sqlite/sqlite_aclk.c
index 98932809..950856d9 100644
--- a/database/sqlite/sqlite_aclk.c
+++ b/database/sqlite/sqlite_aclk.c
@@ -10,6 +10,11 @@
 #include "../../aclk/aclk.h"
 #endif
 
+void sanity_check(void) {
+    // make sure the compiler will stop on misconfigurations
+    BUILD_BUG_ON(WORKER_UTILIZATION_MAX_JOB_TYPES < ACLK_MAX_ENUMERATIONS_DEFINED);
+}
+
 const char *aclk_sync_config[] = {
     "CREATE TABLE IF NOT EXISTS dimension_delete (dimension_id blob, dimension_name text, chart_type_id text, "
     "dim_id blob, chart_id blob, host_id blob, date_created);",
@@ -29,6 +34,28 @@ const char *aclk_sync_config[] = {
 
 uv_mutex_t aclk_async_lock;
 struct aclk_database_worker_config  *aclk_thread_head = NULL;
+int retention_running = 0;
+
+#ifdef ENABLE_NEW_CLOUD_PROTOCOL
+static void stop_retention_run()
+{
+    uv_mutex_lock(&aclk_async_lock);
+    retention_running = 0;
+    uv_mutex_unlock(&aclk_async_lock);
+}
+
+static int request_retention_run()
+{
+    int rc = 0;
+    uv_mutex_lock(&aclk_async_lock);
+    if (unlikely(retention_running))
+        rc = 1;
+    else
+        retention_running = 1;
+    uv_mutex_unlock(&aclk_async_lock);
+    return rc;
+}
+#endif
 
 int claimed()
 {
@@ -313,9 +340,6 @@ static void timer_cb(uv_timer_t* handle)
 
     if (aclk_use_new_cloud_arch && aclk_connected) {
         if (wc->rotation_after && wc->rotation_after < now) {
-            cmd.opcode = ACLK_DATABASE_NODE_INFO;
-            aclk_database_enq_cmd_noblock(wc, &cmd);
-
             cmd.opcode = ACLK_DATABASE_UPD_RETENTION;
             if (!aclk_database_enq_cmd_noblock(wc, &cmd))
                 wc->rotation_after += ACLK_DATABASE_ROTATION_INTERVAL;
@@ -339,7 +363,7 @@ static void timer_cb(uv_timer_t* handle)
             }
         }
 
-        if (wc->alert_updates) {
+        if (wc->alert_updates && !wc->pause_alert_updates) {
             cmd.opcode = ACLK_DATABASE_PUSH_ALERT;
             cmd.count = ACLK_MAX_ALERT_UPDATES;
             aclk_database_enq_cmd_noblock(wc, &cmd);
@@ -348,10 +372,65 @@ static void timer_cb(uv_timer_t* handle)
 #endif
 }
 
+
+#ifdef ENABLE_NEW_CLOUD_PROTOCOL
+void after_send_retention(uv_work_t *req, int status)
+{
+    struct aclk_database_worker_config *wc = req->data;
+    (void)status;
+    stop_retention_run();
+    wc->retention_running = 0;
+
+    struct aclk_database_cmd cmd;
+    memset(&cmd, 0, sizeof(cmd));
+    cmd.opcode = ACLK_DATABASE_DIM_DELETION;
+    if (aclk_database_enq_cmd_noblock(wc, &cmd))
+        info("Failed to queue a dimension deletion message");
+
+    cmd.opcode = ACLK_DATABASE_NODE_INFO;
+    if (aclk_database_enq_cmd_noblock(wc, &cmd))
+        info("Failed to queue a node update info message");
+}
+
+
+static void send_retention(uv_work_t *req)
+{
+    struct aclk_database_worker_config *wc = req->data;
+
+    if (unlikely(wc->is_shutting_down))
+        return;
+
+    aclk_update_retention(wc);
+}
+#endif
+
 #define MAX_CMD_BATCH_SIZE (256)
 
 void aclk_database_worker(void *arg)
 {
+    worker_register("ACLKSYNC");
+    worker_register_job_name(ACLK_DATABASE_NOOP,                 "noop");
+#ifdef ENABLE_NEW_CLOUD_PROTOCOL
+    worker_register_job_name(ACLK_DATABASE_ADD_CHART,            "chart add");
+    worker_register_job_name(ACLK_DATABASE_ADD_DIMENSION,        "dimension add");
+    worker_register_job_name(ACLK_DATABASE_PUSH_CHART,           "chart push");
+    worker_register_job_name(ACLK_DATABASE_PUSH_CHART_CONFIG,    "chart conf push");
+    worker_register_job_name(ACLK_DATABASE_RESET_CHART,          "chart reset");
+    worker_register_job_name(ACLK_DATABASE_CHART_ACK,            "chart ack");
+    worker_register_job_name(ACLK_DATABASE_UPD_RETENTION,        "retention check");
+    worker_register_job_name(ACLK_DATABASE_DIM_DELETION,         "dimension delete");
+    worker_register_job_name(ACLK_DATABASE_ORPHAN_HOST,          "node orphan");
+#endif
+    worker_register_job_name(ACLK_DATABASE_ALARM_HEALTH_LOG,     "alert log");
+    worker_register_job_name(ACLK_DATABASE_CLEANUP,              "cleanup");
+    worker_register_job_name(ACLK_DATABASE_DELETE_HOST,          "node delete");
+    worker_register_job_name(ACLK_DATABASE_NODE_INFO,            "node info");
+    worker_register_job_name(ACLK_DATABASE_PUSH_ALERT,           "alert push");
+    worker_register_job_name(ACLK_DATABASE_PUSH_ALERT_CONFIG,    "alert conf push");
+    worker_register_job_name(ACLK_DATABASE_PUSH_ALERT_SNAPSHOT,  "alert snapshot");
+    worker_register_job_name(ACLK_DATABASE_QUEUE_REMOVED_ALERTS, "alerts check");
+    worker_register_job_name(ACLK_DATABASE_TIMER,                "timer");
+
     struct aclk_database_worker_config *wc = arg;
     uv_loop_t *loop;
     int ret;
@@ -401,6 +480,7 @@ void aclk_database_worker(void *arg)
 
     memset(&cmd, 0, sizeof(cmd));
 #ifdef ENABLE_NEW_CLOUD_PROTOCOL
+    uv_work_t retention_work;
     sql_get_last_chart_sequence(wc);
     wc->chart_payload_count = sql_get_pending_count(wc);
     if (!wc->chart_payload_count)
@@ -412,7 +492,9 @@ void aclk_database_worker(void *arg)
     wc->rotation_after = wc->startup_time + ACLK_DATABASE_ROTATION_DELAY;
 
     debug(D_ACLK_SYNC,"Node %s reports pending message count = %u", wc->node_id, wc->chart_payload_count);
+
     while (likely(!netdata_exit)) {
+        worker_is_idle();
         uv_run(loop, UV_RUN_DEFAULT);
 
         /* wait for commands */
@@ -427,6 +509,10 @@ void aclk_database_worker(void *arg)
 
             opcode = cmd.opcode;
             ++cmd_batch_size;
+
+            if(likely(opcode != ACLK_DATABASE_NOOP))
+                worker_is_busy(opcode);
+
             switch (opcode) {
                 case ACLK_DATABASE_NOOP:
                     /* the command queue was empty, do nothing */
@@ -439,6 +525,7 @@ void aclk_database_worker(void *arg)
                     if (wc->host == localhost)
                         sql_check_aclk_table_list(wc);
                     break;
+
                 case ACLK_DATABASE_DELETE_HOST:
                     debug(D_ACLK_SYNC,"Cleaning ACLK tables for %s", (char *) cmd.data);
                     sql_delete_aclk_table_list(wc, cmd);
@@ -504,9 +591,21 @@ void aclk_database_worker(void *arg)
                     aclk_process_dimension_deletion(wc, cmd);
                     break;
                 case ACLK_DATABASE_UPD_RETENTION:
+                    if (unlikely(wc->retention_running))
+                        break;
+
+                    if (unlikely(request_retention_run())) {
+                        wc->rotation_after = now_realtime_sec() + ACLK_DATABASE_RETENTION_RETRY;
+                        break;
+                    }
+
                     debug(D_ACLK_SYNC,"Sending retention info for %s", wc->uuid_str);
-                    aclk_update_retention(wc, cmd);
-                    aclk_process_dimension_deletion(wc, cmd);
+                    retention_work.data = wc;
+                    wc->retention_running = 1;
+                    if (unlikely(uv_queue_work(loop, &retention_work, send_retention, after_send_retention))) {
+                        wc->retention_running = 0;
+                        stop_retention_run();
+                    }
                     break;
 
 // NODE_INSTANCE DETECTION
@@ -535,6 +634,8 @@ void aclk_database_worker(void *arg)
                         cmd.completion = NULL;
                         wc->node_info_send = aclk_database_enq_cmd_noblock(wc, &cmd);
                     }
+                    if (localhost == wc->host)
+                        (void) sqlite3_wal_checkpoint(db_meta, NULL);
                     break;
                 default:
                     debug(D_ACLK_SYNC, "%s: default.", __func__);
@@ -577,6 +678,8 @@ void aclk_database_worker(void *arg)
         wc->host->dbsync_worker = NULL;
     freez(wc);
     rrd_unlock();
+
+    worker_unregister();
     return;
 
 error_after_timer_init:
@@ -585,6 +688,7 @@ error_after_async_init:
     fatal_assert(0 == uv_loop_close(loop));
 error_after_loop_init:
     freez(loop);
+    worker_unregister();
 }
 
 // -------------------------------------------------------------
@@ -628,7 +732,7 @@ void sql_create_aclk_table(RRDHOST *host, uuid_t *host_uuid, uuid_t *node_id)
     db_execute(buffer_tostring(sql));
     buffer_flush(sql);
 
-    buffer_sprintf(sql, TABLE_ACLK_ALERT, uuid_str, uuid_str, uuid_str);
+    buffer_sprintf(sql, TABLE_ACLK_ALERT, uuid_str);
     db_execute(buffer_tostring(sql));
     buffer_flush(sql);
 
diff --git a/database/sqlite/sqlite_aclk.h b/database/sqlite/sqlite_aclk.h
index 894d9348..37e3d453 100644
--- a/database/sqlite/sqlite_aclk.h
+++ b/database/sqlite/sqlite_aclk.h
@@ -16,7 +16,8 @@
 #endif
 #define ACLK_MAX_ALERT_UPDATES  (5)
 #define ACLK_DATABASE_CLEANUP_FIRST  (60)
-#define ACLK_DATABASE_ROTATION_DELAY  (60)
+#define ACLK_DATABASE_ROTATION_DELAY  (180)
+#define ACLK_DATABASE_RETENTION_RETRY (60)
 #define ACLK_DATABASE_CLEANUP_INTERVAL (3600)
 #define ACLK_DATABASE_ROTATION_INTERVAL (3600)
 #define ACLK_DELETE_ACK_INTERNAL (600)
@@ -103,9 +104,7 @@ static inline char *get_str_from_uuid(uuid_t *uuid)
 
 #define TABLE_ACLK_ALERT "CREATE TABLE IF NOT EXISTS aclk_alert_%s (sequence_id INTEGER PRIMARY KEY, " \
         "alert_unique_id, date_created, date_submitted, date_cloud_ack, " \
-        "unique(alert_unique_id)); " \
-        "insert into aclk_alert_%s (alert_unique_id, date_created) " \
-        "select unique_id alert_unique_id, strftime('%%s') date_created from health_log_%s where new_status <> 0 and new_status <> -2 order by unique_id asc on conflict (alert_unique_id) do nothing;"
+        "unique(alert_unique_id));"
 
 #define INDEX_ACLK_CHART "CREATE INDEX IF NOT EXISTS aclk_chart_index_%s ON aclk_chart_%s (unique_id);"
 
@@ -135,7 +134,11 @@ enum aclk_database_opcode {
     ACLK_DATABASE_PUSH_ALERT_CONFIG,
     ACLK_DATABASE_PUSH_ALERT_SNAPSHOT,
     ACLK_DATABASE_QUEUE_REMOVED_ALERTS,
-    ACLK_DATABASE_TIMER
+    ACLK_DATABASE_TIMER,
+
+    // leave this last
+    // we need it to check for worker utilization
+    ACLK_MAX_ENUMERATIONS_DEFINED
 };
 
 struct aclk_chart_payload_t {
@@ -176,6 +179,7 @@ struct aclk_database_worker_config {
     uint64_t alerts_batch_id; // batch id for alerts to use
     uint64_t alerts_start_seq_id; // cloud has asked to start streaming from
     uint64_t alert_sequence_id; // last alert sequence_id
+    int pause_alert_updates;
     uint32_t chart_payload_count;
     uint64_t alerts_snapshot_id; //will contain the snapshot_id value if snapshot was requested
     uint64_t alerts_ack_sequence_id; //last sequence_id ack'ed from cloud via sendsnapshot message
@@ -194,6 +198,7 @@ struct aclk_database_worker_config {
     int node_info_send;
     int chart_pending;
     int chart_reset_count;
+    int retention_running;
     volatile unsigned is_shutting_down;
     volatile unsigned is_orphan;
     struct aclk_database_worker_config  *next;
diff --git a/database/sqlite/sqlite_aclk_alert.c b/database/sqlite/sqlite_aclk_alert.c
index 54e8be4a..53c6c2a6 100644
--- a/database/sqlite/sqlite_aclk_alert.c
+++ b/database/sqlite/sqlite_aclk_alert.c
@@ -8,9 +8,120 @@
 #include "../../aclk/aclk.h"
 #endif
 
+time_t removed_when(uint32_t alarm_id, uint32_t before_unique_id, uint32_t after_unique_id, char *uuid_str) {
+    sqlite3_stmt *res = NULL;
+    int rc = 0;
+    time_t when = 0;
+    char sql[ACLK_SYNC_QUERY_SIZE];
+
+    snprintfz(sql,ACLK_SYNC_QUERY_SIZE-1, "select when_key from health_log_%s where alarm_id = %u " \
+                                          "and unique_id > %u and unique_id < %u " \
+                                          "and new_status = -2;", uuid_str, alarm_id, after_unique_id, before_unique_id);
+
+    rc = sqlite3_prepare_v2(db_meta, sql, -1, &res, 0);
+    if (rc != SQLITE_OK) {
+        error_report("Failed to prepare statement when trying to find removed gap.");
+        return 0;
+    }
+
+    rc = sqlite3_step(res);
+    if (likely(rc == SQLITE_ROW)) {
+        when = (time_t) sqlite3_column_int64(res, 0);
+    }
+
+    rc = sqlite3_finalize(res);
+    if (unlikely(rc != SQLITE_OK))
+        error_report("Failed to finalize statement when trying to find removed gap, rc = %d", rc);
+
+    return when;
+}
+
+#define MAX_REMOVED_PERIOD 900
+//decide if some events should be sent or not
+int should_send_to_cloud(RRDHOST *host, ALARM_ENTRY *ae)
+{
+    sqlite3_stmt *res = NULL;
+    char uuid_str[GUID_LEN + 1];
+    uuid_unparse_lower_fix(&host->host_uuid, uuid_str);
+    int send = 1, rc = 0;
+
+    if (ae->new_status == RRDCALC_STATUS_REMOVED || ae->new_status == RRDCALC_STATUS_UNINITIALIZED) {
+        return 0;
+    }
+
+    if (unlikely(uuid_is_null(ae->config_hash_id))) 
+        return 0;
+
+    char sql[ACLK_SYNC_QUERY_SIZE];
+    uuid_t config_hash_id;
+    RRDCALC_STATUS status;
+    uint32_t unique_id;
+    
+    //get the previous sent event of this alarm_id
+    snprintfz(sql,ACLK_SYNC_QUERY_SIZE-1, "select hl.new_status, hl.config_hash_id, hl.unique_id from health_log_%s hl, aclk_alert_%s aa \
+                         where hl.unique_id = aa.alert_unique_id        \
+                         and hl.alarm_id = %u and hl.unique_id <> %u \
+                         order by alarm_event_id desc LIMIT 1;", uuid_str, uuid_str, ae->alarm_id, ae->unique_id);
+
+    rc = sqlite3_prepare_v2(db_meta, sql, -1, &res, 0);
+    if (rc != SQLITE_OK) {
+        error_report("Failed to prepare statement when trying to filter alert events.");
+        send = 1;
+        return send;
+    }
+
+    rc = sqlite3_step(res);
+    if (likely(rc == SQLITE_ROW)) {
+        status  = (RRDCALC_STATUS) sqlite3_column_int(res, 0);
+        if (sqlite3_column_type(res, 1) != SQLITE_NULL)
+            uuid_copy(config_hash_id, *((uuid_t *) sqlite3_column_blob(res, 1)));
+        unique_id = (uint32_t) sqlite3_column_int64(res, 2);
+        
+    } else {
+        send = 1;
+        goto done;
+    }
+
+    if (ae->new_status != (RRDCALC_STATUS)status) {
+        send = 1;
+        goto done;
+    }
+
+    if (uuid_compare(ae->config_hash_id, config_hash_id)) {
+        send = 1;
+        goto done;
+    }
+
+    //same status, same config
+    if (ae->new_status == RRDCALC_STATUS_CLEAR) {
+        send = 0;
+        goto done;
+    }
+
+    //detect a long off period of the agent, TODO make global
+    if (ae->new_status == RRDCALC_STATUS_WARNING || ae->new_status == RRDCALC_STATUS_CRITICAL) {
+        time_t when = removed_when(ae->alarm_id, ae->unique_id, unique_id, uuid_str);
+
+        if (when && (when + (time_t)MAX_REMOVED_PERIOD) < ae->when) {
+            send = 1;
+            goto done;
+        } else {
+            send = 0;
+            goto done;
+        }
+    }
+     
+done:
+    rc = sqlite3_finalize(res);
+    if (unlikely(rc != SQLITE_OK))
+        error_report("Failed to finalize statement when trying to filter alert events, rc = %d", rc);
+
+    return send;
+}
+
 // will replace call to aclk_update_alarm in health/health_log.c
 // and handle both cases
-int sql_queue_alarm_to_aclk(RRDHOST *host, ALARM_ENTRY *ae)
+int sql_queue_alarm_to_aclk(RRDHOST *host, ALARM_ENTRY *ae, int skip_filter)
 {
     //check aclk architecture and handle old json alarm update to cloud
     //include also the valid statuses for this case
@@ -30,17 +141,15 @@ int sql_queue_alarm_to_aclk(RRDHOST *host, ALARM_ENTRY *ae)
     if (!claimed())
         return 0;
 
-    if (ae->flags & HEALTH_ENTRY_FLAG_ACLK_QUEUED)
+    if (ae->flags & HEALTH_ENTRY_FLAG_ACLK_QUEUED) {
         return 0;
+    }
 
-    if (ae->new_status == RRDCALC_STATUS_REMOVED || ae->new_status == RRDCALC_STATUS_UNINITIALIZED)
-        return 0;
-
-    if (unlikely(!host->dbsync_worker))
-        return 1;
-
-    if (unlikely(uuid_is_null(ae->config_hash_id)))
-        return 0;
+    if (!skip_filter) {
+        if (!should_send_to_cloud(host, ae)) {
+            return 0;
+        }
+    }
 
     int rc = 0;
 
@@ -76,6 +185,10 @@ int sql_queue_alarm_to_aclk(RRDHOST *host, ALARM_ENTRY *ae)
     }
 
     ae->flags |= HEALTH_ENTRY_FLAG_ACLK_QUEUED;
+    struct aclk_database_worker_config *wc  = (struct aclk_database_worker_config *)host->dbsync_worker;
+    if (wc) {
+        wc->pause_alert_updates = 0;
+    }
 
 bind_fail:
     if (unlikely(sqlite3_finalize(res_alert) != SQLITE_OK))
@@ -86,6 +199,7 @@ bind_fail:
 #else
     UNUSED(host);
     UNUSED(ae);
+    UNUSED(skip_filter);
 #endif
     return 0;
 }
@@ -283,6 +397,7 @@ void aclk_push_alert_event(struct aclk_database_worker_config *wc, struct aclk_d
                 wc->alerts_batch_id);
         log_first_sequence_id = 0;
         log_last_sequence_id = 0;
+        wc->pause_alert_updates = 1;
     }
 
     rc = sqlite3_finalize(res);
@@ -296,6 +411,27 @@ void aclk_push_alert_event(struct aclk_database_worker_config *wc, struct aclk_d
     return;
 }
 
+void sql_queue_existing_alerts_to_aclk(RRDHOST *host)
+{
+    char uuid_str[GUID_LEN + 1];
+    uuid_unparse_lower_fix(&host->host_uuid, uuid_str);
+    BUFFER *sql = buffer_create(1024);
+
+    buffer_sprintf(sql,"insert into aclk_alert_%s (alert_unique_id, date_created) " \
+                       "select unique_id alert_unique_id, strftime('%%s') date_created from health_log_%s " \
+                       "where new_status <> 0 and new_status <> -2 and config_hash_id is not null and updated_by_id = 0 " \
+                       "order by unique_id asc on conflict (alert_unique_id) do nothing;", uuid_str, uuid_str);
+
+    db_execute(buffer_tostring(sql));
+
+    buffer_free(sql);
+
+    struct aclk_database_worker_config *wc  = (struct aclk_database_worker_config *)host->dbsync_worker;
+    if (wc) {
+        wc->pause_alert_updates = 0;
+    }
+}
+
 void aclk_send_alarm_health_log(char *node_id)
 {
     if (unlikely(!node_id))
@@ -421,6 +557,8 @@ void aclk_push_alarm_health_log(struct aclk_database_worker_config *wc, struct a
 
     freez(claim_id);
     buffer_free(sql);
+
+    aclk_alert_reloaded = 1;
 #endif
 
     return;
@@ -593,6 +731,9 @@ void aclk_start_alert_streaming(char *node_id, uint64_t batch_id, uint64_t start
             log_access("ACLK STA [%s (N/A)]: Ignoring request to stream alert state changes, health is disabled.", node_id);
             return;
         }
+
+        if (unlikely(batch_id == 1) && unlikely(start_seq_id == 1))
+            sql_queue_existing_alerts_to_aclk(host);
     } else
         wc = (struct aclk_database_worker_config *)find_inactive_wc_by_node_id(node_id);
 
@@ -602,6 +743,7 @@ void aclk_start_alert_streaming(char *node_id, uint64_t batch_id, uint64_t start
         wc->alerts_batch_id = batch_id;
         wc->alerts_start_seq_id = start_seq_id;
         wc->alert_updates = 1;
+        wc->pause_alert_updates = 0;
         __sync_synchronize();
     }
     else
@@ -631,9 +773,11 @@ void sql_process_queue_removed_alerts_to_aclk(struct aclk_database_worker_config
 
     db_execute(buffer_tostring(sql));
 
-    log_access("ACLK STA [%s (%s)]: Queued removed alerts.", wc->node_id, wc->host ? wc->host->hostname : "N/A");
+    log_access("ACLK STA [%s (%s)]: QUEUED REMOVED ALERTS", wc->node_id, wc->host ? wc->host->hostname : "N/A");
 
     buffer_free(sql);
+
+    wc->pause_alert_updates = 0;
 #endif
     return;
 }
@@ -644,6 +788,9 @@ void sql_queue_removed_alerts_to_aclk(RRDHOST *host)
     if (unlikely(!host->dbsync_worker))
         return;
 
+    if (!claimed())
+        return;
+
     struct aclk_database_cmd cmd;
     memset(&cmd, 0, sizeof(cmd));
     cmd.opcode = ACLK_DATABASE_QUEUE_REMOVED_ALERTS;
@@ -912,9 +1059,6 @@ void sql_aclk_alert_clean_dead_entries(RRDHOST *host)
     if (!claimed())
         return;
 
-    if (unlikely(!host->dbsync_worker))
-        return;
-
     char uuid_str[GUID_LEN + 1];
     uuid_unparse_lower_fix(&host->host_uuid, uuid_str);
 
diff --git a/database/sqlite/sqlite_aclk_alert.h b/database/sqlite/sqlite_aclk_alert.h
index 957cb94a..0181b484 100644
--- a/database/sqlite/sqlite_aclk_alert.h
+++ b/database/sqlite/sqlite_aclk_alert.h
@@ -26,5 +26,6 @@ void sql_process_queue_removed_alerts_to_aclk(struct aclk_database_worker_config
 void aclk_push_alert_snapshot_event(struct aclk_database_worker_config *wc, struct aclk_database_cmd cmd);
 void aclk_process_send_alarm_snapshot(char *node_id, char *claim_id, uint64_t snapshot_id, uint64_t sequence_id);
 int get_proto_alert_status(RRDHOST *host, struct proto_alert_status *proto_alert_status);
+extern int sql_queue_alarm_to_aclk(RRDHOST *host, ALARM_ENTRY *ae, int skip_filter);
 
 #endif //NETDATA_SQLITE_ACLK_ALERT_H
diff --git a/database/sqlite/sqlite_aclk_chart.c b/database/sqlite/sqlite_aclk_chart.c
index 7afa1d45..a9db5282 100644
--- a/database/sqlite/sqlite_aclk_chart.c
+++ b/database/sqlite/sqlite_aclk_chart.c
@@ -22,20 +22,20 @@ sql_queue_chart_payload(struct aclk_database_worker_config *wc, void *data, enum
     return rc;
 }
 
-static int payload_sent(char *uuid_str, uuid_t *uuid, void *payload, size_t payload_size)
+static time_t payload_sent(char *uuid_str, uuid_t *uuid, void *payload, size_t payload_size)
 {
     static __thread sqlite3_stmt *res = NULL;
     int rc;
-    int send_status = 0;
+    time_t send_status = 0;
 
     if (unlikely(!res)) {
         char sql[ACLK_SYNC_QUERY_SIZE];
-        snprintfz(sql,ACLK_SYNC_QUERY_SIZE-1, "SELECT 1 FROM aclk_chart_latest_%s acl, aclk_chart_payload_%s acp "
-                            "WHERE acl.unique_id = acp.unique_id AND acl.uuid = @uuid AND acp.payload = @payload;",
-                       uuid_str, uuid_str);
+        snprintfz(sql,ACLK_SYNC_QUERY_SIZE-1, "SELECT acl.date_submitted FROM aclk_chart_latest_%s acl, aclk_chart_payload_%s acp "
+            "WHERE acl.unique_id = acp.unique_id AND acl.uuid = @uuid AND acp.payload = @payload;",
+                  uuid_str, uuid_str);
         rc = prepare_statement(db_meta, sql, &res);
         if (rc != SQLITE_OK) {
-            error_report("Failed to prepare statement to check payload data");
+            error_report("Failed to prepare statement to check payload data on %s", sql);
             return 0;
         }
     }
@@ -49,7 +49,7 @@ static int payload_sent(char *uuid_str, uuid_t *uuid, void *payload, size_t payl
         goto bind_fail;
 
     while (sqlite3_step(res) == SQLITE_ROW) {
-        send_status = sqlite3_column_int(res, 0);
+        send_status = (time_t) sqlite3_column_int64(res, 0);
     }
 
 bind_fail:
@@ -58,23 +58,36 @@ bind_fail:
     return send_status;
 }
 
-static int aclk_add_chart_payload(struct aclk_database_worker_config *wc, uuid_t *uuid, char *claim_id,
-                                 ACLK_PAYLOAD_TYPE payload_type, void *payload, size_t payload_size, int *send_status)
+static int aclk_add_chart_payload(
+    struct aclk_database_worker_config *wc,
+    uuid_t *uuid,
+    char *claim_id,
+    ACLK_PAYLOAD_TYPE payload_type,
+    void *payload,
+    size_t payload_size,
+    time_t *send_status,
+    int check_sent)
 {
     static __thread sqlite3_stmt *res_chart = NULL;
     int rc;
+    time_t date_submitted;
 
-    rc = payload_sent(wc->uuid_str, uuid, payload, payload_size);
-    if (send_status)
-        *send_status = rc;
-    if (rc == 1)
+    if (unlikely(!payload))
         return 0;
 
+    if (check_sent) {
+        date_submitted = payload_sent(wc->uuid_str, uuid, payload, payload_size);
+        if (send_status)
+            *send_status = date_submitted;
+        if (date_submitted)
+            return 0;
+    }
+
     if (unlikely(!res_chart)) {
         char sql[ACLK_SYNC_QUERY_SIZE];
         snprintfz(sql,ACLK_SYNC_QUERY_SIZE-1,
-            "INSERT INTO aclk_chart_payload_%s (unique_id, uuid, claim_id, date_created, type, payload) " \
-            "VALUES (@unique_id, @uuid, @claim_id, strftime('%%s','now'), @type, @payload);", wc->uuid_str);
+                  "INSERT INTO aclk_chart_payload_%s (unique_id, uuid, claim_id, date_created, type, payload) " \
+                  "VALUES (@unique_id, @uuid, @claim_id, strftime('%%s','now'), @type, @payload);", wc->uuid_str);
         rc = prepare_statement(db_meta, sql, &res_chart);
         if (rc != SQLITE_OK) {
             error_report("Failed to prepare statement to store chart payload data");
@@ -146,7 +159,7 @@ int aclk_add_chart_event(struct aclk_database_worker_config *wc, struct aclk_dat
         chart_payload.id = strdupz(st->id);
 
         struct label_index *labels = &st->state->labels;
-        netdata_rwlock_wrlock(&labels->labels_rwlock);
+        netdata_rwlock_rdlock(&labels->labels_rwlock);
         struct label *label_list = labels->head;
         struct label *chart_label = NULL;
         while (label_list) {
@@ -159,7 +172,7 @@ int aclk_add_chart_event(struct aclk_database_worker_config *wc, struct aclk_dat
         size_t size;
         char *payload = generate_chart_instance_updated(&size, &chart_payload);
         if (likely(payload))
-            rc = aclk_add_chart_payload(wc, st->chart_uuid, claim_id, ACLK_PAYLOAD_CHART, (void *) payload, size, NULL);
+            rc = aclk_add_chart_payload(wc, st->chart_uuid, claim_id, ACLK_PAYLOAD_CHART, (void *) payload, size, NULL, 1);
         freez(payload);
         chart_instance_updated_destroy(&chart_payload);
     }
@@ -168,7 +181,7 @@ int aclk_add_chart_event(struct aclk_database_worker_config *wc, struct aclk_dat
 
 static inline int aclk_upd_dimension_event(struct aclk_database_worker_config *wc, char *claim_id, uuid_t *dim_uuid,
         const char *dim_id, const char *dim_name, const char *chart_type_id, time_t first_time, time_t last_time,
-        int *send_status)
+        time_t *send_status)
 {
     int rc = 0;
     size_t size;
@@ -197,7 +210,7 @@ static inline int aclk_upd_dimension_event(struct aclk_database_worker_config *w
     dim_payload.last_timestamp.tv_sec = last_time;
     char *payload = generate_chart_dimension_updated(&size, &dim_payload);
     if (likely(payload))
-        rc = aclk_add_chart_payload(wc, dim_uuid, claim_id, ACLK_PAYLOAD_DIMENSION, (void *)payload, size, send_status);
+        rc = aclk_add_chart_payload(wc, dim_uuid, claim_id, ACLK_PAYLOAD_DIMENSION, (void *)payload, size, send_status, 1);
     freez(payload);
     return rc;
 }
@@ -271,39 +284,22 @@ bind_fail:
 
 int aclk_add_dimension_event(struct aclk_database_worker_config *wc, struct aclk_database_cmd cmd)
 {
-    int rc = 0;
+    int rc = 1;
     CHECK_SQLITE_CONNECTION(db_meta);
 
-    char *claim_id = is_agent_claimed();
-
-    RRDDIM *rd = cmd.data;
-
-    if (likely(claim_id)) {
-        int send_status = 0;
-        time_t now = now_realtime_sec();
-
-        time_t first_t = rd->state->query_ops.oldest_time(rd);
-        time_t last_t = rd->state->query_ops.latest_time(rd);
-
-        int live = ((now - last_t) < (RRDSET_MINIMUM_DIM_LIVE_MULTIPLIER * rd->update_every));
+    struct aclk_chart_dimension_data *aclk_cd_data = cmd.data;
 
-        rc = aclk_upd_dimension_event(
-            wc,
-            claim_id,
-            &rd->state->metric_uuid,
-            rd->id,
-            rd->name,
-            rd->rrdset->id,
-            first_t,
-            live ? 0 : last_t,
-            &send_status);
+    char *claim_id = is_agent_claimed();
+    if (!claim_id)
+        goto cleanup;
 
-        if (!send_status)
-            rd->state->aclk_live_status = live;
+    rc = aclk_add_chart_payload(wc, &aclk_cd_data->uuid, claim_id, ACLK_PAYLOAD_DIMENSION,
+              (void *) aclk_cd_data->payload, aclk_cd_data->payload_size, NULL, aclk_cd_data->check_payload);
 
-        freez(claim_id);
-    }
-    rrddim_flag_clear(rd, RRDDIM_FLAG_ACLK);
+    freez(claim_id);
+cleanup:
+    freez(aclk_cd_data->payload);
+    freez(aclk_cd_data);
     return rc;
 }
 
@@ -337,6 +333,12 @@ void aclk_send_chart_event(struct aclk_database_worker_config *wc, struct aclk_d
     char sql[ACLK_SYNC_QUERY_SIZE];
     static __thread sqlite3_stmt *res = NULL;
 
+    char *hostname = NULL;
+    if (wc->host)
+        hostname = strdupz(wc->host->hostname);
+    else
+        hostname = get_hostname_by_node_id(wc->node_id);
+
     if (unlikely(!res)) {
         snprintfz(sql,ACLK_SYNC_QUERY_SIZE-1,"SELECT ac.sequence_id, acp.payload, ac.date_created, ac.type, ac.uuid  " \
              "FROM aclk_chart_%s ac, aclk_chart_payload_%s acp " \
@@ -346,6 +348,7 @@ void aclk_send_chart_event(struct aclk_database_worker_config *wc, struct aclk_d
         if (rc != SQLITE_OK) {
             error_report("Failed to prepare statement when trying to send a chart update via ACLK");
             freez(claim_id);
+            freez(hostname);
             return;
         }
     }
@@ -419,7 +422,7 @@ void aclk_send_chart_event(struct aclk_database_worker_config *wc, struct aclk_d
             log_access(
                 "ACLK RES [%s (%s)]: CHARTS SENT from %" PRIu64 " to %" PRIu64 " batch=%" PRIu64,
                 wc->node_id,
-                wc->host ? wc->host->hostname : "N/A",
+                hostname ? hostname : "N/A",
                 first_sequence,
                 last_sequence,
                 wc->batch_id);
@@ -440,7 +443,7 @@ void aclk_send_chart_event(struct aclk_database_worker_config *wc, struct aclk_d
             log_access(
                 "ACLK STA [%s (%s)]: Sync of charts and dimensions done in %ld seconds.",
                 wc->node_id,
-                wc->host ? wc->host->hostname : "N/A",
+                hostname ? hostname : "N/A",
                 now_realtime_sec() - wc->startup_time);
     }
 
@@ -459,6 +462,7 @@ bind_fail:
         error_report("Failed to reset statement when pushing chart events, rc = %d", rc);
 
     freez(claim_id);
+    freez(hostname);
     return;
 }
 
@@ -562,7 +566,7 @@ void aclk_receive_chart_ack(struct aclk_database_worker_config *wc, struct aclk_
         error_report("Failed to ACK sequence id, rc = %d", rc);
     else
         log_access(
-            "ACLK STA [%s (%s)]: CHARTS ACKNOWLEDGED in the database upto %" PRIu64,
+            "ACLK STA [%s (%s)]: CHARTS ACKNOWLEDGED IN THE DATABASE UP TO %" PRIu64,
             wc->node_id,
             wc->host ? wc->host->hostname : "N/A",
             cmd.param1);
@@ -583,8 +587,13 @@ void aclk_receive_chart_reset(struct aclk_database_worker_config *wc, struct acl
         cmd.param1);
     db_execute(buffer_tostring(sql));
     if (cmd.param1 == 1) {
+        char *hostname = NULL;
+        if (wc->host)
+            hostname = strdupz(wc->host->hostname);
+        else
+            hostname = get_hostname_by_node_id(wc->node_id);
         buffer_flush(sql);
-        log_access("ACLK REQ [%s (%s)]: Received chart full resync.", wc->node_id, wc->host ? wc->host->hostname : "N/A");
+        log_access("ACLK REQ [%s (%s)]: Received chart full resync.", wc->node_id, hostname? hostname : "N/A");
         buffer_sprintf(sql, "DELETE FROM aclk_chart_payload_%s; DELETE FROM aclk_chart_%s; " \
                             "DELETE FROM aclk_chart_latest_%s;", wc->uuid_str, wc->uuid_str, wc->uuid_str);
         db_lock();
@@ -609,6 +618,7 @@ void aclk_receive_chart_reset(struct aclk_database_worker_config *wc, struct acl
                 RRDDIM *rd;
                 rrddim_foreach_read(rd, st)
                 {
+                    rrddim_flag_clear(rd, RRDDIM_FLAG_ACLK);
                     rd->state->aclk_live_status = (rd->state->aclk_live_status == 0);
                 }
                 rrdset_unlock(st);
@@ -616,9 +626,10 @@ void aclk_receive_chart_reset(struct aclk_database_worker_config *wc, struct acl
             rrdhost_unlock(host);
         } else
             error_report("ACLK synchronization thread for %s is not linked to HOST", wc->host_guid);
+        freez(hostname);
     } else {
         log_access(
-            "ACLK STA [%s (%s)]: Restarting chart sync from sequence %" PRIu64,
+            "ACLK STA [%s (%s)]: RESTARTING CHART SYNC FROM SEQUENCE %" PRIu64,
             wc->node_id,
             wc->host ? wc->host->hostname : "N/A",
             cmd.param1);
@@ -705,25 +716,28 @@ void aclk_start_streaming(char *node_id, uint64_t sequence_id, time_t created_at
     if (unlikely(!node_id))
         return;
 
-    //    log_access("ACLK REQ [%s (N/A)]: CHARTS STREAM from %"PRIu64" t=%ld batch=%"PRIu64, node_id,
-    //          sequence_id, created_at, batch_id);
-
     uuid_t node_uuid;
     if (uuid_parse(node_id, node_uuid)) {
         log_access("ACLK REQ [%s (N/A)]: CHARTS STREAM ignored, invalid node id", node_id);
         return;
     }
 
-    struct aclk_database_worker_config *wc  = NULL;
+    struct aclk_database_worker_config *wc  = find_inactive_wc_by_node_id(node_id);
     rrd_rdlock();
     RRDHOST *host = localhost;
     while(host) {
-        if (host->node_id && !(uuid_compare(*host->node_id, node_uuid))) {
+        if (wc || (host->node_id && !(uuid_compare(*host->node_id, node_uuid)))) {
             rrd_unlock();
-            wc = (struct aclk_database_worker_config *)host->dbsync_worker ?
-                     (struct aclk_database_worker_config *)host->dbsync_worker :
-                     (struct aclk_database_worker_config *)find_inactive_wc_by_node_id(node_id);
+            if (!wc)
+                wc = (struct aclk_database_worker_config *)host->dbsync_worker ?
+                         (struct aclk_database_worker_config *)host->dbsync_worker :
+                         (struct aclk_database_worker_config *)find_inactive_wc_by_node_id(node_id);
+            char *hostname = NULL;
             if (likely(wc)) {
+                if (wc->host)
+                    hostname = strdupz(wc->host->hostname);
+                else
+                    hostname = get_hostname_by_node_id(node_id);
                 wc->chart_reset_count++;
                 __sync_synchronize();
                 wc->chart_updates = 0;
@@ -731,9 +745,10 @@ void aclk_start_streaming(char *node_id, uint64_t sequence_id, time_t created_at
                 __sync_synchronize();
                 wc->batch_created = now_realtime_sec();
                 log_access(
-                    "ACLK REQ [%s (%s)]: CHARTS STREAM from %" PRIu64 " t=%ld resets=%d",
+                    "ACLK REQ [%s (%s)]: CHARTS STREAM from %"PRIu64" (LOCAL %"PRIu64") t=%ld resets=%d" ,
                     wc->node_id,
-                    wc->host ? wc->host->hostname : "N/A",
+                    hostname ? hostname : "N/A",
+                    sequence_id + 1,
                     wc->chart_sequence_id,
                     wc->chart_timestamp,
                     wc->chart_reset_count);
@@ -742,7 +757,7 @@ void aclk_start_streaming(char *node_id, uint64_t sequence_id, time_t created_at
                         "ACLK RES [%s (%s)]: CHARTS FULL RESYNC REQUEST "
                         "remote_seq=%" PRIu64 " local_seq=%" PRIu64 " resets=%d ",
                         wc->node_id,
-                        wc->host ? wc->host->hostname : "N/A",
+                        hostname ? hostname : "N/A",
                         sequence_id,
                         wc->chart_sequence_id,
                         wc->chart_reset_count);
@@ -756,7 +771,6 @@ void aclk_start_streaming(char *node_id, uint64_t sequence_id, time_t created_at
                         freez(chart_reset.claim_id);
                         wc->chart_reset_count = -1;
                     }
-                    return;
                 } else {
                     struct aclk_database_cmd cmd;
                     memset(&cmd, 0, sizeof(cmd));
@@ -766,8 +780,8 @@ void aclk_start_streaming(char *node_id, uint64_t sequence_id, time_t created_at
                         log_access(
                             "ACLK REQ [%s (%s)]: CHART RESET from %" PRIu64 " t=%ld batch=%" PRIu64,
                             wc->node_id,
-                            wc->host ? wc->host->hostname : "N/A",
-                            wc->chart_sequence_id,
+                            hostname ? hostname : "N/A",
+                            sequence_id + 1,
                             wc->chart_timestamp,
                             wc->batch_id);
                         cmd.opcode = ACLK_DATABASE_RESET_CHART;
@@ -775,20 +789,15 @@ void aclk_start_streaming(char *node_id, uint64_t sequence_id, time_t created_at
                         cmd.completion = NULL;
                         aclk_database_enq_cmd(wc, &cmd);
                     } else {
-//                        log_access(
-//                            "ACLK RES [%s (%s)]: CHARTS STREAM from %" PRIu64
-//                            " t=%ld resets=%d",
-//                            wc->node_id,
-//                            wc->host ? wc->host->hostname : "N/A",
-//                            wc->chart_sequence_id,
-//                            wc->chart_timestamp,
-//                            wc->chart_reset_count);
                         wc->chart_reset_count = 0;
                         wc->chart_updates = 1;
                     }
                 }
-            } else
-                log_access("ACLK STA [%s (N/A)]: ACLK synchronization thread is not active.", node_id);
+            } else {
+                hostname = get_hostname_by_node_id(node_id);
+                log_access("ACLK STA [%s (%s)]: ACLK synchronization thread is not active.", node_id, hostname ? hostname : "N/A");
+            }
+            freez(hostname);
             return;
         }
         host = host->next;
@@ -838,9 +847,8 @@ failed:
     "SELECT distinct h.host_id, c.update_every, c.type||'.'||c.id FROM chart c, host h "                               \
     "WHERE c.host_id = h.host_id AND c.host_id = @host_id ORDER BY c.update_every ASC;"
 
-void aclk_update_retention(struct aclk_database_worker_config *wc, struct aclk_database_cmd cmd)
+void aclk_update_retention(struct aclk_database_worker_config *wc)
 {
-    UNUSED(cmd);
     int rc;
 
     if (!aclk_use_new_cloud_arch || !aclk_connected)
@@ -887,7 +895,10 @@ void aclk_update_retention(struct aclk_database_worker_config *wc, struct aclk_d
     time_t last_entry_t;
     uint32_t update_every = 0;
     uint32_t dimension_update_count = 0;
-    int send_status;
+    uint32_t total_checked = 0;
+    uint32_t total_deleted= 0;
+    uint32_t total_stopped= 0;
+    time_t send_status;
 
     struct retention_updated rotate_data;
 
@@ -904,7 +915,9 @@ void aclk_update_retention(struct aclk_database_worker_config *wc, struct aclk_d
     rotate_data.node_id = strdupz(wc->node_id);
 
     time_t now = now_realtime_sec();
-    while (sqlite3_step(res) == SQLITE_ROW) {
+    while (sqlite3_step(res) == SQLITE_ROW && dimension_update_count < ACLK_MAX_DIMENSION_CLEANUP) {
+        if (unlikely(netdata_exit))
+            break;
         if (!update_every || update_every != (uint32_t)sqlite3_column_int(res, 1)) {
             if (update_every) {
                 debug(D_ACLK_SYNC, "Update %s for %u oldest time = %ld", wc->host_guid, update_every, start_time);
@@ -942,23 +955,40 @@ void aclk_update_retention(struct aclk_database_worker_config *wc, struct aclk_d
         if (likely(!rc && first_entry_t))
             start_time = MIN(start_time, first_entry_t);
 
-        if (memory_mode == RRD_MEMORY_MODE_DBENGINE && wc->chart_updates) {
+        if (memory_mode == RRD_MEMORY_MODE_DBENGINE && wc->chart_updates && (dimension_update_count < ACLK_MAX_DIMENSION_CLEANUP)) {
             int live = ((now - last_entry_t) < (RRDSET_MINIMUM_DIM_LIVE_MULTIPLIER * update_every));
-            if ((!live || !first_entry_t) && (dimension_update_count < ACLK_MAX_DIMENSION_CLEANUP)) {
-                (void)aclk_upd_dimension_event(
-                    wc,
-                    claim_id,
-                    (uuid_t *)sqlite3_column_blob(res, 0),
-                    (const char *)(const char *)sqlite3_column_text(res, 3),
-                    (const char *)(const char *)sqlite3_column_text(res, 4),
-                    (const char *)(const char *)sqlite3_column_text(res, 2),
-                    first_entry_t,
-                    live ? 0 : last_entry_t,
-                    &send_status);
-                if (!send_status)
+            if (rc) {
+                first_entry_t = 0;
+                last_entry_t = 0;
+                live = 0;
+            }
+            if (!wc->host || !first_entry_t) {
+                if (!first_entry_t) {
+                    delete_dimension_uuid((uuid_t *)sqlite3_column_blob(res, 0));
+                    total_deleted++;
                     dimension_update_count++;
+                }
+                else {
+                    (void)aclk_upd_dimension_event(
+                        wc,
+                        claim_id,
+                        (uuid_t *)sqlite3_column_blob(res, 0),
+                        (const char *)(const char *)sqlite3_column_text(res, 3),
+                        (const char *)(const char *)sqlite3_column_text(res, 4),
+                        (const char *)(const char *)sqlite3_column_text(res, 2),
+                        first_entry_t,
+                        live ? 0 : last_entry_t,
+                        &send_status);
+
+                    if (!send_status) {
+                        if (last_entry_t)
+                            total_stopped++;
+                        dimension_update_count++;
+                    }
+                }
             }
         }
+        total_checked++;
     }
     if (update_every) {
         debug(D_ACLK_SYNC, "Update %s for %u oldest time = %ld", wc->host_guid, update_every, start_time);
@@ -970,7 +1000,20 @@ void aclk_update_retention(struct aclk_database_worker_config *wc, struct aclk_d
         rotate_data.interval_duration_count++;
     }
 
+    char *hostname = NULL;
+    if (!wc->host)
+        hostname = get_hostname_by_node_id(wc->node_id);
+
+    if (dimension_update_count < ACLK_MAX_DIMENSION_CLEANUP && !netdata_exit)
+        log_access("ACLK STA [%s (%s)]: UPDATES %d RETENTION MESSAGE SENT. CHECKED %u DIMENSIONS.  %u DELETED, %u STOPPED COLLECTING",
+                   wc->node_id, wc->host ? wc->host->hostname : hostname ? hostname : "N/A", wc->chart_updates, total_checked, total_deleted, total_stopped);
+    else
+        log_access("ACLK STA [%s (%s)]: UPDATES %d RETENTION MESSAGE NOT SENT. CHECKED %u DIMENSIONS.  %u DELETED, %u STOPPED COLLECTING",
+                   wc->node_id, wc->host ? wc->host->hostname : hostname ? hostname : "N/A", wc->chart_updates, total_checked, total_deleted, total_stopped);
+    freez(hostname);
+
 #ifdef NETDATA_INTERNAL_CHECKS
+    info("Retention update for %s (chart updates = %d)", wc->host_guid, wc->chart_updates);
     for (int i = 0; i < rotate_data.interval_duration_count; ++i)
         info(
             "Update for host %s (node %s) for %u Retention = %u",
@@ -979,7 +1022,8 @@ void aclk_update_retention(struct aclk_database_worker_config *wc, struct aclk_d
             rotate_data.interval_durations[i].update_every,
             rotate_data.interval_durations[i].retention);
 #endif
-    aclk_retention_updated(&rotate_data);
+    if (dimension_update_count < ACLK_MAX_DIMENSION_CLEANUP && !netdata_exit)
+        aclk_retention_updated(&rotate_data);
     freez(rotate_data.node_id);
     freez(rotate_data.interval_durations);
 
@@ -1048,11 +1092,64 @@ void sql_get_last_chart_sequence(struct aclk_database_worker_config *wc)
     return;
 }
 
-int queue_dimension_to_aclk(RRDDIM *rd)
+void queue_dimension_to_aclk(RRDDIM *rd, time_t last_updated)
 {
-    int rc = sql_queue_chart_payload((struct aclk_database_worker_config *) rd->rrdset->rrdhost->dbsync_worker,
-                                     rd, ACLK_DATABASE_ADD_DIMENSION);
-    return rc;
+    int live = !last_updated;
+
+    if (likely(rd->state->aclk_live_status == live))
+        return;
+
+    time_t created_at = rd->state->query_ops.oldest_time(rd);
+
+    if (unlikely(!created_at && rd->updated))
+       created_at = rd->last_collected_time.tv_sec;
+
+    rd->state->aclk_live_status = live;
+
+    struct aclk_database_worker_config *wc = rd->rrdset->rrdhost->dbsync_worker;
+    if (unlikely(!wc))
+        return;
+
+    char *claim_id = is_agent_claimed();
+    if (unlikely(!claim_id))
+        return;
+
+    struct chart_dimension_updated dim_payload;
+    memset(&dim_payload, 0, sizeof(dim_payload));
+    dim_payload.node_id = wc->node_id;
+    dim_payload.claim_id = claim_id;
+    dim_payload.name = rd->name;
+    dim_payload.id = rd->id;
+    dim_payload.chart_id = rd->rrdset->id;
+    dim_payload.created_at.tv_sec = created_at;
+    dim_payload.last_timestamp.tv_sec = last_updated;
+
+    size_t size = 0;
+    char *payload = generate_chart_dimension_updated(&size, &dim_payload);
+
+    freez(claim_id);
+    if (unlikely(!payload))
+        return;
+
+    struct aclk_chart_dimension_data *aclk_cd_data = mallocz(sizeof(*aclk_cd_data));
+    uuid_copy(aclk_cd_data->uuid, rd->state->metric_uuid);
+    aclk_cd_data->payload = payload;
+    aclk_cd_data->payload_size = size;
+    aclk_cd_data->check_payload = 1;
+
+    struct aclk_database_cmd cmd;
+    memset(&cmd, 0, sizeof(cmd));
+
+    cmd.opcode = ACLK_DATABASE_ADD_DIMENSION;
+    cmd.data = aclk_cd_data;
+    int rc = aclk_database_enq_cmd_noblock(wc, &cmd);
+
+    if (unlikely(rc)) {
+        freez(aclk_cd_data->payload);
+        freez(aclk_cd_data);
+        rd->state->aclk_live_status = !live;
+    }
+    return;
 }
 
 void aclk_send_dimension_update(RRDDIM *rd)
@@ -1203,6 +1300,12 @@ void sql_check_chart_liveness(RRDSET *st) {
         return;
 
     rrdset_rdlock(st);
+
+    if (unlikely(!rrdset_flag_check(st, RRDSET_FLAG_ACLK))) {
+        rrdset_unlock(st);
+        return;
+    }
+
     if (unlikely(!rrdset_flag_check(st, RRDSET_FLAG_ACLK))) {
         if (likely(st->dimensions && st->counter_done && !queue_chart_to_aclk(st))) {
             debug(D_ACLK_SYNC,"Check chart liveness [%s] submit chart definition", st->name);
@@ -1215,20 +1318,8 @@ void sql_check_chart_liveness(RRDSET *st) {
 
     debug(D_ACLK_SYNC,"Check chart liveness [%s] scanning dimensions", st->name);
     rrddim_foreach_read(rd, st) {
-        if (!rrddim_flag_check(rd, RRDDIM_FLAG_HIDDEN)) {
-            int live = (mark - rd->last_collected_time.tv_sec) < RRDSET_MINIMUM_DIM_LIVE_MULTIPLIER * rd->update_every;
-            if (unlikely(live != rd->state->aclk_live_status)) {
-                if (likely(rrdset_flag_check(st, RRDSET_FLAG_ACLK))) {
-                    if (likely(!queue_dimension_to_aclk(rd))) {
-                        debug(D_ACLK_SYNC,"Dimension change [%s] on [%s] from live %d --> %d", rd->id, rd->rrdset->name, rd->state->aclk_live_status, live);
-                        rd->state->aclk_live_status = live;
-                        rrddim_flag_set(rd, RRDDIM_FLAG_ACLK);
-                    }
-                }
-            }
-            else
-                debug(D_ACLK_SYNC,"Dimension check [%s] on [%s] liveness matches", rd->id, st->name);
-        }
+        if (!rrddim_flag_check(rd, RRDDIM_FLAG_HIDDEN))
+            queue_dimension_to_aclk(rd, calc_dimension_liveness(rd, mark));
     }
     rrdset_unlock(st);
 }
diff --git a/database/sqlite/sqlite_aclk_chart.h b/database/sqlite/sqlite_aclk_chart.h
index 1d25de24..84325bf6 100644
--- a/database/sqlite/sqlite_aclk_chart.h
+++ b/database/sqlite/sqlite_aclk_chart.h
@@ -16,10 +16,21 @@ extern sqlite3 *db_meta;
 #define RRDSET_MINIMUM_DIM_LIVE_MULTIPLIER   (3)
 #endif
 
+#ifndef RRDSET_MINIMUM_DIM_OFFLINE_MULTIPLIER
+#define RRDSET_MINIMUM_DIM_OFFLINE_MULTIPLIER (30)
+#endif
+
 #ifndef ACLK_MAX_DIMENSION_CLEANUP
 #define ACLK_MAX_DIMENSION_CLEANUP (500)
 #endif
 
+struct aclk_chart_dimension_data {
+    uuid_t uuid;
+    char *payload;
+    size_t payload_size;
+    uint8_t check_payload;
+};
+
 struct aclk_chart_sync_stats {
     int        updates;
     uint64_t   batch_id;
@@ -37,9 +48,8 @@ struct aclk_chart_sync_stats {
 };
 
 extern int queue_chart_to_aclk(RRDSET *st);
-extern int queue_dimension_to_aclk(RRDDIM *rd);
+extern void queue_dimension_to_aclk(RRDDIM *rd, time_t last_updated);
 extern void sql_create_aclk_table(RRDHOST *host, uuid_t *host_uuid, uuid_t *node_id);
-extern int sql_queue_alarm_to_aclk(RRDHOST *host, ALARM_ENTRY *ae);
 int aclk_add_chart_event(struct aclk_database_worker_config *wc, struct aclk_database_cmd cmd);
 int aclk_add_dimension_event(struct aclk_database_worker_config *wc, struct aclk_database_cmd cmd);
 int aclk_send_chart_config(struct aclk_database_worker_config *wc, struct aclk_database_cmd cmd);
@@ -57,4 +67,5 @@ uint32_t sql_get_pending_count(struct aclk_database_worker_config *wc);
 void aclk_send_dimension_update(RRDDIM *rd);
 struct aclk_chart_sync_stats *aclk_get_chart_sync_stats(RRDHOST *host);
 void sql_check_chart_liveness(RRDSET *st);
+void aclk_update_retention(struct aclk_database_worker_config *wc);
 #endif //NETDATA_SQLITE_ACLK_CHART_H
diff --git a/database/sqlite/sqlite_aclk_node.c b/database/sqlite/sqlite_aclk_node.c
index 97e6bebd..239a24b8 100644
--- a/database/sqlite/sqlite_aclk_node.c
+++ b/database/sqlite/sqlite_aclk_node.c
@@ -24,6 +24,15 @@ void sql_build_node_info(struct aclk_database_worker_config *wc, struct aclk_dat
     node_info.child = (wc->host != localhost);
     node_info.ml_info.ml_capable = ml_capable(localhost);
     node_info.ml_info.ml_enabled = ml_enabled(wc->host);
+
+    struct capability instance_caps[] = {
+        { .name = "proto", .version = 1,                     .enabled = 1 },
+        { .name = "ml",    .version = ml_capable(localhost), .enabled = ml_enabled(wc->host) },
+        { .name = "mc",    .version = enable_metric_correlations ? metric_correlations_version : 0, .enabled = enable_metric_correlations },
+        { .name = NULL,    .version = 0,                     .enabled = 0 }
+    };
+    node_info.node_instance_capabilities = instance_caps;
+
     now_realtime_timeval(&node_info.updated_at);
 
     RRDHOST *host = wc->host;
@@ -47,7 +56,7 @@ void sql_build_node_info(struct aclk_database_worker_config *wc, struct aclk_dat
     node_info.data.memory = host->system_info->host_ram_total ? host->system_info->host_ram_total : "0";
     node_info.data.disk_space = host->system_info->host_disk_space ? host->system_info->host_disk_space : "0";
     node_info.data.version = host_version ? host_version : VERSION;
-    node_info.data.release_channel = "nightly";
+    node_info.data.release_channel = (char *) get_release_channel();
     node_info.data.timezone = (char *) host->abbrev_timezone;
     node_info.data.virtualization_type = host->system_info->virtualization ? host->system_info->virtualization : "unknown";
     node_info.data.container_type = host->system_info->container ? host->system_info->container : "unknown";
@@ -55,11 +64,19 @@ void sql_build_node_info(struct aclk_database_worker_config *wc, struct aclk_dat
     node_info.data.services = NULL;   // char **
     node_info.data.service_count = 0;
     node_info.data.machine_guid = wc->host_guid;
+
+    struct capability node_caps[] = {
+        { .name = "ml", .version = host->system_info->ml_capable, .enabled = host->system_info->ml_enabled },
+        { .name = "mc", .version = host->system_info->mc_version ? host->system_info->mc_version : 0, .enabled = host->system_info->mc_version ? 1 : 0 },
+        { .name = NULL, .version = 0, .enabled = 0 }
+    };
+    node_info.node_capabilities = node_caps;
+
     node_info.data.ml_info.ml_capable = host->system_info->ml_capable;
     node_info.data.ml_info.ml_enabled = host->system_info->ml_enabled;
 
     struct label_index *labels = &host->labels;
-    netdata_rwlock_wrlock(&labels->labels_rwlock);
+    netdata_rwlock_rdlock(&labels->labels_rwlock);
     node_info.data.host_labels_head = labels->head;
 
     aclk_update_node_info(&node_info);
diff --git a/database/sqlite/sqlite_aclk_node.h b/database/sqlite/sqlite_aclk_node.h
index 9cb41158..b8f8c6bb 100644
--- a/database/sqlite/sqlite_aclk_node.h
+++ b/database/sqlite/sqlite_aclk_node.h
@@ -4,5 +4,4 @@
 #define NETDATA_SQLITE_ACLK_NODE_H
 
 void sql_build_node_info(struct aclk_database_worker_config *wc, struct aclk_database_cmd cmd);
-void aclk_update_retention(struct aclk_database_worker_config *wc, struct aclk_database_cmd cmd);
 #endif //NETDATA_SQLITE_ACLK_NODE_H
diff --git a/database/sqlite/sqlite_functions.c b/database/sqlite/sqlite_functions.c
index 1e1d2a74..502633c6 100644
--- a/database/sqlite/sqlite_functions.c
+++ b/database/sqlite/sqlite_functions.c
@@ -5,8 +5,6 @@
 #define DB_METADATA_VERSION "1"
 
 const char *database_config[] = {
-    "PRAGMA auto_vacuum=incremental; PRAGMA synchronous=1 ; PRAGMA journal_mode=WAL; PRAGMA temp_store=MEMORY;",
-    "PRAGMA journal_size_limit=16777216;",
     "CREATE TABLE IF NOT EXISTS host(host_id blob PRIMARY KEY, hostname text, "
     "registry_hostname text, update_every int, os text, timezone text, tags text);",
     "CREATE TABLE IF NOT EXISTS chart(chart_id blob PRIMARY KEY, host_id blob, type text, id text, name text, "
@@ -62,6 +60,9 @@ const char *database_cleanup[] = {
     "delete from chart where chart_id not in (select chart_id from dimension);",
     "delete from host where host_id not in (select host_id from chart);",
     "delete from chart_label where chart_id not in (select chart_id from chart);",
+    "DELETE FROM chart_hash_map WHERE chart_id NOT IN (SELECT chart_id FROM chart);",
+    "DELETE FROM chart_hash WHERE hash_id NOT IN (SELECT hash_id FROM chart_hash_map);",
+    "DELETE FROM node_instance WHERE host_id NOT IN (SELECT host_id FROM host);",
     NULL
 };
 
@@ -72,10 +73,12 @@ static uv_mutex_t sqlite_transaction_lock;
 int execute_insert(sqlite3_stmt *res)
 {
     int rc;
-
-    while ((rc = sqlite3_step(res)) != SQLITE_DONE && unlikely(netdata_exit)) {
-        if (likely(rc == SQLITE_BUSY || rc == SQLITE_LOCKED))
+    int cnt = 0;
+    while ((rc = sqlite3_step(res)) != SQLITE_DONE && ++cnt < SQL_MAX_RETRY && likely(!netdata_exit)) {
+        if (likely(rc == SQLITE_BUSY || rc == SQLITE_LOCKED)) {
             usleep(SQLITE_INSERT_DELAY * USEC_PER_MS);
+            error_report("Failed to insert/update, rc = %d -- attempt %d", rc, cnt);
+        }
         else {
             error_report("SQLite error %d", rc);
             break;
@@ -93,8 +96,12 @@ static void add_stmt_to_list(sqlite3_stmt *res)
     static sqlite3_stmt *statements[MAX_OPEN_STATEMENTS];
 
     if (unlikely(!res)) {
-        while (idx > 0)
-            sqlite3_finalize(statements[--idx]);
+        while (idx > 0) {
+            int rc;
+            rc = sqlite3_finalize(statements[--idx]);
+            if (unlikely(rc != SQLITE_OK))
+                error_report("Failed to finalize statement during shutdown, rc = %d", rc);
+        }
         return;
     }
 
@@ -302,7 +309,7 @@ static int attempt_database_fix()
         error_report("Failed to close database, rc = %d", rc);
     info("Attempting to fix database");
     db_meta = NULL;
-    return sql_init_database(DB_CHECK_FIX_DB | DB_CHECK_CONT);
+    return sql_init_database(DB_CHECK_FIX_DB | DB_CHECK_CONT, 0);
 }
 
 static int init_database_batch(int rebuild, int init_type, const char *batch[])
@@ -333,13 +340,17 @@ static int init_database_batch(int rebuild, int init_type, const char *batch[])
  * Initialize the SQLite database
  * Return 0 on success
  */
-int sql_init_database(db_check_action_type_t rebuild)
+int sql_init_database(db_check_action_type_t rebuild, int memory)
 {
     char *err_msg = NULL;
     char sqlite_database[FILENAME_MAX + 1];
     int rc;
 
-    snprintfz(sqlite_database, FILENAME_MAX, "%s/netdata-meta.db", netdata_configured_cache_dir);
+    if (likely(!memory))
+        snprintfz(sqlite_database, FILENAME_MAX, "%s/netdata-meta.db", netdata_configured_cache_dir);
+    else
+        strcpy(sqlite_database, ":memory:");
+
     rc = sqlite3_open(sqlite_database, &db_meta);
     if (rc != SQLITE_OK) {
         error_report("Failed to initialize database at %s, due to \"%s\"", sqlite_database, sqlite3_errstr(rc));
@@ -390,6 +401,40 @@ int sql_init_database(db_check_action_type_t rebuild)
 
     info("SQLite database %s initialization", sqlite_database);
 
+    char buf[1024 + 1] = "";
+    const char *list[2] = { buf, NULL };
+
+    // https://www.sqlite.org/pragma.html#pragma_auto_vacuum
+    // PRAGMA schema.auto_vacuum = 0 | NONE | 1 | FULL | 2 | INCREMENTAL;
+    snprintfz(buf, 1024, "PRAGMA auto_vacuum=%s;", config_get(CONFIG_SECTION_SQLITE, "auto vacuum", "INCREMENTAL"));
+    if(init_database_batch(rebuild, 0, list)) return 1;
+
+    // https://www.sqlite.org/pragma.html#pragma_synchronous
+    // PRAGMA schema.synchronous = 0 | OFF | 1 | NORMAL | 2 | FULL | 3 | EXTRA;
+    snprintfz(buf, 1024, "PRAGMA synchronous=%s;", config_get(CONFIG_SECTION_SQLITE, "synchronous", "NORMAL"));
+    if(init_database_batch(rebuild, 0, list)) return 1;
+
+    // https://www.sqlite.org/pragma.html#pragma_journal_mode
+    // PRAGMA schema.journal_mode = DELETE | TRUNCATE | PERSIST | MEMORY | WAL | OFF
+    snprintfz(buf, 1024, "PRAGMA journal_mode=%s;", config_get(CONFIG_SECTION_SQLITE, "journal mode", "WAL"));
+    if(init_database_batch(rebuild, 0, list)) return 1;
+
+    // https://www.sqlite.org/pragma.html#pragma_temp_store
+    // PRAGMA temp_store = 0 | DEFAULT | 1 | FILE | 2 | MEMORY;
+    snprintfz(buf, 1024, "PRAGMA temp_store=%s;", config_get(CONFIG_SECTION_SQLITE, "temp store", "MEMORY"));
+    if(init_database_batch(rebuild, 0, list)) return 1;
+    
+    // https://www.sqlite.org/pragma.html#pragma_journal_size_limit
+    // PRAGMA schema.journal_size_limit = N ;
+    snprintfz(buf, 1024, "PRAGMA journal_size_limit=%lld;", config_get_number(CONFIG_SECTION_SQLITE, "journal size limit", 16777216));
+    if(init_database_batch(rebuild, 0, list)) return 1;
+
+    // https://www.sqlite.org/pragma.html#pragma_cache_size
+    // PRAGMA schema.cache_size = pages;
+    // PRAGMA schema.cache_size = -kibibytes;
+    snprintfz(buf, 1024, "PRAGMA cache_size=%lld;", config_get_number(CONFIG_SECTION_SQLITE, "cache size", -2000));
+    if(init_database_batch(rebuild, 0, list)) return 1;
+
     if (init_database_batch(rebuild, 0, &database_config[0]))
         return 1;
 
@@ -1160,8 +1205,24 @@ failed:
     return;
 }
 
+void free_temporary_host(RRDHOST *host)
+{
+    if (host) {
+        freez(host->hostname);
+        freez((char *)host->os);
+        freez((char *)host->tags);
+        freez((char *)host->timezone);
+        freez(host->program_name);
+        freez(host->program_version);
+        freez(host->registry_hostname);
+        freez(host->system_info);
+        freez(host);
+    }
+}
+
 #define SELECT_HOST "select host_id, registry_hostname, update_every, os, timezone, tags from host where hostname = @hostname order by rowid desc;"
-#define SELECT_HOST_BY_UUID "select host_id, registry_hostname, update_every, os, timezone, tags from host where host_id = @host_id ;"
+#define SELECT_HOST_BY_UUID "select h.host_id, h.registry_hostname, h.update_every, h.os, h.timezone, h.tags from host h, node_instance ni " \
+    "where (ni.host_id = @host_id or ni.node_id = @host_id) AND ni.host_id = h.host_id;"
 
 RRDHOST *sql_create_host_by_uuid(char *hostname)
 {
@@ -1229,8 +1290,6 @@ failed:
     return host;
 }
 
-#define SQL_MAX_RETRY 100
-
 void db_execute(const char *cmd)
 {
     int rc;
@@ -1430,13 +1489,13 @@ int find_dimension_first_last_t(char *machine_guid, char *chart_id, char *dim_id
 }
 
 #ifdef ENABLE_DBENGINE
-static RRDDIM *create_rrdim_entry(RRDSET *st, char *id, char *name, uuid_t *metric_uuid)
+static RRDDIM *create_rrdim_entry(ONEWAYALLOC *owa, RRDSET *st, char *id, char *name, uuid_t *metric_uuid)
 {
-    RRDDIM *rd = callocz(1, sizeof(*rd));
+    RRDDIM *rd = onewayalloc_callocz(owa, 1, sizeof(*rd));
     rd->rrdset = st;
     rd->last_stored_value = NAN;
     rrddim_flag_set(rd, RRDDIM_FLAG_NONE);
-    rd->state = mallocz(sizeof(*rd->state));
+    rd->state = onewayalloc_mallocz(owa, sizeof(*rd->state));
     rd->rrd_memory_mode = RRD_MEMORY_MODE_DBENGINE;
     rd->state->query_ops.init = rrdeng_load_metric_init;
     rd->state->query_ops.next_metric = rrdeng_load_metric_next;
@@ -1444,11 +1503,11 @@ static RRDDIM *create_rrdim_entry(RRDSET *st, char *id, char *name, uuid_t *metr
     rd->state->query_ops.finalize = rrdeng_load_metric_finalize;
     rd->state->query_ops.latest_time = rrdeng_metric_latest_time;
     rd->state->query_ops.oldest_time = rrdeng_metric_oldest_time;
-    rd->state->rrdeng_uuid = mallocz(sizeof(uuid_t));
+    rd->state->rrdeng_uuid = onewayalloc_mallocz(owa, sizeof(uuid_t));
     uuid_copy(*rd->state->rrdeng_uuid, *metric_uuid);
     uuid_copy(rd->state->metric_uuid, *metric_uuid);
-    rd->id = strdupz(id);
-    rd->name = strdupz(name);
+    rd->id = onewayalloc_strdupz(owa, id);
+    rd->name = onewayalloc_strdupz(owa, name);
     return rd;
 }
 #endif
@@ -1465,7 +1524,7 @@ static RRDDIM *create_rrdim_entry(RRDSET *st, char *id, char *name, uuid_t *metr
     "where d.chart_id = c.chart_id and c.host_id = h.host_id and c.host_id = @host_id and c.type||'.'||c.id = @chart " \
     "order by c.chart_id asc, c.type||'.'||c.id desc;"
 
-void sql_build_context_param_list(struct context_param **param_list, RRDHOST *host, char *context, char *chart)
+void sql_build_context_param_list(ONEWAYALLOC  *owa, struct context_param **param_list, RRDHOST *host, char *context, char *chart)
 {
 #ifdef ENABLE_DBENGINE
     int rc;
@@ -1474,7 +1533,7 @@ void sql_build_context_param_list(struct context_param **param_list, RRDHOST *ho
         return;
 
     if (unlikely(!(*param_list))) {
-        *param_list = mallocz(sizeof(struct context_param));
+        *param_list = onewayalloc_mallocz(owa, sizeof(struct context_param));
         (*param_list)->first_entry_t = LONG_MAX;
         (*param_list)->last_entry_t = 0;
         (*param_list)->rd = NULL;
@@ -1523,21 +1582,21 @@ void sql_build_context_param_list(struct context_param **param_list, RRDHOST *ho
 
         if (!st || uuid_compare(*(uuid_t *)sqlite3_column_blob(res, 7), chart_id)) {
             if (unlikely(st && !st->counter)) {
-                freez(st->context);
-                freez((char *) st->name);
-                freez(st);
+                onewayalloc_freez(owa, st->context);
+                onewayalloc_freez(owa, (char *) st->name);
+                onewayalloc_freez(owa, st);
             }
-            st = callocz(1, sizeof(*st));
+            st = onewayalloc_callocz(owa, 1, sizeof(*st));
             char n[RRD_ID_LENGTH_MAX + 1];
 
             snprintfz(
                 n, RRD_ID_LENGTH_MAX, "%s.%s", (char *)sqlite3_column_text(res, 4),
                 (char *)sqlite3_column_text(res, 3));
-            st->name = strdupz(n);
+            st->name = onewayalloc_strdupz(owa, n);
             st->update_every = sqlite3_column_int(res, 6);
             st->counter = 0;
             if (chart) {
-                st->context = strdupz((char *)sqlite3_column_text(res, 8));
+                st->context = onewayalloc_strdupz(owa, (char *)sqlite3_column_text(res, 8));
                 strncpyz(st->id, chart, RRD_ID_LENGTH_MAX);
             }
             uuid_copy(chart_id, *(uuid_t *)sqlite3_column_blob(res, 7));
@@ -1553,7 +1612,7 @@ void sql_build_context_param_list(struct context_param **param_list, RRDHOST *ho
         st->counter++;
         st->last_entry_t = MAX(st->last_entry_t, (*param_list)->last_entry_t);
 
-        RRDDIM *rd = create_rrdim_entry(st, (char *)sqlite3_column_text(res, 1), (char *)sqlite3_column_text(res, 2), &rrdeng_uuid);
+        RRDDIM *rd = create_rrdim_entry(owa, st, (char *)sqlite3_column_text(res, 1), (char *)sqlite3_column_text(res, 2), &rrdeng_uuid);
         if (sqlite3_column_int(res, 9) == 1)
             rrddim_flag_set(rd, RRDDIM_FLAG_HIDDEN);
         rd->next = (*param_list)->rd;
@@ -1561,13 +1620,13 @@ void sql_build_context_param_list(struct context_param **param_list, RRDHOST *ho
     }
     if (st) {
         if (!st->counter) {
-            freez(st->context);
-            freez((char *)st->name);
-            freez(st);
+            onewayalloc_freez(owa,st->context);
+            onewayalloc_freez(owa,(char *)st->name);
+            onewayalloc_freez(owa,st);
         }
         else
             if (!st->context && context)
-                st->context = strdupz(context);
+                st->context = onewayalloc_strdupz(owa,context);
     }
 
 failed:
diff --git a/database/sqlite/sqlite_functions.h b/database/sqlite/sqlite_functions.h
index 30b8dee6..d2448477 100644
--- a/database/sqlite/sqlite_functions.h
+++ b/database/sqlite/sqlite_functions.h
@@ -24,6 +24,7 @@ typedef enum db_check_action_type {
     DB_CHECK_CONT = 0x00008
 } db_check_action_type_t;
 
+#define SQL_MAX_RETRY (100)
 #define SQLITE_INSERT_DELAY (50)        // Insert delay in case of lock
 
 #define SQL_STORE_HOST "insert or replace into host (host_id,hostname,registry_hostname,update_every,os,timezone,tags) values (?1,?2,?3,?4,?5,?6,?7);"
@@ -56,7 +57,7 @@ typedef enum db_check_action_type {
         return 1;                                                                                                      \
     }
 
-extern int sql_init_database(db_check_action_type_t rebuild);
+extern int sql_init_database(db_check_action_type_t rebuild, int memory);
 extern void sql_close_database(void);
 
 extern int sql_store_host(uuid_t *guid, const char *hostname, const char *registry_hostname, int update_every, const char *os, const char *timezone, const char *tags);
@@ -89,7 +90,7 @@ extern void db_unlock(void);
 extern void db_lock(void);
 extern void delete_dimension_uuid(uuid_t *dimension_uuid);
 extern void sql_store_chart_label(uuid_t *chart_uuid, int source_type, char *label, char *value);
-extern void sql_build_context_param_list(struct context_param **param_list, RRDHOST *host, char *context, char *chart);
+extern void sql_build_context_param_list(ONEWAYALLOC  *owa, struct context_param **param_list, RRDHOST *host, char *context, char *chart);
 extern void store_claim_id(uuid_t *host_id, uuid_t *claim_id);
 extern int update_node_id(uuid_t *host_id, uuid_t *node_id);
 extern int get_node_id(uuid_t *host_id, uuid_t *node_id);
@@ -100,4 +101,5 @@ extern void sql_load_node_id(RRDHOST *host);
 extern void compute_chart_hash(RRDSET *st);
 extern int sql_set_dimension_option(uuid_t *dim_uuid, char *option);
 char *get_hostname_by_node_id(char *node_id);
+void free_temporary_host(RRDHOST *host);
 #endif //NETDATA_SQLITE_FUNCTIONS_H
diff --git a/database/sqlite/sqlite_health.c b/database/sqlite/sqlite_health.c
index 8ba95628..53742a1a 100644
--- a/database/sqlite/sqlite_health.c
+++ b/database/sqlite/sqlite_health.c
@@ -433,6 +433,168 @@ void sql_health_alarm_log_count(RRDHOST *host) {
     info("HEALTH [%s]: Table health_log_%s, contains %lu entries.", host->hostname, uuid_str, host->health_log_entries_written);
 }
 
+#define SQL_INJECT_REMOVED(guid, guid2) "insert into health_log_%s (hostname, unique_id, alarm_id, alarm_event_id, config_hash_id, updated_by_id, updates_id, when_key, duration, non_clear_duration, flags, exec_run_timestamp, " \
+"delay_up_to_timestamp, name, chart, family, exec, recipient, source, units, info, exec_code, new_status, old_status, delay, new_value, old_value, last_repeat, class, component, type) " \
+"select hostname, ?1, ?2, ?3, config_hash_id, 0, ?4, strftime('%%s'), 0, 0, flags, exec_run_timestamp, " \
+"strftime('%%s'), name, chart, family, exec, recipient, source, units, info, exec_code, -2, new_status, delay, NULL, new_value, 0, class, component, type " \
+"from health_log_%s where unique_id = ?5", guid, guid2
+#define SQL_INJECT_REMOVED_UPDATE(guid) "update health_log_%s set flags = flags | ?1, updated_by_id = ?2 where unique_id = ?3; ", guid
+void sql_inject_removed_status(char *uuid_str, uint32_t alarm_id, uint32_t alarm_event_id, uint32_t unique_id, uint32_t max_unique_id)
+{
+    int rc = 0;
+    char command[MAX_HEALTH_SQL_SIZE + 1];
+
+    if (!alarm_id || !alarm_event_id || !unique_id || !max_unique_id)
+        return;
+
+    sqlite3_stmt *res = NULL;
+
+    snprintfz(command, MAX_HEALTH_SQL_SIZE, SQL_INJECT_REMOVED(uuid_str, uuid_str));
+    rc = sqlite3_prepare_v2(db_meta, command, -1, &res, 0);
+    if (rc != SQLITE_OK) {
+        error_report("Failed to prepare statement when trying to inject removed event");
+        return;
+    }
+
+    rc = sqlite3_bind_int64(res, 1, (sqlite3_int64) max_unique_id);
+    if (unlikely(rc != SQLITE_OK)) {
+        error_report("Failed to bind max_unique_id parameter for SQL_INJECT_REMOVED");
+        goto failed;
+    }
+
+    rc = sqlite3_bind_int64(res, 2, (sqlite3_int64) alarm_id);
+    if (unlikely(rc != SQLITE_OK)) {
+        error_report("Failed to bind alarm_id parameter for SQL_INJECT_REMOVED");
+        goto failed;
+    }
+
+    rc = sqlite3_bind_int64(res, 3, (sqlite3_int64) alarm_event_id + 1);
+    if (unlikely(rc != SQLITE_OK)) {
+        error_report("Failed to bind alarm_event_id parameter for SQL_INJECT_REMOVED");
+        goto failed;
+    }
+
+    rc = sqlite3_bind_int64(res, 4, (sqlite3_int64) unique_id);
+    if (unlikely(rc != SQLITE_OK)) {
+        error_report("Failed to bind unique_id parameter for SQL_INJECT_REMOVED");
+        goto failed;
+    }
+
+    rc = sqlite3_bind_int64(res, 5, (sqlite3_int64) unique_id);
+    if (unlikely(rc != SQLITE_OK)) {
+        error_report("Failed to bind unique_id parameter for SQL_INJECT_REMOVED");
+        goto failed;
+    }
+
+    rc = execute_insert(res);
+    if (unlikely(rc != SQLITE_DONE)) {
+        error_report("HEALTH [N/A]: Failed to execute SQL_INJECT_REMOVED, rc = %d", rc);
+        goto failed;
+    }
+
+    if (unlikely(sqlite3_finalize(res) != SQLITE_OK))
+        error_report("HEALTH [N/A]: Failed to finalize the prepared statement for injecting removed event.");
+
+    //update the old entry
+    snprintfz(command, MAX_HEALTH_SQL_SIZE, SQL_INJECT_REMOVED_UPDATE(uuid_str));
+    rc = sqlite3_prepare_v2(db_meta, command, -1, &res, 0);
+    if (rc != SQLITE_OK) {
+        error_report("Failed to prepare statement when trying to update during inject removed event");
+        return;
+    }
+
+    rc = sqlite3_bind_int64(res, 1, (sqlite3_int64) HEALTH_ENTRY_FLAG_UPDATED);
+    if (unlikely(rc != SQLITE_OK)) {
+        error_report("Failed to bind flags parameter for SQL_INJECT_REMOVED (update)");
+        goto failed;
+    }
+
+    rc = sqlite3_bind_int64(res, 2, (sqlite3_int64) max_unique_id);
+    if (unlikely(rc != SQLITE_OK)) {
+        error_report("Failed to bind max_unique_id parameter for SQL_INJECT_REMOVED (update)");
+        goto failed;
+    }
+
+    rc = sqlite3_bind_int64(res, 3, (sqlite3_int64) unique_id);
+    if (unlikely(rc != SQLITE_OK)) {
+        error_report("Failed to bind unique_id parameter for SQL_INJECT_REMOVED (update)");
+        goto failed;
+    }
+
+    rc = execute_insert(res);
+    if (unlikely(rc != SQLITE_DONE)) {
+        error_report("HEALTH [N/A]: Failed to execute SQL_INJECT_REMOVED_UPDATE, rc = %d", rc);
+        goto failed;
+    }
+
+failed:
+    if (unlikely(sqlite3_finalize(res) != SQLITE_OK))
+        error_report("HEALTH [N/A]: Failed to finalize the prepared statement for injecting removed event.");
+    return;
+
+}
+
+#define SQL_SELECT_MAX_UNIQUE_ID(guid) "SELECT MAX(unique_id) from health_log_%s", guid
+uint32_t sql_get_max_unique_id (char *uuid_str)
+{
+    int rc = 0;
+    char command[MAX_HEALTH_SQL_SIZE + 1];
+    uint32_t max_unique_id = 0;
+
+    sqlite3_stmt *res = NULL;
+
+    snprintfz(command, MAX_HEALTH_SQL_SIZE, SQL_SELECT_MAX_UNIQUE_ID(uuid_str));
+    rc = sqlite3_prepare_v2(db_meta, command, -1, &res, 0);
+    if (rc != SQLITE_OK) {
+        error_report("Failed to prepare statement when trying to get max unique id");
+        return 0;
+    }
+
+     while (sqlite3_step(res) == SQLITE_ROW) {
+         max_unique_id = (uint32_t) sqlite3_column_int64(res, 0);
+     }
+
+     rc = sqlite3_finalize(res);
+     if (unlikely(rc != SQLITE_OK))
+         error_report("Failed to finalize the statement");
+
+     return max_unique_id;
+}
+
+#define SQL_SELECT_LAST_STATUSES(guid) "SELECT new_status, unique_id, alarm_id, alarm_event_id from health_log_%s group by alarm_id having max(alarm_event_id)", guid
+void sql_check_removed_alerts_state(char *uuid_str)
+{
+    int rc = 0;
+    char command[MAX_HEALTH_SQL_SIZE + 1];
+    RRDCALC_STATUS status;
+    uint32_t alarm_id = 0, alarm_event_id = 0, unique_id = 0, max_unique_id = 0;
+
+    sqlite3_stmt *res = NULL;
+
+    snprintfz(command, MAX_HEALTH_SQL_SIZE, SQL_SELECT_LAST_STATUSES(uuid_str));
+    rc = sqlite3_prepare_v2(db_meta, command, -1, &res, 0);
+    if (rc != SQLITE_OK) {
+        error_report("Failed to prepare statement when trying to check removed statuses");
+        return;
+    }
+
+     while (sqlite3_step(res) == SQLITE_ROW) {
+         status  = (RRDCALC_STATUS) sqlite3_column_int(res, 0);
+         unique_id = (uint32_t) sqlite3_column_int64(res, 1);
+         alarm_id = (uint32_t) sqlite3_column_int64(res, 2);
+         alarm_event_id = (uint32_t) sqlite3_column_int64(res, 3);
+         if (unlikely(status != RRDCALC_STATUS_REMOVED)) {
+             if (unlikely(!max_unique_id))
+                 max_unique_id = sql_get_max_unique_id (uuid_str);
+             sql_inject_removed_status (uuid_str, alarm_id, alarm_event_id, unique_id, ++max_unique_id);
+         }
+     }
+
+     rc = sqlite3_finalize(res);
+     if (unlikely(rc != SQLITE_OK))
+         error_report("Failed to finalize the statement");
+}
+
 /* Health related SQL queries
    Load from the health log table
 */
@@ -454,6 +616,8 @@ void sql_health_alarm_log_load(RRDHOST *host) {
     char uuid_str[GUID_LEN + 1];
     uuid_unparse_lower_fix(&host->host_uuid, uuid_str);
 
+    sql_check_removed_alerts_state(uuid_str);
+
     snprintfz(command, MAX_HEALTH_SQL_SIZE, SQL_LOAD_HEALTH_LOG(uuid_str, host->health_log.max));
 
     rc = sqlite3_prepare_v2(db_meta, command, -1, &res, 0);
diff --git a/database/storage_engine.c b/database/storage_engine.c
new file mode 100644
index 00000000..36f01de1
--- /dev/null
+++ b/database/storage_engine.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "storage_engine.h"
+#include "ram/rrddim_mem.h"
+#ifdef ENABLE_DBENGINE
+#include "engine/rrdengineapi.h"
+#endif
+
+#define im_collect_ops { \
+    .init = rrddim_collect_init,\
+    .store_metric = rrddim_collect_store_metric,\
+    .finalize = rrddim_collect_finalize\
+}
+
+#define im_query_ops { \
+    .init = rrddim_query_init, \
+    .next_metric = rrddim_query_next_metric, \
+    .is_finished = rrddim_query_is_finished, \
+    .finalize = rrddim_query_finalize, \
+    .latest_time = rrddim_query_latest_time, \
+    .oldest_time = rrddim_query_oldest_time \
+}
+
+static STORAGE_ENGINE engines[] = {
+    {
+        .id = RRD_MEMORY_MODE_NONE,
+        .name = RRD_MEMORY_MODE_NONE_NAME,
+        .api = {
+            .collect_ops = im_collect_ops,
+            .query_ops = im_query_ops
+        }
+    },
+    {
+        .id = RRD_MEMORY_MODE_RAM,
+        .name = RRD_MEMORY_MODE_RAM_NAME,
+        .api = {
+            .collect_ops = im_collect_ops,
+            .query_ops = im_query_ops
+        }
+    },
+    {
+        .id = RRD_MEMORY_MODE_MAP,
+        .name = RRD_MEMORY_MODE_MAP_NAME,
+        .api = {
+            .collect_ops = im_collect_ops,
+            .query_ops = im_query_ops
+        }
+    },
+    {
+        .id = RRD_MEMORY_MODE_SAVE,
+        .name = RRD_MEMORY_MODE_SAVE_NAME,
+        .api = {
+            .collect_ops = im_collect_ops,
+            .query_ops = im_query_ops
+        }
+    },
+    {
+        .id = RRD_MEMORY_MODE_ALLOC,
+        .name = RRD_MEMORY_MODE_ALLOC_NAME,
+        .api = {
+            .collect_ops = im_collect_ops,
+            .query_ops = im_query_ops
+        }
+    },
+#ifdef ENABLE_DBENGINE
+    {
+        .id = RRD_MEMORY_MODE_DBENGINE,
+        .name = RRD_MEMORY_MODE_DBENGINE_NAME,
+        .api = {
+            .collect_ops = {
+                .init = rrdeng_store_metric_init,
+                .store_metric = rrdeng_store_metric_next,
+                .finalize = rrdeng_store_metric_finalize
+            },
+            .query_ops = {
+                .init = rrdeng_load_metric_init,
+                .next_metric = rrdeng_load_metric_next,
+                .is_finished = rrdeng_load_metric_is_finished,
+                .finalize = rrdeng_load_metric_finalize,
+                .latest_time = rrdeng_metric_latest_time,
+                .oldest_time = rrdeng_metric_oldest_time
+            }
+        }
+    },
+#endif
+    { .id = RRD_MEMORY_MODE_NONE, .name = NULL }
+};
+
+STORAGE_ENGINE* storage_engine_find(const char* name)
+{
+    for (STORAGE_ENGINE* it = engines; it->name; it++) {
+        if (strcmp(it->name, name) == 0)
+            return it;
+    }
+    return NULL;
+}
+
+STORAGE_ENGINE* storage_engine_get(RRD_MEMORY_MODE mmode)
+{
+    for (STORAGE_ENGINE* it = engines; it->name; it++) {
+        if (it->id == mmode)
+            return it;
+    }
+    return NULL;
+}
+
+STORAGE_ENGINE* storage_engine_foreach_init()
+{
+    // Assuming at least one engine exists
+    return &engines[0];
+}
+
+STORAGE_ENGINE* storage_engine_foreach_next(STORAGE_ENGINE* it)
+{
+    if (!it || !it->name)
+        return NULL;
+
+    it++;
+    return it->name ? it : NULL;
+}
diff --git a/database/storage_engine.h b/database/storage_engine.h
new file mode 100644
index 00000000..0aa70d09
--- /dev/null
+++ b/database/storage_engine.h
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#ifndef NETDATA_STORAGEENGINEAPI_H
+#define NETDATA_STORAGEENGINEAPI_H
+
+#include "rrd.h"
+
+typedef struct storage_engine STORAGE_ENGINE;
+
+// ------------------------------------------------------------------------
+// function pointers for all APIs provided by a storge engine
+typedef struct storage_engine_api {
+    struct rrddim_collect_ops collect_ops;
+    struct rrddim_query_ops query_ops;
+} STORAGE_ENGINE_API;
+
+struct storage_engine {
+    RRD_MEMORY_MODE id;
+    const char* name;
+    STORAGE_ENGINE_API api;
+};
+
+extern STORAGE_ENGINE* storage_engine_get(RRD_MEMORY_MODE mmode);
+extern STORAGE_ENGINE* storage_engine_find(const char* name);
+
+// Iterator over existing engines
+extern STORAGE_ENGINE* storage_engine_foreach_init();
+extern STORAGE_ENGINE* storage_engine_foreach_next(STORAGE_ENGINE* it);
+
+#endif