Adding upstream version 1.29.3.upstream/1.29.3upstream

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

1 files changed, 1266 insertions, 0 deletions

diff --git a/database/engine/rrdengine.c b/database/engine/rrdengine.c
new file mode 100644
index 0000000..43135ff
--- /dev/null
+++ b/database/engine/rrdengine.c
@@ -0,0 +1,1266 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+#define NETDATA_RRD_INTERNALS
+
+#include "rrdengine.h"
+
+rrdeng_stats_t global_io_errors = 0;
+rrdeng_stats_t global_fs_errors = 0;
+rrdeng_stats_t rrdeng_reserved_file_descriptors = 0;
+rrdeng_stats_t global_pg_cache_over_half_dirty_events = 0;
+rrdeng_stats_t global_flushing_pressure_page_deletions = 0;
+
+static void sanity_check(void)
+{
+    /* Magic numbers must fit in the super-blocks */
+    BUILD_BUG_ON(strlen(RRDENG_DF_MAGIC) > RRDENG_MAGIC_SZ);
+    BUILD_BUG_ON(strlen(RRDENG_JF_MAGIC) > RRDENG_MAGIC_SZ);
+
+    /* Version strings must fit in the super-blocks */
+    BUILD_BUG_ON(strlen(RRDENG_DF_VER) > RRDENG_VER_SZ);
+    BUILD_BUG_ON(strlen(RRDENG_JF_VER) > RRDENG_VER_SZ);
+
+    /* Data file super-block cannot be larger than RRDENG_BLOCK_SIZE */
+    BUILD_BUG_ON(RRDENG_DF_SB_PADDING_SZ < 0);
+
+    BUILD_BUG_ON(sizeof(uuid_t) != UUID_SZ); /* check UUID size */
+
+    /* page count must fit in 8 bits */
+    BUILD_BUG_ON(MAX_PAGES_PER_EXTENT > 255);
+
+    /* extent cache count must fit in 32 bits */
+    BUILD_BUG_ON(MAX_CACHED_EXTENTS > 32);
+
+    /* page info scratch space must be able to hold 2 32-bit integers */
+    BUILD_BUG_ON(sizeof(((struct rrdeng_page_info *)0)->scratch) < 2 * sizeof(uint32_t));
+}
+
+/* always inserts into tail */
+static inline void xt_cache_replaceQ_insert(struct rrdengine_worker_config* wc,
+                                            struct extent_cache_element *xt_cache_elem)
+{
+    struct extent_cache *xt_cache = &wc->xt_cache;
+
+    xt_cache_elem->prev = NULL;
+    xt_cache_elem->next = NULL;
+
+    if (likely(NULL != xt_cache->replaceQ_tail)) {
+        xt_cache_elem->prev = xt_cache->replaceQ_tail;
+        xt_cache->replaceQ_tail->next = xt_cache_elem;
+    }
+    if (unlikely(NULL == xt_cache->replaceQ_head)) {
+        xt_cache->replaceQ_head = xt_cache_elem;
+    }
+    xt_cache->replaceQ_tail = xt_cache_elem;
+}
+
+static inline void xt_cache_replaceQ_delete(struct rrdengine_worker_config* wc,
+                                            struct extent_cache_element *xt_cache_elem)
+{
+    struct extent_cache *xt_cache = &wc->xt_cache;
+    struct extent_cache_element *prev, *next;
+
+    prev = xt_cache_elem->prev;
+    next = xt_cache_elem->next;
+
+    if (likely(NULL != prev)) {
+        prev->next = next;
+    }
+    if (likely(NULL != next)) {
+        next->prev = prev;
+    }
+    if (unlikely(xt_cache_elem == xt_cache->replaceQ_head)) {
+        xt_cache->replaceQ_head = next;
+    }
+    if (unlikely(xt_cache_elem == xt_cache->replaceQ_tail)) {
+        xt_cache->replaceQ_tail = prev;
+    }
+    xt_cache_elem->prev = xt_cache_elem->next = NULL;
+}
+
+static inline void xt_cache_replaceQ_set_hot(struct rrdengine_worker_config* wc,
+                                             struct extent_cache_element *xt_cache_elem)
+{
+    xt_cache_replaceQ_delete(wc, xt_cache_elem);
+    xt_cache_replaceQ_insert(wc, xt_cache_elem);
+}
+
+/* Returns the index of the cached extent if it was successfully inserted in the extent cache, otherwise -1 */
+static int try_insert_into_xt_cache(struct rrdengine_worker_config* wc, struct extent_info *extent)
+{
+    struct extent_cache *xt_cache = &wc->xt_cache;
+    struct extent_cache_element *xt_cache_elem;
+    unsigned idx;
+    int ret;
+
+    ret = find_first_zero(xt_cache->allocation_bitmap);
+    if (-1 == ret || ret >= MAX_CACHED_EXTENTS) {
+        for (xt_cache_elem = xt_cache->replaceQ_head ; NULL != xt_cache_elem ; xt_cache_elem = xt_cache_elem->next) {
+            idx = xt_cache_elem - xt_cache->extent_array;
+            if (!check_bit(xt_cache->inflight_bitmap, idx)) {
+                xt_cache_replaceQ_delete(wc, xt_cache_elem);
+                break;
+            }
+        }
+        if (NULL == xt_cache_elem)
+            return -1;
+    } else {
+        idx = (unsigned)ret;
+        xt_cache_elem = &xt_cache->extent_array[idx];
+    }
+    xt_cache_elem->extent = extent;
+    xt_cache_elem->fileno = extent->datafile->fileno;
+    xt_cache_elem->inflight_io_descr = NULL;
+    xt_cache_replaceQ_insert(wc, xt_cache_elem);
+    modify_bit(&xt_cache->allocation_bitmap, idx, 1);
+
+    return (int)idx;
+}
+
+/**
+ * Returns 0 if the cached extent was found in the extent cache, 1 otherwise.
+ * Sets *idx to point to the position of the extent inside the cache.
+ **/
+static uint8_t lookup_in_xt_cache(struct rrdengine_worker_config* wc, struct extent_info *extent, unsigned *idx)
+{
+    struct extent_cache *xt_cache = &wc->xt_cache;
+    struct extent_cache_element *xt_cache_elem;
+    unsigned i;
+
+    for (i = 0 ; i < MAX_CACHED_EXTENTS ; ++i) {
+        xt_cache_elem = &xt_cache->extent_array[i];
+        if (check_bit(xt_cache->allocation_bitmap, i) && xt_cache_elem->extent == extent &&
+            xt_cache_elem->fileno == extent->datafile->fileno) {
+            *idx = i;
+            return 0;
+        }
+    }
+    return 1;
+}
+
+#if 0 /* disabled code */
+static void delete_from_xt_cache(struct rrdengine_worker_config* wc, unsigned idx)
+{
+    struct extent_cache *xt_cache = &wc->xt_cache;
+    struct extent_cache_element *xt_cache_elem;
+
+    xt_cache_elem = &xt_cache->extent_array[idx];
+    xt_cache_replaceQ_delete(wc, xt_cache_elem);
+    xt_cache_elem->extent = NULL;
+    modify_bit(&wc->xt_cache.allocation_bitmap, idx, 0); /* invalidate it */
+    modify_bit(&wc->xt_cache.inflight_bitmap, idx, 0); /* not in-flight anymore */
+}
+#endif
+
+void enqueue_inflight_read_to_xt_cache(struct rrdengine_worker_config* wc, unsigned idx,
+                                       struct extent_io_descriptor *xt_io_descr)
+{
+    struct extent_cache *xt_cache = &wc->xt_cache;
+    struct extent_cache_element *xt_cache_elem;
+    struct extent_io_descriptor *old_next;
+
+    xt_cache_elem = &xt_cache->extent_array[idx];
+    old_next = xt_cache_elem->inflight_io_descr->next;
+    xt_cache_elem->inflight_io_descr->next = xt_io_descr;
+    xt_io_descr->next = old_next;
+}
+
+void read_cached_extent_cb(struct rrdengine_worker_config* wc, unsigned idx, struct extent_io_descriptor *xt_io_descr)
+{
+    unsigned i, j, page_offset;
+    struct rrdengine_instance *ctx = wc->ctx;
+    struct rrdeng_page_descr *descr;
+    struct page_cache_descr *pg_cache_descr;
+    void *page;
+    struct extent_info *extent = xt_io_descr->descr_array[0]->extent;
+
+    for (i = 0 ; i < xt_io_descr->descr_count; ++i) {
+        page = mallocz(RRDENG_BLOCK_SIZE);
+        descr = xt_io_descr->descr_array[i];
+        for (j = 0, page_offset = 0 ; j < extent->number_of_pages ; ++j) {
+            /* care, we don't hold the descriptor mutex */
+            if (!uuid_compare(*extent->pages[j]->id, *descr->id) &&
+                extent->pages[j]->page_length == descr->page_length &&
+                extent->pages[j]->start_time == descr->start_time &&
+                extent->pages[j]->end_time == descr->end_time) {
+                break;
+            }
+            page_offset += extent->pages[j]->page_length;
+
+        }
+        /* care, we don't hold the descriptor mutex */
+       (void) memcpy(page, wc->xt_cache.extent_array[idx].pages + page_offset, descr->page_length);
+
+        rrdeng_page_descr_mutex_lock(ctx, descr);
+        pg_cache_descr = descr->pg_cache_descr;
+        pg_cache_descr->page = page;
+        pg_cache_descr->flags |= RRD_PAGE_POPULATED;
+        pg_cache_descr->flags &= ~RRD_PAGE_READ_PENDING;
+        rrdeng_page_descr_mutex_unlock(ctx, descr);
+        pg_cache_replaceQ_insert(ctx, descr);
+        if (xt_io_descr->release_descr) {
+            pg_cache_put(ctx, descr);
+        } else {
+            debug(D_RRDENGINE, "%s: Waking up waiters.", __func__);
+            pg_cache_wake_up_waiters(ctx, descr);
+        }
+    }
+    if (xt_io_descr->completion)
+        complete(xt_io_descr->completion);
+    freez(xt_io_descr);
+}
+
+void read_extent_cb(uv_fs_t* req)
+{
+    struct rrdengine_worker_config* wc = req->loop->data;
+    struct rrdengine_instance *ctx = wc->ctx;
+    struct extent_io_descriptor *xt_io_descr;
+    struct rrdeng_page_descr *descr;
+    struct page_cache_descr *pg_cache_descr;
+    int ret;
+    unsigned i, j, count;
+    void *page, *uncompressed_buf = NULL;
+    uint32_t payload_length, payload_offset, page_offset, uncompressed_payload_length = 0;
+    uint8_t have_read_error = 0;
+    /* persistent structures */
+    struct rrdeng_df_extent_header *header;
+    struct rrdeng_df_extent_trailer *trailer;
+    uLong crc;
+
+    xt_io_descr = req->data;
+    header = xt_io_descr->buf;
+    payload_length = header->payload_length;
+    count = header->number_of_pages;
+    payload_offset = sizeof(*header) + sizeof(header->descr[0]) * count;
+    trailer = xt_io_descr->buf + xt_io_descr->bytes - sizeof(*trailer);
+
+    if (req->result < 0) {
+        struct rrdengine_datafile *datafile = xt_io_descr->descr_array[0]->extent->datafile;
+
+        ++ctx->stats.io_errors;
+        rrd_stat_atomic_add(&global_io_errors, 1);
+        have_read_error = 1;
+        error("%s: uv_fs_read - %s - extent at offset %"PRIu64"(%u) in datafile %u-%u.", __func__,
+              uv_strerror((int)req->result), xt_io_descr->pos, xt_io_descr->bytes, datafile->tier, datafile->fileno);
+        goto after_crc_check;
+    }
+    crc = crc32(0L, Z_NULL, 0);
+    crc = crc32(crc, xt_io_descr->buf, xt_io_descr->bytes - sizeof(*trailer));
+    ret = crc32cmp(trailer->checksum, crc);
+#ifdef NETDATA_INTERNAL_CHECKS
+    {
+        struct rrdengine_datafile *datafile = xt_io_descr->descr_array[0]->extent->datafile;
+        debug(D_RRDENGINE, "%s: Extent at offset %"PRIu64"(%u) was read from datafile %u-%u. CRC32 check: %s", __func__,
+              xt_io_descr->pos, xt_io_descr->bytes, datafile->tier, datafile->fileno, ret ? "FAILED" : "SUCCEEDED");
+    }
+#endif
+    if (unlikely(ret)) {
+        struct rrdengine_datafile *datafile = xt_io_descr->descr_array[0]->extent->datafile;
+
+        ++ctx->stats.io_errors;
+        rrd_stat_atomic_add(&global_io_errors, 1);
+        have_read_error = 1;
+        error("%s: Extent at offset %"PRIu64"(%u) was read from datafile %u-%u. CRC32 check: FAILED", __func__,
+              xt_io_descr->pos, xt_io_descr->bytes, datafile->tier, datafile->fileno);
+    }
+
+after_crc_check:
+    if (!have_read_error && RRD_NO_COMPRESSION != header->compression_algorithm) {
+        uncompressed_payload_length = 0;
+        for (i = 0 ; i < count ; ++i) {
+            uncompressed_payload_length += header->descr[i].page_length;
+        }
+        uncompressed_buf = mallocz(uncompressed_payload_length);
+        ret = LZ4_decompress_safe(xt_io_descr->buf + payload_offset, uncompressed_buf,
+                                  payload_length, uncompressed_payload_length);
+        ctx->stats.before_decompress_bytes += payload_length;
+        ctx->stats.after_decompress_bytes += ret;
+        debug(D_RRDENGINE, "LZ4 decompressed %u bytes to %d bytes.", payload_length, ret);
+        /* care, we don't hold the descriptor mutex */
+    }
+    {
+        uint8_t xt_is_cached = 0;
+        unsigned xt_idx;
+        struct extent_info *extent = xt_io_descr->descr_array[0]->extent;
+
+        xt_is_cached = !lookup_in_xt_cache(wc, extent, &xt_idx);
+        if (xt_is_cached && check_bit(wc->xt_cache.inflight_bitmap, xt_idx)) {
+            struct extent_cache *xt_cache = &wc->xt_cache;
+            struct extent_cache_element *xt_cache_elem = &xt_cache->extent_array[xt_idx];
+            struct extent_io_descriptor *curr, *next;
+
+            if (have_read_error) {
+                memset(xt_cache_elem->pages, 0, sizeof(xt_cache_elem->pages));
+            } else if (RRD_NO_COMPRESSION == header->compression_algorithm) {
+                (void)memcpy(xt_cache_elem->pages, xt_io_descr->buf + payload_offset, payload_length);
+            } else {
+                (void)memcpy(xt_cache_elem->pages, uncompressed_buf, uncompressed_payload_length);
+            }
+            /* complete all connected in-flight read requests */
+            for (curr = xt_cache_elem->inflight_io_descr->next ; curr ; curr = next) {
+                next = curr->next;
+                read_cached_extent_cb(wc, xt_idx, curr);
+            }
+            xt_cache_elem->inflight_io_descr = NULL;
+            modify_bit(&xt_cache->inflight_bitmap, xt_idx, 0); /* not in-flight anymore */
+        }
+    }
+
+    for (i = 0 ; i < xt_io_descr->descr_count; ++i) {
+        page = mallocz(RRDENG_BLOCK_SIZE);
+        descr = xt_io_descr->descr_array[i];
+        for (j = 0, page_offset = 0; j < count; ++j) {
+            /* care, we don't hold the descriptor mutex */
+            if (!uuid_compare(*(uuid_t *) header->descr[j].uuid, *descr->id) &&
+                header->descr[j].page_length == descr->page_length &&
+                header->descr[j].start_time == descr->start_time &&
+                header->descr[j].end_time == descr->end_time) {
+                break;
+            }
+            page_offset += header->descr[j].page_length;
+        }
+        /* care, we don't hold the descriptor mutex */
+        if (have_read_error) {
+            /* Applications should make sure NULL values match 0 as does SN_EMPTY_SLOT */
+            memset(page, 0, descr->page_length);
+        } else if (RRD_NO_COMPRESSION == header->compression_algorithm) {
+            (void) memcpy(page, xt_io_descr->buf + payload_offset + page_offset, descr->page_length);
+        } else {
+            (void) memcpy(page, uncompressed_buf + page_offset, descr->page_length);
+        }
+        rrdeng_page_descr_mutex_lock(ctx, descr);
+        pg_cache_descr = descr->pg_cache_descr;
+        pg_cache_descr->page = page;
+        pg_cache_descr->flags |= RRD_PAGE_POPULATED;
+        pg_cache_descr->flags &= ~RRD_PAGE_READ_PENDING;
+        rrdeng_page_descr_mutex_unlock(ctx, descr);
+        pg_cache_replaceQ_insert(ctx, descr);
+        if (xt_io_descr->release_descr) {
+            pg_cache_put(ctx, descr);
+        } else {
+            debug(D_RRDENGINE, "%s: Waking up waiters.", __func__);
+            pg_cache_wake_up_waiters(ctx, descr);
+        }
+    }
+    if (!have_read_error && RRD_NO_COMPRESSION != header->compression_algorithm) {
+        freez(uncompressed_buf);
+    }
+    if (xt_io_descr->completion)
+        complete(xt_io_descr->completion);
+    uv_fs_req_cleanup(req);
+    free(xt_io_descr->buf);
+    freez(xt_io_descr);
+}
+
+
+static void do_read_extent(struct rrdengine_worker_config* wc,
+                           struct rrdeng_page_descr **descr,
+                           unsigned count,
+                           uint8_t release_descr)
+{
+    struct rrdengine_instance *ctx = wc->ctx;
+    struct page_cache_descr *pg_cache_descr;
+    int ret;
+    unsigned i, size_bytes, pos, real_io_size;
+//    uint32_t payload_length;
+    struct extent_io_descriptor *xt_io_descr;
+    struct rrdengine_datafile *datafile;
+    struct extent_info *extent = descr[0]->extent;
+    uint8_t xt_is_cached = 0, xt_is_inflight = 0;
+    unsigned xt_idx;
+
+    datafile = extent->datafile;
+    pos = extent->offset;
+    size_bytes = extent->size;
+
+    xt_io_descr = callocz(1, sizeof(*xt_io_descr));
+    for (i = 0 ; i < count; ++i) {
+        rrdeng_page_descr_mutex_lock(ctx, descr[i]);
+        pg_cache_descr = descr[i]->pg_cache_descr;
+        pg_cache_descr->flags |= RRD_PAGE_READ_PENDING;
+//        payload_length = descr[i]->page_length;
+        rrdeng_page_descr_mutex_unlock(ctx, descr[i]);
+
+        xt_io_descr->descr_array[i] = descr[i];
+    }
+    xt_io_descr->descr_count = count;
+    xt_io_descr->bytes = size_bytes;
+    xt_io_descr->pos = pos;
+    xt_io_descr->req.data = xt_io_descr;
+    xt_io_descr->completion = NULL;
+    /* xt_io_descr->descr_commit_idx_array[0] */
+    xt_io_descr->release_descr = release_descr;
+
+    xt_is_cached = !lookup_in_xt_cache(wc, extent, &xt_idx);
+    if (xt_is_cached) {
+        xt_cache_replaceQ_set_hot(wc, &wc->xt_cache.extent_array[xt_idx]);
+        xt_is_inflight = check_bit(wc->xt_cache.inflight_bitmap, xt_idx);
+        if (xt_is_inflight) {
+            enqueue_inflight_read_to_xt_cache(wc, xt_idx, xt_io_descr);
+            return;
+        }
+        return read_cached_extent_cb(wc, xt_idx, xt_io_descr);
+    } else {
+        ret = try_insert_into_xt_cache(wc, extent);
+        if (-1 != ret) {
+            xt_idx = (unsigned)ret;
+            modify_bit(&wc->xt_cache.inflight_bitmap, xt_idx, 1);
+            wc->xt_cache.extent_array[xt_idx].inflight_io_descr = xt_io_descr;
+        }
+    }
+
+    ret = posix_memalign((void *)&xt_io_descr->buf, RRDFILE_ALIGNMENT, ALIGN_BYTES_CEILING(size_bytes));
+    if (unlikely(ret)) {
+        fatal("posix_memalign:%s", strerror(ret));
+        /* freez(xt_io_descr);
+    return;*/
+    }
+    real_io_size = ALIGN_BYTES_CEILING(size_bytes);
+    xt_io_descr->iov = uv_buf_init((void *)xt_io_descr->buf, real_io_size);
+    ret = uv_fs_read(wc->loop, &xt_io_descr->req, datafile->file, &xt_io_descr->iov, 1, pos, read_extent_cb);
+    fatal_assert(-1 != ret);
+    ctx->stats.io_read_bytes += real_io_size;
+    ++ctx->stats.io_read_requests;
+    ctx->stats.io_read_extent_bytes += real_io_size;
+    ++ctx->stats.io_read_extents;
+    ctx->stats.pg_cache_backfills += count;
+}
+
+static void commit_data_extent(struct rrdengine_worker_config* wc, struct extent_io_descriptor *xt_io_descr)
+{
+    struct rrdengine_instance *ctx = wc->ctx;
+    unsigned count, payload_length, descr_size, size_bytes;
+    void *buf;
+    /* persistent structures */
+    struct rrdeng_df_extent_header *df_header;
+    struct rrdeng_jf_transaction_header *jf_header;
+    struct rrdeng_jf_store_data *jf_metric_data;
+    struct rrdeng_jf_transaction_trailer *jf_trailer;
+    uLong crc;
+
+    df_header = xt_io_descr->buf;
+    count = df_header->number_of_pages;
+    descr_size = sizeof(*jf_metric_data->descr) * count;
+    payload_length = sizeof(*jf_metric_data) + descr_size;
+    size_bytes = sizeof(*jf_header) + payload_length + sizeof(*jf_trailer);
+
+    buf = wal_get_transaction_buffer(wc, size_bytes);
+
+    jf_header = buf;
+    jf_header->type = STORE_DATA;
+    jf_header->reserved = 0;
+    jf_header->id = ctx->commit_log.transaction_id++;
+    jf_header->payload_length = payload_length;
+
+    jf_metric_data = buf + sizeof(*jf_header);
+    jf_metric_data->extent_offset = xt_io_descr->pos;
+    jf_metric_data->extent_size = xt_io_descr->bytes;
+    jf_metric_data->number_of_pages = count;
+    memcpy(jf_metric_data->descr, df_header->descr, descr_size);
+
+    jf_trailer = buf + sizeof(*jf_header) + payload_length;
+    crc = crc32(0L, Z_NULL, 0);
+    crc = crc32(crc, buf, sizeof(*jf_header) + payload_length);
+    crc32set(jf_trailer->checksum, crc);
+}
+
+static void do_commit_transaction(struct rrdengine_worker_config* wc, uint8_t type, void *data)
+{
+    switch (type) {
+    case STORE_DATA:
+        commit_data_extent(wc, (struct extent_io_descriptor *)data);
+        break;
+    default:
+        fatal_assert(type == STORE_DATA);
+        break;
+    }
+}
+
+static void after_invalidate_oldest_committed(struct rrdengine_worker_config* wc)
+{
+    int error;
+
+    error = uv_thread_join(wc->now_invalidating_dirty_pages);
+    if (error) {
+        error("uv_thread_join(): %s", uv_strerror(error));
+    }
+    freez(wc->now_invalidating_dirty_pages);
+    wc->now_invalidating_dirty_pages = NULL;
+    wc->cleanup_thread_invalidating_dirty_pages = 0;
+}
+
+static void invalidate_oldest_committed(void *arg)
+{
+    struct rrdengine_instance *ctx = arg;
+    struct rrdengine_worker_config *wc = &ctx->worker_config;
+    struct page_cache *pg_cache = &ctx->pg_cache;
+    int ret;
+    struct rrdeng_page_descr *descr;
+    struct page_cache_descr *pg_cache_descr;
+    Pvoid_t *PValue;
+    Word_t Index;
+    unsigned nr_committed_pages;
+
+    do {
+        uv_rwlock_wrlock(&pg_cache->committed_page_index.lock);
+        for (Index = 0,
+             PValue = JudyLFirst(pg_cache->committed_page_index.JudyL_array, &Index, PJE0),
+             descr = unlikely(NULL == PValue) ? NULL : *PValue;
+
+             descr != NULL;
+
+             PValue = JudyLNext(pg_cache->committed_page_index.JudyL_array, &Index, PJE0),
+                     descr = unlikely(NULL == PValue) ? NULL : *PValue) {
+            fatal_assert(0 != descr->page_length);
+
+            rrdeng_page_descr_mutex_lock(ctx, descr);
+            pg_cache_descr = descr->pg_cache_descr;
+            if (!(pg_cache_descr->flags & RRD_PAGE_WRITE_PENDING) && pg_cache_try_get_unsafe(descr, 1)) {
+                rrdeng_page_descr_mutex_unlock(ctx, descr);
+
+                ret = JudyLDel(&pg_cache->committed_page_index.JudyL_array, Index, PJE0);
+                fatal_assert(1 == ret);
+                break;
+            }
+            rrdeng_page_descr_mutex_unlock(ctx, descr);
+        }
+        uv_rwlock_wrunlock(&pg_cache->committed_page_index.lock);
+
+        if (!descr) {
+            info("Failed to invalidate any dirty pages to relieve page cache pressure.");
+
+            goto out;
+        }
+        pg_cache_punch_hole(ctx, descr, 1, 1, NULL);
+
+        uv_rwlock_wrlock(&pg_cache->committed_page_index.lock);
+        nr_committed_pages = --pg_cache->committed_page_index.nr_committed_pages;
+        uv_rwlock_wrunlock(&pg_cache->committed_page_index.lock);
+        rrd_stat_atomic_add(&ctx->stats.flushing_pressure_page_deletions, 1);
+        rrd_stat_atomic_add(&global_flushing_pressure_page_deletions, 1);
+
+    } while (nr_committed_pages >= pg_cache_committed_hard_limit(ctx));
+out:
+    wc->cleanup_thread_invalidating_dirty_pages = 1;
+    /* wake up event loop */
+    fatal_assert(0 == uv_async_send(&wc->async));
+}
+
+void rrdeng_invalidate_oldest_committed(struct rrdengine_worker_config* wc)
+{
+    struct rrdengine_instance *ctx = wc->ctx;
+    struct page_cache *pg_cache = &ctx->pg_cache;
+    unsigned nr_committed_pages;
+    int error;
+
+    if (unlikely(ctx->quiesce != NO_QUIESCE)) /* Shutting down */
+        return;
+
+    uv_rwlock_rdlock(&pg_cache->committed_page_index.lock);
+    nr_committed_pages = pg_cache->committed_page_index.nr_committed_pages;
+    uv_rwlock_rdunlock(&pg_cache->committed_page_index.lock);
+
+    if (nr_committed_pages >= pg_cache_committed_hard_limit(ctx)) {
+        /* delete the oldest page in memory */
+        if (wc->now_invalidating_dirty_pages) {
+            /* already deleting a page */
+            return;
+        }
+        errno = 0;
+        error("Failed to flush dirty buffers quickly enough in dbengine instance \"%s\". "
+              "Metric data are being deleted, please reduce disk load or use a faster disk.", ctx->dbfiles_path);
+
+        wc->now_invalidating_dirty_pages = mallocz(sizeof(*wc->now_invalidating_dirty_pages));
+        wc->cleanup_thread_invalidating_dirty_pages = 0;
+
+        error = uv_thread_create(wc->now_invalidating_dirty_pages, invalidate_oldest_committed, ctx);
+        if (error) {
+            error("uv_thread_create(): %s", uv_strerror(error));
+            freez(wc->now_invalidating_dirty_pages);
+            wc->now_invalidating_dirty_pages = NULL;
+        }
+    }
+}
+
+void flush_pages_cb(uv_fs_t* req)
+{
+    struct rrdengine_worker_config* wc = req->loop->data;
+    struct rrdengine_instance *ctx = wc->ctx;
+    struct page_cache *pg_cache = &ctx->pg_cache;
+    struct extent_io_descriptor *xt_io_descr;
+    struct rrdeng_page_descr *descr;
+    struct page_cache_descr *pg_cache_descr;
+    unsigned i, count;
+
+    xt_io_descr = req->data;
+    if (req->result < 0) {
+        ++ctx->stats.io_errors;
+        rrd_stat_atomic_add(&global_io_errors, 1);
+        error("%s: uv_fs_write: %s", __func__, uv_strerror((int)req->result));
+    }
+#ifdef NETDATA_INTERNAL_CHECKS
+    {
+        struct rrdengine_datafile *datafile = xt_io_descr->descr_array[0]->extent->datafile;
+        debug(D_RRDENGINE, "%s: Extent at offset %"PRIu64"(%u) was written to datafile %u-%u. Waking up waiters.",
+              __func__, xt_io_descr->pos, xt_io_descr->bytes, datafile->tier, datafile->fileno);
+    }
+#endif
+    count = xt_io_descr->descr_count;
+    for (i = 0 ; i < count ; ++i) {
+        /* care, we don't hold the descriptor mutex */
+        descr = xt_io_descr->descr_array[i];
+
+        pg_cache_replaceQ_insert(ctx, descr);
+
+        rrdeng_page_descr_mutex_lock(ctx, descr);
+        pg_cache_descr = descr->pg_cache_descr;
+        pg_cache_descr->flags &= ~(RRD_PAGE_DIRTY | RRD_PAGE_WRITE_PENDING);
+        /* wake up waiters, care no reference being held */
+        pg_cache_wake_up_waiters_unsafe(descr);
+        rrdeng_page_descr_mutex_unlock(ctx, descr);
+    }
+    if (xt_io_descr->completion)
+        complete(xt_io_descr->completion);
+    uv_fs_req_cleanup(req);
+    free(xt_io_descr->buf);
+    freez(xt_io_descr);
+
+    uv_rwlock_wrlock(&pg_cache->committed_page_index.lock);
+    pg_cache->committed_page_index.nr_committed_pages -= count;
+    uv_rwlock_wrunlock(&pg_cache->committed_page_index.lock);
+    wc->inflight_dirty_pages -= count;
+}
+
+/*
+ * completion must be NULL or valid.
+ * Returns 0 when no flushing can take place.
+ * Returns datafile bytes to be written on successful flushing initiation.
+ */
+static int do_flush_pages(struct rrdengine_worker_config* wc, int force, struct completion *completion)
+{
+    struct rrdengine_instance *ctx = wc->ctx;
+    struct page_cache *pg_cache = &ctx->pg_cache;
+    int ret;
+    int compressed_size, max_compressed_size = 0;
+    unsigned i, count, size_bytes, pos, real_io_size;
+    uint32_t uncompressed_payload_length, payload_offset;
+    struct rrdeng_page_descr *descr, *eligible_pages[MAX_PAGES_PER_EXTENT];
+    struct page_cache_descr *pg_cache_descr;
+    struct extent_io_descriptor *xt_io_descr;
+    void *compressed_buf = NULL;
+    Word_t descr_commit_idx_array[MAX_PAGES_PER_EXTENT];
+    Pvoid_t *PValue;
+    Word_t Index;
+    uint8_t compression_algorithm = ctx->global_compress_alg;
+    struct extent_info *extent;
+    struct rrdengine_datafile *datafile;
+    /* persistent structures */
+    struct rrdeng_df_extent_header *header;
+    struct rrdeng_df_extent_trailer *trailer;
+    uLong crc;
+
+    if (force) {
+        debug(D_RRDENGINE, "Asynchronous flushing of extent has been forced by page pressure.");
+    }
+    uv_rwlock_wrlock(&pg_cache->committed_page_index.lock);
+    for (Index = 0, count = 0, uncompressed_payload_length = 0,
+         PValue = JudyLFirst(pg_cache->committed_page_index.JudyL_array, &Index, PJE0),
+         descr = unlikely(NULL == PValue) ? NULL : *PValue ;
+
+         descr != NULL && count != MAX_PAGES_PER_EXTENT ;
+
+         PValue = JudyLNext(pg_cache->committed_page_index.JudyL_array, &Index, PJE0),
+         descr = unlikely(NULL == PValue) ? NULL : *PValue) {
+        uint8_t page_write_pending;
+
+        fatal_assert(0 != descr->page_length);
+        page_write_pending = 0;
+
+        rrdeng_page_descr_mutex_lock(ctx, descr);
+        pg_cache_descr = descr->pg_cache_descr;
+        if (!(pg_cache_descr->flags & RRD_PAGE_WRITE_PENDING)) {
+            page_write_pending = 1;
+            /* care, no reference being held */
+            pg_cache_descr->flags |= RRD_PAGE_WRITE_PENDING;
+            uncompressed_payload_length += descr->page_length;
+            descr_commit_idx_array[count] = Index;
+            eligible_pages[count++] = descr;
+        }
+        rrdeng_page_descr_mutex_unlock(ctx, descr);
+
+        if (page_write_pending) {
+            ret = JudyLDel(&pg_cache->committed_page_index.JudyL_array, Index, PJE0);
+            fatal_assert(1 == ret);
+        }
+    }
+    uv_rwlock_wrunlock(&pg_cache->committed_page_index.lock);
+
+    if (!count) {
+        debug(D_RRDENGINE, "%s: no pages eligible for flushing.", __func__);
+        if (completion)
+            complete(completion);
+        return 0;
+    }
+    wc->inflight_dirty_pages += count;
+
+    xt_io_descr = mallocz(sizeof(*xt_io_descr));
+    payload_offset = sizeof(*header) + count * sizeof(header->descr[0]);
+    switch (compression_algorithm) {
+    case RRD_NO_COMPRESSION:
+        size_bytes = payload_offset + uncompressed_payload_length + sizeof(*trailer);
+        break;
+    default: /* Compress */
+        fatal_assert(uncompressed_payload_length < LZ4_MAX_INPUT_SIZE);
+        max_compressed_size = LZ4_compressBound(uncompressed_payload_length);
+        compressed_buf = mallocz(max_compressed_size);
+        size_bytes = payload_offset + MAX(uncompressed_payload_length, (unsigned)max_compressed_size) + sizeof(*trailer);
+        break;
+    }
+    ret = posix_memalign((void *)&xt_io_descr->buf, RRDFILE_ALIGNMENT, ALIGN_BYTES_CEILING(size_bytes));
+    if (unlikely(ret)) {
+        fatal("posix_memalign:%s", strerror(ret));
+        /* freez(xt_io_descr);*/
+    }
+    (void) memcpy(xt_io_descr->descr_array, eligible_pages, sizeof(struct rrdeng_page_descr *) * count);
+    xt_io_descr->descr_count = count;
+
+    pos = 0;
+    header = xt_io_descr->buf;
+    header->compression_algorithm = compression_algorithm;
+    header->number_of_pages = count;
+    pos += sizeof(*header);
+
+    extent = mallocz(sizeof(*extent) + count * sizeof(extent->pages[0]));
+    datafile = ctx->datafiles.last;  /* TODO: check for exceeded size quota */
+    extent->offset = datafile->pos;
+    extent->number_of_pages = count;
+    extent->datafile = datafile;
+    extent->next = NULL;
+
+    for (i = 0 ; i < count ; ++i) {
+        /* This is here for performance reasons */
+        xt_io_descr->descr_commit_idx_array[i] = descr_commit_idx_array[i];
+
+        descr = xt_io_descr->descr_array[i];
+        header->descr[i].type = PAGE_METRICS;
+        uuid_copy(*(uuid_t *)header->descr[i].uuid, *descr->id);
+        header->descr[i].page_length = descr->page_length;
+        header->descr[i].start_time = descr->start_time;
+        header->descr[i].end_time = descr->end_time;
+        pos += sizeof(header->descr[i]);
+    }
+    for (i = 0 ; i < count ; ++i) {
+        descr = xt_io_descr->descr_array[i];
+        /* care, we don't hold the descriptor mutex */
+        (void) memcpy(xt_io_descr->buf + pos, descr->pg_cache_descr->page, descr->page_length);
+        descr->extent = extent;
+        extent->pages[i] = descr;
+
+        pos += descr->page_length;
+    }
+    df_extent_insert(extent);
+
+    switch (compression_algorithm) {
+    case RRD_NO_COMPRESSION:
+        header->payload_length = uncompressed_payload_length;
+        break;
+    default: /* Compress */
+        compressed_size = LZ4_compress_default(xt_io_descr->buf + payload_offset, compressed_buf,
+                                               uncompressed_payload_length, max_compressed_size);
+        ctx->stats.before_compress_bytes += uncompressed_payload_length;
+        ctx->stats.after_compress_bytes += compressed_size;
+        debug(D_RRDENGINE, "LZ4 compressed %"PRIu32" bytes to %d bytes.", uncompressed_payload_length, compressed_size);
+        (void) memcpy(xt_io_descr->buf + payload_offset, compressed_buf, compressed_size);
+        freez(compressed_buf);
+        size_bytes = payload_offset + compressed_size + sizeof(*trailer);
+        header->payload_length = compressed_size;
+        break;
+    }
+    extent->size = size_bytes;
+    xt_io_descr->bytes = size_bytes;
+    xt_io_descr->pos = datafile->pos;
+    xt_io_descr->req.data = xt_io_descr;
+    xt_io_descr->completion = completion;
+
+    trailer = xt_io_descr->buf + size_bytes - sizeof(*trailer);
+    crc = crc32(0L, Z_NULL, 0);
+    crc = crc32(crc, xt_io_descr->buf, size_bytes - sizeof(*trailer));
+    crc32set(trailer->checksum, crc);
+
+    real_io_size = ALIGN_BYTES_CEILING(size_bytes);
+    xt_io_descr->iov = uv_buf_init((void *)xt_io_descr->buf, real_io_size);
+    ret = uv_fs_write(wc->loop, &xt_io_descr->req, datafile->file, &xt_io_descr->iov, 1, datafile->pos, flush_pages_cb);
+    fatal_assert(-1 != ret);
+    ctx->stats.io_write_bytes += real_io_size;
+    ++ctx->stats.io_write_requests;
+    ctx->stats.io_write_extent_bytes += real_io_size;
+    ++ctx->stats.io_write_extents;
+    do_commit_transaction(wc, STORE_DATA, xt_io_descr);
+    datafile->pos += ALIGN_BYTES_CEILING(size_bytes);
+    ctx->disk_space += ALIGN_BYTES_CEILING(size_bytes);
+    rrdeng_test_quota(wc);
+
+    return ALIGN_BYTES_CEILING(size_bytes);
+}
+
+static void after_delete_old_data(struct rrdengine_worker_config* wc)
+{
+    struct rrdengine_instance *ctx = wc->ctx;
+    struct rrdengine_datafile *datafile;
+    struct rrdengine_journalfile *journalfile;
+    unsigned deleted_bytes, journalfile_bytes, datafile_bytes;
+    int ret, error;
+    char path[RRDENG_PATH_MAX];
+
+    datafile = ctx->datafiles.first;
+    journalfile = datafile->journalfile;
+    datafile_bytes = datafile->pos;
+    journalfile_bytes = journalfile->pos;
+    deleted_bytes = 0;
+
+    info("Deleting data and journal file pair.");
+    datafile_list_delete(ctx, datafile);
+    ret = destroy_journal_file(journalfile, datafile);
+    if (!ret) {
+        generate_journalfilepath(datafile, path, sizeof(path));
+        info("Deleted journal file \"%s\".", path);
+        deleted_bytes += journalfile_bytes;
+    }
+    ret = destroy_data_file(datafile);
+    if (!ret) {
+        generate_datafilepath(datafile, path, sizeof(path));
+        info("Deleted data file \"%s\".", path);
+        deleted_bytes += datafile_bytes;
+    }
+    freez(journalfile);
+    freez(datafile);
+
+    ctx->disk_space -= deleted_bytes;
+    info("Reclaimed %u bytes of disk space.", deleted_bytes);
+
+    error = uv_thread_join(wc->now_deleting_files);
+    if (error) {
+        error("uv_thread_join(): %s", uv_strerror(error));
+    }
+    freez(wc->now_deleting_files);
+    /* unfreeze command processing */
+    wc->now_deleting_files = NULL;
+
+    wc->cleanup_thread_deleting_files = 0;
+
+    /* interrupt event loop */
+    uv_stop(wc->loop);
+}
+
+static void delete_old_data(void *arg)
+{
+    struct rrdengine_instance *ctx = arg;
+    struct rrdengine_worker_config* wc = &ctx->worker_config;
+    struct rrdengine_datafile *datafile;
+    struct extent_info *extent, *next;
+    struct rrdeng_page_descr *descr;
+    unsigned count, i;
+    uint8_t can_delete_metric;
+    uuid_t metric_id;
+
+    /* Safe to use since it will be deleted after we are done */
+    datafile = ctx->datafiles.first;
+
+    for (extent = datafile->extents.first ; extent != NULL ; extent = next) {
+        count = extent->number_of_pages;
+        for (i = 0 ; i < count ; ++i) {
+            descr = extent->pages[i];
+            can_delete_metric = pg_cache_punch_hole(ctx, descr, 0, 0, &metric_id);
+            if (unlikely(can_delete_metric && ctx->metalog_ctx->initialized)) {
+                /*
+                 * If the metric is empty, has no active writers and if the metadata log has been initialized then
+                 * attempt to delete the corresponding netdata dimension.
+                 */
+                metalog_delete_dimension_by_uuid(ctx->metalog_ctx, &metric_id);
+            }
+        }
+        next = extent->next;
+        freez(extent);
+    }
+    wc->cleanup_thread_deleting_files = 1;
+    /* wake up event loop */
+    fatal_assert(0 == uv_async_send(&wc->async));
+}
+
+void rrdeng_test_quota(struct rrdengine_worker_config* wc)
+{
+    struct rrdengine_instance *ctx = wc->ctx;
+    struct rrdengine_datafile *datafile;
+    unsigned current_size, target_size;
+    uint8_t out_of_space, only_one_datafile;
+    int ret, error;
+
+    out_of_space = 0;
+    /* Do not allow the pinned pages to exceed the disk space quota to avoid deadlocks */
+    if (unlikely(ctx->disk_space > MAX(ctx->max_disk_space, 2 * ctx->metric_API_max_producers * RRDENG_BLOCK_SIZE))) {
+        out_of_space = 1;
+    }
+    datafile = ctx->datafiles.last;
+    current_size = datafile->pos;
+    target_size = ctx->max_disk_space / TARGET_DATAFILES;
+    target_size = MIN(target_size, MAX_DATAFILE_SIZE);
+    target_size = MAX(target_size, MIN_DATAFILE_SIZE);
+    only_one_datafile = (datafile == ctx->datafiles.first) ? 1 : 0;
+    if (unlikely(current_size >= target_size || (out_of_space && only_one_datafile))) {
+        /* Finalize data and journal file and create a new pair */
+        wal_flush_transaction_buffer(wc);
+        ret = create_new_datafile_pair(ctx, 1, ctx->last_fileno + 1);
+        if (likely(!ret)) {
+            ++ctx->last_fileno;
+        }
+    }
+    if (unlikely(out_of_space && NO_QUIESCE == ctx->quiesce)) {
+        /* delete old data */
+        if (wc->now_deleting_files) {
+            /* already deleting data */
+            return;
+        }
+        if (NULL == ctx->datafiles.first->next) {
+            error("Cannot delete data file \"%s/"DATAFILE_PREFIX RRDENG_FILE_NUMBER_PRINT_TMPL DATAFILE_EXTENSION"\""
+                 " to reclaim space, there are no other file pairs left.",
+                 ctx->dbfiles_path, ctx->datafiles.first->tier, ctx->datafiles.first->fileno);
+            return;
+        }
+        info("Deleting data file \"%s/"DATAFILE_PREFIX RRDENG_FILE_NUMBER_PRINT_TMPL DATAFILE_EXTENSION"\".",
+             ctx->dbfiles_path, ctx->datafiles.first->tier, ctx->datafiles.first->fileno);
+        wc->now_deleting_files = mallocz(sizeof(*wc->now_deleting_files));
+        wc->cleanup_thread_deleting_files = 0;
+
+        error = uv_thread_create(wc->now_deleting_files, delete_old_data, ctx);
+        if (error) {
+            error("uv_thread_create(): %s", uv_strerror(error));
+            freez(wc->now_deleting_files);
+            wc->now_deleting_files = NULL;
+        }
+    }
+}
+
+static inline int rrdeng_threads_alive(struct rrdengine_worker_config* wc)
+{
+    if (wc->now_invalidating_dirty_pages || wc->now_deleting_files) {
+        return 1;
+    }
+    return 0;
+}
+
+static void rrdeng_cleanup_finished_threads(struct rrdengine_worker_config* wc)
+{
+    struct rrdengine_instance *ctx = wc->ctx;
+
+    if (unlikely(wc->cleanup_thread_invalidating_dirty_pages)) {
+        after_invalidate_oldest_committed(wc);
+    }
+    if (unlikely(wc->cleanup_thread_deleting_files)) {
+        after_delete_old_data(wc);
+    }
+    if (unlikely(SET_QUIESCE == ctx->quiesce && !rrdeng_threads_alive(wc))) {
+        ctx->quiesce = QUIESCED;
+        complete(&ctx->rrdengine_completion);
+    }
+}
+
+/* return 0 on success */
+int init_rrd_files(struct rrdengine_instance *ctx)
+{
+    return init_data_files(ctx);
+}
+
+void finalize_rrd_files(struct rrdengine_instance *ctx)
+{
+    return finalize_data_files(ctx);
+}
+
+void rrdeng_init_cmd_queue(struct rrdengine_worker_config* wc)
+{
+    wc->cmd_queue.head = wc->cmd_queue.tail = 0;
+    wc->queue_size = 0;
+    fatal_assert(0 == uv_cond_init(&wc->cmd_cond));
+    fatal_assert(0 == uv_mutex_init(&wc->cmd_mutex));
+}
+
+void rrdeng_enq_cmd(struct rrdengine_worker_config* wc, struct rrdeng_cmd *cmd)
+{
+    unsigned queue_size;
+
+    /* wait for free space in queue */
+    uv_mutex_lock(&wc->cmd_mutex);
+    while ((queue_size = wc->queue_size) == RRDENG_CMD_Q_MAX_SIZE) {
+        uv_cond_wait(&wc->cmd_cond, &wc->cmd_mutex);
+    }
+    fatal_assert(queue_size < RRDENG_CMD_Q_MAX_SIZE);
+    /* enqueue command */
+    wc->cmd_queue.cmd_array[wc->cmd_queue.tail] = *cmd;
+    wc->cmd_queue.tail = wc->cmd_queue.tail != RRDENG_CMD_Q_MAX_SIZE - 1 ?
+                         wc->cmd_queue.tail + 1 : 0;
+    wc->queue_size = queue_size + 1;
+    uv_mutex_unlock(&wc->cmd_mutex);
+
+    /* wake up event loop */
+    fatal_assert(0 == uv_async_send(&wc->async));
+}
+
+struct rrdeng_cmd rrdeng_deq_cmd(struct rrdengine_worker_config* wc)
+{
+    struct rrdeng_cmd ret;
+    unsigned queue_size;
+
+    uv_mutex_lock(&wc->cmd_mutex);
+    queue_size = wc->queue_size;
+    if (queue_size == 0) {
+        ret.opcode = RRDENG_NOOP;
+    } else {
+        /* dequeue command */
+        ret = wc->cmd_queue.cmd_array[wc->cmd_queue.head];
+        if (queue_size == 1) {
+            wc->cmd_queue.head = wc->cmd_queue.tail = 0;
+        } else {
+            wc->cmd_queue.head = wc->cmd_queue.head != RRDENG_CMD_Q_MAX_SIZE - 1 ?
+                                 wc->cmd_queue.head + 1 : 0;
+        }
+        wc->queue_size = queue_size - 1;
+
+        /* wake up producers */
+        uv_cond_signal(&wc->cmd_cond);
+    }
+    uv_mutex_unlock(&wc->cmd_mutex);
+
+    return ret;
+}
+
+void async_cb(uv_async_t *handle)
+{
+    uv_stop(handle->loop);
+    uv_update_time(handle->loop);
+    debug(D_RRDENGINE, "%s called, active=%d.", __func__, uv_is_active((uv_handle_t *)handle));
+}
+
+/* Flushes dirty pages when timer expires */
+#define TIMER_PERIOD_MS (1000)
+
+void timer_cb(uv_timer_t* handle)
+{
+    struct rrdengine_worker_config* wc = handle->data;
+    struct rrdengine_instance *ctx = wc->ctx;
+
+    uv_stop(handle->loop);
+    uv_update_time(handle->loop);
+    if (unlikely(!ctx->metalog_ctx->initialized))
+        return; /* Wait for the metadata log to initialize */
+    rrdeng_test_quota(wc);
+    debug(D_RRDENGINE, "%s: timeout reached.", __func__);
+    if (likely(!wc->now_deleting_files && !wc->now_invalidating_dirty_pages)) {
+        /* There is free space so we can write to disk and we are not actively deleting dirty buffers */
+        struct page_cache *pg_cache = &ctx->pg_cache;
+        unsigned long total_bytes, bytes_written, nr_committed_pages, bytes_to_write = 0, producers, low_watermark,
+                      high_watermark;
+
+        uv_rwlock_rdlock(&pg_cache->committed_page_index.lock);
+        nr_committed_pages = pg_cache->committed_page_index.nr_committed_pages;
+        uv_rwlock_rdunlock(&pg_cache->committed_page_index.lock);
+        producers = ctx->metric_API_max_producers;
+        /* are flushable pages more than 25% of the maximum page cache size */
+        high_watermark = (ctx->max_cache_pages * 25LLU) / 100;
+        low_watermark = (ctx->max_cache_pages * 5LLU) / 100; /* 5%, must be smaller than high_watermark */
+
+        /* Flush more pages only if disk can keep up */
+        if (wc->inflight_dirty_pages < high_watermark + producers) {
+            if (nr_committed_pages > producers &&
+                /* committed to be written pages are more than the produced number */
+                nr_committed_pages - producers > high_watermark) {
+                /* Flushing speed must increase to stop page cache from filling with dirty pages */
+                bytes_to_write = (nr_committed_pages - producers - low_watermark) * RRDENG_BLOCK_SIZE;
+            }
+            bytes_to_write = MAX(DATAFILE_IDEAL_IO_SIZE, bytes_to_write);
+
+            debug(D_RRDENGINE, "Flushing pages to disk.");
+            for (total_bytes = bytes_written = do_flush_pages(wc, 0, NULL);
+                 bytes_written && (total_bytes < bytes_to_write);
+                 total_bytes += bytes_written) {
+                bytes_written = do_flush_pages(wc, 0, NULL);
+            }
+        }
+    }
+#ifdef NETDATA_INTERNAL_CHECKS
+    {
+        char buf[4096];
+        debug(D_RRDENGINE, "%s", get_rrdeng_statistics(wc->ctx, buf, sizeof(buf)));
+    }
+#endif
+}
+
+#define MAX_CMD_BATCH_SIZE (256)
+
+void rrdeng_worker(void* arg)
+{
+    struct rrdengine_worker_config* wc = arg;
+    struct rrdengine_instance *ctx = wc->ctx;
+    uv_loop_t* loop;
+    int shutdown, ret;
+    enum rrdeng_opcode opcode;
+    uv_timer_t timer_req;
+    struct rrdeng_cmd cmd;
+    unsigned cmd_batch_size;
+
+    rrdeng_init_cmd_queue(wc);
+
+    loop = wc->loop = mallocz(sizeof(uv_loop_t));
+    ret = uv_loop_init(loop);
+    if (ret) {
+        error("uv_loop_init(): %s", uv_strerror(ret));
+        goto error_after_loop_init;
+    }
+    loop->data = wc;
+
+    ret = uv_async_init(wc->loop, &wc->async, async_cb);
+    if (ret) {
+        error("uv_async_init(): %s", uv_strerror(ret));
+        goto error_after_async_init;
+    }
+    wc->async.data = wc;
+
+    wc->now_deleting_files = NULL;
+    wc->cleanup_thread_deleting_files = 0;
+
+    wc->now_invalidating_dirty_pages = NULL;
+    wc->cleanup_thread_invalidating_dirty_pages = 0;
+    wc->inflight_dirty_pages = 0;
+
+    /* dirty page flushing timer */
+    ret = uv_timer_init(loop, &timer_req);
+    if (ret) {
+        error("uv_timer_init(): %s", uv_strerror(ret));
+        goto error_after_timer_init;
+    }
+    timer_req.data = wc;
+
+    wc->error = 0;
+    /* wake up initialization thread */
+    complete(&ctx->rrdengine_completion);
+
+    fatal_assert(0 == uv_timer_start(&timer_req, timer_cb, TIMER_PERIOD_MS, TIMER_PERIOD_MS));
+    shutdown = 0;
+    while (likely(shutdown == 0 || rrdeng_threads_alive(wc))) {
+        uv_run(loop, UV_RUN_DEFAULT);
+        rrdeng_cleanup_finished_threads(wc);
+
+        /* wait for commands */
+        cmd_batch_size = 0;
+        do {
+            /*
+             * Avoid starving the loop when there are too many commands coming in.
+             * timer_cb will interrupt the loop again to allow serving more commands.
+             */
+            if (unlikely(cmd_batch_size >= MAX_CMD_BATCH_SIZE))
+                break;
+
+            cmd = rrdeng_deq_cmd(wc);
+            opcode = cmd.opcode;
+            ++cmd_batch_size;
+
+            switch (opcode) {
+            case RRDENG_NOOP:
+                /* the command queue was empty, do nothing */
+                break;
+            case RRDENG_SHUTDOWN:
+                shutdown = 1;
+                break;
+            case RRDENG_QUIESCE:
+                ctx->drop_metrics_under_page_cache_pressure = 0;
+                ctx->quiesce = SET_QUIESCE;
+                fatal_assert(0 == uv_timer_stop(&timer_req));
+                uv_close((uv_handle_t *)&timer_req, NULL);
+                while (do_flush_pages(wc, 1, NULL)) {
+                    ; /* Force flushing of all committed pages. */
+                }
+                wal_flush_transaction_buffer(wc);
+                if (!rrdeng_threads_alive(wc)) {
+                    ctx->quiesce = QUIESCED;
+                    complete(&ctx->rrdengine_completion);
+                }
+                break;
+            case RRDENG_READ_PAGE:
+                do_read_extent(wc, &cmd.read_page.page_cache_descr, 1, 0);
+                break;
+            case RRDENG_READ_EXTENT:
+                do_read_extent(wc, cmd.read_extent.page_cache_descr, cmd.read_extent.page_count, 1);
+                break;
+            case RRDENG_COMMIT_PAGE:
+                do_commit_transaction(wc, STORE_DATA, NULL);
+                break;
+            case RRDENG_FLUSH_PAGES: {
+                if (wc->now_invalidating_dirty_pages) {
+                    /* Do not flush if the disk cannot keep up */
+                    complete(cmd.completion);
+                } else {
+                    (void)do_flush_pages(wc, 1, cmd.completion);
+                }
+                break;
+            case RRDENG_INVALIDATE_OLDEST_MEMORY_PAGE:
+                rrdeng_invalidate_oldest_committed(wc);
+                break;
+            }
+            default:
+                debug(D_RRDENGINE, "%s: default.", __func__);
+                break;
+            }
+        } while (opcode != RRDENG_NOOP);
+    }
+
+    /* cleanup operations of the event loop */
+    info("Shutting down RRD engine event loop.");
+
+    /*
+     * uv_async_send after uv_close does not seem to crash in linux at the moment,
+     * it is however undocumented behaviour and we need to be aware if this becomes
+     * an issue in the future.
+     */
+    uv_close((uv_handle_t *)&wc->async, NULL);
+
+    while (do_flush_pages(wc, 1, NULL)) {
+        ; /* Force flushing of all committed pages. */
+    }
+    wal_flush_transaction_buffer(wc);
+    uv_run(loop, UV_RUN_DEFAULT);
+
+    info("Shutting down RRD engine event loop complete.");
+    /* TODO: don't let the API block by waiting to enqueue commands */
+    uv_cond_destroy(&wc->cmd_cond);
+/*  uv_mutex_destroy(&wc->cmd_mutex); */
+    fatal_assert(0 == uv_loop_close(loop));
+    freez(loop);
+
+    return;
+
+error_after_timer_init:
+    uv_close((uv_handle_t *)&wc->async, NULL);
+error_after_async_init:
+    fatal_assert(0 == uv_loop_close(loop));
+error_after_loop_init:
+    freez(loop);
+
+    wc->error = UV_EAGAIN;
+    /* wake up initialization thread */
+    complete(&ctx->rrdengine_completion);
+}
+
+/* C entry point for development purposes
+ * make "LDFLAGS=-errdengine_main"
+ */
+void rrdengine_main(void)
+{
+    int ret;
+    struct rrdengine_instance *ctx;
+
+    sanity_check();
+    ret = rrdeng_init(NULL, &ctx, "/tmp", RRDENG_MIN_PAGE_CACHE_SIZE_MB, RRDENG_MIN_DISK_SPACE_MB);
+    if (ret) {
+        exit(ret);
+    }
+    rrdeng_exit(ctx);
+    fprintf(stderr, "Hello world!");
+    exit(0);
+}