Merging upstream version 1.45.3+dfsg.

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

1 files changed, 2035 insertions, 0 deletions

diff --git a/src/streaming/replication.c b/src/streaming/replication.c
new file mode 100644
index 000000000..6f68fedae
--- /dev/null
+++ b/src/streaming/replication.c
@@ -0,0 +1,2035 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "replication.h"
+#include "Judy.h"
+
+#define STREAMING_START_MAX_SENDER_BUFFER_PERCENTAGE_ALLOWED 50ULL
+#define MAX_REPLICATION_MESSAGE_PERCENT_SENDER_BUFFER 25ULL
+#define MAX_SENDER_BUFFER_PERCENTAGE_ALLOWED 50ULL
+#define MIN_SENDER_BUFFER_PERCENTAGE_ALLOWED 10ULL
+
+#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_PREPARE_QUERY                        5
+#define WORKER_JOB_CHECK_CONSISTENCY                    6
+#define WORKER_JOB_BUFFER_COMMIT                        7
+#define WORKER_JOB_CLEANUP                              8
+#define WORKER_JOB_WAIT                                 9
+
+// master thread worker jobs
+#define WORKER_JOB_STATISTICS                           10
+#define WORKER_JOB_CUSTOM_METRIC_PENDING_REQUESTS       11
+#define WORKER_JOB_CUSTOM_METRIC_SKIPPED_NO_ROOM        12
+#define WORKER_JOB_CUSTOM_METRIC_COMPLETION             13
+#define WORKER_JOB_CUSTOM_METRIC_ADDED                  14
+#define WORKER_JOB_CUSTOM_METRIC_DONE                   15
+#define WORKER_JOB_CUSTOM_METRIC_SENDER_RESETS          16
+#define WORKER_JOB_CUSTOM_METRIC_SENDER_FULL            17
+
+#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) {
+    spinlock_lock(&replication_queries.spinlock);
+    struct replication_query_statistics ret = replication_queries;
+    spinlock_unlock(&replication_queries.spinlock);
+    return ret;
+}
+
+size_t replication_buffers_allocated = 0;
+
+size_t replication_allocated_buffers(void) {
+    return __atomic_load_n(&replication_buffers_allocated, __ATOMIC_RELAXED);
+}
+
+// ----------------------------------------------------------------------------
+// sending replication replies
+
+struct replication_dimension {
+    STORAGE_POINT sp;
+    struct storage_engine_query_handle handle;
+    bool enabled;
+    bool skip;
+
+    DICTIONARY *dict;
+    const DICTIONARY_ITEM *rda;
+    RRDDIM *rd;
+};
+
+struct replication_query {
+    RRDSET *st;
+
+    struct {
+        time_t first_entry_t;
+        time_t last_entry_t;
+    } db;
+
+    struct {                         // what the parent requested
+        time_t after;
+        time_t before;
+        bool enable_streaming;
+    } request;
+
+    struct {                         // what the child will do
+        time_t after;
+        time_t before;
+        bool enable_streaming;
+
+        bool locked_data_collection;
+        bool execute;
+        bool interrupted;
+        STREAM_CAPABILITIES capabilities;
+    } query;
+
+    time_t wall_clock_time;
+
+    size_t points_read;
+    size_t points_generated;
+
+    STORAGE_ENGINE_BACKEND backend;
+    struct replication_request *rq;
+
+    size_t dimensions;
+    struct replication_dimension data[];
+};
+
+static struct replication_query *replication_query_prepare(
+        RRDSET *st,
+        time_t db_first_entry,
+        time_t db_last_entry,
+        time_t requested_after,
+        time_t requested_before,
+        bool requested_enable_streaming,
+        time_t query_after,
+        time_t query_before,
+        bool query_enable_streaming,
+        time_t wall_clock_time,
+        STREAM_CAPABILITIES capabilities
+) {
+    size_t dimensions = rrdset_number_of_dimensions(st);
+    struct replication_query *q = callocz(1, sizeof(struct replication_query) + dimensions * sizeof(struct replication_dimension));
+    __atomic_add_fetch(&replication_buffers_allocated, sizeof(struct replication_query) + dimensions * sizeof(struct replication_dimension), __ATOMIC_RELAXED);
+
+    q->dimensions = dimensions;
+    q->st = st;
+
+    q->db.first_entry_t = db_first_entry;
+    q->db.last_entry_t = db_last_entry;
+
+    q->request.after = requested_after,
+    q->request.before = requested_before,
+    q->request.enable_streaming = requested_enable_streaming,
+
+    q->query.after = query_after;
+    q->query.before = query_before;
+    q->query.enable_streaming = query_enable_streaming;
+    q->query.capabilities = capabilities;
+
+    q->wall_clock_time = wall_clock_time;
+
+    if (!q->dimensions || !q->query.after || !q->query.before) {
+        q->query.execute = false;
+        q->dimensions = 0;
+        return q;
+    }
+
+    if(q->query.enable_streaming) {
+        spinlock_lock(&st->data_collection_lock);
+        q->query.locked_data_collection = true;
+
+        if (st->last_updated.tv_sec > q->query.before) {
+#ifdef NETDATA_LOG_REPLICATION_REQUESTS
+            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) q->query.before,
+                           (unsigned long long) st->last_updated.tv_sec
+            );
+#endif
+            q->query.before = MIN(st->last_updated.tv_sec, wall_clock_time);
+        }
+    }
+
+    q->backend = st->rrdhost->db[0].eng->seb;
+
+    // prepare our array of dimensions
+    size_t count = 0;
+    RRDDIM *rd;
+    rrddim_foreach_read(rd, st) {
+        if (unlikely(!rd || !rd_dfe.item || !rrddim_check_upstream_exposed(rd)))
+            continue;
+
+        if (unlikely(rd_dfe.counter >= q->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 = &q->data[rd_dfe.counter];
+
+        d->dict = rd_dfe.dict;
+        d->rda = dictionary_acquired_item_dup(rd_dfe.dict, rd_dfe.item);
+        d->rd = rd;
+
+        storage_engine_query_init(q->backend, rd->tiers[0].smh, &d->handle, q->query.after, q->query.before,
+                     q->query.locked_data_collection ? STORAGE_PRIORITY_HIGH : STORAGE_PRIORITY_LOW);
+        d->enabled = true;
+        d->skip = false;
+        count++;
+    }
+    rrddim_foreach_done(rd);
+
+    if(!count) {
+        // no data for this chart
+
+        q->query.execute = false;
+
+        if(q->query.locked_data_collection) {
+            spinlock_unlock(&st->data_collection_lock);
+            q->query.locked_data_collection = false;
+        }
+
+    }
+    else {
+        // we have data for this chart
+
+        q->query.execute = true;
+    }
+
+    return q;
+}
+
+static void replication_send_chart_collection_state(BUFFER *wb, RRDSET *st, STREAM_CAPABILITIES capabilities) {
+    bool with_slots = (capabilities & STREAM_CAP_SLOTS) ? true : false;
+    NUMBER_ENCODING integer_encoding = (capabilities & STREAM_CAP_IEEE754) ? NUMBER_ENCODING_BASE64 : NUMBER_ENCODING_DECIMAL;
+    RRDDIM *rd;
+    rrddim_foreach_read(rd, st){
+        if (!rrddim_check_upstream_exposed(rd)) continue;
+
+        buffer_fast_strcat(wb, PLUGINSD_KEYWORD_REPLAY_RRDDIM_STATE, sizeof(PLUGINSD_KEYWORD_REPLAY_RRDDIM_STATE) - 1);
+
+        if(with_slots) {
+            buffer_fast_strcat(wb, " "PLUGINSD_KEYWORD_SLOT":", sizeof(PLUGINSD_KEYWORD_SLOT) - 1 + 2);
+            buffer_print_uint64_encoded(wb, integer_encoding, rd->rrdpush.sender.dim_slot);
+        }
+
+        buffer_fast_strcat(wb, " '", 2);
+        buffer_fast_strcat(wb, rrddim_id(rd), string_strlen(rd->id));
+        buffer_fast_strcat(wb, "' ", 2);
+        buffer_print_uint64_encoded(wb, integer_encoding, (usec_t) rd->collector.last_collected_time.tv_sec * USEC_PER_SEC +
+                                                          (usec_t) rd->collector.last_collected_time.tv_usec);
+        buffer_fast_strcat(wb, " ", 1);
+        buffer_print_int64_encoded(wb, integer_encoding, rd->collector.last_collected_value);
+        buffer_fast_strcat(wb, " ", 1);
+        buffer_print_netdata_double_encoded(wb, integer_encoding, rd->collector.last_calculated_value);
+        buffer_fast_strcat(wb, " ", 1);
+        buffer_print_netdata_double_encoded(wb, integer_encoding, rd->collector.last_stored_value);
+        buffer_fast_strcat(wb, "\n", 1);
+    }
+    rrddim_foreach_done(rd);
+
+    buffer_fast_strcat(wb, PLUGINSD_KEYWORD_REPLAY_RRDSET_STATE " ", sizeof(PLUGINSD_KEYWORD_REPLAY_RRDSET_STATE) - 1 + 1);
+    buffer_print_uint64_encoded(wb, integer_encoding, (usec_t) st->last_collected_time.tv_sec * USEC_PER_SEC + (usec_t) st->last_collected_time.tv_usec);
+    buffer_fast_strcat(wb, " ", 1);
+    buffer_print_uint64_encoded(wb, integer_encoding, (usec_t) st->last_updated.tv_sec * USEC_PER_SEC + (usec_t) st->last_updated.tv_usec);
+    buffer_fast_strcat(wb, "\n", 1);
+}
+
+static void replication_query_finalize(BUFFER *wb, struct replication_query *q, bool executed) {
+    size_t dimensions = q->dimensions;
+
+    if(wb && q->query.enable_streaming)
+        replication_send_chart_collection_state(wb, q->st, q->query.capabilities);
+
+    if(q->query.locked_data_collection) {
+        spinlock_unlock(&q->st->data_collection_lock);
+        q->query.locked_data_collection = false;
+    }
+
+    // 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 = &q->data[i];
+        if (unlikely(!d->enabled)) continue;
+
+        storage_engine_query_finalize(&d->handle);
+
+        dictionary_acquired_item_release(d->dict, d->rda);
+
+        // update global statistics
+        queries++;
+    }
+
+    if(executed) {
+        spinlock_lock(&replication_queries.spinlock);
+        replication_queries.queries_started += queries;
+        replication_queries.queries_finished += queries;
+        replication_queries.points_read += q->points_read;
+        replication_queries.points_generated += q->points_generated;
+
+        if(q->st && q->st->rrdhost->sender) {
+            struct sender_state *s = q->st->rrdhost->sender;
+            s->replication.latest_completed_before_t = q->query.before;
+        }
+
+        spinlock_unlock(&replication_queries.spinlock);
+    }
+
+    __atomic_sub_fetch(&replication_buffers_allocated, sizeof(struct replication_query) + dimensions * sizeof(struct replication_dimension), __ATOMIC_RELAXED);
+    freez(q);
+}
+
+static void replication_query_align_to_optimal_before(struct replication_query *q) {
+    if(!q->query.execute || q->query.enable_streaming)
+        return;
+
+    size_t dimensions = q->dimensions;
+    time_t expanded_before = 0;
+
+    for (size_t i = 0; i < dimensions; i++) {
+        struct replication_dimension *d = &q->data[i];
+        if(unlikely(!d->enabled)) continue;
+
+        time_t new_before = storage_engine_align_to_optimal_before(&d->handle);
+        if (!expanded_before || new_before < expanded_before)
+            expanded_before = new_before;
+    }
+
+    if(expanded_before > q->query.before                                 && // it is later than the original
+        (expanded_before - q->query.before) / q->st->update_every < 1024 && // it is reasonable (up to a page)
+        expanded_before < q->st->last_updated.tv_sec                     && // it is not the chart's last updated time
+        expanded_before < q->wall_clock_time)                               // it is not later than the wall clock time
+        q->query.before = expanded_before;
+}
+
+static bool replication_query_execute(BUFFER *wb, struct replication_query *q, size_t max_msg_size) {
+    replication_query_align_to_optimal_before(q);
+
+    bool with_slots = (q->query.capabilities & STREAM_CAP_SLOTS) ? true : false;
+    NUMBER_ENCODING integer_encoding = (q->query.capabilities & STREAM_CAP_IEEE754) ? NUMBER_ENCODING_BASE64 : NUMBER_ENCODING_DECIMAL;
+    time_t after = q->query.after;
+    time_t before = q->query.before;
+    size_t dimensions = q->dimensions;
+    time_t wall_clock_time = q->wall_clock_time;
+
+    bool finished_with_gap = false;
+    size_t points_read = 0, points_generated = 0;
+
+#ifdef NETDATA_LOG_REPLICATION_REQUESTS
+    time_t actual_after = 0, actual_before = 0;
+#endif
+
+    time_t now = after + 1;
+    time_t last_end_time_in_buffer = 0;
+    while(now <= before) {
+        time_t min_start_time = 0, max_start_time = 0, min_end_time = 0, max_end_time = 0, min_update_every = 0, max_update_every = 0;
+        for (size_t i = 0; i < dimensions ;i++) {
+            struct replication_dimension *d = &q->data[i];
+            if(unlikely(!d->enabled || d->skip)) continue;
+
+            // fetch the first valid point for the dimension
+            int max_skip = 1000;
+            while(d->sp.end_time_s < now && !storage_engine_query_is_finished(&d->handle) && max_skip-- >= 0) {
+                d->sp = storage_engine_query_next_metric(&d->handle);
+                points_read++;
+            }
+
+            if(max_skip <= 0) {
+                d->skip = true;
+
+                nd_log_limit_static_global_var(erl, 1, 0);
+                nd_log_limit(&erl, NDLS_DAEMON, NDLP_ERR,
+                            "STREAM_SENDER REPLAY ERROR: 'host:%s/chart:%s/dim:%s': db does not advance the query "
+                            "beyond time %llu (tried 1000 times to get the next point and always got back a point in the past)",
+                            rrdhost_hostname(q->st->rrdhost), rrdset_id(q->st), rrddim_id(d->rd),
+                            (unsigned long long) now);
+
+                continue;
+            }
+
+            if(unlikely(d->sp.end_time_s < now || d->sp.end_time_s < d->sp.start_time_s))
+                // this dimension does not provide any data
+                continue;
+
+            time_t update_every = d->sp.end_time_s - d->sp.start_time_s;
+            if(unlikely(!update_every))
+                update_every = q->st->update_every;
+
+            if(unlikely(!min_update_every))
+                min_update_every = update_every;
+
+            if(unlikely(!min_start_time))
+                min_start_time = d->sp.start_time_s;
+
+            if(unlikely(!min_end_time))
+                min_end_time = d->sp.end_time_s;
+
+            min_update_every = MIN(min_update_every, update_every);
+            max_update_every = MAX(max_update_every, update_every);
+
+            min_start_time = MIN(min_start_time, d->sp.start_time_s);
+            max_start_time = MAX(max_start_time, d->sp.start_time_s);
+
+            min_end_time = MIN(min_end_time, d->sp.end_time_s);
+            max_end_time = MAX(max_end_time, d->sp.end_time_s);
+        }
+
+        if (unlikely(min_update_every != max_update_every ||
+                     min_start_time != max_start_time)) {
+
+            time_t fix_min_start_time;
+            if(last_end_time_in_buffer &&
+                last_end_time_in_buffer >= min_start_time &&
+                last_end_time_in_buffer <= max_start_time) {
+                fix_min_start_time = last_end_time_in_buffer;
+            }
+            else
+                fix_min_start_time = min_end_time - min_update_every;
+
+#ifdef NETDATA_INTERNAL_CHECKS
+            nd_log_limit_static_global_var(erl, 1, 0);
+            nd_log_limit(&erl,  NDLS_DAEMON, NDLP_WARNING,
+                         "REPLAY WARNING: 'host:%s/chart:%s' "
+                         "misaligned dimensions, "
+                         "update every (min: %ld, max: %ld), "
+                         "start time (min: %ld, max: %ld), "
+                         "end time (min %ld, max %ld), "
+                         "now %ld, last end time sent %ld, "
+                         "min start time is fixed to %ld",
+                        rrdhost_hostname(q->st->rrdhost), rrdset_id(q->st),
+                        min_update_every, max_update_every,
+                        min_start_time, max_start_time,
+                        min_end_time, max_end_time,
+                        now, last_end_time_in_buffer,
+                        fix_min_start_time
+                        );
+#endif
+
+            min_start_time = fix_min_start_time;
+        }
+
+        if(likely(min_start_time <= now && min_end_time >= now)) {
+            // we have a valid point
+
+            if (unlikely(min_end_time == min_start_time))
+                min_start_time = min_end_time - q->st->update_every;
+
+#ifdef NETDATA_LOG_REPLICATION_REQUESTS
+            if (unlikely(!actual_after))
+                actual_after = min_end_time;
+
+            actual_before = min_end_time;
+#endif
+
+            if(buffer_strlen(wb) > max_msg_size && last_end_time_in_buffer) {
+                q->query.before = last_end_time_in_buffer;
+                q->query.enable_streaming = false;
+
+                internal_error(true, "REPLICATION: current buffer size %zu is more than the "
+                                     "max message size %zu for chart '%s' of host '%s'. "
+                                     "Interrupting replication request (%ld to %ld, %s) at %ld to %ld, %s.",
+                               buffer_strlen(wb), max_msg_size, rrdset_id(q->st), rrdhost_hostname(q->st->rrdhost),
+                               q->request.after, q->request.before, q->request.enable_streaming?"true":"false",
+                               q->query.after, q->query.before, q->query.enable_streaming?"true":"false");
+
+                q->query.interrupted = true;
+
+                break;
+            }
+            last_end_time_in_buffer = min_end_time;
+
+            buffer_fast_strcat(wb, PLUGINSD_KEYWORD_REPLAY_BEGIN, sizeof(PLUGINSD_KEYWORD_REPLAY_BEGIN) - 1);
+
+            if(with_slots) {
+                buffer_fast_strcat(wb, " "PLUGINSD_KEYWORD_SLOT":", sizeof(PLUGINSD_KEYWORD_SLOT) - 1 + 2);
+                buffer_print_uint64_encoded(wb, integer_encoding, q->st->rrdpush.sender.chart_slot);
+            }
+
+            buffer_fast_strcat(wb, " '' ", 4);
+            buffer_print_uint64_encoded(wb, integer_encoding, min_start_time);
+            buffer_fast_strcat(wb, " ", 1);
+            buffer_print_uint64_encoded(wb, integer_encoding, min_end_time);
+            buffer_fast_strcat(wb, " ", 1);
+            buffer_print_uint64_encoded(wb, integer_encoding, wall_clock_time);
+            buffer_fast_strcat(wb, "\n", 1);
+
+            // output the replay values for this time
+            for (size_t i = 0; i < dimensions; i++) {
+                struct replication_dimension *d = &q->data[i];
+                if (unlikely(!d->enabled)) continue;
+
+                if (likely( d->sp.start_time_s <= min_end_time &&
+                            d->sp.end_time_s >= min_end_time &&
+                            !storage_point_is_unset(d->sp) &&
+                            !storage_point_is_gap(d->sp))) {
+
+                    buffer_fast_strcat(wb, PLUGINSD_KEYWORD_REPLAY_SET, sizeof(PLUGINSD_KEYWORD_REPLAY_SET) - 1);
+
+                    if(with_slots) {
+                        buffer_fast_strcat(wb, " "PLUGINSD_KEYWORD_SLOT":", sizeof(PLUGINSD_KEYWORD_SLOT) - 1 + 2);
+                        buffer_print_uint64_encoded(wb, integer_encoding, d->rd->rrdpush.sender.dim_slot);
+                    }
+
+                    buffer_fast_strcat(wb, " \"", 2);
+                    buffer_fast_strcat(wb, rrddim_id(d->rd), string_strlen(d->rd->id));
+                    buffer_fast_strcat(wb, "\" ", 2);
+                    buffer_print_netdata_double_encoded(wb, integer_encoding, d->sp.sum);
+                    buffer_fast_strcat(wb, " ", 1);
+                    buffer_print_sn_flags(wb, d->sp.flags, q->query.capabilities & STREAM_CAP_INTERPOLATED);
+                    buffer_fast_strcat(wb, "\n", 1);
+
+                    points_generated++;
+                }
+            }
+
+            now = min_end_time + 1;
+        }
+        else if(unlikely(min_end_time < now))
+            // the query does not progress
+            break;
+        else {
+            // we have gap - all points are in the future
+            now = min_start_time;
+
+            if(min_start_time > before && !points_generated) {
+                before = q->query.before = min_start_time - 1;
+                finished_with_gap = true;
+                break;
+            }
+        }
+    }
+
+#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(q->st->rrdhost), rrdset_id(q->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(q->st->rrdhost), rrdset_id(q->st),
+                       (unsigned long long)after, (unsigned long long)before);
+#endif // NETDATA_LOG_REPLICATION_REQUESTS
+
+    q->points_read += points_read;
+    q->points_generated += points_generated;
+
+    if(last_end_time_in_buffer < before - q->st->update_every)
+        finished_with_gap = true;
+
+    return finished_with_gap;
+}
+
+static struct replication_query *replication_response_prepare(
+        RRDSET *st,
+        bool requested_enable_streaming,
+        time_t requested_after,
+        time_t requested_before,
+        STREAM_CAPABILITIES capabilities
+        ) {
+    time_t wall_clock_time = now_realtime_sec();
+
+    if(requested_after > requested_before) {
+        // flip them
+        time_t t = requested_before;
+        requested_before = requested_after;
+        requested_after = t;
+    }
+
+    if(requested_after > wall_clock_time) {
+        requested_after = 0;
+        requested_before = 0;
+        requested_enable_streaming = true;
+    }
+
+    if(requested_before > wall_clock_time) {
+        requested_before = wall_clock_time;
+        requested_enable_streaming = true;
+    }
+
+    time_t query_after = requested_after;
+    time_t query_before = requested_before;
+    bool query_enable_streaming = requested_enable_streaming;
+
+    time_t db_first_entry = 0, db_last_entry = 0;
+    rrdset_get_retention_of_tier_for_collected_chart(
+            st, &db_first_entry, &db_last_entry, wall_clock_time, 0);
+
+    if(requested_after == 0 && requested_before == 0 && requested_enable_streaming == true) {
+        // no data requested - just enable streaming
+        ;
+    }
+    else {
+        if (query_after < db_first_entry)
+            query_after = db_first_entry;
+
+        if (query_before > db_last_entry)
+            query_before = db_last_entry;
+
+        // if the parent asked us to start streaming, then fill the rest with the data that we have
+        if (requested_enable_streaming)
+            query_before = db_last_entry;
+
+        if (query_after > query_before) {
+            time_t tmp = query_before;
+            query_before = query_after;
+            query_after = tmp;
+        }
+
+        query_enable_streaming = (requested_enable_streaming ||
+                                  query_before == db_last_entry ||
+                                  !requested_after ||
+                                  !requested_before) ? true : false;
+    }
+
+    return replication_query_prepare(
+            st,
+            db_first_entry, db_last_entry,
+            requested_after, requested_before, requested_enable_streaming,
+            query_after, query_before, query_enable_streaming,
+            wall_clock_time, capabilities);
+}
+
+void replication_response_cancel_and_finalize(struct replication_query *q) {
+    replication_query_finalize(NULL, q, false);
+}
+
+static bool sender_is_still_connected_for_this_request(struct replication_request *rq);
+
+bool replication_response_execute_and_finalize(struct replication_query *q, size_t max_msg_size) {
+    bool with_slots = (q->query.capabilities & STREAM_CAP_SLOTS) ? true : false;
+    NUMBER_ENCODING integer_encoding = (q->query.capabilities & STREAM_CAP_IEEE754) ? NUMBER_ENCODING_BASE64 : NUMBER_ENCODING_DECIMAL;
+    struct replication_request *rq = q->rq;
+    RRDSET *st = q->st;
+    RRDHOST *host = st->rrdhost;
+
+    // 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_fast_strcat(wb, PLUGINSD_KEYWORD_REPLAY_BEGIN, sizeof(PLUGINSD_KEYWORD_REPLAY_BEGIN) - 1);
+
+    if(with_slots) {
+        buffer_fast_strcat(wb, " "PLUGINSD_KEYWORD_SLOT":", sizeof(PLUGINSD_KEYWORD_SLOT) - 1 + 2);
+        buffer_print_uint64_encoded(wb, integer_encoding, q->st->rrdpush.sender.chart_slot);
+    }
+
+    buffer_fast_strcat(wb, " '", 2);
+    buffer_fast_strcat(wb, rrdset_id(st), string_strlen(st->id));
+    buffer_fast_strcat(wb, "'\n", 2);
+
+    bool locked_data_collection = q->query.locked_data_collection;
+    q->query.locked_data_collection = false;
+
+    bool finished_with_gap = false;
+    if(q->query.execute)
+        finished_with_gap = replication_query_execute(wb, q, max_msg_size);
+
+    time_t after = q->request.after;
+    time_t before = q->query.before;
+    bool enable_streaming = q->query.enable_streaming;
+
+    replication_query_finalize(wb, q, q->query.execute);
+    q = NULL; // IMPORTANT: q is invalid now
+
+    // get a fresh retention to send to the parent
+    time_t wall_clock_time = now_realtime_sec();
+    time_t db_first_entry, db_last_entry;
+    rrdset_get_retention_of_tier_for_collected_chart(st, &db_first_entry, &db_last_entry, wall_clock_time, 0);
+
+    // end with first/last entries we have, and the first start time and
+    // last end time of the data we sent
+
+    buffer_fast_strcat(wb, PLUGINSD_KEYWORD_REPLAY_END " ", sizeof(PLUGINSD_KEYWORD_REPLAY_END) - 1 + 1);
+    buffer_print_int64_encoded(wb, integer_encoding, st->update_every);
+    buffer_fast_strcat(wb, " ", 1);
+    buffer_print_uint64_encoded(wb, integer_encoding, db_first_entry);
+    buffer_fast_strcat(wb, " ", 1);
+    buffer_print_uint64_encoded(wb, integer_encoding, db_last_entry);
+
+    buffer_fast_strcat(wb, enable_streaming ? " true  " : " false ", 7);
+
+    buffer_print_uint64_encoded(wb, integer_encoding, after);
+    buffer_fast_strcat(wb, " ", 1);
+    buffer_print_uint64_encoded(wb, integer_encoding, before);
+    buffer_fast_strcat(wb, " ", 1);
+    buffer_print_uint64_encoded(wb, integer_encoding, wall_clock_time);
+    buffer_fast_strcat(wb, "\n", 1);
+
+    worker_is_busy(WORKER_JOB_BUFFER_COMMIT);
+    sender_commit(host->sender, wb, STREAM_TRAFFIC_TYPE_REPLICATION);
+    worker_is_busy(WORKER_JOB_CLEANUP);
+
+    if(enable_streaming) {
+        if(sender_is_still_connected_for_this_request(rq)) {
+            // 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);
+
+                if(!finished_with_gap)
+                    st->rrdpush.sender.resync_time_s = 0;
+
+#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), rrdset_id(st));
+        }
+    }
+
+    if(locked_data_collection)
+        spinlock_unlock(&st->data_collection_lock);
+
+    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 wall_clock_time;             // the current time of the child
+        bool fixed_last_entry;              // when set we set the last entry to wall clock time
+    } 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
+        time_t wall_clock_time;                         // 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 void replicate_log_request(struct replication_request_details *r, const char *msg) {
+#ifdef NETDATA_INTERNAL_CHECKS
+    internal_error(true,
+#else
+    nd_log_limit_static_global_var(erl, 1, 0);
+    nd_log_limit(&erl, NDLS_DAEMON, NDLP_ERR,
+#endif
+                "REPLAY ERROR: 'host:%s/chart:%s' child sent: "
+                "db from %ld to %ld%s, wall clock time %ld, "
+                "last request from %ld to %ld, "
+                "issue: %s - "
+                "sending replication request from %ld to %ld, start streaming %s",
+                rrdhost_hostname(r->st->rrdhost), rrdset_id(r->st),
+                r->child_db.first_entry_t,
+                r->child_db.last_entry_t, r->child_db.fixed_last_entry ? " (fixed)" : "",
+                r->child_db.wall_clock_time,
+                r->last_request.after,
+                r->last_request.before,
+                msg,
+                r->wanted.after,
+                r->wanted.before,
+                r->wanted.start_streaming ? "true" : "false");
+}
+
+static bool send_replay_chart_cmd(struct replication_request_details *r, const char *msg, bool log) {
+    RRDSET *st = r->st;
+
+    if(log)
+        replicate_log_request(r, msg);
+
+    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, 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.wall_clock_time, (r->child_db.wall_clock_time == r->local_db.wall_clock_time) ? "SAME" : (r->child_db.wall_clock_time < r->local_db.wall_clock_time) ? "BEHIND" : "AHEAD"
+                   , r->local_db.first_entry_t, r->local_db.last_entry_t
+                   , r->local_db.wall_clock_time
+                   , 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, sizeof(buffer) - 1, 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);
+
+    ssize_t ret = r->caller.callback(buffer, r->caller.data);
+    if (ret < 0) {
+        netdata_log_error("REPLAY ERROR: 'host:%s/chart:%s' failed to send replication request to child (error %zd)",
+              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 child_first_entry, time_t child_last_entry, time_t child_wall_clock_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 = child_first_entry,
+                    .last_entry_t = child_last_entry,
+                    .wall_clock_time = child_wall_clock_time,
+                    .fixed_last_entry = false,
+            },
+
+            .local_db = {
+                    .first_entry_t = 0,
+                    .last_entry_t = 0,
+                    .wall_clock_time  = now_realtime_sec(),
+            },
+
+            .last_request = {
+                    .after = prev_first_entry_wanted,
+                    .before = prev_last_entry_wanted,
+            },
+
+            .wanted = {
+                    .after = 0,
+                    .before = 0,
+                    .start_streaming = true,
+            },
+    };
+
+    if(r.child_db.last_entry_t > r.child_db.wall_clock_time) {
+        replicate_log_request(&r, "child's db last entry > child's wall clock time");
+        r.child_db.last_entry_t = r.child_db.wall_clock_time;
+        r.child_db.fixed_last_entry = true;
+    }
+
+    rrdset_get_retention_of_tier_for_collected_chart(r.st, &r.local_db.first_entry_t, &r.local_db.last_entry_t, r.local_db.wall_clock_time, 0);
+
+    // 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.wall_clock_time - 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.wall_clock_time;
+
+    // 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", false);
+
+    if (unlikely(!rrdset_number_of_dimensions(st)))
+        return send_replay_chart_cmd(&r, "empty replication request, chart has no dimensions", false);
+
+    if (unlikely(!r.child_db.first_entry_t || !r.child_db.last_entry_t))
+        return send_replay_chart_cmd(&r, "empty replication request, child has no stored data", false);
+
+    if (unlikely(r.child_db.first_entry_t < 0 || r.child_db.last_entry_t < 0))
+        return send_replay_chart_cmd(&r, "empty replication request, child db timestamps are invalid", true);
+
+    if (unlikely(r.child_db.first_entry_t > r.child_db.wall_clock_time))
+        return send_replay_chart_cmd(&r, "empty replication request, child db first entry is after its wall clock time", true);
+
+    if (unlikely(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)", true);
+
+    if (unlikely(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", false);
+
+    // 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 = 0;
+        r.wanted.before = 0;
+        r.wanted.start_streaming = true;
+        return send_replay_chart_cmd(&r, "empty replication request, wanted after computed bigger than wanted before", true);
+    }
+
+    // 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.wall_clock_time - r.wanted.after <= host->rrdpush_replication_step ||
+            r.wanted.before >= r.child_db.last_entry_t ||
+            r.wanted.before >= r.child_db.wall_clock_time ||
+            r.wanted.before >= r.local_db.wall_clock_time);
+
+    // the wanted timeframe is now r.wanted.after -> r.wanted.before
+    // send it
+    return send_replay_chart_cmd(&r, "OK", false);
+}
+
+// ----------------------------------------------------------------------------
+// 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)
+
+    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 start_streaming;               // true, when the parent wants to send the rest of the data (before is overwritten) and enable normal streaming
+    bool indexed_in_judy;               // true when the request is indexed in judy
+    bool not_indexed_buffer_full;       // true when the request is not indexed because the sender is full
+    bool not_indexed_preprocessing;     // true when the request is not indexed, but it is pending in preprocessing
+
+    // prepare ahead members - preprocessing
+    bool found;                         // used as a result boolean for the find call
+    bool executed;                      // used to detect if we have skipped requests while preprocessing
+    RRDSET *st;                         // caching of the chart during preprocessing
+    struct replication_query *q;        // the preprocessing query initialization
+};
+
+// 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 {
+    ARAL *aral_rse;
+
+    SPINLOCK spinlock;
+
+    struct {
+        size_t pending;                 // number of requests pending in the queue
+
+        // statistics
+        size_t added;                   // number of requests added to the queue
+        size_t removed;                 // number of requests removed from the queue
+        size_t pending_no_room;         // number of requests skipped, because the sender has no room for responses
+        size_t senders_full;             // number of times a sender reset our last position in the queue
+        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 {
+        Word_t unique_id;               // the last unique id we gave to a request (auto-increment, starting from 1)
+        size_t executed;                // the number of replication requests executed
+        size_t latest_first_time;       // the 'after' timestamp of the last request we executed
+        size_t memory;                  // the total memory allocated by replication
+    } atomic;                           // access should be with atomic operations
+
+    struct {
+        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 = {
+        .aral_rse = NULL,
+        .spinlock = NETDATA_SPINLOCK_INITIALIZER,
+        .unsafe = {
+                .pending = 0,
+
+                .added = 0,
+                .removed = 0,
+                .pending_no_room = 0,
+                .sender_resets = 0,
+                .senders_full = 0,
+
+                .first_time_t = 0,
+
+                .queue = {
+                        .after = 0,
+                        .unique_id = 0,
+                        .JudyL_array = NULL,
+                },
+        },
+        .atomic = {
+                .unique_id = 0,
+                .executed = 0,
+                .latest_first_time = 0,
+                .memory = 0,
+        },
+        .main_thread = {
+                .last_executed = 0,
+                .threads = 0,
+                .threads_ptrs = NULL,
+        },
+};
+
+size_t replication_allocated_memory(void) {
+    return __atomic_load_n(&replication_globals.atomic.memory, __ATOMIC_RELAXED);
+}
+
+#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)
+            spinlock_lock(&replication_globals.spinlock);
+    }
+    else if(mode == 'U') { // (U)nlock
+        if(--recursions == 0)
+            spinlock_unlock(&replication_globals.spinlock);
+    }
+    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 inline struct replication_sort_entry *replication_sort_entry_create(struct replication_request *rq) {
+    struct replication_sort_entry *rse = aral_mallocz(replication_globals.aral_rse);
+    __atomic_add_fetch(&replication_globals.atomic.memory, sizeof(struct replication_sort_entry), __ATOMIC_RELAXED);
+
+    rrdpush_sender_pending_replication_requests_plus_one(rq->sender);
+
+    // copy the request
+    rse->rq = rq;
+    rse->unique_id = __atomic_add_fetch(&replication_globals.atomic.unique_id, 1, __ATOMIC_SEQ_CST);
+
+    // 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;
+    rq->not_indexed_buffer_full = false;
+    rq->not_indexed_preprocessing = false;
+    return rse;
+}
+
+static void replication_sort_entry_destroy(struct replication_sort_entry *rse) {
+    aral_freez(replication_globals.aral_rse, rse);
+    __atomic_sub_fetch(&replication_globals.atomic.memory, sizeof(struct replication_sort_entry), __ATOMIC_RELAXED);
+}
+
+static void replication_sort_entry_add(struct replication_request *rq) {
+    if(unlikely(rrdpush_sender_replication_buffer_full_get(rq->sender))) {
+        rq->indexed_in_judy = false;
+        rq->not_indexed_buffer_full = true;
+        rq->not_indexed_preprocessing = false;
+        replication_recursive_lock();
+        replication_globals.unsafe.pending_no_room++;
+        replication_recursive_unlock();
+        return;
+    }
+
+    // cache this, because it will be changed
+    bool decrement_no_room = rq->not_indexed_buffer_full;
+
+    struct replication_sort_entry *rse = replication_sort_entry_create(rq);
+
+    replication_recursive_lock();
+
+    if(decrement_no_room)
+        replication_globals.unsafe.pending_no_room--;
+
+//    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
+    size_t mem_before_outer_judyl = JudyLMemUsed(replication_globals.unsafe.queue.JudyL_array);
+    inner_judy_ptr = JudyLIns(&replication_globals.unsafe.queue.JudyL_array, (Word_t) rq->after, PJE0);
+    size_t mem_after_outer_judyl = JudyLMemUsed(replication_globals.unsafe.queue.JudyL_array);
+    if(unlikely(!inner_judy_ptr || inner_judy_ptr == PJERR))
+        fatal("REPLICATION: corrupted outer judyL");
+
+    // add it to the inner judy, using unique_id as key
+    size_t mem_before_inner_judyl = JudyLMemUsed(*inner_judy_ptr);
+    Pvoid_t *item = JudyLIns(inner_judy_ptr, rq->unique_id, PJE0);
+    size_t mem_after_inner_judyl = JudyLMemUsed(*inner_judy_ptr);
+    if(unlikely(!item || item == PJERR))
+        fatal("REPLICATION: corrupted inner judyL");
+
+    *item = rse;
+    rq->indexed_in_judy = true;
+    rq->not_indexed_buffer_full = false;
+    rq->not_indexed_preprocessing = false;
+
+    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();
+
+    __atomic_add_fetch(&replication_globals.atomic.memory, (mem_after_inner_judyl - mem_before_inner_judyl) + (mem_after_outer_judyl - mem_before_outer_judyl), __ATOMIC_RELAXED);
+}
+
+static bool replication_sort_entry_unlink_and_free_unsafe(struct replication_sort_entry *rse, Pvoid_t **inner_judy_ppptr, bool preprocessing) {
+    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;
+    rse->rq->not_indexed_preprocessing = preprocessing;
+
+    size_t memory_saved = 0;
+
+    // delete it from the inner judy
+    size_t mem_before_inner_judyl = JudyLMemUsed(**inner_judy_ppptr);
+    JudyLDel(*inner_judy_ppptr, rse->rq->unique_id, PJE0);
+    size_t mem_after_inner_judyl = JudyLMemUsed(**inner_judy_ppptr);
+    memory_saved = mem_before_inner_judyl - mem_after_inner_judyl;
+
+    // if no items left, delete it from the outer judy
+    if(**inner_judy_ppptr == NULL) {
+        size_t mem_before_outer_judyl = JudyLMemUsed(replication_globals.unsafe.queue.JudyL_array);
+        JudyLDel(&replication_globals.unsafe.queue.JudyL_array, rse->rq->after, PJE0);
+        size_t mem_after_outer_judyl = JudyLMemUsed(replication_globals.unsafe.queue.JudyL_array);
+        memory_saved += mem_before_outer_judyl - mem_after_outer_judyl;
+        inner_judy_deleted = true;
+    }
+
+    // free memory
+    replication_sort_entry_destroy(rse);
+
+    __atomic_sub_fetch(&replication_globals.atomic.memory, memory_saved, __ATOMIC_RELAXED);
+
+    return inner_judy_deleted;
+}
+
+static void replication_sort_entry_del(struct replication_request *rq, bool buffer_full) {
+    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, false);
+
+                if(buffer_full) {
+                    replication_globals.unsafe.pending_no_room++;
+                    rq->not_indexed_buffer_full = true;
+                }
+            }
+        }
+
+        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 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 = JudyLFirstThenNext(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;
+
+                // 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, true))
+                    // we removed the item from the outer JudyL
+                    break;
+            }
+
+            // 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 && rq->not_indexed_buffer_full && !rq->not_indexed_preprocessing) {
+        // we can replace this command
+        internal_error(
+                true,
+                "STREAM %s [send to %s]: REPLAY: 'host:%s/chart:%s' replacing 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");
+
+        rq->after = rq_new->after;
+        rq->before = rq_new->before;
+        rq->start_streaming = rq_new->start_streaming;
+    }
+    else if(!rq->indexed_in_judy && !rq->not_indexed_preprocessing) {
+        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, false);
+
+    else if(rq->not_indexed_buffer_full) {
+        replication_recursive_lock();
+        replication_globals.unsafe.pending_no_room--;
+        replication_recursive_unlock();
+    }
+
+    string_freez(rq->chart_id);
+}
+
+static bool sender_is_still_connected_for_this_request(struct replication_request *rq) {
+    return rq->sender_last_flush_ut == rrdpush_sender_get_flush_time(rq->sender);
+}
+
+static bool replication_execute_request(struct replication_request *rq, bool workers) {
+    bool ret = false;
+
+    if(!rq->st) {
+        if(likely(workers))
+            worker_is_busy(WORKER_JOB_FIND_CHART);
+
+        rq->st = rrdset_find(rq->sender->host, string2str(rq->chart_id));
+    }
+
+    if(!rq->st) {
+        internal_error(true, "REPLAY ERROR: 'host:%s/chart:%s' not found",
+                       rrdhost_hostname(rq->sender->host), string2str(rq->chart_id));
+
+        goto cleanup;
+    }
+
+    netdata_thread_disable_cancelability();
+
+    if(!rq->q) {
+        if(likely(workers))
+            worker_is_busy(WORKER_JOB_PREPARE_QUERY);
+
+        rq->q = replication_response_prepare(
+                rq->st,
+                rq->start_streaming,
+                rq->after,
+                rq->before,
+                rq->sender->capabilities);
+    }
+
+    if(likely(workers))
+        worker_is_busy(WORKER_JOB_QUERYING);
+
+    // send the replication data
+    rq->q->rq = rq;
+    replication_response_execute_and_finalize(
+            rq->q, (size_t)((unsigned long long)rq->sender->host->sender->buffer->max_size * MAX_REPLICATION_MESSAGE_PERCENT_SENDER_BUFFER / 100ULL));
+
+    rq->q = NULL;
+    netdata_thread_enable_cancelability();
+
+    __atomic_add_fetch(&replication_globals.atomic.executed, 1, __ATOMIC_RELAXED);
+
+    ret = true;
+
+cleanup:
+    if(rq->q) {
+        replication_response_cancel_and_finalize(rq->q);
+        rq->q = NULL;
+    }
+
+    string_freez(rq->chart_id);
+    worker_is_idle();
+    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),
+            .indexed_in_judy = false,
+            .not_indexed_buffer_full = false,
+            .not_indexed_preprocessing = false,
+    };
+
+    if(!sender->replication.oldest_request_after_t || rq.after < sender->replication.oldest_request_after_t)
+        sender->replication.oldest_request_after_t = rq.after;
+
+    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
+    dictionary_flush(sender->replication.requests);
+}
+
+void replication_init_sender(struct sender_state *sender) {
+    sender->replication.requests = dictionary_create_advanced(DICT_OPTION_DONT_OVERWRITE_VALUE | DICT_OPTION_FIXED_SIZE,
+                                                              NULL, sizeof(struct replication_request));
+
+    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(unlikely(percentage > MAX_SENDER_BUFFER_PERCENTAGE_ALLOWED && !rrdpush_sender_replication_buffer_full_get(s))) {
+        rrdpush_sender_replication_buffer_full_set(s, true);
+
+        struct replication_request *rq;
+        dfe_start_read(s->replication.requests, rq) {
+            if(rq->indexed_in_judy)
+                replication_sort_entry_del(rq, true);
+        }
+        dfe_done(rq);
+
+        replication_recursive_lock();
+        replication_globals.unsafe.senders_full++;
+        replication_recursive_unlock();
+    }
+    else if(unlikely(percentage < MIN_SENDER_BUFFER_PERCENTAGE_ALLOWED && rrdpush_sender_replication_buffer_full_get(s))) {
+        rrdpush_sender_replication_buffer_full_set(s, false);
+
+        struct replication_request *rq;
+        dfe_start_read(s->replication.requests, rq) {
+            if(!rq->indexed_in_judy && (rq->not_indexed_buffer_full || rq->not_indexed_preprocessing))
+                replication_sort_entry_add(rq);
+        }
+        dfe_done(rq);
+
+        replication_recursive_lock();
+        replication_globals.unsafe.senders_full--;
+        replication_globals.unsafe.sender_resets++;
+        // replication_set_next_point_in_time(0, 0);
+        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);
+    netdata_log_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_PREPARE_QUERY, "prepare query");
+    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");
+    worker_register_job_name(WORKER_JOB_WAIT, "wait");
+
+    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_SKIPPED_NO_ROOM, "no room 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_SENDER_RESETS, "sender resets", "resets/s", WORKER_METRIC_INCREMENTAL_TOTAL);
+        worker_register_job_custom_metric(WORKER_JOB_CUSTOM_METRIC_SENDER_FULL, "senders full", "senders", WORKER_METRIC_ABSOLUTE);
+    }
+}
+
+#define REQUEST_OK (0)
+#define REQUEST_QUEUE_EMPTY (-1)
+#define REQUEST_CHART_NOT_FOUND (-2)
+
+static __thread struct replication_thread_pipeline {
+    int max_requests_ahead;
+    struct replication_request *rqs;
+    int rqs_last_executed, rqs_last_prepared;
+    size_t queue_rounds;
+} rtp = {
+        .max_requests_ahead = 0,
+        .rqs = NULL,
+        .rqs_last_executed = 0,
+        .rqs_last_prepared = 0,
+        .queue_rounds = 0,
+};
+
+static void replication_pipeline_cancel_and_cleanup(void) {
+    if(!rtp.rqs)
+        return;
+
+    struct replication_request *rq;
+    size_t cancelled = 0;
+
+    do {
+        if (++rtp.rqs_last_executed >= rtp.max_requests_ahead)
+            rtp.rqs_last_executed = 0;
+
+        rq = &rtp.rqs[rtp.rqs_last_executed];
+
+        if (rq->q) {
+            internal_fatal(rq->executed, "REPLAY FATAL: query has already been executed!");
+            internal_fatal(!rq->found, "REPLAY FATAL: orphan q in rq");
+
+            replication_response_cancel_and_finalize(rq->q);
+            rq->q = NULL;
+            cancelled++;
+        }
+
+        rq->executed = true;
+        rq->found = false;
+
+    } while (rtp.rqs_last_executed != rtp.rqs_last_prepared);
+
+    internal_error(true, "REPLICATION: cancelled %zu inflight queries", cancelled);
+
+    freez(rtp.rqs);
+    rtp.rqs = NULL;
+    rtp.max_requests_ahead = 0;
+    rtp.rqs_last_executed = 0;
+    rtp.rqs_last_prepared = 0;
+    rtp.queue_rounds = 0;
+}
+
+static int replication_pipeline_execute_next(void) {
+    struct replication_request *rq;
+
+    if(unlikely(!rtp.rqs)) {
+        rtp.max_requests_ahead = (int)get_netdata_cpus() / 2;
+
+        if(rtp.max_requests_ahead > libuv_worker_threads * 2)
+            rtp.max_requests_ahead = libuv_worker_threads * 2;
+
+        if(rtp.max_requests_ahead < 2)
+            rtp.max_requests_ahead = 2;
+
+        rtp.rqs = callocz(rtp.max_requests_ahead, sizeof(struct replication_request));
+        __atomic_add_fetch(&replication_buffers_allocated, rtp.max_requests_ahead * sizeof(struct replication_request), __ATOMIC_RELAXED);
+    }
+
+    // fill the queue
+    do {
+        if(++rtp.rqs_last_prepared >= rtp.max_requests_ahead) {
+            rtp.rqs_last_prepared = 0;
+            rtp.queue_rounds++;
+        }
+
+        internal_fatal(rtp.rqs[rtp.rqs_last_prepared].q,
+                       "REPLAY FATAL: slot is used by query that has not been executed!");
+
+        worker_is_busy(WORKER_JOB_FIND_NEXT);
+        rtp.rqs[rtp.rqs_last_prepared] = replication_request_get_first_available();
+        rq = &rtp.rqs[rtp.rqs_last_prepared];
+
+        if(rq->found) {
+            if (!rq->st) {
+                worker_is_busy(WORKER_JOB_FIND_CHART);
+                rq->st = rrdset_find(rq->sender->host, string2str(rq->chart_id));
+            }
+
+            if (rq->st && !rq->q) {
+                worker_is_busy(WORKER_JOB_PREPARE_QUERY);
+                rq->q = replication_response_prepare(
+                        rq->st,
+                        rq->start_streaming,
+                        rq->after,
+                        rq->before,
+                        rq->sender->capabilities);
+            }
+
+            rq->executed = false;
+        }
+
+    } while(rq->found && rtp.rqs_last_prepared != rtp.rqs_last_executed);
+
+    // pick the first usable
+    do {
+        if (++rtp.rqs_last_executed >= rtp.max_requests_ahead)
+            rtp.rqs_last_executed = 0;
+
+        rq = &rtp.rqs[rtp.rqs_last_executed];
+
+        if(rq->found) {
+            internal_fatal(rq->executed, "REPLAY FATAL: query has already been executed!");
+
+            if (rq->sender_last_flush_ut != rrdpush_sender_get_flush_time(rq->sender)) {
+                // the sender has reconnected since this request was queued,
+                // we can safely throw it away, since the parent will resend it
+                replication_response_cancel_and_finalize(rq->q);
+                rq->executed = true;
+                rq->found = false;
+                rq->q = NULL;
+            }
+            else if (rrdpush_sender_replication_buffer_full_get(rq->sender)) {
+                // the sender buffer is full, so we can ignore this request,
+                // it has already been marked as 'preprocessed' in the dictionary,
+                // and the sender will put it back in when there is
+                // enough room in the buffer for processing replication requests
+                replication_response_cancel_and_finalize(rq->q);
+                rq->executed = true;
+                rq->found = false;
+                rq->q = NULL;
+            }
+            else {
+                // we can execute this,
+                // delete it from the dictionary
+                worker_is_busy(WORKER_JOB_DELETE_ENTRY);
+                dictionary_del(rq->sender->replication.requests, string2str(rq->chart_id));
+            }
+        }
+        else
+            internal_fatal(rq->q, "REPLAY FATAL: slot status says slot is empty, but it has a pending query!");
+
+    } while(!rq->found && rtp.rqs_last_executed != rtp.rqs_last_prepared);
+
+    if(unlikely(!rq->found)) {
+        worker_is_idle();
+        return REQUEST_QUEUE_EMPTY;
+    }
+
+    replication_set_latest_first_time(rq->after);
+
+    bool chart_found = replication_execute_request(rq, true);
+    rq->executed = true;
+    rq->found = false;
+    rq->q = NULL;
+
+    if(unlikely(!chart_found)) {
+        worker_is_idle();
+        return REQUEST_CHART_NOT_FOUND;
+    }
+
+    worker_is_idle();
+    return REQUEST_OK;
+}
+
+static void replication_worker_cleanup(void *ptr __maybe_unused) {
+    replication_pipeline_cancel_and_cleanup();
+    worker_unregister();
+}
+
+static void *replication_worker_thread(void *ptr) {
+    replication_initialize_workers(false);
+
+    netdata_thread_cleanup_push(replication_worker_cleanup, ptr) {
+        while (service_running(SERVICE_REPLICATION)) {
+            if (unlikely(replication_pipeline_execute_next() == REQUEST_QUEUE_EMPTY)) {
+                sender_thread_buffer_free();
+                worker_is_busy(WORKER_JOB_WAIT);
+                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;
+
+    replication_pipeline_cancel_and_cleanup();
+
+    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]);
+        __atomic_sub_fetch(&replication_buffers_allocated, sizeof(netdata_thread_t), __ATOMIC_RELAXED);
+    }
+    freez(replication_globals.main_thread.threads_ptrs);
+    replication_globals.main_thread.threads_ptrs = NULL;
+    __atomic_sub_fetch(&replication_buffers_allocated, threads * sizeof(netdata_thread_t), __ATOMIC_RELAXED);
+
+    aral_destroy(replication_globals.aral_rse);
+    replication_globals.aral_rse = NULL;
+
+    // custom code
+    worker_unregister();
+
+    static_thread->enabled = NETDATA_MAIN_THREAD_EXITED;
+}
+
+void replication_initialize(void) {
+    replication_globals.aral_rse = aral_create("rse", sizeof(struct replication_sort_entry),
+                                               0, 65536, aral_by_size_statistics(),
+                                               NULL, NULL, false, false);
+}
+
+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) {
+        netdata_log_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 *));
+        __atomic_add_fetch(&replication_buffers_allocated, threads * sizeof(netdata_thread_t), __ATOMIC_RELAXED);
+
+        for(int i = 0; i < threads ;i++) {
+            char tag[NETDATA_THREAD_TAG_MAX + 1];
+            snprintfz(tag, NETDATA_THREAD_TAG_MAX, "REPLAY[%d]", i + 2);
+            replication_globals.main_thread.threads_ptrs[i] = mallocz(sizeof(netdata_thread_t));
+            __atomic_add_fetch(&replication_buffers_allocated, sizeof(netdata_thread_t), __ATOMIC_RELAXED);
+            netdata_thread_create(replication_globals.main_thread.threads_ptrs[i], tag,
+                                  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(service_running(SERVICE_REPLICATION)) {
+
+        // 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;
+
+            worker_is_busy(WORKER_JOB_STATISTICS);
+            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(--run_verification_countdown == 0) {
+                if (!replication_globals.unsafe.pending && !replication_globals.unsafe.pending_no_room) {
+                    // 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;
+                }
+                else
+                    run_verification_countdown = ITERATIONS_IDLE_WITHOUT_PENDING_TO_RUN_SENDER_VERIFICATION;
+            }
+
+            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_NO_ROOM, (NETDATA_DOUBLE)replication_globals.unsafe.pending_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_SENDER_FULL, (NETDATA_DOUBLE)replication_globals.unsafe.senders_full);
+
+            replication_recursive_unlock();
+            worker_is_idle();
+        }
+
+        if(unlikely(replication_pipeline_execute_next() == REQUEST_QUEUE_EMPTY)) {
+
+            worker_is_busy(WORKER_JOB_WAIT);
+            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;
+                sender_thread_buffer_free();
+            }
+
+            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_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;
+}