Adding upstream version 1.37.0.upstream/1.37.0

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

1 files changed, 1407 insertions, 0 deletions

diff --git a/streaming/replication.c b/streaming/replication.c
new file mode 100644
index 000000000..8fa501061
--- /dev/null
+++ b/streaming/replication.c
@@ -0,0 +1,1407 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "replication.h"
+#include "Judy.h"
+
+#define STREAMING_START_MAX_SENDER_BUFFER_PERCENTAGE_ALLOWED 50
+#define MAX_SENDER_BUFFER_PERCENTAGE_ALLOWED 20
+#define MIN_SENDER_BUFFER_PERCENTAGE_ALLOWED 10
+
+#define WORKER_JOB_FIND_NEXT                            1
+#define WORKER_JOB_QUERYING                             2
+#define WORKER_JOB_DELETE_ENTRY                         3
+#define WORKER_JOB_FIND_CHART                           4
+#define WORKER_JOB_CHECK_CONSISTENCY                    5
+#define WORKER_JOB_BUFFER_COMMIT                        6
+#define WORKER_JOB_CLEANUP                              7
+
+// master thread worker jobs
+#define WORKER_JOB_STATISTICS                           8
+#define WORKER_JOB_CUSTOM_METRIC_PENDING_REQUESTS       9
+#define WORKER_JOB_CUSTOM_METRIC_COMPLETION             10
+#define WORKER_JOB_CUSTOM_METRIC_ADDED                  11
+#define WORKER_JOB_CUSTOM_METRIC_DONE                   12
+#define WORKER_JOB_CUSTOM_METRIC_SKIPPED_NOT_CONNECTED  13
+#define WORKER_JOB_CUSTOM_METRIC_SKIPPED_NO_ROOM        14
+#define WORKER_JOB_CUSTOM_METRIC_WAITS                  15
+#define WORKER_JOB_CUSTOM_METRIC_SENDER_RESETS          16
+
+#define ITERATIONS_IDLE_WITHOUT_PENDING_TO_RUN_SENDER_VERIFICATION 30
+#define SECONDS_TO_RESET_POINT_IN_TIME 10
+
+static struct replication_query_statistics replication_queries = {
+        .spinlock = NETDATA_SPINLOCK_INITIALIZER,
+        .queries_started = 0,
+        .queries_finished = 0,
+        .points_read = 0,
+        .points_generated = 0,
+};
+
+struct replication_query_statistics replication_get_query_statistics(void) {
+    netdata_spinlock_lock(&replication_queries.spinlock);
+    struct replication_query_statistics ret = replication_queries;
+    netdata_spinlock_unlock(&replication_queries.spinlock);
+    return ret;
+}
+
+// ----------------------------------------------------------------------------
+// sending replication replies
+
+struct replication_dimension {
+    STORAGE_POINT sp;
+    struct storage_engine_query_handle handle;
+    bool enabled;
+
+    DICTIONARY *dict;
+    const DICTIONARY_ITEM *rda;
+    RRDDIM *rd;
+};
+
+static time_t replicate_chart_timeframe(BUFFER *wb, RRDSET *st, time_t after, time_t before, bool enable_streaming, time_t wall_clock_time) {
+    size_t dimensions = rrdset_number_of_dimensions(st);
+    size_t points_read = 0, points_generated = 0;
+
+    struct storage_engine_query_ops *ops = &st->rrdhost->db[0].eng->api.query_ops;
+    struct replication_dimension data[dimensions];
+    memset(data, 0, sizeof(data));
+
+    if(enable_streaming && st->last_updated.tv_sec > before) {
+        internal_error(true, "STREAM_SENDER REPLAY: 'host:%s/chart:%s' has start_streaming = true, adjusting replication before timestamp from %llu to %llu",
+                       rrdhost_hostname(st->rrdhost), rrdset_id(st),
+                       (unsigned long long)before,
+                       (unsigned long long)st->last_updated.tv_sec
+        );
+        before = st->last_updated.tv_sec;
+    }
+
+    // prepare our array of dimensions
+    {
+        RRDDIM *rd;
+        rrddim_foreach_read(rd, st) {
+            if(unlikely(!rd || !rd_dfe.item || !rd->exposed))
+                continue;
+
+            if (unlikely(rd_dfe.counter >= dimensions)) {
+                internal_error(true, "STREAM_SENDER REPLAY ERROR: 'host:%s/chart:%s' has more dimensions than the replicated ones",
+                               rrdhost_hostname(st->rrdhost), rrdset_id(st));
+                break;
+            }
+
+            struct replication_dimension *d = &data[rd_dfe.counter];
+
+            d->dict = rd_dfe.dict;
+            d->rda = dictionary_acquired_item_dup(rd_dfe.dict, rd_dfe.item);
+            d->rd = rd;
+
+            ops->init(rd->tiers[0]->db_metric_handle, &d->handle, after, before);
+            d->enabled = true;
+        }
+        rrddim_foreach_done(rd);
+    }
+
+    time_t now = after + 1, actual_after = 0, actual_before = 0; (void)actual_before;
+    while(now <= before) {
+        time_t min_start_time = 0, min_end_time = 0;
+        for (size_t i = 0; i < dimensions ;i++) {
+            struct replication_dimension *d = &data[i];
+            if(unlikely(!d->enabled)) continue;
+
+            // fetch the first valid point for the dimension
+            int max_skip = 100;
+            while(d->sp.end_time < now && !ops->is_finished(&d->handle) && max_skip-- > 0) {
+                d->sp = ops->next_metric(&d->handle);
+                points_read++;
+            }
+
+            internal_error(max_skip <= 0,
+                           "STREAM_SENDER REPLAY ERROR: 'host:%s/chart:%s/dim:%s': db does not advance the query beyond time %llu",
+                            rrdhost_hostname(st->rrdhost), rrdset_id(st), rrddim_id(d->rd), (unsigned long long) now);
+
+            if(unlikely(d->sp.end_time < now || storage_point_is_unset(d->sp) || storage_point_is_empty(d->sp)))
+                continue;
+
+            if(unlikely(!min_start_time)) {
+                min_start_time = d->sp.start_time;
+                min_end_time = d->sp.end_time;
+            }
+            else {
+                min_start_time = MIN(min_start_time, d->sp.start_time);
+                min_end_time = MIN(min_end_time, d->sp.end_time);
+            }
+        }
+
+        if(unlikely(min_start_time > wall_clock_time + 1 || min_end_time > wall_clock_time + st->update_every + 1)) {
+            internal_error(true,
+                           "STREAM_SENDER REPLAY ERROR: 'host:%s/chart:%s': db provided future start time %llu or end time %llu (now is %llu)",
+                            rrdhost_hostname(st->rrdhost), rrdset_id(st),
+                           (unsigned long long)min_start_time,
+                           (unsigned long long)min_end_time,
+                           (unsigned long long)wall_clock_time);
+            break;
+        }
+
+        if(unlikely(min_end_time < now)) {
+#ifdef NETDATA_LOG_REPLICATION_REQUESTS
+            internal_error(true,
+                           "STREAM_SENDER REPLAY: 'host:%s/chart:%s': no data on any dimension beyond time %llu",
+                           rrdhost_hostname(st->rrdhost), rrdset_id(st), (unsigned long long)now);
+#endif // NETDATA_LOG_REPLICATION_REQUESTS
+            break;
+        }
+
+        if(unlikely(min_end_time <= min_start_time))
+            min_start_time = min_end_time - st->update_every;
+
+        if(unlikely(!actual_after)) {
+            actual_after = min_end_time;
+            actual_before = min_end_time;
+        }
+        else
+            actual_before = min_end_time;
+
+        buffer_sprintf(wb, PLUGINSD_KEYWORD_REPLAY_BEGIN " '' %llu %llu %llu\n"
+                       , (unsigned long long)min_start_time
+                       , (unsigned long long)min_end_time
+                       , (unsigned long long)wall_clock_time
+                       );
+
+        // output the replay values for this time
+        for (size_t i = 0; i < dimensions ;i++) {
+            struct replication_dimension *d = &data[i];
+            if(unlikely(!d->enabled)) continue;
+
+            if(likely(d->sp.start_time <= min_end_time && d->sp.end_time >= min_end_time))
+                buffer_sprintf(wb, PLUGINSD_KEYWORD_REPLAY_SET " \"%s\" " NETDATA_DOUBLE_FORMAT " \"%s\"\n",
+                               rrddim_id(d->rd), d->sp.sum, d->sp.flags & SN_FLAG_RESET ? "R" : "");
+
+            else
+                buffer_sprintf(wb, PLUGINSD_KEYWORD_REPLAY_SET " \"%s\" NAN \"E\"\n",
+                               rrddim_id(d->rd));
+
+            points_generated++;
+        }
+
+        now = min_end_time + 1;
+    }
+
+#ifdef NETDATA_LOG_REPLICATION_REQUESTS
+    if(actual_after) {
+        char actual_after_buf[LOG_DATE_LENGTH + 1], actual_before_buf[LOG_DATE_LENGTH + 1];
+        log_date(actual_after_buf, LOG_DATE_LENGTH, actual_after);
+        log_date(actual_before_buf, LOG_DATE_LENGTH, actual_before);
+        internal_error(true,
+                       "STREAM_SENDER REPLAY: 'host:%s/chart:%s': sending data %llu [%s] to %llu [%s] (requested %llu [delta %lld] to %llu [delta %lld])",
+                       rrdhost_hostname(st->rrdhost), rrdset_id(st),
+                       (unsigned long long)actual_after, actual_after_buf, (unsigned long long)actual_before, actual_before_buf,
+                       (unsigned long long)after, (long long)(actual_after - after), (unsigned long long)before, (long long)(actual_before - before));
+    }
+    else
+        internal_error(true,
+                       "STREAM_SENDER REPLAY: 'host:%s/chart:%s': nothing to send (requested %llu to %llu)",
+                       rrdhost_hostname(st->rrdhost), rrdset_id(st),
+                       (unsigned long long)after, (unsigned long long)before);
+#endif // NETDATA_LOG_REPLICATION_REQUESTS
+
+    // release all the dictionary items acquired
+    // finalize the queries
+    size_t queries = 0;
+    for(size_t i = 0; i < dimensions ;i++) {
+        struct replication_dimension *d = &data[i];
+        if(unlikely(!d->enabled)) continue;
+
+        ops->finalize(&d->handle);
+
+        dictionary_acquired_item_release(d->dict, d->rda);
+
+        // update global statistics
+        queries++;
+    }
+
+    netdata_spinlock_lock(&replication_queries.spinlock);
+    replication_queries.queries_started += queries;
+    replication_queries.queries_finished += queries;
+    replication_queries.points_read += points_read;
+    replication_queries.points_generated += points_generated;
+    netdata_spinlock_unlock(&replication_queries.spinlock);
+
+    return before;
+}
+
+static void replicate_chart_collection_state(BUFFER *wb, RRDSET *st) {
+    RRDDIM *rd;
+    rrddim_foreach_read(rd, st) {
+        if(!rd->exposed) continue;
+
+        buffer_sprintf(wb, PLUGINSD_KEYWORD_REPLAY_RRDDIM_STATE " \"%s\" %llu %lld " NETDATA_DOUBLE_FORMAT " " NETDATA_DOUBLE_FORMAT "\n",
+                       rrddim_id(rd),
+                       (usec_t)rd->last_collected_time.tv_sec * USEC_PER_SEC + (usec_t)rd->last_collected_time.tv_usec,
+                       rd->last_collected_value,
+                       rd->last_calculated_value,
+                       rd->last_stored_value
+        );
+    }
+    rrddim_foreach_done(rd);
+
+    buffer_sprintf(wb, PLUGINSD_KEYWORD_REPLAY_RRDSET_STATE " %llu %llu\n",
+                   (usec_t)st->last_collected_time.tv_sec * USEC_PER_SEC + (usec_t)st->last_collected_time.tv_usec,
+                   (usec_t)st->last_updated.tv_sec * USEC_PER_SEC + (usec_t)st->last_updated.tv_usec
+    );
+}
+
+bool replicate_chart_response(RRDHOST *host, RRDSET *st, bool start_streaming, time_t after, time_t before) {
+    time_t query_after = after;
+    time_t query_before = before;
+    time_t now = now_realtime_sec();
+    time_t tolerance = 2;   // sometimes from the time we get this value, to the time we check,
+                            // a data collection has been made
+                            // so, we give this tolerance to detect invalid timestamps
+
+    // find the first entry we have
+    time_t first_entry_local = rrdset_first_entry_t(st);
+    if(first_entry_local > now + tolerance) {
+        internal_error(true,
+                       "STREAM_SENDER REPLAY ERROR: 'host:%s/chart:%s' db first time %llu is in the future (now is %llu)",
+                       rrdhost_hostname(st->rrdhost), rrdset_id(st),
+                       (unsigned long long)first_entry_local, (unsigned long long)now);
+        first_entry_local = now;
+    }
+
+    if (query_after < first_entry_local)
+        query_after = first_entry_local;
+
+    // find the latest entry we have
+    time_t last_entry_local = st->last_updated.tv_sec;
+    if(!last_entry_local) {
+        internal_error(true,
+                       "STREAM_SENDER REPLAY ERROR: 'host:%s/chart:%s' RRDSET reports last updated time zero.",
+                       rrdhost_hostname(st->rrdhost), rrdset_id(st));
+        last_entry_local = rrdset_last_entry_t(st);
+        if(!last_entry_local) {
+            internal_error(true,
+                           "STREAM_SENDER REPLAY ERROR: 'host:%s/chart:%s' db reports last time zero.",
+                           rrdhost_hostname(st->rrdhost), rrdset_id(st));
+            last_entry_local = now;
+        }
+    }
+
+    if(last_entry_local > now + tolerance) {
+        internal_error(true,
+                       "STREAM_SENDER REPLAY ERROR: 'host:%s/chart:%s' last updated time %llu is in the future (now is %llu)",
+                       rrdhost_hostname(st->rrdhost), rrdset_id(st),
+                       (unsigned long long)last_entry_local, (unsigned long long)now);
+        last_entry_local = now;
+    }
+
+    if (query_before > last_entry_local)
+        query_before = last_entry_local;
+
+    // if the parent asked us to start streaming, then fill the rest with the data that we have
+    if (start_streaming)
+        query_before = last_entry_local;
+
+    if (query_after > query_before) {
+        time_t tmp = query_before;
+        query_before = query_after;
+        query_after = tmp;
+    }
+
+    bool enable_streaming = (start_streaming || query_before == last_entry_local || !after || !before) ? true : false;
+
+    // we might want to optimize this by filling a temporary buffer
+    // and copying the result to the host's buffer in order to avoid
+    // holding the host's buffer lock for too long
+    BUFFER *wb = sender_start(host->sender);
+
+    buffer_sprintf(wb, PLUGINSD_KEYWORD_REPLAY_BEGIN " \"%s\"\n", rrdset_id(st));
+
+    if(after != 0 && before != 0)
+        before = replicate_chart_timeframe(wb, st, query_after, query_before, enable_streaming, now);
+    else {
+        after = 0;
+        before = 0;
+        enable_streaming = true;
+    }
+
+    // get again the world clock time
+    time_t world_clock_time = now_realtime_sec();
+    if(enable_streaming) {
+        if(now < world_clock_time) {
+            // we needed time to execute this request
+            // so, the parent will need to replicate more data
+            enable_streaming = false;
+        }
+        else
+            replicate_chart_collection_state(wb, st);
+    }
+
+    // end with first/last entries we have, and the first start time and
+    // last end time of the data we sent
+    buffer_sprintf(wb, PLUGINSD_KEYWORD_REPLAY_END " %d %llu %llu %s %llu %llu %llu\n",
+
+                   // current chart update every
+                   (int)st->update_every
+
+                   // child first db time, child end db time
+                   , (unsigned long long)first_entry_local, (unsigned long long)last_entry_local
+
+                   // start streaming boolean
+                   , enable_streaming ? "true" : "false"
+
+                   // after requested, before requested ('before' can be altered by the child when the request had enable_streaming true)
+                   , (unsigned long long)after, (unsigned long long)before
+
+                   // child world clock time
+                   , (unsigned long long)world_clock_time
+                   );
+
+    worker_is_busy(WORKER_JOB_BUFFER_COMMIT);
+    sender_commit(host->sender, wb);
+    worker_is_busy(WORKER_JOB_CLEANUP);
+
+    return enable_streaming;
+}
+
+// ----------------------------------------------------------------------------
+// sending replication requests
+
+struct replication_request_details {
+    struct {
+        send_command callback;
+        void *data;
+    } caller;
+
+    RRDHOST *host;
+    RRDSET *st;
+
+    struct {
+        time_t first_entry_t;               // the first entry time the child has
+        time_t last_entry_t;                // the last entry time the child has
+        time_t world_time_t;                // the current time of the child
+    } child_db;
+
+    struct {
+        time_t first_entry_t;               // the first entry time we have
+        time_t last_entry_t;                // the last entry time we have
+        bool last_entry_t_adjusted_to_now;  // true, if the last entry time was in the future, and we fixed
+        time_t now;                         // the current local world clock time
+    } local_db;
+
+    struct {
+        time_t from;                        // the starting time of the entire gap we have
+        time_t to;                          // the ending time of the entire gap we have
+    } gap;
+
+    struct {
+        time_t after;                       // the start time we requested previously from this child
+        time_t before;                      // the end time we requested previously from this child
+    } last_request;
+
+    struct {
+        time_t after;                       // the start time of this replication request - the child will add 1 second
+        time_t before;                      // the end time of this replication request
+        bool start_streaming;               // true when we want the child to send anything remaining and start streaming - the child will overwrite 'before'
+    } wanted;
+};
+
+static bool send_replay_chart_cmd(struct replication_request_details *r, const char *msg __maybe_unused) {
+    RRDSET *st = r->st;
+
+    if(st->rrdhost->receiver && (!st->rrdhost->receiver->replication_first_time_t || r->wanted.after < st->rrdhost->receiver->replication_first_time_t))
+        st->rrdhost->receiver->replication_first_time_t = r->wanted.after;
+
+#ifdef NETDATA_LOG_REPLICATION_REQUESTS
+    st->replay.log_next_data_collection = true;
+
+    char wanted_after_buf[LOG_DATE_LENGTH + 1] = "", wanted_before_buf[LOG_DATE_LENGTH + 1] = "";
+
+    if(r->wanted.after)
+        log_date(wanted_after_buf, LOG_DATE_LENGTH, r->wanted.after);
+
+    if(r->wanted.before)
+        log_date(wanted_before_buf, LOG_DATE_LENGTH, r->wanted.before);
+
+    internal_error(true,
+                   "REPLAY: 'host:%s/chart:%s' sending replication request %ld [%s] to %ld [%s], start streaming '%s': %s: "
+                   "last[%ld - %ld] child[%ld - %ld, now %ld %s] local[%ld - %ld %s, now %ld] gap[%ld - %ld %s] %s"
+                   , rrdhost_hostname(r->host), rrdset_id(r->st)
+                   , r->wanted.after, wanted_after_buf
+                   , r->wanted.before, wanted_before_buf
+                   , r->wanted.start_streaming ? "YES" : "NO"
+                   , msg
+                   , r->last_request.after, r->last_request.before
+                   , r->child_db.first_entry_t, r->child_db.last_entry_t
+                   , r->child_db.world_time_t, (r->child_db.world_time_t == r->local_db.now) ? "SAME" : (r->child_db.world_time_t < r->local_db.now) ? "BEHIND" : "AHEAD"
+                   , r->local_db.first_entry_t, r->local_db.last_entry_t
+                   , r->local_db.last_entry_t_adjusted_to_now?"FIXED":"RAW", r->local_db.now
+                   , r->gap.from, r->gap.to
+                   , (r->gap.from == r->wanted.after) ? "FULL" : "PARTIAL"
+                   , (st->replay.after != 0 || st->replay.before != 0) ? "OVERLAPPING" : ""
+                   );
+
+    st->replay.start_streaming = r->wanted.start_streaming;
+    st->replay.after = r->wanted.after;
+    st->replay.before = r->wanted.before;
+#endif // NETDATA_LOG_REPLICATION_REQUESTS
+
+    char buffer[2048 + 1];
+    snprintfz(buffer, 2048, PLUGINSD_KEYWORD_REPLAY_CHART " \"%s\" \"%s\" %llu %llu\n",
+              rrdset_id(st), r->wanted.start_streaming ? "true" : "false",
+              (unsigned long long)r->wanted.after, (unsigned long long)r->wanted.before);
+
+    int ret = r->caller.callback(buffer, r->caller.data);
+    if (ret < 0) {
+        error("REPLAY ERROR: 'host:%s/chart:%s' failed to send replication request to child (error %d)",
+              rrdhost_hostname(r->host), rrdset_id(r->st), ret);
+        return false;
+    }
+
+    return true;
+}
+
+bool replicate_chart_request(send_command callback, void *callback_data, RRDHOST *host, RRDSET *st,
+                             time_t first_entry_child, time_t last_entry_child, time_t child_world_time,
+                             time_t prev_first_entry_wanted, time_t prev_last_entry_wanted)
+{
+    struct replication_request_details r = {
+            .caller = {
+                    .callback = callback,
+                    .data = callback_data,
+            },
+
+            .host = host,
+            .st = st,
+
+            .child_db = {
+                    .first_entry_t = first_entry_child,
+                    .last_entry_t = last_entry_child,
+                    .world_time_t = child_world_time,
+            },
+
+            .local_db = {
+                    .first_entry_t = rrdset_first_entry_t(st),
+                    .last_entry_t = rrdset_last_entry_t(st),
+                    .last_entry_t_adjusted_to_now = false,
+                    .now  = now_realtime_sec(),
+            },
+
+            .last_request = {
+                    .after = prev_first_entry_wanted,
+                    .before = prev_last_entry_wanted,
+            },
+
+            .wanted = {
+                    .after = 0,
+                    .before = 0,
+                    .start_streaming = true,
+            },
+    };
+
+    // check our local database retention
+    if(r.local_db.last_entry_t > r.local_db.now) {
+        r.local_db.last_entry_t = r.local_db.now;
+        r.local_db.last_entry_t_adjusted_to_now = true;
+    }
+
+    // let's find the GAP we have
+    if(!r.last_request.after || !r.last_request.before) {
+        // there is no previous request
+
+        if(r.local_db.last_entry_t)
+            // we have some data, let's continue from the last point we have
+            r.gap.from = r.local_db.last_entry_t;
+        else
+            // we don't have any data, the gap is the max timeframe we are allowed to replicate
+            r.gap.from = r.local_db.now - r.host->rrdpush_seconds_to_replicate;
+
+    }
+    else {
+        // we had sent a request - let's continue at the point we left it
+        // for this we don't take into account the actual data in our db
+        // because the child may also have gaps, and we need to get over it
+        r.gap.from = r.last_request.before;
+    }
+
+    // we want all the data up to now
+    r.gap.to = r.local_db.now;
+
+    // The gap is now r.gap.from -> r.gap.to
+
+    if (unlikely(!rrdhost_option_check(host, RRDHOST_OPTION_REPLICATION)))
+        return send_replay_chart_cmd(&r, "empty replication request, replication is disabled");
+
+    if (unlikely(!r.child_db.last_entry_t))
+        return send_replay_chart_cmd(&r, "empty replication request, child has no stored data");
+
+    if (unlikely(!rrdset_number_of_dimensions(st)))
+        return send_replay_chart_cmd(&r, "empty replication request, chart has no dimensions");
+
+    if (r.child_db.first_entry_t <= 0)
+        return send_replay_chart_cmd(&r, "empty replication request, first entry of the child db first entry is invalid");
+
+    if (r.child_db.first_entry_t > r.child_db.last_entry_t)
+        return send_replay_chart_cmd(&r, "empty replication request, child timings are invalid (first entry > last entry)");
+
+    if (r.local_db.last_entry_t > r.child_db.last_entry_t)
+        return send_replay_chart_cmd(&r, "empty replication request, local last entry is later than the child one");
+
+    // let's find what the child can provide to fill that gap
+
+    if(r.child_db.first_entry_t > r.gap.from)
+        // the child does not have all the data - let's get what it has
+        r.wanted.after = r.child_db.first_entry_t;
+    else
+        // ok, the child can fill the entire gap we have
+        r.wanted.after = r.gap.from;
+
+    if(r.gap.to - r.wanted.after > host->rrdpush_replication_step)
+        // the duration is too big for one request - let's take the first step
+        r.wanted.before = r.wanted.after + host->rrdpush_replication_step;
+    else
+        // wow, we can do it in one request
+        r.wanted.before = r.gap.to;
+
+    // don't ask from the child more than it has
+    if(r.wanted.before > r.child_db.last_entry_t)
+        r.wanted.before = r.child_db.last_entry_t;
+
+    if(r.wanted.after > r.wanted.before)
+        r.wanted.after = r.wanted.before;
+
+    // the child should start streaming immediately if the wanted duration is small, or we reached the last entry of the child
+    r.wanted.start_streaming = (r.local_db.now - r.wanted.after <= host->rrdpush_replication_step || r.wanted.before == r.child_db.last_entry_t);
+
+    // the wanted timeframe is now r.wanted.after -> r.wanted.before
+    // send it
+    return send_replay_chart_cmd(&r, "OK");
+}
+
+// ----------------------------------------------------------------------------
+// replication thread
+
+// replication request in sender DICTIONARY
+// used for de-duplicating the requests
+struct replication_request {
+    struct sender_state *sender;        // the sender we should put the reply at
+    STRING *chart_id;                   // the chart of the request
+    time_t after;                       // the start time of the query (maybe zero) key for sorting (JudyL)
+    time_t before;                      // the end time of the query (maybe zero)
+    bool start_streaming;               // true, when the parent wants to send the rest of the data (before is overwritten) and enable normal streaming
+
+    usec_t sender_last_flush_ut;        // the timestamp of the sender, at the time we indexed this request
+    Word_t unique_id;                   // auto-increment, later requests have bigger
+    bool found;                         // used as a result boolean for the find call
+    bool indexed_in_judy;               // true when the request is indexed in judy
+};
+
+// replication sort entry in JudyL array
+// used for sorting all requests, across all nodes
+struct replication_sort_entry {
+    struct replication_request *rq;
+
+    size_t unique_id;              // used as a key to identify the sort entry - we never access its contents
+};
+
+#define MAX_REPLICATION_THREADS 20 // + 1 for the main thread
+
+// the global variables for the replication thread
+static struct replication_thread {
+    netdata_mutex_t mutex;
+
+    struct {
+        size_t pending;                 // number of requests pending in the queue
+        Word_t unique_id;               // the last unique id we gave to a request (auto-increment, starting from 1)
+
+        // statistics
+        size_t added;                   // number of requests added to the queue
+        size_t removed;                 // number of requests removed from the queue
+        size_t skipped_not_connected;   // number of requests skipped, because the sender is not connected to a parent
+        size_t skipped_no_room;         // number of requests skipped, because the sender has no room for responses
+//        size_t skipped_no_room_since_last_reset;
+        size_t sender_resets;           // number of times a sender reset our last position in the queue
+        time_t first_time_t;            // the minimum 'after' we encountered
+
+        struct {
+            Word_t after;
+            Word_t unique_id;
+            Pvoid_t JudyL_array;
+        } queue;
+
+    } unsafe;                           // protected from replication_recursive_lock()
+
+    struct {
+        size_t executed;                // the number of replication requests executed
+        size_t latest_first_time;       // the 'after' timestamp of the last request we executed
+    } atomic;                           // access should be with atomic operations
+
+    struct {
+        size_t waits;
+        size_t last_executed;           // caching of the atomic.executed to report number of requests executed since last time
+
+        netdata_thread_t **threads_ptrs;
+        size_t threads;
+    } main_thread;                      // access is allowed only by the main thread
+
+} replication_globals = {
+        .mutex = NETDATA_MUTEX_INITIALIZER,
+        .unsafe = {
+                .pending = 0,
+                .unique_id = 0,
+
+                .added = 0,
+                .removed = 0,
+                .skipped_not_connected = 0,
+                .skipped_no_room = 0,
+//                .skipped_no_room_since_last_reset = 0,
+                .sender_resets = 0,
+
+                .first_time_t = 0,
+
+                .queue = {
+                        .after = 0,
+                        .unique_id = 0,
+                        .JudyL_array = NULL,
+                },
+        },
+        .atomic = {
+                .executed = 0,
+                .latest_first_time = 0,
+        },
+        .main_thread = {
+                .waits = 0,
+                .last_executed = 0,
+                .threads = 0,
+                .threads_ptrs = NULL,
+        },
+};
+
+#define replication_set_latest_first_time(t) __atomic_store_n(&replication_globals.atomic.latest_first_time, t, __ATOMIC_RELAXED)
+#define replication_get_latest_first_time() __atomic_load_n(&replication_globals.atomic.latest_first_time, __ATOMIC_RELAXED)
+
+static inline bool replication_recursive_lock_mode(char mode) {
+    static __thread int recursions = 0;
+
+    if(mode == 'L') { // (L)ock
+        if(++recursions == 1)
+            netdata_mutex_lock(&replication_globals.mutex);
+    }
+    else if(mode == 'U') { // (U)nlock
+        if(--recursions == 0)
+            netdata_mutex_unlock(&replication_globals.mutex);
+    }
+    else if(mode == 'C') { // (C)heck
+        if(recursions > 0)
+            return true;
+        else
+            return false;
+    }
+    else
+        fatal("REPLICATION: unknown lock mode '%c'", mode);
+
+#ifdef NETDATA_INTERNAL_CHECKS
+    if(recursions < 0)
+        fatal("REPLICATION: recursions is %d", recursions);
+#endif
+
+    return true;
+}
+
+#define replication_recursive_lock() replication_recursive_lock_mode('L')
+#define replication_recursive_unlock() replication_recursive_lock_mode('U')
+#define fatal_when_replication_is_not_locked_for_me() do { \
+    if(!replication_recursive_lock_mode('C')) \
+        fatal("REPLICATION: reached %s, but replication is not locked by this thread.", __FUNCTION__); \
+} while(0)
+
+void replication_set_next_point_in_time(time_t after, size_t unique_id) {
+    replication_recursive_lock();
+    replication_globals.unsafe.queue.after = after;
+    replication_globals.unsafe.queue.unique_id = unique_id;
+    replication_recursive_unlock();
+}
+
+// ----------------------------------------------------------------------------
+// replication sort entry management
+
+static struct replication_sort_entry *replication_sort_entry_create_unsafe(struct replication_request *rq) {
+    fatal_when_replication_is_not_locked_for_me();
+
+    struct replication_sort_entry *rse = mallocz(sizeof(struct replication_sort_entry));
+
+    rrdpush_sender_pending_replication_requests_plus_one(rq->sender);
+
+    // copy the request
+    rse->rq = rq;
+    rse->unique_id = ++replication_globals.unsafe.unique_id;
+
+    // save the unique id into the request, to be able to delete it later
+    rq->unique_id = rse->unique_id;
+    rq->indexed_in_judy = false;
+    return rse;
+}
+
+static void replication_sort_entry_destroy(struct replication_sort_entry *rse) {
+    freez(rse);
+}
+
+static struct replication_sort_entry *replication_sort_entry_add(struct replication_request *rq) {
+    replication_recursive_lock();
+
+    struct replication_sort_entry *rse = replication_sort_entry_create_unsafe(rq);
+
+//    if(rq->after < (time_t)replication_globals.protected.queue.after &&
+//        rq->sender->buffer_used_percentage <= MAX_SENDER_BUFFER_PERCENTAGE_ALLOWED &&
+//       !replication_globals.protected.skipped_no_room_since_last_reset) {
+//
+//        // make it find this request first
+//        replication_set_next_point_in_time(rq->after, rq->unique_id);
+//    }
+
+    replication_globals.unsafe.added++;
+    replication_globals.unsafe.pending++;
+
+    Pvoid_t *inner_judy_ptr;
+
+    // find the outer judy entry, using after as key
+    inner_judy_ptr = JudyLGet(replication_globals.unsafe.queue.JudyL_array, (Word_t) rq->after, PJE0);
+    if(!inner_judy_ptr)
+        inner_judy_ptr = JudyLIns(&replication_globals.unsafe.queue.JudyL_array, (Word_t) rq->after, PJE0);
+
+    // add it to the inner judy, using unique_id as key
+    Pvoid_t *item = JudyLIns(inner_judy_ptr, rq->unique_id, PJE0);
+    *item = rse;
+    rq->indexed_in_judy = true;
+
+    if(!replication_globals.unsafe.first_time_t || rq->after < replication_globals.unsafe.first_time_t)
+        replication_globals.unsafe.first_time_t = rq->after;
+
+    replication_recursive_unlock();
+
+    return rse;
+}
+
+static bool replication_sort_entry_unlink_and_free_unsafe(struct replication_sort_entry *rse, Pvoid_t **inner_judy_ppptr) {
+    fatal_when_replication_is_not_locked_for_me();
+
+    bool inner_judy_deleted = false;
+
+    replication_globals.unsafe.removed++;
+    replication_globals.unsafe.pending--;
+
+    rrdpush_sender_pending_replication_requests_minus_one(rse->rq->sender);
+
+    rse->rq->indexed_in_judy = false;
+
+    // delete it from the inner judy
+    JudyLDel(*inner_judy_ppptr, rse->rq->unique_id, PJE0);
+
+    // if no items left, delete it from the outer judy
+    if(**inner_judy_ppptr == NULL) {
+        JudyLDel(&replication_globals.unsafe.queue.JudyL_array, rse->rq->after, PJE0);
+        inner_judy_deleted = true;
+    }
+
+    // free memory
+    replication_sort_entry_destroy(rse);
+
+    return inner_judy_deleted;
+}
+
+static void replication_sort_entry_del(struct replication_request *rq) {
+    Pvoid_t *inner_judy_pptr;
+    struct replication_sort_entry *rse_to_delete = NULL;
+
+    replication_recursive_lock();
+    if(rq->indexed_in_judy) {
+
+        inner_judy_pptr = JudyLGet(replication_globals.unsafe.queue.JudyL_array, rq->after, PJE0);
+        if (inner_judy_pptr) {
+            Pvoid_t *our_item_pptr = JudyLGet(*inner_judy_pptr, rq->unique_id, PJE0);
+            if (our_item_pptr) {
+                rse_to_delete = *our_item_pptr;
+                replication_sort_entry_unlink_and_free_unsafe(rse_to_delete, &inner_judy_pptr);
+            }
+        }
+
+        if (!rse_to_delete)
+            fatal("REPLAY: 'host:%s/chart:%s' Cannot find sort entry to delete for time %ld.",
+                  rrdhost_hostname(rq->sender->host), string2str(rq->chart_id), rq->after);
+
+    }
+
+    replication_recursive_unlock();
+}
+
+static inline PPvoid_t JudyLFirstOrNext(Pcvoid_t PArray, Word_t * PIndex, bool first) {
+    if(unlikely(first))
+        return JudyLFirst(PArray, PIndex, PJE0);
+
+    return JudyLNext(PArray, PIndex, PJE0);
+}
+
+static struct replication_request replication_request_get_first_available() {
+    Pvoid_t *inner_judy_pptr;
+
+    replication_recursive_lock();
+
+    struct replication_request rq_to_return = (struct replication_request){ .found = false };
+
+    if(unlikely(!replication_globals.unsafe.queue.after || !replication_globals.unsafe.queue.unique_id)) {
+        replication_globals.unsafe.queue.after = 0;
+        replication_globals.unsafe.queue.unique_id = 0;
+    }
+
+    Word_t started_after = replication_globals.unsafe.queue.after;
+
+    size_t round = 0;
+    while(!rq_to_return.found) {
+        round++;
+
+        if(round > 2)
+            break;
+
+        if(round == 2) {
+            if(started_after == 0)
+                break;
+
+            replication_globals.unsafe.queue.after = 0;
+            replication_globals.unsafe.queue.unique_id = 0;
+        }
+
+        bool find_same_after = true;
+        while (!rq_to_return.found && (inner_judy_pptr = JudyLFirstOrNext(replication_globals.unsafe.queue.JudyL_array, &replication_globals.unsafe.queue.after, find_same_after))) {
+            Pvoid_t *our_item_pptr;
+
+            if(unlikely(round == 2 && replication_globals.unsafe.queue.after > started_after))
+                break;
+
+            while (!rq_to_return.found && (our_item_pptr = JudyLNext(*inner_judy_pptr, &replication_globals.unsafe.queue.unique_id, PJE0))) {
+                struct replication_sort_entry *rse = *our_item_pptr;
+                struct replication_request *rq = rse->rq;
+                struct sender_state *s = rq->sender;
+
+                if (likely(rrdpush_sender_get_buffer_used_percent(s) <= MAX_SENDER_BUFFER_PERCENTAGE_ALLOWED)) {
+                    // there is room for this request in the sender buffer
+
+                    bool sender_is_connected =
+                            rrdhost_flag_check(s->host, RRDHOST_FLAG_RRDPUSH_SENDER_CONNECTED);
+
+                    bool sender_has_been_flushed_since_this_request =
+                            rq->sender_last_flush_ut != rrdpush_sender_get_flush_time(s);
+
+                    if (unlikely(!sender_is_connected || sender_has_been_flushed_since_this_request)) {
+                        // skip this request, the sender is not connected, or it has reconnected
+
+                        replication_globals.unsafe.skipped_not_connected++;
+                        if (replication_sort_entry_unlink_and_free_unsafe(rse, &inner_judy_pptr))
+                            // we removed the item from the outer JudyL
+                            break;
+                    }
+                    else {
+                        // this request is good to execute
+
+                        // copy the request to return it
+                        rq_to_return = *rq;
+                        rq_to_return.chart_id = string_dup(rq_to_return.chart_id);
+
+                        // set the return result to found
+                        rq_to_return.found = true;
+
+                        if (replication_sort_entry_unlink_and_free_unsafe(rse, &inner_judy_pptr))
+                            // we removed the item from the outer JudyL
+                            break;
+                    }
+                }
+                else {
+                    replication_globals.unsafe.skipped_no_room++;
+//                replication_globals.protected.skipped_no_room_since_last_reset++;
+                }
+            }
+
+            // call JudyLNext from now on
+            find_same_after = false;
+
+            // prepare for the next iteration on the outer loop
+            replication_globals.unsafe.queue.unique_id = 0;
+        }
+    }
+
+    replication_recursive_unlock();
+    return rq_to_return;
+}
+
+// ----------------------------------------------------------------------------
+// replication request management
+
+static void replication_request_react_callback(const DICTIONARY_ITEM *item __maybe_unused, void *value __maybe_unused, void *sender_state __maybe_unused) {
+    struct sender_state *s = sender_state; (void)s;
+    struct replication_request *rq = value;
+
+    // IMPORTANT:
+    // We use the react instead of the insert callback
+    // because we want the item to be atomically visible
+    // to our replication thread, immediately after.
+
+    // If we put this at the insert callback, the item is not guaranteed
+    // to be atomically visible to others, so the replication thread
+    // may see the replication sort entry, but fail to find the dictionary item
+    // related to it.
+
+    replication_sort_entry_add(rq);
+
+    // this request is about a unique chart for this sender
+    rrdpush_sender_replicating_charts_plus_one(s);
+}
+
+static bool replication_request_conflict_callback(const DICTIONARY_ITEM *item __maybe_unused, void *old_value, void *new_value, void *sender_state) {
+    struct sender_state *s = sender_state; (void)s;
+    struct replication_request *rq = old_value; (void)rq;
+    struct replication_request *rq_new = new_value;
+
+    replication_recursive_lock();
+
+    if(!rq->indexed_in_judy) {
+        replication_sort_entry_add(rq);
+        internal_error(
+                true,
+                "STREAM %s [send to %s]: REPLAY: 'host:%s/chart:%s' adding duplicate replication command received (existing from %llu to %llu [%s], new from %llu to %llu [%s])",
+                rrdhost_hostname(s->host), s->connected_to, rrdhost_hostname(s->host), dictionary_acquired_item_name(item),
+                (unsigned long long)rq->after, (unsigned long long)rq->before, rq->start_streaming ? "true" : "false",
+                (unsigned long long)rq_new->after, (unsigned long long)rq_new->before, rq_new->start_streaming ? "true" : "false");
+    }
+    else {
+        internal_error(
+                true,
+                "STREAM %s [send to %s]: REPLAY: 'host:%s/chart:%s' ignoring duplicate replication command received (existing from %llu to %llu [%s], new from %llu to %llu [%s])",
+                rrdhost_hostname(s->host), s->connected_to, rrdhost_hostname(s->host),
+                dictionary_acquired_item_name(item),
+                (unsigned long long) rq->after, (unsigned long long) rq->before, rq->start_streaming ? "true" : "false",
+                (unsigned long long) rq_new->after, (unsigned long long) rq_new->before, rq_new->start_streaming ? "true" : "false");
+    }
+
+    replication_recursive_unlock();
+
+    string_freez(rq_new->chart_id);
+    return false;
+}
+
+static void replication_request_delete_callback(const DICTIONARY_ITEM *item __maybe_unused, void *value, void *sender_state __maybe_unused) {
+    struct replication_request *rq = value;
+
+    // this request is about a unique chart for this sender
+    rrdpush_sender_replicating_charts_minus_one(rq->sender);
+
+    if(rq->indexed_in_judy)
+        replication_sort_entry_del(rq);
+
+    string_freez(rq->chart_id);
+}
+
+static bool replication_execute_request(struct replication_request *rq, bool workers) {
+    bool ret = false;
+
+    if(likely(workers))
+        worker_is_busy(WORKER_JOB_FIND_CHART);
+
+    RRDSET *st = rrdset_find(rq->sender->host, string2str(rq->chart_id));
+    if(!st) {
+        internal_error(true, "REPLAY ERROR: 'host:%s/chart:%s' not found",
+                       rrdhost_hostname(rq->sender->host), string2str(rq->chart_id));
+
+        goto cleanup;
+    }
+
+    if(likely(workers))
+        worker_is_busy(WORKER_JOB_QUERYING);
+
+    netdata_thread_disable_cancelability();
+
+    // send the replication data
+    bool start_streaming = replicate_chart_response(
+            st->rrdhost, st, rq->start_streaming, rq->after, rq->before);
+
+    netdata_thread_enable_cancelability();
+
+    if(start_streaming && rq->sender_last_flush_ut == rrdpush_sender_get_flush_time(rq->sender)) {
+        // enable normal streaming if we have to
+        // but only if the sender buffer has not been flushed since we started
+
+        if(rrdset_flag_check(st, RRDSET_FLAG_SENDER_REPLICATION_IN_PROGRESS)) {
+            rrdset_flag_clear(st, RRDSET_FLAG_SENDER_REPLICATION_IN_PROGRESS);
+            rrdset_flag_set(st, RRDSET_FLAG_SENDER_REPLICATION_FINISHED);
+            rrdhost_sender_replicating_charts_minus_one(st->rrdhost);
+
+#ifdef NETDATA_LOG_REPLICATION_REQUESTS
+            internal_error(true, "STREAM_SENDER REPLAY: 'host:%s/chart:%s' streaming starts",
+                           rrdhost_hostname(st->rrdhost), rrdset_id(st));
+#endif
+        }
+        else
+            internal_error(true, "REPLAY ERROR: 'host:%s/chart:%s' received start streaming command, but the chart is not in progress replicating",
+                           rrdhost_hostname(st->rrdhost), string2str(rq->chart_id));
+    }
+
+    __atomic_add_fetch(&replication_globals.atomic.executed, 1, __ATOMIC_RELAXED);
+
+    ret = true;
+
+cleanup:
+    string_freez(rq->chart_id);
+    return ret;
+}
+
+// ----------------------------------------------------------------------------
+// public API
+
+void replication_add_request(struct sender_state *sender, const char *chart_id, time_t after, time_t before, bool start_streaming) {
+    struct replication_request rq = {
+            .sender = sender,
+            .chart_id = string_strdupz(chart_id),
+            .after = after,
+            .before = before,
+            .start_streaming = start_streaming,
+            .sender_last_flush_ut = rrdpush_sender_get_flush_time(sender),
+    };
+
+    if(start_streaming && rrdpush_sender_get_buffer_used_percent(sender) <= STREAMING_START_MAX_SENDER_BUFFER_PERCENTAGE_ALLOWED)
+        replication_execute_request(&rq, false);
+
+    else
+        dictionary_set(sender->replication.requests, chart_id, &rq, sizeof(struct replication_request));
+}
+
+void replication_sender_delete_pending_requests(struct sender_state *sender) {
+    // allow the dictionary destructor to go faster on locks
+    replication_recursive_lock();
+    dictionary_flush(sender->replication.requests);
+    replication_recursive_unlock();
+}
+
+void replication_init_sender(struct sender_state *sender) {
+    sender->replication.requests = dictionary_create(DICT_OPTION_DONT_OVERWRITE_VALUE);
+    dictionary_register_react_callback(sender->replication.requests, replication_request_react_callback, sender);
+    dictionary_register_conflict_callback(sender->replication.requests, replication_request_conflict_callback, sender);
+    dictionary_register_delete_callback(sender->replication.requests, replication_request_delete_callback, sender);
+}
+
+void replication_cleanup_sender(struct sender_state *sender) {
+    // allow the dictionary destructor to go faster on locks
+    replication_recursive_lock();
+    dictionary_destroy(sender->replication.requests);
+    replication_recursive_unlock();
+}
+
+void replication_recalculate_buffer_used_ratio_unsafe(struct sender_state *s) {
+    size_t available = cbuffer_available_size_unsafe(s->host->sender->buffer);
+    size_t percentage = (s->buffer->max_size - available) * 100 / s->buffer->max_size;
+
+    if(percentage > MAX_SENDER_BUFFER_PERCENTAGE_ALLOWED)
+        s->replication.unsafe.reached_max = true;
+
+    if(s->replication.unsafe.reached_max &&
+        percentage <= MIN_SENDER_BUFFER_PERCENTAGE_ALLOWED) {
+        s->replication.unsafe.reached_max = false;
+        replication_recursive_lock();
+//        replication_set_next_point_in_time(0, 0);
+        replication_globals.unsafe.sender_resets++;
+        replication_recursive_unlock();
+    }
+
+    rrdpush_sender_set_buffer_used_percent(s, percentage);
+}
+
+// ----------------------------------------------------------------------------
+// replication thread
+
+static size_t verify_host_charts_are_streaming_now(RRDHOST *host) {
+    internal_error(
+            host->sender &&
+            !rrdpush_sender_pending_replication_requests(host->sender) &&
+            dictionary_entries(host->sender->replication.requests) != 0,
+            "REPLICATION SUMMARY: 'host:%s' reports %zu pending replication requests, but its chart replication index says there are %zu charts pending replication",
+            rrdhost_hostname(host),
+            rrdpush_sender_pending_replication_requests(host->sender),
+            dictionary_entries(host->sender->replication.requests)
+            );
+
+    size_t ok = 0;
+    size_t errors = 0;
+
+    RRDSET *st;
+    rrdset_foreach_read(st, host) {
+        RRDSET_FLAGS flags = rrdset_flag_check(st, RRDSET_FLAG_SENDER_REPLICATION_IN_PROGRESS | RRDSET_FLAG_SENDER_REPLICATION_FINISHED);
+
+        bool is_error = false;
+
+        if(!flags) {
+            internal_error(
+                    true,
+                    "REPLICATION SUMMARY: 'host:%s/chart:%s' is neither IN PROGRESS nor FINISHED",
+                    rrdhost_hostname(host), rrdset_id(st)
+            );
+            is_error = true;
+        }
+
+        if(!(flags & RRDSET_FLAG_SENDER_REPLICATION_FINISHED) || (flags & RRDSET_FLAG_SENDER_REPLICATION_IN_PROGRESS)) {
+            internal_error(
+                    true,
+                    "REPLICATION SUMMARY: 'host:%s/chart:%s' is IN PROGRESS although replication is finished",
+                    rrdhost_hostname(host), rrdset_id(st)
+            );
+            is_error = true;
+        }
+
+        if(is_error)
+            errors++;
+        else
+            ok++;
+    }
+    rrdset_foreach_done(st);
+
+    internal_error(errors,
+                   "REPLICATION SUMMARY: 'host:%s' finished replicating %zu charts, but %zu charts are still in progress although replication finished",
+                   rrdhost_hostname(host), ok, errors);
+
+    return errors;
+}
+
+static void verify_all_hosts_charts_are_streaming_now(void) {
+    worker_is_busy(WORKER_JOB_CHECK_CONSISTENCY);
+
+    size_t errors = 0;
+    RRDHOST *host;
+    dfe_start_read(rrdhost_root_index, host)
+        errors += verify_host_charts_are_streaming_now(host);
+    dfe_done(host);
+
+    size_t executed = __atomic_load_n(&replication_globals.atomic.executed, __ATOMIC_RELAXED);
+    info("REPLICATION SUMMARY: finished, executed %zu replication requests, %zu charts pending replication",
+         executed - replication_globals.main_thread.last_executed, errors);
+    replication_globals.main_thread.last_executed = executed;
+}
+
+static void replication_initialize_workers(bool master) {
+    worker_register("REPLICATION");
+    worker_register_job_name(WORKER_JOB_FIND_NEXT, "find next");
+    worker_register_job_name(WORKER_JOB_QUERYING, "querying");
+    worker_register_job_name(WORKER_JOB_DELETE_ENTRY, "dict delete");
+    worker_register_job_name(WORKER_JOB_FIND_CHART, "find chart");
+    worker_register_job_name(WORKER_JOB_CHECK_CONSISTENCY, "check consistency");
+    worker_register_job_name(WORKER_JOB_BUFFER_COMMIT, "commit");
+    worker_register_job_name(WORKER_JOB_CLEANUP, "cleanup");
+
+    if(master) {
+        worker_register_job_name(WORKER_JOB_STATISTICS, "statistics");
+        worker_register_job_custom_metric(WORKER_JOB_CUSTOM_METRIC_PENDING_REQUESTS, "pending requests", "requests", WORKER_METRIC_ABSOLUTE);
+        worker_register_job_custom_metric(WORKER_JOB_CUSTOM_METRIC_COMPLETION, "completion", "%", WORKER_METRIC_ABSOLUTE);
+        worker_register_job_custom_metric(WORKER_JOB_CUSTOM_METRIC_ADDED, "added requests", "requests/s", WORKER_METRIC_INCREMENTAL_TOTAL);
+        worker_register_job_custom_metric(WORKER_JOB_CUSTOM_METRIC_DONE, "finished requests", "requests/s", WORKER_METRIC_INCREMENTAL_TOTAL);
+        worker_register_job_custom_metric(WORKER_JOB_CUSTOM_METRIC_SKIPPED_NOT_CONNECTED, "not connected requests", "requests/s", WORKER_METRIC_INCREMENTAL_TOTAL);
+        worker_register_job_custom_metric(WORKER_JOB_CUSTOM_METRIC_SKIPPED_NO_ROOM, "no room requests", "requests/s", WORKER_METRIC_INCREMENTAL_TOTAL);
+        worker_register_job_custom_metric(WORKER_JOB_CUSTOM_METRIC_SENDER_RESETS, "sender resets", "resets/s", WORKER_METRIC_INCREMENTAL_TOTAL);
+        worker_register_job_custom_metric(WORKER_JOB_CUSTOM_METRIC_WAITS, "waits", "waits/s", WORKER_METRIC_INCREMENTAL_TOTAL);
+    }
+}
+
+#define REQUEST_OK (0)
+#define REQUEST_QUEUE_EMPTY (-1)
+#define REQUEST_CHART_NOT_FOUND (-2)
+
+static int replication_execute_next_pending_request(void) {
+    worker_is_busy(WORKER_JOB_FIND_NEXT);
+    struct replication_request rq = replication_request_get_first_available();
+
+    if(unlikely(!rq.found))
+        return REQUEST_QUEUE_EMPTY;
+
+    // delete the request from the dictionary
+    worker_is_busy(WORKER_JOB_DELETE_ENTRY);
+    if(!dictionary_del(rq.sender->replication.requests, string2str(rq.chart_id)))
+        error("REPLAY ERROR: 'host:%s/chart:%s' failed to be deleted from sender pending charts index",
+              rrdhost_hostname(rq.sender->host), string2str(rq.chart_id));
+
+    replication_set_latest_first_time(rq.after);
+
+    if(unlikely(!replication_execute_request(&rq, true)))
+        return REQUEST_CHART_NOT_FOUND;
+
+    return REQUEST_OK;
+}
+
+static void replication_worker_cleanup(void *ptr __maybe_unused) {
+    worker_unregister();
+}
+
+static void *replication_worker_thread(void *ptr) {
+    replication_initialize_workers(false);
+
+    netdata_thread_cleanup_push(replication_worker_cleanup, ptr);
+
+    while(!netdata_exit) {
+        if(unlikely(replication_execute_next_pending_request() == REQUEST_QUEUE_EMPTY)) {
+            worker_is_idle();
+            sleep_usec(1 * USEC_PER_SEC);
+        }
+    }
+
+    netdata_thread_cleanup_pop(1);
+    return NULL;
+}
+
+static void replication_main_cleanup(void *ptr) {
+    struct netdata_static_thread *static_thread = (struct netdata_static_thread *)ptr;
+    static_thread->enabled = NETDATA_MAIN_THREAD_EXITING;
+
+    int threads = (int)replication_globals.main_thread.threads;
+    for(int i = 0; i < threads ;i++) {
+        netdata_thread_join(*replication_globals.main_thread.threads_ptrs[i], NULL);
+        freez(replication_globals.main_thread.threads_ptrs[i]);
+    }
+    freez(replication_globals.main_thread.threads_ptrs);
+    replication_globals.main_thread.threads_ptrs = NULL;
+
+    // custom code
+    worker_unregister();
+
+    static_thread->enabled = NETDATA_MAIN_THREAD_EXITED;
+}
+
+void *replication_thread_main(void *ptr __maybe_unused) {
+    replication_initialize_workers(true);
+
+    int threads = config_get_number(CONFIG_SECTION_DB, "replication threads", 1);
+    if(threads < 1 || threads > MAX_REPLICATION_THREADS) {
+        error("replication threads given %d is invalid, resetting to 1", threads);
+        threads = 1;
+    }
+
+    if(--threads) {
+        replication_globals.main_thread.threads = threads;
+        replication_globals.main_thread.threads_ptrs = mallocz(threads * sizeof(netdata_thread_t *));
+
+        for(int i = 0; i < threads ;i++) {
+            replication_globals.main_thread.threads_ptrs[i] = mallocz(sizeof(netdata_thread_t));
+            netdata_thread_create(replication_globals.main_thread.threads_ptrs[i], "REPLICATION",
+                                  NETDATA_THREAD_OPTION_JOINABLE, replication_worker_thread, NULL);
+        }
+    }
+
+    netdata_thread_cleanup_push(replication_main_cleanup, ptr);
+
+    // start from 100% completed
+    worker_set_metric(WORKER_JOB_CUSTOM_METRIC_COMPLETION, 100.0);
+
+    long run_verification_countdown = LONG_MAX; // LONG_MAX to prevent an initial verification when no replication ever took place
+    bool slow = true; // control the time we sleep - it has to start with true!
+    usec_t last_now_mono_ut = now_monotonic_usec();
+    time_t replication_reset_next_point_in_time_countdown = SECONDS_TO_RESET_POINT_IN_TIME; // restart from the beginning every 10 seconds
+
+    size_t last_executed = 0;
+    size_t last_sender_resets = 0;
+
+    while(!netdata_exit) {
+
+        // statistics
+        usec_t now_mono_ut = now_monotonic_usec();
+        if(unlikely(now_mono_ut - last_now_mono_ut > default_rrd_update_every * USEC_PER_SEC)) {
+            last_now_mono_ut = now_mono_ut;
+
+            replication_recursive_lock();
+
+            size_t current_executed = __atomic_load_n(&replication_globals.atomic.executed, __ATOMIC_RELAXED);
+            if(last_executed != current_executed) {
+                run_verification_countdown = ITERATIONS_IDLE_WITHOUT_PENDING_TO_RUN_SENDER_VERIFICATION;
+                last_executed = current_executed;
+                slow = false;
+            }
+
+            if(replication_reset_next_point_in_time_countdown-- == 0) {
+                // once per second, make it scan all the pending requests next time
+                replication_set_next_point_in_time(0, 0);
+//                replication_globals.protected.skipped_no_room_since_last_reset = 0;
+                replication_reset_next_point_in_time_countdown = SECONDS_TO_RESET_POINT_IN_TIME;
+            }
+
+            if(!replication_globals.unsafe.pending && --run_verification_countdown == 0) {
+                // reset the statistics about completion percentage
+                replication_globals.unsafe.first_time_t = 0;
+                replication_set_latest_first_time(0);
+
+                verify_all_hosts_charts_are_streaming_now();
+
+                run_verification_countdown = LONG_MAX;
+                slow = true;
+            }
+
+            worker_is_busy(WORKER_JOB_STATISTICS);
+
+            time_t latest_first_time_t = replication_get_latest_first_time();
+            if(latest_first_time_t && replication_globals.unsafe.pending) {
+                // completion percentage statistics
+                time_t now = now_realtime_sec();
+                time_t total = now - replication_globals.unsafe.first_time_t;
+                time_t done = latest_first_time_t - replication_globals.unsafe.first_time_t;
+                worker_set_metric(WORKER_JOB_CUSTOM_METRIC_COMPLETION,
+                                  (NETDATA_DOUBLE) done * 100.0 / (NETDATA_DOUBLE) total);
+            }
+            else
+                worker_set_metric(WORKER_JOB_CUSTOM_METRIC_COMPLETION, 100.0);
+
+            worker_set_metric(WORKER_JOB_CUSTOM_METRIC_PENDING_REQUESTS, (NETDATA_DOUBLE)replication_globals.unsafe.pending);
+            worker_set_metric(WORKER_JOB_CUSTOM_METRIC_ADDED, (NETDATA_DOUBLE)replication_globals.unsafe.added);
+            worker_set_metric(WORKER_JOB_CUSTOM_METRIC_DONE, (NETDATA_DOUBLE)__atomic_load_n(&replication_globals.atomic.executed, __ATOMIC_RELAXED));
+            worker_set_metric(WORKER_JOB_CUSTOM_METRIC_SKIPPED_NOT_CONNECTED, (NETDATA_DOUBLE)replication_globals.unsafe.skipped_not_connected);
+            worker_set_metric(WORKER_JOB_CUSTOM_METRIC_SKIPPED_NO_ROOM, (NETDATA_DOUBLE)replication_globals.unsafe.skipped_no_room);
+            worker_set_metric(WORKER_JOB_CUSTOM_METRIC_SENDER_RESETS, (NETDATA_DOUBLE)replication_globals.unsafe.sender_resets);
+            worker_set_metric(WORKER_JOB_CUSTOM_METRIC_WAITS, (NETDATA_DOUBLE)replication_globals.main_thread.waits);
+
+            replication_recursive_unlock();
+        }
+
+        if(unlikely(replication_execute_next_pending_request() == REQUEST_QUEUE_EMPTY)) {
+            replication_recursive_lock();
+
+            // the timeout also defines now frequently we will traverse all the pending requests
+            // when the outbound buffers of all senders is full
+            usec_t timeout;
+            if(slow)
+                // no work to be done, wait for a request to come in
+                timeout = 1000 * USEC_PER_MS;
+
+            else if(replication_globals.unsafe.pending > 0) {
+                if(replication_globals.unsafe.sender_resets == last_sender_resets) {
+                    timeout = 1000 * USEC_PER_MS;
+                }
+                else {
+                    // there are pending requests waiting to be executed,
+                    // but none could be executed at this time.
+                    // try again after this time.
+                    timeout = 100 * USEC_PER_MS;
+                }
+
+                last_sender_resets = replication_globals.unsafe.sender_resets;
+            }
+            else {
+                // no requests pending, but there were requests recently (run_verification_countdown)
+                // so, try in a short time.
+                // if this is big, one chart replicating will be slow to finish (ping - pong just one chart)
+                timeout = 10 * USEC_PER_MS;
+                last_sender_resets = replication_globals.unsafe.sender_resets;
+            }
+
+            replication_globals.main_thread.waits++;
+            replication_recursive_unlock();
+
+            worker_is_idle();
+            sleep_usec(timeout);
+
+            // make it scan all the pending requests next time
+            replication_set_next_point_in_time(0, 0);
+            replication_reset_next_point_in_time_countdown = SECONDS_TO_RESET_POINT_IN_TIME;
+
+            continue;
+        }
+    }
+
+    netdata_thread_cleanup_pop(1);
+    return NULL;
+}