Merging upstream version 1.38.0.

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

1 files changed, 909 insertions, 774 deletions

diff --git a/database/engine/rrdengineapi.c b/database/engine/rrdengineapi.c
index 4525b041..27497bbb 100755
--- a/database/engine/rrdengineapi.c
+++ b/database/engine/rrdengineapi.c
@@ -1,6 +1,5 @@
 // SPDX-License-Identifier: GPL-3.0-or-later
 #include "rrdengine.h"
-#include "../storage_engine.h"
 
 /* Default global database instance */
 struct rrdengine_instance multidb_ctx_storage_tier0;
@@ -8,12 +7,21 @@ struct rrdengine_instance multidb_ctx_storage_tier1;
 struct rrdengine_instance multidb_ctx_storage_tier2;
 struct rrdengine_instance multidb_ctx_storage_tier3;
 struct rrdengine_instance multidb_ctx_storage_tier4;
+
+#define mrg_metric_ctx(metric) (struct rrdengine_instance *)mrg_metric_section(main_mrg, metric)
+
 #if RRD_STORAGE_TIERS != 5
 #error RRD_STORAGE_TIERS is not 5 - you need to add allocations here
 #endif
 struct rrdengine_instance *multidb_ctx[RRD_STORAGE_TIERS];
 uint8_t tier_page_type[RRD_STORAGE_TIERS] = {PAGE_METRICS, PAGE_TIER, PAGE_TIER, PAGE_TIER, PAGE_TIER};
 
+#if defined(ENV32BIT)
+size_t tier_page_size[RRD_STORAGE_TIERS] = {2048, 1024, 192, 192, 192};
+#else
+size_t tier_page_size[RRD_STORAGE_TIERS] = {4096, 2048, 384, 384, 384};
+#endif
+
 #if PAGE_TYPE_MAX != 1
 #error PAGE_TYPE_MAX is not 1 - you need to add allocations here
 #endif
@@ -27,14 +35,17 @@ __attribute__((constructor)) void initialize_multidb_ctx(void) {
     multidb_ctx[4] = &multidb_ctx_storage_tier4;
 }
 
-int db_engine_use_malloc = 0;
 int default_rrdeng_page_fetch_timeout = 3;
 int default_rrdeng_page_fetch_retries = 3;
-int default_rrdeng_page_cache_mb = 32;
+int db_engine_journal_check = 0;
 int default_rrdeng_disk_quota_mb = 256;
 int default_multidb_disk_quota_mb = 256;
-/* Default behaviour is to unblock data collection if the page cache is full of dirty pages by dropping metrics */
-uint8_t rrdeng_drop_metrics_under_page_cache_pressure = 1;
+
+#if defined(ENV32BIT)
+int default_rrdeng_page_cache_mb = 16;
+#else
+int default_rrdeng_page_cache_mb = 32;
+#endif
 
 // ----------------------------------------------------------------------------
 // metrics groups
@@ -90,161 +101,207 @@ void rrdeng_generate_legacy_uuid(const char *dim_id, const char *chart_id, uuid_
     memcpy(ret_uuid, hash_value, sizeof(uuid_t));
 }
 
-/* Transform legacy UUID to be unique across hosts deterministically */
-void rrdeng_convert_legacy_uuid_to_multihost(char machine_guid[GUID_LEN + 1], uuid_t *legacy_uuid, uuid_t *ret_uuid)
-{
-    EVP_MD_CTX *evpctx;
-    unsigned char hash_value[EVP_MAX_MD_SIZE];
-    unsigned int hash_len;
-
-    evpctx = EVP_MD_CTX_create();
-    EVP_DigestInit_ex(evpctx, EVP_sha256(), NULL);
-    EVP_DigestUpdate(evpctx, machine_guid, GUID_LEN);
-    EVP_DigestUpdate(evpctx, *legacy_uuid, sizeof(uuid_t));
-    EVP_DigestFinal_ex(evpctx, hash_value, &hash_len);
-    EVP_MD_CTX_destroy(evpctx);
-    fatal_assert(hash_len > sizeof(uuid_t));
-    memcpy(ret_uuid, hash_value, sizeof(uuid_t));
-}
-
-STORAGE_METRIC_HANDLE *rrdeng_metric_get_legacy(STORAGE_INSTANCE *db_instance, const char *rd_id, const char *st_id) {
+static METRIC *rrdeng_metric_get_legacy(STORAGE_INSTANCE *db_instance, const char *rd_id, const char *st_id) {
+    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
     uuid_t legacy_uuid;
     rrdeng_generate_legacy_uuid(rd_id, st_id, &legacy_uuid);
-    return rrdeng_metric_get(db_instance, &legacy_uuid);
+    return mrg_metric_get_and_acquire(main_mrg, &legacy_uuid, (Word_t) ctx);
 }
 
 // ----------------------------------------------------------------------------
 // metric handle
 
 void rrdeng_metric_release(STORAGE_METRIC_HANDLE *db_metric_handle) {
-    struct pg_cache_page_index *page_index = (struct pg_cache_page_index *)db_metric_handle;
-
-    __atomic_sub_fetch(&page_index->refcount, 1, __ATOMIC_SEQ_CST);
+    METRIC *metric = (METRIC *)db_metric_handle;
+    mrg_metric_release(main_mrg, metric);
 }
 
 STORAGE_METRIC_HANDLE *rrdeng_metric_dup(STORAGE_METRIC_HANDLE *db_metric_handle) {
-    struct pg_cache_page_index *page_index = (struct pg_cache_page_index *)db_metric_handle;
-    __atomic_add_fetch(&page_index->refcount, 1, __ATOMIC_SEQ_CST);
-    return db_metric_handle;
+    METRIC *metric = (METRIC *)db_metric_handle;
+    return (STORAGE_METRIC_HANDLE *) mrg_metric_dup(main_mrg, metric);
 }
 
 STORAGE_METRIC_HANDLE *rrdeng_metric_get(STORAGE_INSTANCE *db_instance, uuid_t *uuid) {
     struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
-    struct page_cache *pg_cache = &ctx->pg_cache;
-    struct pg_cache_page_index *page_index = NULL;
-
-    uv_rwlock_rdlock(&pg_cache->metrics_index.lock);
-    Pvoid_t *PValue = JudyHSGet(pg_cache->metrics_index.JudyHS_array, uuid, sizeof(uuid_t));
-    if (likely(NULL != PValue))
-        page_index = *PValue;
-    uv_rwlock_rdunlock(&pg_cache->metrics_index.lock);
-
-    if (likely(page_index))
-        __atomic_add_fetch(&page_index->refcount, 1, __ATOMIC_SEQ_CST);
-
-    return (STORAGE_METRIC_HANDLE *)page_index;
+    return (STORAGE_METRIC_HANDLE *) mrg_metric_get_and_acquire(main_mrg, uuid, (Word_t) ctx);
 }
 
-STORAGE_METRIC_HANDLE *rrdeng_metric_create(STORAGE_INSTANCE *db_instance, uuid_t *uuid) {
+static METRIC *rrdeng_metric_create(STORAGE_INSTANCE *db_instance, uuid_t *uuid) {
     internal_fatal(!db_instance, "DBENGINE: db_instance is NULL");
 
     struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
-    struct pg_cache_page_index *page_index;
-    struct page_cache *pg_cache = &ctx->pg_cache;
-
-    uv_rwlock_wrlock(&pg_cache->metrics_index.lock);
-    Pvoid_t *PValue = JudyHSIns(&pg_cache->metrics_index.JudyHS_array, uuid, sizeof(uuid_t), PJE0);
-    fatal_assert(NULL == *PValue); /* TODO: figure out concurrency model */
-    *PValue = page_index = create_page_index(uuid, ctx);
-    page_index->prev = pg_cache->metrics_index.last_page_index;
-    pg_cache->metrics_index.last_page_index = page_index;
-    page_index->refcount = 1;
-    uv_rwlock_wrunlock(&pg_cache->metrics_index.lock);
-
-    return (STORAGE_METRIC_HANDLE *)page_index;
+    MRG_ENTRY entry = {
+            .section = (Word_t)ctx,
+            .first_time_s = 0,
+            .last_time_s = 0,
+            .latest_update_every_s = 0,
+    };
+    uuid_copy(entry.uuid, *uuid);
+
+    METRIC *metric = mrg_metric_add_and_acquire(main_mrg, entry, NULL);
+    return metric;
 }
 
 STORAGE_METRIC_HANDLE *rrdeng_metric_get_or_create(RRDDIM *rd, STORAGE_INSTANCE *db_instance) {
-    STORAGE_METRIC_HANDLE *db_metric_handle;
-
-    db_metric_handle = rrdeng_metric_get(db_instance, &rd->metric_uuid);
-    if(!db_metric_handle) {
-        db_metric_handle = rrdeng_metric_get_legacy(db_instance, rrddim_id(rd), rrdset_id(rd->rrdset));
-        if(db_metric_handle) {
-            struct pg_cache_page_index *page_index = (struct pg_cache_page_index *)db_metric_handle;
-            uuid_copy(rd->metric_uuid, page_index->id);
+    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
+    METRIC *metric;
+
+    metric = mrg_metric_get_and_acquire(main_mrg, &rd->metric_uuid, (Word_t) ctx);
+
+    if(unlikely(!metric)) {
+        if(unlikely(ctx->config.legacy)) {
+            // this is a single host database
+            // generate uuid from the chart and dimensions ids
+            // and overwrite the one supplied by rrddim
+            metric = rrdeng_metric_get_legacy(db_instance, rrddim_id(rd), rrdset_id(rd->rrdset));
+            if (metric)
+                uuid_copy(rd->metric_uuid, *mrg_metric_uuid(main_mrg, metric));
         }
+
+        if(likely(!metric))
+            metric = rrdeng_metric_create(db_instance, &rd->metric_uuid);
     }
-    if(!db_metric_handle)
-        db_metric_handle = rrdeng_metric_create(db_instance, &rd->metric_uuid);
 
 #ifdef NETDATA_INTERNAL_CHECKS
-    struct pg_cache_page_index *page_index = (struct pg_cache_page_index *)db_metric_handle;
-    if(uuid_compare(rd->metric_uuid, page_index->id) != 0) {
+    if(uuid_compare(rd->metric_uuid, *mrg_metric_uuid(main_mrg, metric)) != 0) {
         char uuid1[UUID_STR_LEN + 1];
         char uuid2[UUID_STR_LEN + 1];
 
         uuid_unparse(rd->metric_uuid, uuid1);
-        uuid_unparse(page_index->id, uuid2);
-        fatal("DBENGINE: uuids do not match, asked for metric '%s', but got page_index of metric '%s'", uuid1, uuid2);
+        uuid_unparse(*mrg_metric_uuid(main_mrg, metric), uuid2);
+        fatal("DBENGINE: uuids do not match, asked for metric '%s', but got metric '%s'", uuid1, uuid2);
     }
 
-    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
-    if(page_index->ctx != ctx)
-        fatal("DBENGINE: mixed up rrdengine instances, asked for metric from %p, got from %p", ctx, page_index->ctx);
+    if(mrg_metric_ctx(metric) != ctx)
+        fatal("DBENGINE: mixed up db instances, asked for metric from %p, got from %p",
+              ctx, mrg_metric_ctx(metric));
 #endif
 
-    return db_metric_handle;
+    return (STORAGE_METRIC_HANDLE *)metric;
 }
 
 
 // ----------------------------------------------------------------------------
 // collect ops
 
+static inline void check_and_fix_mrg_update_every(struct rrdeng_collect_handle *handle) {
+    if(unlikely((time_t)(handle->update_every_ut / USEC_PER_SEC) != mrg_metric_get_update_every_s(main_mrg, handle->metric))) {
+        internal_error(true, "DBENGINE: collection handle has update every %ld, but the metric registry has %ld. Fixing it.",
+              (time_t)(handle->update_every_ut / USEC_PER_SEC), mrg_metric_get_update_every_s(main_mrg, handle->metric));
+
+        if(unlikely(!handle->update_every_ut))
+            handle->update_every_ut = (usec_t)mrg_metric_get_update_every_s(main_mrg, handle->metric) * USEC_PER_SEC;
+        else
+            mrg_metric_set_update_every(main_mrg, handle->metric, (time_t)(handle->update_every_ut / USEC_PER_SEC));
+    }
+}
+
+static inline bool check_completed_page_consistency(struct rrdeng_collect_handle *handle __maybe_unused) {
+#ifdef NETDATA_INTERNAL_CHECKS
+    if (unlikely(!handle->page || !handle->page_entries_max || !handle->page_position || !handle->page_end_time_ut))
+        return false;
+
+    struct rrdengine_instance *ctx = mrg_metric_ctx(handle->metric);
+
+    uuid_t *uuid = mrg_metric_uuid(main_mrg, handle->metric);
+    time_t start_time_s = pgc_page_start_time_s(handle->page);
+    time_t end_time_s = pgc_page_end_time_s(handle->page);
+    time_t update_every_s = pgc_page_update_every_s(handle->page);
+    size_t page_length = handle->page_position * CTX_POINT_SIZE_BYTES(ctx);
+    size_t entries = handle->page_position;
+    time_t overwrite_zero_update_every_s = (time_t)(handle->update_every_ut / USEC_PER_SEC);
+
+    if(end_time_s > max_acceptable_collected_time())
+        handle->page_flags |= RRDENG_PAGE_COMPLETED_IN_FUTURE;
+
+    VALIDATED_PAGE_DESCRIPTOR vd = validate_page(
+            uuid,
+            start_time_s,
+            end_time_s,
+            update_every_s,
+            page_length,
+            ctx->config.page_type,
+            entries,
+            0, // do not check for future timestamps - we inherit the timestamps of the children
+            overwrite_zero_update_every_s,
+            false,
+            "collected",
+            handle->page_flags);
+
+    return vd.is_valid;
+#else
+    return true;
+#endif
+}
+
 /*
  * Gets a handle for storing metrics to the database.
  * The handle must be released with rrdeng_store_metric_final().
  */
 STORAGE_COLLECT_HANDLE *rrdeng_store_metric_init(STORAGE_METRIC_HANDLE *db_metric_handle, uint32_t update_every, STORAGE_METRICS_GROUP *smg) {
-    struct pg_cache_page_index *page_index = (struct pg_cache_page_index *)db_metric_handle;
+    METRIC *metric = (METRIC *)db_metric_handle;
+    struct rrdengine_instance *ctx = mrg_metric_ctx(metric);
+
+    bool is_1st_metric_writer = true;
+    if(!mrg_metric_set_writer(main_mrg, metric)) {
+        is_1st_metric_writer = false;
+        char uuid[UUID_STR_LEN + 1];
+        uuid_unparse(*mrg_metric_uuid(main_mrg, metric), uuid);
+        error("DBENGINE: metric '%s' is already collected and should not be collected twice - expect gaps on the charts", uuid);
+    }
+
+    metric = mrg_metric_dup(main_mrg, metric);
+
     struct rrdeng_collect_handle *handle;
 
     handle = callocz(1, sizeof(struct rrdeng_collect_handle));
-    handle->page_index = page_index;
-    handle->descr = NULL;
-    handle->unaligned_page = 0;
-    page_index->latest_update_every_s = update_every;
+    handle->metric = metric;
+    handle->page = NULL;
+    handle->page_position = 0;
+    handle->page_entries_max = 0;
+    handle->update_every_ut = (usec_t)update_every * USEC_PER_SEC;
+    handle->options = is_1st_metric_writer ? RRDENG_1ST_METRIC_WRITER : 0;
+
+    __atomic_add_fetch(&ctx->atomic.collectors_running, 1, __ATOMIC_RELAXED);
+    if(!is_1st_metric_writer)
+        __atomic_add_fetch(&ctx->atomic.collectors_running_duplicate, 1, __ATOMIC_RELAXED);
+
+    mrg_metric_set_update_every(main_mrg, metric, update_every);
 
     handle->alignment = (struct pg_alignment *)smg;
     rrdeng_page_alignment_acquire(handle->alignment);
 
-    uv_rwlock_wrlock(&page_index->lock);
-    ++page_index->writers;
-    uv_rwlock_wrunlock(&page_index->lock);
+    // this is important!
+    // if we don't set the page_end_time_ut during the first collection
+    // data collection may be able to go back in time and during the addition of new pages
+    // clean pages may be found matching ours!
+
+    time_t db_first_time_s, db_last_time_s, db_update_every_s;
+    mrg_metric_get_retention(main_mrg, metric, &db_first_time_s, &db_last_time_s, &db_update_every_s);
+    handle->page_end_time_ut = (usec_t)db_last_time_s * USEC_PER_SEC;
 
     return (STORAGE_COLLECT_HANDLE *)handle;
 }
 
 /* The page must be populated and referenced */
-static int page_has_only_empty_metrics(struct rrdeng_page_descr *descr)
-{
-    switch(descr->type) {
+static bool page_has_only_empty_metrics(struct rrdeng_collect_handle *handle) {
+    switch(handle->type) {
         case PAGE_METRICS: {
-            size_t slots = descr->page_length / PAGE_POINT_SIZE_BYTES(descr);
-            storage_number *array = (storage_number *)descr->pg_cache_descr->page;
+            size_t slots = handle->page_position;
+            storage_number *array = (storage_number *)pgc_page_data(handle->page);
             for (size_t i = 0 ; i < slots; ++i) {
                 if(does_storage_number_exist(array[i]))
-                    return 0;
+                    return false;
             }
         }
         break;
 
         case PAGE_TIER: {
-            size_t slots = descr->page_length / PAGE_POINT_SIZE_BYTES(descr);
-            storage_number_tier1_t *array = (storage_number_tier1_t *)descr->pg_cache_descr->page;
+            size_t slots = handle->page_position;
+            storage_number_tier1_t *array = (storage_number_tier1_t *)pgc_page_data(handle->page);
             for (size_t i = 0 ; i < slots; ++i) {
                 if(fpclassify(array[i].sum_value) != FP_NAN)
-                    return 0;
+                    return false;
             }
         }
         break;
@@ -252,422 +309,585 @@ static int page_has_only_empty_metrics(struct rrdeng_page_descr *descr)
         default: {
             static bool logged = false;
             if(!logged) {
-                error("DBENGINE: cannot check page for nulls on unknown page type id %d", descr->type);
+                error("DBENGINE: cannot check page for nulls on unknown page type id %d", (mrg_metric_ctx(handle->metric))->config.page_type);
                 logged = true;
             }
-            return 0;
+            return false;
         }
     }
 
-    return 1;
+    return true;
 }
 
 void rrdeng_store_metric_flush_current_page(STORAGE_COLLECT_HANDLE *collection_handle) {
     struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;
-    // struct rrdeng_metric_handle *metric_handle = (struct rrdeng_metric_handle *)handle->metric_handle;
-    struct rrdengine_instance *ctx = handle->page_index->ctx;
-    struct rrdeng_page_descr *descr = handle->descr;
-
-    if (unlikely(!ctx)) return;
-    if (unlikely(!descr)) return;
-
-    if (likely(descr->page_length)) {
-        int page_is_empty;
-
-        rrd_stat_atomic_add(&ctx->stats.metric_API_producers, -1);
-
-        page_is_empty = page_has_only_empty_metrics(descr);
-        if (page_is_empty) {
-            print_page_cache_descr(descr, "Page has empty metrics only, deleting", true);
-            pg_cache_put(ctx, descr);
-            pg_cache_punch_hole(ctx, descr, 1, 0, NULL);
-        } else
-            rrdeng_commit_page(ctx, descr, handle->page_correlation_id);
-    } else {
-        dbengine_page_free(descr->pg_cache_descr->page);
-        rrdeng_destroy_pg_cache_descr(ctx, descr->pg_cache_descr);
-        rrdeng_page_descr_freez(descr);
+
+    if (unlikely(!handle->page))
+        return;
+
+    if(!handle->page_position || page_has_only_empty_metrics(handle))
+        pgc_page_to_clean_evict_or_release(main_cache, handle->page);
+
+    else {
+        check_completed_page_consistency(handle);
+        mrg_metric_set_clean_latest_time_s(main_mrg, handle->metric, pgc_page_end_time_s(handle->page));
+        pgc_page_hot_to_dirty_and_release(main_cache, handle->page);
     }
-    handle->descr = NULL;
-}
 
-static void rrdeng_store_metric_next_internal(STORAGE_COLLECT_HANDLE *collection_handle,
-                              usec_t point_in_time_ut,
-                              NETDATA_DOUBLE n,
-                              NETDATA_DOUBLE min_value,
-                              NETDATA_DOUBLE max_value,
-                              uint16_t count,
-                              uint16_t anomaly_count,
-                              SN_FLAGS flags)
-{
-    struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;
-    struct pg_cache_page_index *page_index = handle->page_index;
-    struct rrdengine_instance *ctx = handle->page_index->ctx;
-    struct page_cache *pg_cache = &ctx->pg_cache;
-    struct rrdeng_page_descr *descr = handle->descr;
+    mrg_metric_set_hot_latest_time_s(main_mrg, handle->metric, 0);
 
-    void *page;
-    uint8_t must_flush_unaligned_page = 0, perfect_page_alignment = 0;
+    handle->page = NULL;
+    handle->page_flags = 0;
+    handle->page_position = 0;
+    handle->page_entries_max = 0;
 
-    if (descr) {
-        /* Make alignment decisions */
+    // important!
+    // we should never zero page end time ut, because this will allow
+    // collection to go back in time
+    // handle->page_end_time_ut = 0;
+    // handle->page_start_time_ut;
+
+    check_and_fix_mrg_update_every(handle);
+}
+
+static void rrdeng_store_metric_create_new_page(struct rrdeng_collect_handle *handle,
+                struct rrdengine_instance *ctx,
+                usec_t point_in_time_ut,
+                void *data,
+                size_t data_size) {
+    time_t point_in_time_s = (time_t)(point_in_time_ut / USEC_PER_SEC);
+    const time_t update_every_s = (time_t)(handle->update_every_ut / USEC_PER_SEC);
+
+    PGC_ENTRY page_entry = {
+            .section = (Word_t) ctx,
+            .metric_id = mrg_metric_id(main_mrg, handle->metric),
+            .start_time_s = point_in_time_s,
+            .end_time_s = point_in_time_s,
+            .size = data_size,
+            .data = data,
+            .update_every_s = update_every_s,
+            .hot = true
+    };
+
+    size_t conflicts = 0;
+    bool added = true;
+    PGC_PAGE *page = pgc_page_add_and_acquire(main_cache, page_entry, &added);
+    while (unlikely(!added)) {
+        conflicts++;
+
+        char uuid[UUID_STR_LEN + 1];
+        uuid_unparse(*mrg_metric_uuid(main_mrg, handle->metric), uuid);
 
 #ifdef NETDATA_INTERNAL_CHECKS
-        if(descr->end_time_ut + page_index->latest_update_every_s * USEC_PER_SEC != point_in_time_ut) {
-            char buffer[200 + 1];
-            snprintfz(buffer, 200,
-                      "metrics collected are %s, end_time_ut = %llu, point_in_time_ut = %llu, update_every = %u, delta = %llu",
-                      (point_in_time_ut / USEC_PER_SEC - descr->end_time_ut / USEC_PER_SEC > page_index->latest_update_every_s)?"far apart":"not aligned",
-                      descr->end_time_ut / USEC_PER_SEC,
-                      point_in_time_ut / USEC_PER_SEC,
-                      page_index->latest_update_every_s,
-                      point_in_time_ut / USEC_PER_SEC - descr->end_time_ut / USEC_PER_SEC);
-            print_page_cache_descr(descr, buffer, false);
-        }
+        internal_error(true,
+#else
+        error_limit_static_global_var(erl, 1, 0);
+        error_limit(&erl,
 #endif
+              "DBENGINE: metric '%s' new page from %ld to %ld, update every %ld, has a conflict in main cache "
+              "with existing %s%s page from %ld to %ld, update every %ld - "
+              "is it collected more than once?",
+              uuid,
+              page_entry.start_time_s, page_entry.end_time_s, (time_t)page_entry.update_every_s,
+              pgc_is_page_hot(page) ? "hot" : "not-hot",
+              pgc_page_data(page) == DBENGINE_EMPTY_PAGE ? " gap" : "",
+              pgc_page_start_time_s(page), pgc_page_end_time_s(page), pgc_page_update_every_s(page)
+              );
+
+        pgc_page_release(main_cache, page);
+
+        point_in_time_ut -= handle->update_every_ut;
+        point_in_time_s = (time_t)(point_in_time_ut / USEC_PER_SEC);
+        page_entry.start_time_s = point_in_time_s;
+        page_entry.end_time_s = point_in_time_s;
+        page = pgc_page_add_and_acquire(main_cache, page_entry, &added);
+    }
 
-        if (descr->page_length == handle->alignment->page_length) {
-            /* this is the leading dimension that defines chart alignment */
-            perfect_page_alignment = 1;
-        }
-        /* is the metric far enough out of alignment with the others? */
-        if (unlikely(descr->page_length + PAGE_POINT_SIZE_BYTES(descr) < handle->alignment->page_length)) {
-            handle->unaligned_page = 1;
-            print_page_cache_descr(descr, "Metric page is not aligned with chart", true);
-        }
-        if (unlikely(handle->unaligned_page &&
-                     /* did the other metrics change page? */
-                     handle->alignment->page_length <= PAGE_POINT_SIZE_BYTES(descr))) {
-            print_page_cache_descr(descr, "must_flush_unaligned_page = 1", true);
-            must_flush_unaligned_page = 1;
-            handle->unaligned_page = 0;
-        }
+    handle->page_entries_max = data_size / CTX_POINT_SIZE_BYTES(ctx);
+    handle->page_start_time_ut = point_in_time_ut;
+    handle->page_end_time_ut = point_in_time_ut;
+    handle->page_position = 1; // zero is already in our data
+    handle->page = page;
+    handle->page_flags = conflicts? RRDENG_PAGE_CONFLICT : 0;
+
+    if(point_in_time_s > max_acceptable_collected_time())
+        handle->page_flags |= RRDENG_PAGE_CREATED_IN_FUTURE;
+
+    check_and_fix_mrg_update_every(handle);
+}
+
+static void *rrdeng_alloc_new_metric_data(struct rrdeng_collect_handle *handle, size_t *data_size, usec_t point_in_time_ut) {
+    struct rrdengine_instance *ctx = mrg_metric_ctx(handle->metric);
+    size_t size;
+
+    if(handle->options & RRDENG_FIRST_PAGE_ALLOCATED) {
+        // any page except the first
+        size = tier_page_size[ctx->config.tier];
     }
-    if (unlikely(NULL == descr ||
-                 descr->page_length + PAGE_POINT_SIZE_BYTES(descr) > RRDENG_BLOCK_SIZE ||
-                 must_flush_unaligned_page)) {
+    else {
+        size_t final_slots = 0;
 
-        if(descr) {
-            print_page_cache_descr(descr, "flushing metric", true);
-            rrdeng_store_metric_flush_current_page(collection_handle);
+        // the first page
+        handle->options |= RRDENG_FIRST_PAGE_ALLOCATED;
+        size_t max_size = tier_page_size[ctx->config.tier];
+        size_t max_slots = max_size / CTX_POINT_SIZE_BYTES(ctx);
+
+        if(handle->alignment->initial_slots) {
+            final_slots = handle->alignment->initial_slots;
         }
+        else {
+            max_slots -= 3;
 
-        page = rrdeng_create_page(ctx, &page_index->id, &descr);
-        fatal_assert(page);
+            size_t smaller_slot = indexing_partition((Word_t)handle->alignment, max_slots);
+            final_slots = smaller_slot;
 
-        descr->update_every_s = page_index->latest_update_every_s;
-        handle->descr = descr;
+            time_t now_s = (time_t)(point_in_time_ut / USEC_PER_SEC);
+            size_t current_pos = (now_s % max_slots);
 
-        handle->page_correlation_id = rrd_atomic_fetch_add(&pg_cache->committed_page_index.latest_corr_id, 1);
+            if(current_pos > final_slots)
+                final_slots += max_slots - current_pos;
 
-        if (0 == handle->alignment->page_length) {
-            /* this is the leading dimension that defines chart alignment */
-            perfect_page_alignment = 1;
+            else if(current_pos < final_slots)
+                final_slots -= current_pos;
+
+            if(final_slots < 3) {
+                final_slots += 3;
+                smaller_slot += 3;
+
+                if(smaller_slot >= max_slots)
+                    smaller_slot -= max_slots;
+            }
+
+            max_slots += 3;
+            handle->alignment->initial_slots = smaller_slot + 3;
+
+            internal_fatal(handle->alignment->initial_slots < 3 || handle->alignment->initial_slots >= max_slots, "ooops! wrong distribution of metrics across time");
+            internal_fatal(final_slots < 3 || final_slots >= max_slots, "ooops! wrong distribution of metrics across time");
         }
+
+        size = final_slots * CTX_POINT_SIZE_BYTES(ctx);
     }
 
-    page = descr->pg_cache_descr->page;
+    *data_size = size;
+    return dbengine_page_alloc(size);
+}
+
+static void rrdeng_store_metric_append_point(STORAGE_COLLECT_HANDLE *collection_handle,
+                                             const usec_t point_in_time_ut,
+                                             const NETDATA_DOUBLE n,
+                                             const NETDATA_DOUBLE min_value,
+                                             const NETDATA_DOUBLE max_value,
+                                             const uint16_t count,
+                                             const uint16_t anomaly_count,
+                                             const SN_FLAGS flags)
+{
+    struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;
+    struct rrdengine_instance *ctx = mrg_metric_ctx(handle->metric);
 
-    switch (descr->type) {
+    bool perfect_page_alignment = false;
+    void *data;
+    size_t data_size;
+
+    if(likely(handle->page)) {
+        /* Make alignment decisions */
+        if (handle->page_position == handle->alignment->page_position) {
+            /* this is the leading dimension that defines chart alignment */
+            perfect_page_alignment = true;
+        }
+
+        /* is the metric far enough out of alignment with the others? */
+        if (unlikely(handle->page_position + 1 < handle->alignment->page_position))
+            handle->options |= RRDENG_CHO_UNALIGNED;
+
+        if (unlikely((handle->options & RRDENG_CHO_UNALIGNED) &&
+                     /* did the other metrics change page? */
+                     handle->alignment->page_position <= 1)) {
+            handle->options &= ~RRDENG_CHO_UNALIGNED;
+            handle->page_flags |= RRDENG_PAGE_UNALIGNED;
+            rrdeng_store_metric_flush_current_page(collection_handle);
+
+            data = rrdeng_alloc_new_metric_data(handle, &data_size, point_in_time_ut);
+        }
+        else {
+            data = pgc_page_data(handle->page);
+            data_size = pgc_page_data_size(main_cache, handle->page);
+        }
+    }
+    else
+        data = rrdeng_alloc_new_metric_data(handle, &data_size, point_in_time_ut);
+
+    switch (ctx->config.page_type) {
         case PAGE_METRICS: {
-            ((storage_number *)page)[descr->page_length / PAGE_POINT_SIZE_BYTES(descr)] = pack_storage_number(n, flags);
+            storage_number *tier0_metric_data = data;
+            tier0_metric_data[handle->page_position] = pack_storage_number(n, flags);
         }
         break;
 
         case PAGE_TIER: {
+            storage_number_tier1_t *tier12_metric_data = data;
             storage_number_tier1_t number_tier1;
             number_tier1.sum_value = (float)n;
             number_tier1.min_value = (float)min_value;
             number_tier1.max_value = (float)max_value;
             number_tier1.anomaly_count = anomaly_count;
             number_tier1.count = count;
-            ((storage_number_tier1_t *)page)[descr->page_length / PAGE_POINT_SIZE_BYTES(descr)] = number_tier1;
+            tier12_metric_data[handle->page_position] = number_tier1;
         }
         break;
 
         default: {
             static bool logged = false;
             if(!logged) {
-                error("DBENGINE: cannot store metric on unknown page type id %d", descr->type);
+                error("DBENGINE: cannot store metric on unknown page type id %d", ctx->config.page_type);
                 logged = true;
             }
         }
         break;
     }
 
-    pg_cache_atomic_set_pg_info(descr, point_in_time_ut, descr->page_length + PAGE_POINT_SIZE_BYTES(descr));
+    if(unlikely(!handle->page)){
+        rrdeng_store_metric_create_new_page(handle, ctx, point_in_time_ut, data, data_size);
+        // handle->position is set to 1 already
 
-    if (perfect_page_alignment)
-        handle->alignment->page_length = descr->page_length;
-    if (unlikely(INVALID_TIME == descr->start_time_ut)) {
-        unsigned long new_metric_API_producers, old_metric_API_max_producers, ret_metric_API_max_producers;
-        descr->start_time_ut = point_in_time_ut;
-
-        new_metric_API_producers = rrd_atomic_add_fetch(&ctx->stats.metric_API_producers, 1);
-        while (unlikely(new_metric_API_producers > (old_metric_API_max_producers = ctx->metric_API_max_producers))) {
-            /* Increase ctx->metric_API_max_producers */
-            ret_metric_API_max_producers = ulong_compare_and_swap(&ctx->metric_API_max_producers,
-                                                                  old_metric_API_max_producers,
-                                                                  new_metric_API_producers);
-            if (old_metric_API_max_producers == ret_metric_API_max_producers) {
-                /* success */
-                break;
-            }
+        if (0 == handle->alignment->page_position) {
+            /* this is the leading dimension that defines chart alignment */
+            perfect_page_alignment = true;
+        }
+    }
+    else {
+        // update an existing page
+        pgc_page_hot_set_end_time_s(main_cache, handle->page, (time_t) (point_in_time_ut / USEC_PER_SEC));
+        handle->page_end_time_ut = point_in_time_ut;
+
+        if(unlikely(++handle->page_position >= handle->page_entries_max)) {
+            internal_fatal(handle->page_position > handle->page_entries_max, "DBENGINE: exceeded page max number of points");
+            handle->page_flags |= RRDENG_PAGE_FULL;
+            rrdeng_store_metric_flush_current_page(collection_handle);
         }
+    }
+
+    if (perfect_page_alignment)
+        handle->alignment->page_position = handle->page_position;
+
+    // update the metric information
+    mrg_metric_set_hot_latest_time_s(main_mrg, handle->metric, (time_t) (point_in_time_ut / USEC_PER_SEC));
+}
+
+static void store_metric_next_error_log(struct rrdeng_collect_handle *handle, usec_t point_in_time_ut, const char *msg) {
+    time_t point_in_time_s = (time_t)(point_in_time_ut / USEC_PER_SEC);
+    char uuid[UUID_STR_LEN + 1];
+    uuid_unparse(*mrg_metric_uuid(main_mrg, handle->metric), uuid);
 
-        pg_cache_insert(ctx, page_index, descr);
-    } else {
-        pg_cache_add_new_metric_time(page_index, descr);
+    BUFFER *wb = NULL;
+    if(handle->page && handle->page_flags) {
+        wb = buffer_create(0, NULL);
+        collect_page_flags_to_buffer(wb, handle->page_flags);
     }
 
-//    {
-//        unsigned char u[16] = { 0x0C, 0x0A, 0x40, 0xD6, 0x2A, 0x43, 0x4A, 0x7C, 0x95, 0xF7, 0xD1, 0x1E, 0x0C, 0x9E, 0x8A, 0xE7 };
-//        if(uuid_compare(u, page_index->id) == 0) {
-//            char buffer[100];
-//            snprintfz(buffer, 100, "store system.cpu, collect:%u, page_index first:%u, last:%u",
-//                      (uint32_t)(point_in_time / USEC_PER_SEC),
-//                      (uint32_t)(page_index->oldest_time / USEC_PER_SEC),
-//                      (uint32_t)(page_index->latest_time / USEC_PER_SEC));
-//
-//            print_page_cache_descr(descr, buffer, false);
-//        }
-//    }
+    error_limit_static_global_var(erl, 1, 0);
+    error_limit(&erl,
+                "DBENGINE: metric '%s' collected point at %ld, %s last collection at %ld, "
+                "update every %ld, %s page from %ld to %ld, position %u (of %u), flags: %s",
+                uuid,
+                point_in_time_s,
+                msg,
+                (time_t)(handle->page_end_time_ut / USEC_PER_SEC),
+                (time_t)(handle->update_every_ut / USEC_PER_SEC),
+                handle->page ? "current" : "*LAST*",
+                (time_t)(handle->page_start_time_ut / USEC_PER_SEC),
+                (time_t)(handle->page_end_time_ut / USEC_PER_SEC),
+                handle->page_position, handle->page_entries_max,
+                wb ? buffer_tostring(wb) : ""
+    );
+
+    buffer_free(wb);
 }
 
 void rrdeng_store_metric_next(STORAGE_COLLECT_HANDLE *collection_handle,
-                              usec_t point_in_time_ut,
-                              NETDATA_DOUBLE n,
-                              NETDATA_DOUBLE min_value,
-                              NETDATA_DOUBLE max_value,
-                              uint16_t count,
-                              uint16_t anomaly_count,
-                              SN_FLAGS flags)
+                              const usec_t point_in_time_ut,
+                              const NETDATA_DOUBLE n,
+                              const NETDATA_DOUBLE min_value,
+                              const NETDATA_DOUBLE max_value,
+                              const uint16_t count,
+                              const uint16_t anomaly_count,
+                              const SN_FLAGS flags)
 {
     struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;
-    struct pg_cache_page_index *page_index = handle->page_index;
-    struct rrdeng_page_descr *descr = handle->descr;
-
-    if(likely(descr)) {
-        usec_t last_point_in_time_ut = descr->end_time_ut;
-        usec_t update_every_ut = page_index->latest_update_every_s * USEC_PER_SEC;
-        size_t points_gap = (point_in_time_ut <= last_point_in_time_ut) ?
-                                (size_t)0 :
-                                (size_t)((point_in_time_ut - last_point_in_time_ut) / update_every_ut);
-
-        if(unlikely(points_gap != 1)) {
-            if (unlikely(points_gap <= 0)) {
-                time_t now = now_realtime_sec();
-                static __thread size_t counter = 0;
-                static __thread time_t last_time_logged = 0;
-                counter++;
-
-                if(now - last_time_logged > 600) {
-                    error("DBENGINE: collected point is in the past (repeated %zu times in the last %zu secs). Ignoring these data collection points.",
-                          counter, (size_t)(last_time_logged?(now - last_time_logged):0));
-
-                    last_time_logged = now;
-                    counter = 0;
-                }
-                return;
-            }
 
-            size_t point_size = PAGE_POINT_SIZE_BYTES(descr);
-            size_t page_size_in_points = RRDENG_BLOCK_SIZE / point_size;
-            size_t used_points = descr->page_length / point_size;
-            size_t remaining_points_in_page = page_size_in_points - used_points;
+#ifdef NETDATA_INTERNAL_CHECKS
+    if(unlikely(point_in_time_ut > (usec_t)max_acceptable_collected_time() * USEC_PER_SEC))
+        handle->page_flags |= RRDENG_PAGE_FUTURE_POINT;
+#endif
+
+    if(likely(handle->page_end_time_ut + handle->update_every_ut == point_in_time_ut)) {
+        // happy path
+        ;
+    }
+    else if(unlikely(point_in_time_ut < handle->page_end_time_ut)) {
+        handle->page_flags |= RRDENG_PAGE_PAST_COLLECTION;
+        store_metric_next_error_log(handle, point_in_time_ut, "is older than the");
+        return;
+    }
 
-            bool new_point_is_aligned = true;
-            if(unlikely((point_in_time_ut - last_point_in_time_ut) / points_gap != update_every_ut))
-                new_point_is_aligned = false;
+    else if(unlikely(point_in_time_ut == handle->page_end_time_ut)) {
+        handle->page_flags |= RRDENG_PAGE_REPEATED_COLLECTION;
+        store_metric_next_error_log(handle, point_in_time_ut, "is at the same time as the");
+        return;
+    }
 
-            if(unlikely(points_gap > remaining_points_in_page || !new_point_is_aligned)) {
-//                char buffer[200];
-//                snprintfz(buffer, 200, "data collection skipped %zu points, last stored point %llu, new point %llu, update every %d. Cutting page.",
-//                      points_gap, last_point_in_time_ut / USEC_PER_SEC, point_in_time_ut / USEC_PER_SEC, page_index->latest_update_every_s);
-//                print_page_cache_descr(descr, buffer, false);
+    else if(handle->page) {
+        usec_t delta_ut = point_in_time_ut - handle->page_end_time_ut;
 
+        if(unlikely(delta_ut < handle->update_every_ut)) {
+            handle->page_flags |= RRDENG_PAGE_STEP_TOO_SMALL;
+            rrdeng_store_metric_flush_current_page(collection_handle);
+        }
+        else if(unlikely(delta_ut % handle->update_every_ut)) {
+            handle->page_flags |= RRDENG_PAGE_STEP_UNALIGNED;
+            rrdeng_store_metric_flush_current_page(collection_handle);
+        }
+        else {
+            size_t points_gap = delta_ut / handle->update_every_ut;
+            size_t page_remaining_points = handle->page_entries_max - handle->page_position;
+
+            if(points_gap >= page_remaining_points) {
+                handle->page_flags |= RRDENG_PAGE_BIG_GAP;
                 rrdeng_store_metric_flush_current_page(collection_handle);
             }
             else {
-//                char buffer[200];
-//                snprintfz(buffer, 200, "data collection skipped %zu points, last stored point %llu, new point %llu, update every %d. Filling the gap.",
-//                      points_gap, last_point_in_time_ut / USEC_PER_SEC, point_in_time_ut / USEC_PER_SEC, page_index->latest_update_every_s);
-//                print_page_cache_descr(descr, buffer, false);
-
                 // loop to fill the gap
-                usec_t step_ut = page_index->latest_update_every_s * USEC_PER_SEC;
-                usec_t last_point_filled_ut = last_point_in_time_ut + step_ut;
-
-                while (last_point_filled_ut < point_in_time_ut) {
-                    rrdeng_store_metric_next_internal(
-                        collection_handle, last_point_filled_ut, NAN, NAN, NAN,
-                        1, 0, SN_EMPTY_SLOT);
-
-                    last_point_filled_ut += step_ut;
+                handle->page_flags |= RRDENG_PAGE_GAP;
+
+                usec_t stop_ut = point_in_time_ut - handle->update_every_ut;
+                for(usec_t this_ut = handle->page_end_time_ut + handle->update_every_ut;
+                    this_ut <= stop_ut ;
+                    this_ut = handle->page_end_time_ut + handle->update_every_ut) {
+                    rrdeng_store_metric_append_point(
+                            collection_handle,
+                            this_ut,
+                            NAN, NAN, NAN,
+                            1, 0,
+                            SN_EMPTY_SLOT);
                 }
             }
         }
     }
 
-    rrdeng_store_metric_next_internal(collection_handle, point_in_time_ut, n, min_value, max_value, count, anomaly_count, flags);
+    rrdeng_store_metric_append_point(collection_handle,
+                                     point_in_time_ut,
+                                     n, min_value, max_value,
+                                     count, anomaly_count,
+                                     flags);
 }
 
-
 /*
  * Releases the database reference from the handle for storing metrics.
  * Returns 1 if it's safe to delete the dimension.
  */
 int rrdeng_store_metric_finalize(STORAGE_COLLECT_HANDLE *collection_handle) {
     struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;
-    struct pg_cache_page_index *page_index = handle->page_index;
-
-    uint8_t can_delete_metric = 0;
+    struct rrdengine_instance *ctx = mrg_metric_ctx(handle->metric);
 
+    handle->page_flags |= RRDENG_PAGE_COLLECT_FINALIZE;
     rrdeng_store_metric_flush_current_page(collection_handle);
-    uv_rwlock_wrlock(&page_index->lock);
+    rrdeng_page_alignment_release(handle->alignment);
 
-    if (!--page_index->writers && !page_index->page_count)
-        can_delete_metric = 1;
+    __atomic_sub_fetch(&ctx->atomic.collectors_running, 1, __ATOMIC_RELAXED);
+    if(!(handle->options & RRDENG_1ST_METRIC_WRITER))
+        __atomic_sub_fetch(&ctx->atomic.collectors_running_duplicate, 1, __ATOMIC_RELAXED);
 
-    uv_rwlock_wrunlock(&page_index->lock);
+    if((handle->options & RRDENG_1ST_METRIC_WRITER) && !mrg_metric_clear_writer(main_mrg, handle->metric))
+        internal_fatal(true, "DBENGINE: metric is already released");
 
-    rrdeng_page_alignment_release(handle->alignment);
+    time_t first_time_s, last_time_s, update_every_s;
+    mrg_metric_get_retention(main_mrg, handle->metric, &first_time_s, &last_time_s, &update_every_s);
+
+    mrg_metric_release(main_mrg, handle->metric);
     freez(handle);
 
-    return can_delete_metric;
+    if(!first_time_s && !last_time_s)
+        return 1;
+
+    return 0;
 }
 
 void rrdeng_store_metric_change_collection_frequency(STORAGE_COLLECT_HANDLE *collection_handle, int update_every) {
     struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;
-    struct pg_cache_page_index *page_index = handle->page_index;
+    check_and_fix_mrg_update_every(handle);
+
+    METRIC *metric = handle->metric;
+    usec_t update_every_ut = (usec_t)update_every * USEC_PER_SEC;
+
+    if(update_every_ut == handle->update_every_ut)
+        return;
+
+    handle->page_flags |= RRDENG_PAGE_UPDATE_EVERY_CHANGE;
     rrdeng_store_metric_flush_current_page(collection_handle);
-    uv_rwlock_rdlock(&page_index->lock);
-    page_index->latest_update_every_s = update_every;
-    uv_rwlock_rdunlock(&page_index->lock);
+    mrg_metric_set_update_every(main_mrg, metric, update_every);
+    handle->update_every_ut = update_every_ut;
 }
 
 // ----------------------------------------------------------------------------
 // query ops
 
-//static inline uint32_t *pginfo_to_dt(struct rrdeng_page_info *page_info)
-//{
-//    return (uint32_t *)&page_info->scratch[0];
-//}
-//
-//static inline uint32_t *pginfo_to_points(struct rrdeng_page_info *page_info)
-//{
-//    return (uint32_t *)&page_info->scratch[sizeof(uint32_t)];
-//}
-//
+#ifdef NETDATA_INTERNAL_CHECKS
+SPINLOCK global_query_handle_spinlock = NETDATA_SPINLOCK_INITIALIZER;
+static struct rrdeng_query_handle *global_query_handle_ll = NULL;
+static void register_query_handle(struct rrdeng_query_handle *handle) {
+    handle->query_pid = gettid();
+    handle->started_time_s = now_realtime_sec();
+
+    netdata_spinlock_lock(&global_query_handle_spinlock);
+    DOUBLE_LINKED_LIST_APPEND_ITEM_UNSAFE(global_query_handle_ll, handle, prev, next);
+    netdata_spinlock_unlock(&global_query_handle_spinlock);
+}
+static void unregister_query_handle(struct rrdeng_query_handle *handle) {
+    netdata_spinlock_lock(&global_query_handle_spinlock);
+    DOUBLE_LINKED_LIST_REMOVE_ITEM_UNSAFE(global_query_handle_ll, handle, prev, next);
+    netdata_spinlock_unlock(&global_query_handle_spinlock);
+}
+#else
+static void register_query_handle(struct rrdeng_query_handle *handle __maybe_unused) {
+    ;
+}
+static void unregister_query_handle(struct rrdeng_query_handle *handle __maybe_unused) {
+    ;
+}
+#endif
+
 /*
  * Gets a handle for loading metrics from the database.
  * The handle must be released with rrdeng_load_metric_final().
  */
-void rrdeng_load_metric_init(STORAGE_METRIC_HANDLE *db_metric_handle, struct storage_engine_query_handle *rrdimm_handle, time_t start_time_s, time_t end_time_s)
+void rrdeng_load_metric_init(STORAGE_METRIC_HANDLE *db_metric_handle,
+                             struct storage_engine_query_handle *rrddim_handle,
+                             time_t start_time_s,
+                             time_t end_time_s,
+                             STORAGE_PRIORITY priority)
 {
-    struct pg_cache_page_index *page_index = (struct pg_cache_page_index *)db_metric_handle;
-    struct rrdengine_instance *ctx = page_index->ctx;
+    usec_t started_ut = now_monotonic_usec();
 
-    // fprintf(stderr, "%s: %s/%s start time %ld, end time %ld\n", __FUNCTION__ , rd->rrdset->name, rd->name, start_time, end_time);
+    netdata_thread_disable_cancelability();
 
+    METRIC *metric = (METRIC *)db_metric_handle;
+    struct rrdengine_instance *ctx = mrg_metric_ctx(metric);
     struct rrdeng_query_handle *handle;
-    unsigned pages_nr;
 
-    if(!page_index->latest_update_every_s)
-        page_index->latest_update_every_s = default_rrd_update_every;
+    handle = rrdeng_query_handle_get();
+    register_query_handle(handle);
 
-    rrdimm_handle->start_time_s = start_time_s;
-    rrdimm_handle->end_time_s = end_time_s;
+    if(unlikely(priority < STORAGE_PRIORITY_HIGH))
+        priority = STORAGE_PRIORITY_HIGH;
+    else if(unlikely(priority > STORAGE_PRIORITY_BEST_EFFORT))
+        priority = STORAGE_PRIORITY_BEST_EFFORT;
 
-    handle = callocz(1, sizeof(struct rrdeng_query_handle));
-    handle->wanted_start_time_s = start_time_s;
-    handle->now_s = start_time_s;
-    handle->position = 0;
     handle->ctx = ctx;
-    handle->descr = NULL;
-    handle->dt_s = page_index->latest_update_every_s;
-    rrdimm_handle->handle = (STORAGE_QUERY_HANDLE *)handle;
-    pages_nr = pg_cache_preload(ctx, &page_index->id, start_time_s * USEC_PER_SEC, end_time_s * USEC_PER_SEC,
-                                NULL, &handle->page_index);
-    if (unlikely(NULL == handle->page_index || 0 == pages_nr))
-        // there are no metrics to load
-        handle->wanted_start_time_s = INVALID_TIME;
-}
+    handle->metric = metric;
+    handle->priority = priority;
+
+    // IMPORTANT!
+    // It is crucial not to exceed the db boundaries, because dbengine
+    // now has gap caching, so when a gap is detected a negative page
+    // is inserted into the main cache, to avoid scanning the journals
+    // again for pages matching the gap.
+
+    time_t db_first_time_s, db_last_time_s, db_update_every_s;
+    mrg_metric_get_retention(main_mrg, metric, &db_first_time_s, &db_last_time_s, &db_update_every_s);
+
+    if(is_page_in_time_range(start_time_s, end_time_s, db_first_time_s, db_last_time_s) == PAGE_IS_IN_RANGE) {
+        handle->start_time_s = MAX(start_time_s, db_first_time_s);
+        handle->end_time_s = MIN(end_time_s, db_last_time_s);
+        handle->now_s = handle->start_time_s;
+
+        handle->dt_s = db_update_every_s;
+        if (!handle->dt_s) {
+            handle->dt_s = default_rrd_update_every;
+            mrg_metric_set_update_every_s_if_zero(main_mrg, metric, default_rrd_update_every);
+        }
 
-static int rrdeng_load_page_next(struct storage_engine_query_handle *rrdimm_handle, bool debug_this __maybe_unused) {
-    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrdimm_handle->handle;
+        rrddim_handle->handle = (STORAGE_QUERY_HANDLE *) handle;
+        rrddim_handle->start_time_s = handle->start_time_s;
+        rrddim_handle->end_time_s = handle->end_time_s;
+        rrddim_handle->priority = priority;
 
-    struct rrdengine_instance *ctx = handle->ctx;
-    struct rrdeng_page_descr *descr = handle->descr;
+        pg_cache_preload(handle);
 
-    uint32_t page_length;
-    usec_t page_end_time_ut;
-    unsigned position;
+        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.query_time_init, now_monotonic_usec() - started_ut, __ATOMIC_RELAXED);
+    }
+    else {
+        handle->start_time_s = start_time_s;
+        handle->end_time_s = end_time_s;
+        handle->now_s = start_time_s;
+        handle->dt_s = db_update_every_s;
+
+        rrddim_handle->handle = (STORAGE_QUERY_HANDLE *) handle;
+        rrddim_handle->start_time_s = handle->start_time_s;
+        rrddim_handle->end_time_s = 0;
+        rrddim_handle->priority = priority;
+    }
+}
 
-    if (likely(descr)) {
-        // Drop old page's reference
+static bool rrdeng_load_page_next(struct storage_engine_query_handle *rrddim_handle, bool debug_this __maybe_unused) {
+    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrddim_handle->handle;
+    struct rrdengine_instance *ctx = handle->ctx;
 
-#ifdef NETDATA_INTERNAL_CHECKS
-        rrd_stat_atomic_add(&ctx->stats.metric_API_consumers, -1);
-#endif
+    if (likely(handle->page)) {
+        // we have a page to release
+        pgc_page_release(main_cache, handle->page);
+        handle->page = NULL;
+    }
 
-        pg_cache_put(ctx, descr);
-        handle->descr = NULL;
-        handle->wanted_start_time_s = (time_t)((handle->page_end_time_ut / USEC_PER_SEC) + handle->dt_s);
+    if (unlikely(handle->now_s > rrddim_handle->end_time_s))
+        return false;
 
-        if (unlikely(handle->wanted_start_time_s > rrdimm_handle->end_time_s))
-            return 1;
-    }
+    size_t entries;
+    handle->page = pg_cache_lookup_next(ctx, handle->pdc, handle->now_s, handle->dt_s, &entries);
+    if (unlikely(!handle->page))
+        return false;
 
-    usec_t wanted_start_time_ut = handle->wanted_start_time_s * USEC_PER_SEC;
-    descr = pg_cache_lookup_next(ctx, handle->page_index, &handle->page_index->id,
-        wanted_start_time_ut, rrdimm_handle->end_time_s * USEC_PER_SEC);
-    if (NULL == descr)
-        return 1;
+    internal_fatal(pgc_page_data(handle->page) == DBENGINE_EMPTY_PAGE, "Empty page returned");
 
-#ifdef NETDATA_INTERNAL_CHECKS
-    rrd_stat_atomic_add(&ctx->stats.metric_API_consumers, 1);
-#endif
+    time_t page_start_time_s = pgc_page_start_time_s(handle->page);
+    time_t page_end_time_s = pgc_page_end_time_s(handle->page);
+    time_t page_update_every_s = pgc_page_update_every_s(handle->page);
 
-    handle->descr = descr;
-    pg_cache_atomic_get_pg_info(descr, &page_end_time_ut, &page_length);
-    if (unlikely(INVALID_TIME == descr->start_time_ut || INVALID_TIME == page_end_time_ut || 0 == descr->update_every_s)) {
-        error("DBENGINE: discarding invalid page descriptor (start_time = %llu, end_time = %llu, update_every_s = %d)",
-              descr->start_time_ut, page_end_time_ut, descr->update_every_s);
-        return 1;
-    }
+    unsigned position;
+    if(likely(handle->now_s >= page_start_time_s && handle->now_s <= page_end_time_s)) {
+
+        if(unlikely(entries == 1 || page_start_time_s == page_end_time_s || !page_update_every_s)) {
+            position = 0;
+            handle->now_s = page_start_time_s;
+        }
+        else {
+            position = (handle->now_s - page_start_time_s) * (entries - 1) / (page_end_time_s - page_start_time_s);
+            time_t point_end_time_s = page_start_time_s + position * page_update_every_s;
+            while(point_end_time_s < handle->now_s && position + 1 < entries) {
+                // https://github.com/netdata/netdata/issues/14411
+                // we really need a while() here, because the delta may be
+                // 2 points at higher tiers
+                position++;
+                point_end_time_s = page_start_time_s + position * page_update_every_s;
+            }
+            handle->now_s = point_end_time_s;
+        }
 
-    if (unlikely(descr->start_time_ut != page_end_time_ut && wanted_start_time_ut > descr->start_time_ut)) {
-        // we're in the middle of the page somewhere
-        unsigned entries = page_length / PAGE_POINT_SIZE_BYTES(descr);
-        position = ((uint64_t)(wanted_start_time_ut - descr->start_time_ut)) * (entries - 1) /
-                   (page_end_time_ut - descr->start_time_ut);
+        internal_fatal(position >= entries, "DBENGINE: wrong page position calculation");
     }
-    else
+    else if(handle->now_s < page_start_time_s) {
+        handle->now_s = page_start_time_s;
         position = 0;
+    }
+    else {
+        internal_fatal(true, "DBENGINE: this page is entirely in our past and should not be accepted for this query in the first place");
+        handle->now_s = page_end_time_s;
+        position = entries - 1;
+    }
 
-    handle->page_end_time_ut = page_end_time_ut;
-    handle->page_length = page_length;
-    handle->entries = page_length / PAGE_POINT_SIZE_BYTES(descr);
-    handle->page = descr->pg_cache_descr->page;
-    handle->dt_s = descr->update_every_s;
+    handle->entries = entries;
     handle->position = position;
-
-//    if(debug_this)
-//        info("DBENGINE: rrdeng_load_page_next(), "
-//             "position:%d, "
-//             "start_time_ut:%llu, "
-//             "page_end_time_ut:%llu, "
-//             "next_page_time_ut:%llu, "
-//             "in_out:%s"
-//             , position
-//             , descr->start_time_ut
-//             , page_end_time_ut
-//             ,
-//            wanted_start_time_ut, in_out?"true":"false"
-//             );
-
-    return 0;
+    handle->metric_data = pgc_page_data((PGC_PAGE *)handle->page);
+    handle->dt_s = page_update_every_s;
+    return true;
 }
 
 // Returns the metric and sets its timestamp into current_time
@@ -675,75 +895,28 @@ static int rrdeng_load_page_next(struct storage_engine_query_handle *rrdimm_hand
 // IT IS REQUIRED TO **ALWAYS** KEEP TRACK OF TIME, EVEN OUTSIDE THE DATABASE BOUNDARIES
 STORAGE_POINT rrdeng_load_metric_next(struct storage_engine_query_handle *rrddim_handle) {
     struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrddim_handle->handle;
-    // struct rrdeng_metric_handle *metric_handle = handle->metric_handle;
-
-    struct rrdeng_page_descr *descr = handle->descr;
-    time_t now = handle->now_s + handle->dt_s;
-
-//    bool debug_this = false;
-//    {
-//        unsigned char u[16] = { 0x0C, 0x0A, 0x40, 0xD6, 0x2A, 0x43, 0x4A, 0x7C, 0x95, 0xF7, 0xD1, 0x1E, 0x0C, 0x9E, 0x8A, 0xE7 };
-//        if(uuid_compare(u, handle->page_index->id) == 0) {
-//            char buffer[100];
-//            snprintfz(buffer, 100, "load system.cpu, now:%u, dt:%u, position:%u page_index first:%u, last:%u",
-//                      (uint32_t)(now),
-//                      (uint32_t)(handle->dt_s),
-//                      (uint32_t)(handle->position),
-//                      (uint32_t)(handle->page_index->oldest_time / USEC_PER_SEC),
-//                      (uint32_t)(handle->page_index->latest_time / USEC_PER_SEC));
-//
-//            print_page_cache_descr(descr, buffer, false);
-//            debug_this = true;
-//        }
-//    }
-
     STORAGE_POINT sp;
-    unsigned position = handle->position + 1;
-    storage_number_tier1_t tier1_value;
-
-    if (unlikely(INVALID_TIME == handle->wanted_start_time_s)) {
-        handle->wanted_start_time_s = INVALID_TIME;
-        handle->now_s = now;
-        storage_point_empty(sp, now - handle->dt_s, now);
-        return sp;
+
+    if (unlikely(handle->now_s > rrddim_handle->end_time_s)) {
+        storage_point_empty(sp, handle->now_s - handle->dt_s, handle->now_s);
+        goto prepare_for_next_iteration;
     }
 
-    if (unlikely(!descr || position >= handle->entries)) {
+    if (unlikely(!handle->page || handle->position >= handle->entries)) {
         // We need to get a new page
-        if(rrdeng_load_page_next(rrddim_handle, false)) {
-            // next calls will not load any more metrics
-            handle->wanted_start_time_s = INVALID_TIME;
-            handle->now_s = now;
-            storage_point_empty(sp, now - handle->dt_s, now);
-            return sp;
-        }
 
-        descr = handle->descr;
-        position = handle->position;
-        now = (time_t)((descr->start_time_ut / USEC_PER_SEC) + position * descr->update_every_s);
-
-//        if(debug_this) {
-//            char buffer[100];
-//            snprintfz(buffer, 100, "NEW PAGE system.cpu, now:%u, dt:%u, position:%u page_index first:%u, last:%u",
-//                      (uint32_t)(now),
-//                      (uint32_t)(handle->dt_s),
-//                      (uint32_t)(handle->position),
-//                      (uint32_t)(handle->page_index->oldest_time / USEC_PER_SEC),
-//                      (uint32_t)(handle->page_index->latest_time / USEC_PER_SEC));
-//
-//            print_page_cache_descr(descr, buffer, false);
-//        }
+        if (!rrdeng_load_page_next(rrddim_handle, false)) {
+            storage_point_empty(sp, handle->now_s - handle->dt_s, handle->now_s);
+            goto prepare_for_next_iteration;
+        }
     }
 
-    sp.start_time = now - handle->dt_s;
-    sp.end_time = now;
-
-    handle->position = position;
-    handle->now_s = now;
+    sp.start_time_s = handle->now_s - handle->dt_s;
+    sp.end_time_s = handle->now_s;
 
-    switch(descr->type) {
+    switch(handle->ctx->config.page_type) {
         case PAGE_METRICS: {
-            storage_number n = handle->page[position];
+            storage_number n = handle->metric_data[handle->position];
             sp.min = sp.max = sp.sum = unpack_storage_number(n);
             sp.flags = n & SN_USER_FLAGS;
             sp.count = 1;
@@ -752,7 +925,7 @@ STORAGE_POINT rrdeng_load_metric_next(struct storage_engine_query_handle *rrddim
         break;
 
         case PAGE_TIER: {
-            tier1_value = ((storage_number_tier1_t *)handle->page)[position];
+            storage_number_tier1_t tier1_value = ((storage_number_tier1_t *)handle->metric_data)[handle->position];
             sp.flags = tier1_value.anomaly_count ? SN_FLAG_NONE : SN_FLAG_NOT_ANOMALOUS;
             sp.count = tier1_value.count;
             sp.anomaly_count = tier1_value.anomaly_count;
@@ -766,204 +939,98 @@ STORAGE_POINT rrdeng_load_metric_next(struct storage_engine_query_handle *rrddim
         default: {
             static bool logged = false;
             if(!logged) {
-                error("DBENGINE: unknown page type %d found. Cannot decode it. Ignoring its metrics.", descr->type);
+                error("DBENGINE: unknown page type %d found. Cannot decode it. Ignoring its metrics.", handle->ctx->config.page_type);
                 logged = true;
             }
-            storage_point_empty(sp, sp.start_time, sp.end_time);
+            storage_point_empty(sp, sp.start_time_s, sp.end_time_s);
         }
         break;
     }
 
-    if (unlikely(now >= rrddim_handle->end_time_s)) {
-        // next calls will not load any more metrics
-        handle->wanted_start_time_s = INVALID_TIME;
-    }
+prepare_for_next_iteration:
+    internal_fatal(sp.end_time_s < rrddim_handle->start_time_s, "DBENGINE: this point is too old for this query");
+    internal_fatal(sp.end_time_s < handle->now_s, "DBENGINE: this point is too old for this point in time");
 
-//    if(debug_this)
-//        info("DBENGINE: returning point: "
-//             "time from %ld to %ld   //  query from %ld to %ld   //   wanted_start_time_s %ld"
-//             , sp.start_time, sp.end_time
-//             , rrddim_handle->start_time_s, rrddim_handle->end_time_s
-//             , handle->wanted_start_time_s
-//             );
+    handle->now_s += handle->dt_s;
+    handle->position++;
 
     return sp;
 }
 
-int rrdeng_load_metric_is_finished(struct storage_engine_query_handle *rrdimm_handle)
-{
-    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrdimm_handle->handle;
-    return (INVALID_TIME == handle->wanted_start_time_s);
+int rrdeng_load_metric_is_finished(struct storage_engine_query_handle *rrddim_handle) {
+    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrddim_handle->handle;
+    return (handle->now_s > rrddim_handle->end_time_s);
 }
 
 /*
  * Releases the database reference from the handle for loading metrics.
  */
-void rrdeng_load_metric_finalize(struct storage_engine_query_handle *rrdimm_handle)
+void rrdeng_load_metric_finalize(struct storage_engine_query_handle *rrddim_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;
+    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrddim_handle->handle;
 
-    if (descr) {
-#ifdef NETDATA_INTERNAL_CHECKS
-        rrd_stat_atomic_add(&ctx->stats.metric_API_consumers, -1);
-#endif
-        pg_cache_put(ctx, descr);
-    }
+    if (handle->page)
+        pgc_page_release(main_cache, handle->page);
 
-    // whatever is allocated at rrdeng_load_metric_init() should be freed here
-    freez(handle);
-    rrdimm_handle->handle = NULL;
-}
+    if(!pdc_release_and_destroy_if_unreferenced(handle->pdc, false, false))
+        __atomic_store_n(&handle->pdc->workers_should_stop, true, __ATOMIC_RELAXED);
 
-time_t rrdeng_metric_latest_time(STORAGE_METRIC_HANDLE *db_metric_handle) {
-    struct pg_cache_page_index *page_index = (struct pg_cache_page_index *)db_metric_handle;
-    return (time_t)(page_index->latest_time_ut / USEC_PER_SEC);
-}
-time_t rrdeng_metric_oldest_time(STORAGE_METRIC_HANDLE *db_metric_handle) {
-    struct pg_cache_page_index *page_index = (struct pg_cache_page_index *)db_metric_handle;
-    return (time_t)(page_index->oldest_time_ut / USEC_PER_SEC);
+    unregister_query_handle(handle);
+    rrdeng_query_handle_release(handle);
+    rrddim_handle->handle = NULL;
+    netdata_thread_enable_cancelability();
 }
 
-int rrdeng_metric_retention_by_uuid(STORAGE_INSTANCE *si, uuid_t *dim_uuid, time_t *first_entry_t, time_t *last_entry_t)
-{
-    struct page_cache *pg_cache;
-    struct rrdengine_instance *ctx;
-    Pvoid_t *PValue;
-    struct pg_cache_page_index *page_index = NULL;
+time_t rrdeng_load_align_to_optimal_before(struct storage_engine_query_handle *rrddim_handle) {
+    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrddim_handle->handle;
 
-    ctx = (struct rrdengine_instance *)si;
-    if (unlikely(!ctx)) {
-        error("DBENGINE: invalid STORAGE INSTANCE to %s()", __FUNCTION__);
-        return 1;
+    if(handle->pdc) {
+        rrdeng_prep_wait(handle->pdc);
+        if (handle->pdc->optimal_end_time_s > rrddim_handle->end_time_s)
+            rrddim_handle->end_time_s = handle->pdc->optimal_end_time_s;
     }
-    pg_cache = &ctx->pg_cache;
 
-    uv_rwlock_rdlock(&pg_cache->metrics_index.lock);
-    PValue = JudyHSGet(pg_cache->metrics_index.JudyHS_array, dim_uuid, sizeof(uuid_t));
-    if (likely(NULL != PValue)) {
-        page_index = *PValue;
-    }
-    uv_rwlock_rdunlock(&pg_cache->metrics_index.lock);
+    return rrddim_handle->end_time_s;
+}
 
-    if (likely(page_index)) {
-        *first_entry_t = page_index->oldest_time_ut / USEC_PER_SEC;
-        *last_entry_t = page_index->latest_time_ut / USEC_PER_SEC;
-        return 0;
-    }
+time_t rrdeng_metric_latest_time(STORAGE_METRIC_HANDLE *db_metric_handle) {
+    METRIC *metric = (METRIC *)db_metric_handle;
+    time_t latest_time_s = 0;
 
-    return 1;
-}
+    if (metric)
+        latest_time_s = mrg_metric_get_latest_time_s(main_mrg, metric);
 
-/* Also gets a reference for the page */
-void *rrdeng_create_page(struct rrdengine_instance *ctx, uuid_t *id, struct rrdeng_page_descr **ret_descr)
-{
-    struct rrdeng_page_descr *descr;
-    struct page_cache_descr *pg_cache_descr;
-    void *page;
-    /* TODO: check maximum number of pages in page cache limit */
-
-    descr = pg_cache_create_descr();
-    descr->id = id; /* TODO: add page type: metric, log, something? */
-    descr->type = ctx->page_type;
-    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;
-    pg_cache_descr->flags = RRD_PAGE_DIRTY /*| RRD_PAGE_LOCKED */ | RRD_PAGE_POPULATED /* | BEING_COLLECTED */;
-    pg_cache_descr->refcnt = 1;
-
-    debug(D_RRDENGINE, "Created new page:");
-    if (unlikely(debug_flags & D_RRDENGINE))
-        print_page_cache_descr(descr, "", true);
-    rrdeng_page_descr_mutex_unlock(ctx, descr);
-    *ret_descr = descr;
-    return page;
+    return latest_time_s;
 }
 
-/* The page must not be empty */
-void rrdeng_commit_page(struct rrdengine_instance *ctx, struct rrdeng_page_descr *descr,
-                        Word_t page_correlation_id)
-{
-    struct page_cache *pg_cache = &ctx->pg_cache;
-    Pvoid_t *PValue;
-    unsigned nr_committed_pages;
+time_t rrdeng_metric_oldest_time(STORAGE_METRIC_HANDLE *db_metric_handle) {
+    METRIC *metric = (METRIC *)db_metric_handle;
 
-    if (unlikely(NULL == descr)) {
-        debug(D_RRDENGINE, "%s: page descriptor is NULL, page has already been force-committed.", __func__);
-        return;
-    }
-    fatal_assert(descr->page_length);
-
-    uv_rwlock_wrlock(&pg_cache->committed_page_index.lock);
-    PValue = JudyLIns(&pg_cache->committed_page_index.JudyL_array, page_correlation_id, PJE0);
-    *PValue = descr;
-    nr_committed_pages = ++pg_cache->committed_page_index.nr_committed_pages;
-    uv_rwlock_wrunlock(&pg_cache->committed_page_index.lock);
-
-    if (nr_committed_pages >= pg_cache_hard_limit(ctx) / 2) {
-        /* over 50% of pages have not been committed yet */
-
-        if (ctx->drop_metrics_under_page_cache_pressure &&
-            nr_committed_pages >= pg_cache_committed_hard_limit(ctx)) {
-            /* 100% of pages are dirty */
-            struct rrdeng_cmd cmd;
-
-            cmd.opcode = RRDENG_INVALIDATE_OLDEST_MEMORY_PAGE;
-            rrdeng_enq_cmd(&ctx->worker_config, &cmd);
-        } else {
-            if (0 == (unsigned long) ctx->stats.pg_cache_over_half_dirty_events) {
-                /* only print the first time */
-                errno = 0;
-                error("Failed to flush dirty buffers quickly enough in dbengine instance \"%s\". "
-                      "Metric data at risk of not being stored in the database, "
-                      "please reduce disk load or use a faster disk.", ctx->dbfiles_path);
-            }
-            rrd_stat_atomic_add(&ctx->stats.pg_cache_over_half_dirty_events, 1);
-            rrd_stat_atomic_add(&global_pg_cache_over_half_dirty_events, 1);
-        }
-    }
+    time_t oldest_time_s = 0;
+    if (metric)
+        oldest_time_s = mrg_metric_get_first_time_s(main_mrg, metric);
 
-    pg_cache_put(ctx, descr);
+    return oldest_time_s;
 }
 
-/* Gets a reference for the page */
-void *rrdeng_get_latest_page(struct rrdengine_instance *ctx, uuid_t *id, void **handle)
+bool rrdeng_metric_retention_by_uuid(STORAGE_INSTANCE *db_instance, uuid_t *dim_uuid, time_t *first_entry_s, time_t *last_entry_s)
 {
-    struct rrdeng_page_descr *descr;
-    struct page_cache_descr *pg_cache_descr;
-
-    debug(D_RRDENGINE, "Reading existing page:");
-    descr = pg_cache_lookup(ctx, NULL, id, INVALID_TIME);
-    if (NULL == descr) {
-        *handle = NULL;
-
-        return NULL;
+    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
+    if (unlikely(!ctx)) {
+        error("DBENGINE: invalid STORAGE INSTANCE to %s()", __FUNCTION__);
+        return false;
     }
-    *handle = descr;
-    pg_cache_descr = descr->pg_cache_descr;
 
-    return pg_cache_descr->page;
-}
+    METRIC *metric = mrg_metric_get_and_acquire(main_mrg, dim_uuid, (Word_t) ctx);
+    if (unlikely(!metric))
+        return false;
 
-/* Gets a reference for the page */
-void *rrdeng_get_page(struct rrdengine_instance *ctx, uuid_t *id, usec_t point_in_time_ut, void **handle)
-{
-    struct rrdeng_page_descr *descr;
-    struct page_cache_descr *pg_cache_descr;
+    time_t update_every_s;
+    mrg_metric_get_retention(main_mrg, metric, first_entry_s, last_entry_s, &update_every_s);
 
-    debug(D_RRDENGINE, "Reading existing page:");
-    descr = pg_cache_lookup(ctx, NULL, id, point_in_time_ut);
-    if (NULL == descr) {
-        *handle = NULL;
-
-        return NULL;
-    }
-    *handle = descr;
-    pg_cache_descr = descr->pg_cache_descr;
+    mrg_metric_release(main_mrg, metric);
 
-    return pg_cache_descr->page;
+    return true;
 }
 
 /*
@@ -977,62 +1044,126 @@ void rrdeng_get_37_statistics(struct rrdengine_instance *ctx, unsigned long long
     if (ctx == NULL)
         return;
 
-    struct page_cache *pg_cache = &ctx->pg_cache;
-
-    array[0] = (uint64_t)ctx->stats.metric_API_producers;
-    array[1] = (uint64_t)ctx->stats.metric_API_consumers;
-    array[2] = (uint64_t)pg_cache->page_descriptors;
-    array[3] = (uint64_t)pg_cache->populated_pages;
-    array[4] = (uint64_t)pg_cache->committed_page_index.nr_committed_pages;
-    array[5] = (uint64_t)ctx->stats.pg_cache_insertions;
-    array[6] = (uint64_t)ctx->stats.pg_cache_deletions;
-    array[7] = (uint64_t)ctx->stats.pg_cache_hits;
-    array[8] = (uint64_t)ctx->stats.pg_cache_misses;
-    array[9] = (uint64_t)ctx->stats.pg_cache_backfills;
-    array[10] = (uint64_t)ctx->stats.pg_cache_evictions;
-    array[11] = (uint64_t)ctx->stats.before_compress_bytes;
-    array[12] = (uint64_t)ctx->stats.after_compress_bytes;
-    array[13] = (uint64_t)ctx->stats.before_decompress_bytes;
-    array[14] = (uint64_t)ctx->stats.after_decompress_bytes;
-    array[15] = (uint64_t)ctx->stats.io_write_bytes;
-    array[16] = (uint64_t)ctx->stats.io_write_requests;
-    array[17] = (uint64_t)ctx->stats.io_read_bytes;
-    array[18] = (uint64_t)ctx->stats.io_read_requests;
-    array[19] = (uint64_t)ctx->stats.io_write_extent_bytes;
-    array[20] = (uint64_t)ctx->stats.io_write_extents;
-    array[21] = (uint64_t)ctx->stats.io_read_extent_bytes;
-    array[22] = (uint64_t)ctx->stats.io_read_extents;
-    array[23] = (uint64_t)ctx->stats.datafile_creations;
-    array[24] = (uint64_t)ctx->stats.datafile_deletions;
-    array[25] = (uint64_t)ctx->stats.journalfile_creations;
-    array[26] = (uint64_t)ctx->stats.journalfile_deletions;
-    array[27] = (uint64_t)ctx->stats.page_cache_descriptors;
-    array[28] = (uint64_t)ctx->stats.io_errors;
-    array[29] = (uint64_t)ctx->stats.fs_errors;
-    array[30] = (uint64_t)global_io_errors;
-    array[31] = (uint64_t)global_fs_errors;
-    array[32] = (uint64_t)rrdeng_reserved_file_descriptors;
-    array[33] = (uint64_t)ctx->stats.pg_cache_over_half_dirty_events;
-    array[34] = (uint64_t)global_pg_cache_over_half_dirty_events;
-    array[35] = (uint64_t)ctx->stats.flushing_pressure_page_deletions;
-    array[36] = (uint64_t)global_flushing_pressure_page_deletions;
-    fatal_assert(RRDENG_NR_STATS == 37);
+    array[0] = (uint64_t)__atomic_load_n(&ctx->atomic.collectors_running, __ATOMIC_RELAXED); // API producers
+    array[1] = (uint64_t)__atomic_load_n(&ctx->atomic.inflight_queries, __ATOMIC_RELAXED);   // API consumers
+    array[2] = 0;
+    array[3] = 0;
+    array[4] = 0;
+    array[5] = 0; // (uint64_t)ctx->stats.pg_cache_insertions;
+    array[6] = 0; // (uint64_t)ctx->stats.pg_cache_deletions;
+    array[7] = 0; // (uint64_t)ctx->stats.pg_cache_hits;
+    array[8] = 0; // (uint64_t)ctx->stats.pg_cache_misses;
+    array[9] = 0; // (uint64_t)ctx->stats.pg_cache_backfills;
+    array[10] = 0; // (uint64_t)ctx->stats.pg_cache_evictions;
+    array[11] = (uint64_t)__atomic_load_n(&ctx->stats.before_compress_bytes, __ATOMIC_RELAXED); // used
+    array[12] = (uint64_t)__atomic_load_n(&ctx->stats.after_compress_bytes, __ATOMIC_RELAXED); // used
+    array[13] = (uint64_t)__atomic_load_n(&ctx->stats.before_decompress_bytes, __ATOMIC_RELAXED);
+    array[14] = (uint64_t)__atomic_load_n(&ctx->stats.after_decompress_bytes, __ATOMIC_RELAXED);
+    array[15] = (uint64_t)__atomic_load_n(&ctx->stats.io_write_bytes, __ATOMIC_RELAXED); // used
+    array[16] = (uint64_t)__atomic_load_n(&ctx->stats.io_write_requests, __ATOMIC_RELAXED); // used
+    array[17] = (uint64_t)__atomic_load_n(&ctx->stats.io_read_bytes, __ATOMIC_RELAXED);
+    array[18] = (uint64_t)__atomic_load_n(&ctx->stats.io_read_requests, __ATOMIC_RELAXED); // used
+    array[19] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.io_write_extent_bytes, __ATOMIC_RELAXED);
+    array[20] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.io_write_extents, __ATOMIC_RELAXED);
+    array[21] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.io_read_extent_bytes, __ATOMIC_RELAXED);
+    array[22] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.io_read_extents, __ATOMIC_RELAXED);
+    array[23] = (uint64_t)__atomic_load_n(&ctx->stats.datafile_creations, __ATOMIC_RELAXED);
+    array[24] = (uint64_t)__atomic_load_n(&ctx->stats.datafile_deletions, __ATOMIC_RELAXED);
+    array[25] = (uint64_t)__atomic_load_n(&ctx->stats.journalfile_creations, __ATOMIC_RELAXED);
+    array[26] = (uint64_t)__atomic_load_n(&ctx->stats.journalfile_deletions, __ATOMIC_RELAXED);
+    array[27] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.page_cache_descriptors, __ATOMIC_RELAXED);
+    array[28] = (uint64_t)__atomic_load_n(&ctx->stats.io_errors, __ATOMIC_RELAXED);
+    array[29] = (uint64_t)__atomic_load_n(&ctx->stats.fs_errors, __ATOMIC_RELAXED);
+    array[30] = (uint64_t)__atomic_load_n(&global_io_errors, __ATOMIC_RELAXED); // used
+    array[31] = (uint64_t)__atomic_load_n(&global_fs_errors, __ATOMIC_RELAXED); // used
+    array[32] = (uint64_t)__atomic_load_n(&rrdeng_reserved_file_descriptors, __ATOMIC_RELAXED); // used
+    array[33] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.pg_cache_over_half_dirty_events, __ATOMIC_RELAXED);
+    array[34] = (uint64_t)__atomic_load_n(&global_pg_cache_over_half_dirty_events, __ATOMIC_RELAXED); // used
+    array[35] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.flushing_pressure_page_deletions, __ATOMIC_RELAXED);
+    array[36] = (uint64_t)__atomic_load_n(&global_flushing_pressure_page_deletions, __ATOMIC_RELAXED); // used
+    array[37] = 0; //(uint64_t)pg_cache->active_descriptors;
+
+    fatal_assert(RRDENG_NR_STATS == 38);
 }
 
-/* Releases reference to page */
-void rrdeng_put_page(struct rrdengine_instance *ctx, void *handle)
-{
-    (void)ctx;
-    pg_cache_put(ctx, (struct rrdeng_page_descr *)handle);
+static void rrdeng_populate_mrg(struct rrdengine_instance *ctx) {
+    uv_rwlock_rdlock(&ctx->datafiles.rwlock);
+    size_t datafiles = 0;
+    for(struct rrdengine_datafile *df = ctx->datafiles.first; df ;df = df->next)
+        datafiles++;
+    uv_rwlock_rdunlock(&ctx->datafiles.rwlock);
+
+    size_t cpus = get_netdata_cpus() / storage_tiers;
+    if(cpus > datafiles)
+        cpus = datafiles;
+
+    if(cpus < 1)
+        cpus = 1;
+
+    if(cpus > (size_t)libuv_worker_threads)
+        cpus = (size_t)libuv_worker_threads;
+
+    if(cpus > MRG_PARTITIONS)
+        cpus = MRG_PARTITIONS;
+
+    info("DBENGINE: populating retention to MRG from %zu journal files of tier %d, using %zu threads...", datafiles, ctx->config.tier, cpus);
+
+    if(datafiles > 2) {
+        struct rrdengine_datafile *datafile;
+
+        datafile = ctx->datafiles.first->prev;
+        if(!(datafile->journalfile->v2.flags & JOURNALFILE_FLAG_IS_AVAILABLE))
+            datafile = datafile->prev;
+
+        if(datafile->journalfile->v2.flags & JOURNALFILE_FLAG_IS_AVAILABLE) {
+            journalfile_v2_populate_retention_to_mrg(ctx, datafile->journalfile);
+            datafile->populate_mrg.populated = true;
+        }
+
+        datafile = ctx->datafiles.first;
+        if(datafile->journalfile->v2.flags & JOURNALFILE_FLAG_IS_AVAILABLE) {
+            journalfile_v2_populate_retention_to_mrg(ctx, datafile->journalfile);
+            datafile->populate_mrg.populated = true;
+        }
+    }
+
+    ctx->loading.populate_mrg.size = cpus;
+    ctx->loading.populate_mrg.array = callocz(ctx->loading.populate_mrg.size, sizeof(struct completion));
+
+    for (size_t i = 0; i < ctx->loading.populate_mrg.size; i++) {
+        completion_init(&ctx->loading.populate_mrg.array[i]);
+        rrdeng_enq_cmd(ctx, RRDENG_OPCODE_CTX_POPULATE_MRG, NULL, &ctx->loading.populate_mrg.array[i],
+                       STORAGE_PRIORITY_INTERNAL_DBENGINE, NULL, NULL);
+    }
+}
+
+void rrdeng_readiness_wait(struct rrdengine_instance *ctx) {
+    for (size_t i = 0; i < ctx->loading.populate_mrg.size; i++) {
+        completion_wait_for(&ctx->loading.populate_mrg.array[i]);
+        completion_destroy(&ctx->loading.populate_mrg.array[i]);
+    }
+
+    freez(ctx->loading.populate_mrg.array);
+    ctx->loading.populate_mrg.array = NULL;
+    ctx->loading.populate_mrg.size = 0;
+
+    info("DBENGINE: tier %d is ready for data collection and queries", ctx->config.tier);
+}
+
+bool rrdeng_is_legacy(STORAGE_INSTANCE *db_instance) {
+    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
+    return ctx->config.legacy;
 }
 
+void rrdeng_exit_mode(struct rrdengine_instance *ctx) {
+    __atomic_store_n(&ctx->quiesce.exit_mode, true, __ATOMIC_RELAXED);
+}
 /*
  * Returns 0 on success, negative on error
  */
-int rrdeng_init(RRDHOST *host, struct rrdengine_instance **ctxp, char *dbfiles_path, unsigned page_cache_mb,
+int rrdeng_init(struct rrdengine_instance **ctxp, const char *dbfiles_path,
                 unsigned disk_space_mb, size_t tier) {
     struct rrdengine_instance *ctx;
-    int error;
     uint32_t max_open_files;
 
     max_open_files = rlimit_nofile.rlim_cur / 4;
@@ -1053,182 +1184,185 @@ int rrdeng_init(RRDHOST *host, struct rrdengine_instance **ctxp, char *dbfiles_p
     if(NULL == ctxp) {
         ctx = multidb_ctx[tier];
         memset(ctx, 0, sizeof(*ctx));
+        ctx->config.legacy = false;
     }
     else {
         *ctxp = ctx = callocz(1, sizeof(*ctx));
+        ctx->config.legacy = true;
     }
-    ctx->tier = tier;
-    ctx->page_type = tier_page_type[tier];
-    ctx->global_compress_alg = RRD_LZ4;
-    if (page_cache_mb < RRDENG_MIN_PAGE_CACHE_SIZE_MB)
-        page_cache_mb = RRDENG_MIN_PAGE_CACHE_SIZE_MB;
-    ctx->max_cache_pages = page_cache_mb * (1048576LU / RRDENG_BLOCK_SIZE);
-    /* try to keep 5% of the page cache free */
-    ctx->cache_pages_low_watermark = (ctx->max_cache_pages * 95LLU) / 100;
+
+    ctx->config.tier = (int)tier;
+    ctx->config.page_type = tier_page_type[tier];
+    ctx->config.global_compress_alg = RRD_LZ4;
     if (disk_space_mb < RRDENG_MIN_DISK_SPACE_MB)
         disk_space_mb = RRDENG_MIN_DISK_SPACE_MB;
-    ctx->max_disk_space = disk_space_mb * 1048576LLU;
-    strncpyz(ctx->dbfiles_path, dbfiles_path, sizeof(ctx->dbfiles_path) - 1);
-    ctx->dbfiles_path[sizeof(ctx->dbfiles_path) - 1] = '\0';
-    if (NULL == host)
-        strncpyz(ctx->machine_guid, registry_get_this_machine_guid(), GUID_LEN);
-    else
-        strncpyz(ctx->machine_guid, host->machine_guid, GUID_LEN);
-
-    ctx->drop_metrics_under_page_cache_pressure = rrdeng_drop_metrics_under_page_cache_pressure;
-    ctx->metric_API_max_producers = 0;
-    ctx->quiesce = NO_QUIESCE;
-    ctx->host = host;
-
-    memset(&ctx->worker_config, 0, sizeof(ctx->worker_config));
-    ctx->worker_config.ctx = ctx;
-    init_page_cache(ctx);
-    init_commit_log(ctx);
-    error = init_rrd_files(ctx);
-    if (error) {
-        goto error_after_init_rrd_files;
-    }
+    ctx->config.max_disk_space = disk_space_mb * 1048576LLU;
+    strncpyz(ctx->config.dbfiles_path, dbfiles_path, sizeof(ctx->config.dbfiles_path) - 1);
+    ctx->config.dbfiles_path[sizeof(ctx->config.dbfiles_path) - 1] = '\0';
 
-    completion_init(&ctx->rrdengine_completion);
-    fatal_assert(0 == uv_thread_create(&ctx->worker_config.thread, rrdeng_worker, &ctx->worker_config));
-    /* 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, "LIBUV_WORKER");
-    if (ctx->worker_config.error) {
-        goto error_after_rrdeng_worker;
-    }
-//    error = metalog_init(ctx);
-//    if (error) {
-//        error("Failed to initialize metadata log file event loop.");
-//        goto error_after_rrdeng_worker;
-//    }
+    ctx->atomic.transaction_id = 1;
+    ctx->quiesce.enabled = false;
 
-    return 0;
+    if (rrdeng_dbengine_spawn(ctx) && !init_rrd_files(ctx)) {
+        // success - we run this ctx too
+        rrdeng_populate_mrg(ctx);
+        return 0;
+    }
 
-error_after_rrdeng_worker:
-    finalize_rrd_files(ctx);
-error_after_init_rrd_files:
-    free_page_cache(ctx);
-    if (!is_storage_engine_shared((STORAGE_INSTANCE *)ctx)) {
+    if (ctx->config.legacy) {
         freez(ctx);
         if (ctxp)
             *ctxp = NULL;
     }
+
     rrd_stat_atomic_add(&rrdeng_reserved_file_descriptors, -RRDENG_FD_BUDGET_PER_INSTANCE);
     return UV_EIO;
 }
 
+size_t rrdeng_collectors_running(struct rrdengine_instance *ctx) {
+    return __atomic_load_n(&ctx->atomic.collectors_running, __ATOMIC_RELAXED);
+}
+
 /*
  * Returns 0 on success, 1 on error
  */
-int rrdeng_exit(struct rrdengine_instance *ctx)
-{
-    struct rrdeng_cmd cmd;
-
-    if (NULL == ctx) {
+int rrdeng_exit(struct rrdengine_instance *ctx) {
+    if (NULL == ctx)
         return 1;
+
+    // FIXME - ktsaou - properly cleanup ctx
+    // 1. make sure all collectors are stopped
+    // 2. make new queries will not be accepted (this is quiesce that has already run)
+    // 3. flush this section of the main cache
+    // 4. then wait for completion
+
+    bool logged = false;
+    while(__atomic_load_n(&ctx->atomic.collectors_running, __ATOMIC_RELAXED) && !unittest_running) {
+        if(!logged) {
+            info("DBENGINE: waiting for collectors to finish on tier %d...", (ctx->config.legacy) ? -1 : ctx->config.tier);
+            logged = true;
+        }
+        sleep_usec(100 * USEC_PER_MS);
     }
 
-    /* TODO: add page to page cache */
-    cmd.opcode = RRDENG_SHUTDOWN;
-    rrdeng_enq_cmd(&ctx->worker_config, &cmd);
+    info("DBENGINE: flushing main cache for tier %d", (ctx->config.legacy) ? -1 : ctx->config.tier);
+    pgc_flush_all_hot_and_dirty_pages(main_cache, (Word_t)ctx);
 
-    fatal_assert(0 == uv_thread_join(&ctx->worker_config.thread));
+    info("DBENGINE: shutting down tier %d", (ctx->config.legacy) ? -1 : ctx->config.tier);
+    struct completion completion = {};
+    completion_init(&completion);
+    rrdeng_enq_cmd(ctx, RRDENG_OPCODE_CTX_SHUTDOWN, NULL, &completion, STORAGE_PRIORITY_BEST_EFFORT, NULL, NULL);
+    completion_wait_for(&completion);
+    completion_destroy(&completion);
 
     finalize_rrd_files(ctx);
-    //metalog_exit(ctx->metalog_ctx);
-    free_page_cache(ctx);
 
-    if(!is_storage_engine_shared((STORAGE_INSTANCE *)ctx))
+    if(ctx->config.legacy)
         freez(ctx);
 
     rrd_stat_atomic_add(&rrdeng_reserved_file_descriptors, -RRDENG_FD_BUDGET_PER_INSTANCE);
     return 0;
 }
 
-void rrdeng_prepare_exit(struct rrdengine_instance *ctx)
-{
-    struct rrdeng_cmd cmd;
-
-    if (NULL == ctx) {
+void rrdeng_prepare_exit(struct rrdengine_instance *ctx) {
+    if (NULL == ctx)
         return;
-    }
-
-    completion_init(&ctx->rrdengine_completion);
-    cmd.opcode = RRDENG_QUIESCE;
-    rrdeng_enq_cmd(&ctx->worker_config, &cmd);
 
-    /* wait for dbengine to quiesce */
-    completion_wait_for(&ctx->rrdengine_completion);
-    completion_destroy(&ctx->rrdengine_completion);
+    // FIXME - ktsaou - properly cleanup ctx
+    // 1. make sure all collectors are stopped
 
-    //metalog_prepare_exit(ctx->metalog_ctx);
+    completion_init(&ctx->quiesce.completion);
+    rrdeng_enq_cmd(ctx, RRDENG_OPCODE_CTX_QUIESCE, NULL, NULL, STORAGE_PRIORITY_INTERNAL_DBENGINE, NULL, NULL);
 }
 
-RRDENG_SIZE_STATS rrdeng_size_statistics(struct rrdengine_instance *ctx) {
-    RRDENG_SIZE_STATS stats = { 0 };
+static void populate_v2_statistics(struct rrdengine_datafile *datafile, RRDENG_SIZE_STATS *stats)
+{
+    struct journal_v2_header *j2_header = journalfile_v2_data_acquire(datafile->journalfile, NULL, 0, 0);
+    void *data_start = (void *)j2_header;
 
-    for(struct pg_cache_page_index *page_index = ctx->pg_cache.metrics_index.last_page_index;
-        page_index != NULL ;page_index = page_index->prev) {
-        stats.metrics++;
-        stats.metrics_pages += page_index->page_count;
+    if(unlikely(!j2_header))
+        return;
+
+    stats->extents += j2_header->extent_count;
+
+    unsigned entries;
+    struct journal_extent_list *extent_list = (void *) (data_start + j2_header->extent_offset);
+    for (entries = 0; entries < j2_header->extent_count; entries++) {
+        stats->extents_compressed_bytes += extent_list->datafile_size;
+        stats->extents_pages += extent_list->pages;
+        extent_list++;
     }
 
-    for(struct rrdengine_datafile *df = ctx->datafiles.first; df ;df = df->next) {
-        stats.datafiles++;
+    struct journal_metric_list *metric = (void *) (data_start + j2_header->metric_offset);
+    time_t journal_start_time_s = (time_t) (j2_header->start_time_ut / USEC_PER_SEC);
 
-        for(struct extent_info *ei = df->extents.first; ei ; ei = ei->next) {
-            stats.extents++;
-            stats.extents_compressed_bytes += ei->size;
+    stats->metrics += j2_header->metric_count;
+    for (entries = 0; entries < j2_header->metric_count; entries++) {
 
-            for(int p = 0; p < ei->number_of_pages ;p++) {
-                struct rrdeng_page_descr *descr = ei->pages[p];
+        struct journal_page_header *metric_list_header = (void *) (data_start + metric->page_offset);
+        stats->metrics_pages += metric_list_header->entries;
+        struct journal_page_list *descr =  (void *) (data_start + metric->page_offset + sizeof(struct journal_page_header));
+        for (uint32_t idx=0; idx < metric_list_header->entries; idx++) {
 
-                usec_t update_every_usec;
+            time_t update_every_s;
 
-                size_t points = descr->page_length / PAGE_POINT_SIZE_BYTES(descr);
+            size_t points = descr->page_length / CTX_POINT_SIZE_BYTES(datafile->ctx);
 
-                if(likely(points > 1))
-                    update_every_usec = (descr->end_time_ut - descr->start_time_ut) / (points - 1);
-                else {
-                    update_every_usec = default_rrd_update_every * get_tier_grouping(ctx->tier) * USEC_PER_SEC;
-                    stats.single_point_pages++;
-                }
+            time_t start_time_s = journal_start_time_s + descr->delta_start_s;
+            time_t end_time_s = journal_start_time_s + descr->delta_end_s;
 
-                time_t duration_secs = (time_t)((descr->end_time_ut - descr->start_time_ut + update_every_usec)/USEC_PER_SEC);
+            if(likely(points > 1))
+                update_every_s = (time_t) ((end_time_s - start_time_s) / (points - 1));
+            else {
+                update_every_s = (time_t) (default_rrd_update_every * get_tier_grouping(datafile->ctx->config.tier));
+                stats->single_point_pages++;
+            }
 
-                stats.extents_pages++;
-                stats.pages_uncompressed_bytes += descr->page_length;
-                stats.pages_duration_secs += duration_secs;
-                stats.points += points;
+            time_t duration_s = (time_t)((end_time_s - start_time_s + update_every_s));
 
-                stats.page_types[descr->type].pages++;
-                stats.page_types[descr->type].pages_uncompressed_bytes += descr->page_length;
-                stats.page_types[descr->type].pages_duration_secs += duration_secs;
-                stats.page_types[descr->type].points += points;
+            stats->pages_uncompressed_bytes += descr->page_length;
+            stats->pages_duration_secs += duration_s;
+            stats->points += points;
 
-                if(!stats.first_t || (descr->start_time_ut - update_every_usec) < stats.first_t)
-                    stats.first_t = (descr->start_time_ut - update_every_usec) / USEC_PER_SEC;
+            stats->page_types[descr->type].pages++;
+            stats->page_types[descr->type].pages_uncompressed_bytes += descr->page_length;
+            stats->page_types[descr->type].pages_duration_secs += duration_s;
+            stats->page_types[descr->type].points += points;
 
-                if(!stats.last_t || descr->end_time_ut > stats.last_t)
-                    stats.last_t = descr->end_time_ut / USEC_PER_SEC;
-            }
+            if(!stats->first_time_s || (start_time_s - update_every_s) < stats->first_time_s)
+                stats->first_time_s = (start_time_s - update_every_s);
+
+            if(!stats->last_time_s || end_time_s > stats->last_time_s)
+                stats->last_time_s = end_time_s;
+
+            descr++;
         }
+        metric++;
     }
 
+    journalfile_v2_data_release(datafile->journalfile);
+}
+
+RRDENG_SIZE_STATS rrdeng_size_statistics(struct rrdengine_instance *ctx) {
+    RRDENG_SIZE_STATS stats = { 0 };
 
-    stats.currently_collected_metrics = ctx->stats.metric_API_producers;
-    stats.max_concurrently_collected_metrics = ctx->metric_API_max_producers;
+    uv_rwlock_rdlock(&ctx->datafiles.rwlock);
+    for(struct rrdengine_datafile *df = ctx->datafiles.first; df ;df = df->next) {
+        stats.datafiles++;
+        populate_v2_statistics(df, &stats);
+    }
+    uv_rwlock_rdunlock(&ctx->datafiles.rwlock);
+
+    stats.currently_collected_metrics = __atomic_load_n(&ctx->atomic.collectors_running, __ATOMIC_RELAXED);
 
     internal_error(stats.metrics_pages != stats.extents_pages + stats.currently_collected_metrics,
                    "DBENGINE: metrics pages is %zu, but extents pages is %zu and API consumers is %zu",
                    stats.metrics_pages, stats.extents_pages, stats.currently_collected_metrics);
 
-    stats.disk_space = ctx->disk_space;
-    stats.max_disk_space = ctx->max_disk_space;
+    stats.disk_space = ctx_current_disk_space_get(ctx);
+    stats.max_disk_space = ctx->config.max_disk_space;
 
-    stats.database_retention_secs = (time_t)(stats.last_t - stats.first_t);
+    stats.database_retention_secs = (time_t)(stats.last_time_s - stats.first_time_s);
 
     if(stats.extents_pages)
         stats.average_page_size_bytes = (double)stats.pages_uncompressed_bytes / (double)stats.extents_pages;
@@ -1252,21 +1386,22 @@ RRDENG_SIZE_STATS rrdeng_size_statistics(struct rrdengine_instance *ctx) {
         }
     }
 
-    stats.sizeof_metric = struct_natural_alignment(sizeof(struct pg_cache_page_index) + sizeof(struct pg_alignment));
-    stats.sizeof_page = struct_natural_alignment(sizeof(struct rrdeng_page_descr));
+//    stats.sizeof_metric = 0;
     stats.sizeof_datafile = struct_natural_alignment(sizeof(struct rrdengine_datafile)) + struct_natural_alignment(sizeof(struct rrdengine_journalfile));
-    stats.sizeof_page_in_cache = struct_natural_alignment(sizeof(struct page_cache_descr));
-    stats.sizeof_point_data = page_type_size[ctx->page_type];
-    stats.sizeof_page_data = RRDENG_BLOCK_SIZE;
+    stats.sizeof_page_in_cache = 0; // struct_natural_alignment(sizeof(struct page_cache_descr));
+    stats.sizeof_point_data = page_type_size[ctx->config.page_type];
+    stats.sizeof_page_data = tier_page_size[ctx->config.tier];
     stats.pages_per_extent = rrdeng_pages_per_extent;
 
-    stats.sizeof_extent = sizeof(struct extent_info);
-    stats.sizeof_page_in_extent = sizeof(struct rrdeng_page_descr *);
-
-    stats.sizeof_metric_in_index = 40;
-    stats.sizeof_page_in_index = 24;
+//    stats.sizeof_metric_in_index = 40;
+//    stats.sizeof_page_in_index = 24;
 
-    stats.default_granularity_secs = (size_t)default_rrd_update_every * get_tier_grouping(ctx->tier);
+    stats.default_granularity_secs = (size_t)default_rrd_update_every * get_tier_grouping(ctx->config.tier);
 
     return stats;
 }
+
+struct rrdeng_cache_efficiency_stats rrdeng_get_cache_efficiency_stats(void) {
+    // FIXME - make cache efficiency stats atomic
+    return rrdeng_cache_efficiency_stats;
+}