Adding upstream version 1.46.3.

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

1 files changed, 1117 insertions, 0 deletions

diff --git a/src/database/engine/pagecache.c b/src/database/engine/pagecache.c
new file mode 100644
index 000000000..a88992223
--- /dev/null
+++ b/src/database/engine/pagecache.c
@@ -0,0 +1,1117 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+#define NETDATA_RRD_INTERNALS
+
+#include "rrdengine.h"
+
+MRG *main_mrg = NULL;
+PGC *main_cache = NULL;
+PGC *open_cache = NULL;
+PGC *extent_cache = NULL;
+struct rrdeng_cache_efficiency_stats rrdeng_cache_efficiency_stats = {};
+
+static void main_cache_free_clean_page_callback(PGC *cache __maybe_unused, PGC_ENTRY entry __maybe_unused)
+{
+    // Release storage associated with the page
+    pgd_free(entry.data);
+}
+
+static void main_cache_flush_dirty_page_init_callback(PGC *cache __maybe_unused, Word_t section) {
+    struct rrdengine_instance *ctx = (struct rrdengine_instance *) section;
+
+    // mark ctx as having flushing in progress
+    __atomic_add_fetch(&ctx->atomic.extents_currently_being_flushed, 1, __ATOMIC_RELAXED);
+}
+
+static void main_cache_flush_dirty_page_callback(PGC *cache __maybe_unused, PGC_ENTRY *entries_array __maybe_unused, PGC_PAGE **pages_array __maybe_unused, size_t entries __maybe_unused)
+{
+    if(!entries)
+        return;
+
+     struct rrdengine_instance *ctx = (struct rrdengine_instance *) entries_array[0].section;
+
+    struct page_descr_with_data *base = NULL;
+
+    for (size_t Index = 0 ; Index < entries; Index++) {
+        time_t start_time_s = entries_array[Index].start_time_s;
+        time_t end_time_s = entries_array[Index].end_time_s;
+        struct page_descr_with_data *descr = page_descriptor_get();
+
+        descr->id = mrg_metric_uuid(main_mrg, (METRIC *) entries_array[Index].metric_id);
+        descr->metric_id = entries_array[Index].metric_id;
+        descr->start_time_ut = start_time_s * USEC_PER_SEC;
+        descr->end_time_ut = end_time_s * USEC_PER_SEC;
+        descr->update_every_s = entries_array[Index].update_every_s;
+
+        descr->pgd = pgc_page_data(pages_array[Index]);
+        descr->type = pgd_type(descr->pgd);
+        descr->page_length = pgd_disk_footprint(descr->pgd);
+
+        DOUBLE_LINKED_LIST_APPEND_ITEM_UNSAFE(base, descr, link.prev, link.next);
+
+        // TODO: ask @stelfrag/@ktsaou about this.
+        // internal_fatal(descr->page_length > RRDENG_BLOCK_SIZE, "DBENGINE: faulty page length calculation");
+    }
+
+    struct completion completion;
+    completion_init(&completion);
+    rrdeng_enq_cmd(ctx, RRDENG_OPCODE_EXTENT_WRITE, base, &completion, STORAGE_PRIORITY_INTERNAL_DBENGINE, NULL, NULL);
+    completion_wait_for(&completion);
+    completion_destroy(&completion);
+}
+
+static void open_cache_free_clean_page_callback(PGC *cache __maybe_unused, PGC_ENTRY entry __maybe_unused)
+{
+    struct rrdengine_datafile *datafile = entry.data;
+    datafile_release(datafile, DATAFILE_ACQUIRE_OPEN_CACHE);
+}
+
+static void open_cache_flush_dirty_page_callback(PGC *cache __maybe_unused, PGC_ENTRY *entries_array __maybe_unused, PGC_PAGE **pages_array __maybe_unused, size_t entries __maybe_unused)
+{
+    ;
+}
+
+static void extent_cache_free_clean_page_callback(PGC *cache __maybe_unused, PGC_ENTRY entry __maybe_unused)
+{
+    dbengine_extent_free(entry.data, entry.size);
+}
+
+static void extent_cache_flush_dirty_page_callback(PGC *cache __maybe_unused, PGC_ENTRY *entries_array __maybe_unused, PGC_PAGE **pages_array __maybe_unused, size_t entries __maybe_unused)
+{
+    ;
+}
+
+inline TIME_RANGE_COMPARE is_page_in_time_range(time_t page_first_time_s, time_t page_last_time_s, time_t wanted_start_time_s, time_t wanted_end_time_s) {
+    // page_first_time_s <= wanted_end_time_s && page_last_time_s >= wanted_start_time_s
+
+    if(page_last_time_s < wanted_start_time_s)
+        return PAGE_IS_IN_THE_PAST;
+
+    if(page_first_time_s > wanted_end_time_s)
+        return PAGE_IS_IN_THE_FUTURE;
+
+    return PAGE_IS_IN_RANGE;
+}
+
+static inline struct page_details *pdc_find_page_for_time(
+        Pcvoid_t PArray,
+        time_t wanted_time_s,
+        size_t *gaps,
+        PDC_PAGE_STATUS mode,
+        PDC_PAGE_STATUS skip_list
+) {
+    Word_t PIndexF = wanted_time_s, PIndexL = wanted_time_s;
+    Pvoid_t *PValueF, *PValueL;
+    struct page_details *pdF = NULL, *pdL = NULL;
+    bool firstF = true, firstL = true;
+
+    PDC_PAGE_STATUS ignore_list = PDC_PAGE_QUERY_GLOBAL_SKIP_LIST | skip_list;
+
+    while ((PValueF = PDCJudyLFirstThenNext(PArray, &PIndexF, &firstF))) {
+        pdF = *PValueF;
+
+        PDC_PAGE_STATUS status = __atomic_load_n(&pdF->status, __ATOMIC_ACQUIRE);
+        if (!(status & (ignore_list | mode)))
+            break;
+
+        pdF = NULL;
+    }
+
+    while ((PValueL = PDCJudyLLastThenPrev(PArray, &PIndexL, &firstL))) {
+        pdL = *PValueL;
+
+        PDC_PAGE_STATUS status = __atomic_load_n(&pdL->status, __ATOMIC_ACQUIRE);
+        if(status & mode) {
+            // don't go all the way back to the beginning
+            // stop at the last processed
+            pdL = NULL;
+            break;
+        }
+
+        if (!(status & ignore_list))
+            break;
+
+        pdL = NULL;
+    }
+
+    TIME_RANGE_COMPARE rcF = (pdF) ? is_page_in_time_range(pdF->first_time_s, pdF->last_time_s, wanted_time_s, wanted_time_s) : PAGE_IS_IN_THE_FUTURE;
+    TIME_RANGE_COMPARE rcL = (pdL) ? is_page_in_time_range(pdL->first_time_s, pdL->last_time_s, wanted_time_s, wanted_time_s) : PAGE_IS_IN_THE_PAST;
+
+    if (!pdF || pdF == pdL) {
+        // F is missing, or they are the same
+        // return L
+        (*gaps) += (rcL == PAGE_IS_IN_RANGE) ? 0 : 1;
+        return pdL;
+    }
+
+    if (!pdL) {
+        // L is missing
+        // return F
+        (*gaps) += (rcF == PAGE_IS_IN_RANGE) ? 0 : 1;
+        return pdF;
+    }
+
+    if (rcF == rcL) {
+        // both are on the same side,
+        // but they are different pages
+
+        switch (rcF) {
+            case PAGE_IS_IN_RANGE:
+                // pick the higher resolution
+                if (pdF->update_every_s && pdF->update_every_s < pdL->update_every_s)
+                    return pdF;
+
+                if (pdL->update_every_s && pdL->update_every_s < pdF->update_every_s)
+                    return pdL;
+
+                // same resolution - pick the one that starts earlier
+                if (pdL->first_time_s < pdF->first_time_s)
+                    return pdL;
+
+                return pdF;
+                break;
+
+            case PAGE_IS_IN_THE_FUTURE:
+                (*gaps)++;
+
+                // pick the one that starts earlier
+                if (pdL->first_time_s < pdF->first_time_s)
+                    return pdL;
+
+                return pdF;
+                break;
+
+            default:
+            case PAGE_IS_IN_THE_PAST:
+                (*gaps)++;
+                return NULL;
+                break;
+        }
+    }
+
+    if(rcF == PAGE_IS_IN_RANGE) {
+        // (*gaps) += 0;
+        return pdF;
+    }
+
+    if(rcL == PAGE_IS_IN_RANGE) {
+        // (*gaps) += 0;
+        return pdL;
+    }
+
+    if(rcF == PAGE_IS_IN_THE_FUTURE) {
+        (*gaps)++;
+        return pdF;
+    }
+
+    if(rcL == PAGE_IS_IN_THE_FUTURE) {
+        (*gaps)++;
+        return pdL;
+    }
+
+    // impossible case
+    (*gaps)++;
+    return NULL;
+}
+
+static size_t get_page_list_from_pgc(PGC *cache, METRIC *metric, struct rrdengine_instance *ctx,
+        time_t wanted_start_time_s, time_t wanted_end_time_s,
+        Pvoid_t *JudyL_page_array, size_t *cache_gaps,
+        bool open_cache_mode, PDC_PAGE_STATUS tags) {
+
+    size_t pages_found_in_cache = 0;
+    Word_t metric_id = mrg_metric_id(main_mrg, metric);
+
+    time_t now_s = wanted_start_time_s;
+    uint32_t dt_s = mrg_metric_get_update_every_s(main_mrg, metric);
+
+    if(!dt_s)
+        dt_s = default_rrd_update_every;
+
+    time_t previous_page_end_time_s = now_s - dt_s;
+    bool first = true;
+
+    do {
+        PGC_PAGE *page = pgc_page_get_and_acquire(
+                cache, (Word_t)ctx, (Word_t)metric_id, now_s,
+                (first) ? PGC_SEARCH_CLOSEST : PGC_SEARCH_NEXT);
+
+        first = false;
+
+        if(!page) {
+            if(previous_page_end_time_s < wanted_end_time_s)
+                (*cache_gaps)++;
+
+            break;
+        }
+
+        time_t page_start_time_s = pgc_page_start_time_s(page);
+        time_t page_end_time_s = pgc_page_end_time_s(page);
+        uint32_t page_update_every_s = pgc_page_update_every_s(page);
+
+        if(!page_update_every_s)
+            page_update_every_s = dt_s;
+
+        if(is_page_in_time_range(page_start_time_s, page_end_time_s, wanted_start_time_s, wanted_end_time_s) != PAGE_IS_IN_RANGE) {
+            // not a useful page for this query
+            pgc_page_release(cache, page);
+            page = NULL;
+
+            if(previous_page_end_time_s < wanted_end_time_s)
+                (*cache_gaps)++;
+
+            break;
+        }
+
+        if (page_start_time_s - previous_page_end_time_s > dt_s)
+            (*cache_gaps)++;
+
+        Pvoid_t *PValue = PDCJudyLIns(JudyL_page_array, (Word_t) page_start_time_s, PJE0);
+        if (!PValue || PValue == PJERR)
+            fatal("DBENGINE: corrupted judy array in %s()", __FUNCTION__ );
+
+        if (unlikely(*PValue))
+            // already exists in our list
+            pgc_page_release(cache, page);
+
+        else {
+
+            internal_fatal(pgc_page_metric(page) != metric_id, "Wrong metric id in page found in cache");
+            internal_fatal(pgc_page_section(page) != (Word_t)ctx, "Wrong section in page found in cache");
+
+            struct page_details *pd = page_details_get();
+            pd->metric_id = metric_id;
+            pd->first_time_s = page_start_time_s;
+            pd->last_time_s = page_end_time_s;
+            pd->update_every_s = page_update_every_s;
+            pd->page = (open_cache_mode) ? NULL : page;
+            pd->status |= tags;
+
+            if((pd->page)) {
+                pd->status |= PDC_PAGE_READY | PDC_PAGE_PRELOADED;
+
+                if(pgd_is_empty(pgc_page_data(page)))
+                    pd->status |= PDC_PAGE_EMPTY;
+            }
+
+            if(open_cache_mode) {
+                struct rrdengine_datafile *datafile = pgc_page_data(page);
+                if(datafile_acquire(datafile, DATAFILE_ACQUIRE_PAGE_DETAILS)) { // for pd
+                    struct extent_io_data *xio = (struct extent_io_data *) pgc_page_custom_data(cache, page);
+                    pd->datafile.ptr = pgc_page_data(page);
+                    pd->datafile.file = xio->file;
+                    pd->datafile.extent.pos = xio->pos;
+                    pd->datafile.extent.bytes = xio->bytes;
+                    pd->datafile.fileno = pd->datafile.ptr->fileno;
+                    pd->status |= PDC_PAGE_DATAFILE_ACQUIRED | PDC_PAGE_DISK_PENDING;
+                }
+                else {
+                    pd->status |= PDC_PAGE_FAILED | PDC_PAGE_FAILED_TO_ACQUIRE_DATAFILE;
+                }
+                pgc_page_release(cache, page);
+            }
+
+            *PValue = pd;
+
+            pages_found_in_cache++;
+        }
+
+        // prepare for the next iteration
+        previous_page_end_time_s = page_end_time_s;
+
+        if(page_update_every_s > 0)
+            dt_s = page_update_every_s;
+
+        // we are going to as for the NEXT page
+        // so, set this to our first time
+        now_s = page_start_time_s;
+
+    } while(now_s <= wanted_end_time_s);
+
+    return pages_found_in_cache;
+}
+
+static void pgc_inject_gap(struct rrdengine_instance *ctx, METRIC *metric, time_t start_time_s, time_t end_time_s) {
+
+    time_t db_first_time_s, db_last_time_s;
+    mrg_metric_get_retention(main_mrg, metric, &db_first_time_s, &db_last_time_s, NULL);
+
+    if(is_page_in_time_range(start_time_s, end_time_s, db_first_time_s, db_last_time_s) != PAGE_IS_IN_RANGE)
+        return;
+
+    PGC_ENTRY page_entry = {
+            .hot = false,
+            .section = (Word_t)ctx,
+            .metric_id = (Word_t)metric,
+            .start_time_s = MAX(start_time_s, db_first_time_s),
+            .end_time_s = MIN(end_time_s, db_last_time_s),
+            .update_every_s = 0,
+            .size = 0,
+            .data = PGD_EMPTY,
+    };
+
+    if(page_entry.start_time_s >= page_entry.end_time_s)
+        return;
+
+    PGC_PAGE *page = pgc_page_add_and_acquire(main_cache, page_entry, NULL);
+    pgc_page_release(main_cache, page);
+}
+
+static size_t list_has_time_gaps(
+        struct rrdengine_instance *ctx,
+        METRIC *metric,
+        Pvoid_t JudyL_page_array,
+        time_t wanted_start_time_s,
+        time_t wanted_end_time_s,
+        size_t *pages_total,
+        size_t *pages_found_pass4,
+        size_t *pages_to_load_from_disk,
+        size_t *pages_overlapping,
+        time_t *optimal_end_time_s,
+        bool populate_gaps,
+        PDC_PAGE_STATUS *common_status
+) {
+    // we will recalculate these, so zero them
+    *pages_to_load_from_disk = 0;
+    *pages_overlapping = 0;
+    *optimal_end_time_s = 0;
+    *common_status = 0;
+
+    bool first;
+    Pvoid_t *PValue;
+    Word_t this_page_start_time;
+    struct page_details *pd;
+
+    size_t gaps = 0;
+    Word_t metric_id = mrg_metric_id(main_mrg, metric);
+
+    // ------------------------------------------------------------------------
+    // PASS 1: remove the preprocessing flags from the pages in PDC
+
+    first = true;
+    this_page_start_time = 0;
+    while((PValue = PDCJudyLFirstThenNext(JudyL_page_array, &this_page_start_time, &first))) {
+        pd = *PValue;
+        pd->status &= ~(PDC_PAGE_SKIP|PDC_PAGE_PREPROCESSED);
+    }
+
+    // ------------------------------------------------------------------------
+    // PASS 2: emulate processing to find the useful pages
+
+    time_t now_s = wanted_start_time_s;
+    time_t dt_s = mrg_metric_get_update_every_s(main_mrg, metric);
+    if(!dt_s)
+        dt_s = default_rrd_update_every;
+
+    size_t pages_pass2 = 0, pages_pass3 = 0;
+    while((pd = pdc_find_page_for_time(
+            JudyL_page_array, now_s, &gaps,
+            PDC_PAGE_PREPROCESSED, 0))) {
+
+        pd->status |= PDC_PAGE_PREPROCESSED;
+        pages_pass2++;
+
+        if(pd->update_every_s)
+            dt_s = pd->update_every_s;
+
+        if(populate_gaps && pd->first_time_s > now_s)
+            pgc_inject_gap(ctx, metric, now_s, pd->first_time_s);
+
+        now_s = pd->last_time_s + dt_s;
+        if(now_s > wanted_end_time_s) {
+            *optimal_end_time_s = pd->last_time_s;
+            break;
+        }
+    }
+
+    if(populate_gaps && now_s < wanted_end_time_s)
+        pgc_inject_gap(ctx, metric, now_s, wanted_end_time_s);
+
+    // ------------------------------------------------------------------------
+    // PASS 3: mark as skipped all the pages not useful
+
+    first = true;
+    this_page_start_time = 0;
+    while((PValue = PDCJudyLFirstThenNext(JudyL_page_array, &this_page_start_time, &first))) {
+        pd = *PValue;
+
+        internal_fatal(pd->metric_id != metric_id, "pd has wrong metric_id");
+
+        if(!(pd->status & PDC_PAGE_PREPROCESSED)) {
+            (*pages_overlapping)++;
+            pd->status |= PDC_PAGE_SKIP;
+            pd->status &= ~(PDC_PAGE_READY | PDC_PAGE_DISK_PENDING);
+            *common_status |= pd->status;
+            continue;
+        }
+
+        pages_pass3++;
+
+        if(!pd->page) {
+            pd->page = pgc_page_get_and_acquire(main_cache, (Word_t) ctx, (Word_t) metric_id, pd->first_time_s, PGC_SEARCH_EXACT);
+
+            if(pd->page) {
+                (*pages_found_pass4)++;
+
+                pd->status &= ~PDC_PAGE_DISK_PENDING;
+                pd->status |= PDC_PAGE_READY | PDC_PAGE_PRELOADED | PDC_PAGE_PRELOADED_PASS4;
+
+                if(pgd_is_empty(pgc_page_data(pd->page)))
+                    pd->status |= PDC_PAGE_EMPTY;
+
+            }
+            else if(!(pd->status & PDC_PAGE_FAILED) && (pd->status & PDC_PAGE_DATAFILE_ACQUIRED)) {
+                (*pages_to_load_from_disk)++;
+
+                pd->status |= PDC_PAGE_DISK_PENDING;
+
+                internal_fatal(pd->status & PDC_PAGE_SKIP, "page is disk pending and skipped");
+                internal_fatal(!pd->datafile.ptr, "datafile is NULL");
+                internal_fatal(!pd->datafile.extent.bytes, "datafile.extent.bytes zero");
+                internal_fatal(!pd->datafile.extent.pos, "datafile.extent.pos is zero");
+                internal_fatal(!pd->datafile.fileno, "datafile.fileno is zero");
+            }
+        }
+        else {
+            pd->status &= ~PDC_PAGE_DISK_PENDING;
+            pd->status |= (PDC_PAGE_READY | PDC_PAGE_PRELOADED);
+        }
+
+        *common_status |= pd->status;
+    }
+
+    internal_fatal(pages_pass2 != pages_pass3,
+                   "DBENGINE: page count does not match");
+
+    *pages_total = pages_pass2;
+
+    return gaps;
+}
+
+// ----------------------------------------------------------------------------
+
+typedef void (*page_found_callback_t)(PGC_PAGE *page, void *data);
+static size_t get_page_list_from_journal_v2(struct rrdengine_instance *ctx, METRIC *metric, usec_t start_time_ut, usec_t end_time_ut, page_found_callback_t callback, void *callback_data) {
+    nd_uuid_t *uuid = mrg_metric_uuid(main_mrg, metric);
+    Word_t metric_id = mrg_metric_id(main_mrg, metric);
+
+    time_t wanted_start_time_s = (time_t)(start_time_ut / USEC_PER_SEC);
+    time_t wanted_end_time_s = (time_t)(end_time_ut / USEC_PER_SEC);
+
+    size_t pages_found = 0;
+
+    NJFV2IDX_FIND_STATE state = {
+            .init = false,
+            .last = 0,
+            .ctx = ctx,
+            .wanted_start_time_s = wanted_start_time_s,
+            .wanted_end_time_s = wanted_end_time_s,
+            .j2_header_acquired = NULL,
+    };
+
+    struct rrdengine_datafile *datafile;
+    while((datafile = njfv2idx_find_and_acquire_j2_header(&state))) {
+        struct journal_v2_header *j2_header = state.j2_header_acquired;
+
+        if (unlikely(!j2_header))
+            continue;
+
+        time_t journal_start_time_s = (time_t)(j2_header->start_time_ut / USEC_PER_SEC);
+
+        // the datafile possibly contains useful data for this query
+
+        size_t journal_metric_count = (size_t)j2_header->metric_count;
+        struct journal_metric_list *uuid_list = (struct journal_metric_list *)((uint8_t *) j2_header + j2_header->metric_offset);
+        struct journal_metric_list *uuid_entry = bsearch(uuid,uuid_list,journal_metric_count,sizeof(*uuid_list), journal_metric_uuid_compare);
+
+        if (unlikely(!uuid_entry)) {
+            // our UUID is not in this datafile
+            journalfile_v2_data_release(datafile->journalfile);
+            continue;
+        }
+
+        struct journal_page_header *page_list_header = (struct journal_page_header *) ((uint8_t *) j2_header + uuid_entry->page_offset);
+        struct journal_page_list *page_list = (struct journal_page_list *)((uint8_t *) page_list_header + sizeof(*page_list_header));
+        struct journal_extent_list *extent_list = (void *)((uint8_t *)j2_header + j2_header->extent_offset);
+        uint32_t uuid_page_entries = page_list_header->entries;
+
+        for (uint32_t index = 0; index < uuid_page_entries; index++) {
+            struct journal_page_list *page_entry_in_journal = &page_list[index];
+
+            time_t page_first_time_s = page_entry_in_journal->delta_start_s + journal_start_time_s;
+            time_t page_last_time_s = page_entry_in_journal->delta_end_s + journal_start_time_s;
+
+            TIME_RANGE_COMPARE prc = is_page_in_time_range(page_first_time_s, page_last_time_s, wanted_start_time_s, wanted_end_time_s);
+            if(prc == PAGE_IS_IN_THE_PAST)
+                continue;
+
+            if(prc == PAGE_IS_IN_THE_FUTURE)
+                break;
+
+            uint32_t page_update_every_s = page_entry_in_journal->update_every_s;
+            size_t page_length = page_entry_in_journal->page_length;
+
+            if(datafile_acquire(datafile, DATAFILE_ACQUIRE_OPEN_CACHE)) { //for open cache item
+                // add this page to open cache
+                bool added = false;
+                struct extent_io_data ei = {
+                        .pos = extent_list[page_entry_in_journal->extent_index].datafile_offset,
+                        .bytes = extent_list[page_entry_in_journal->extent_index].datafile_size,
+                        .page_length = page_length,
+                        .file = datafile->file,
+                        .fileno = datafile->fileno,
+                };
+
+                PGC_PAGE *page = pgc_page_add_and_acquire(open_cache, (PGC_ENTRY) {
+                        .hot = false,
+                        .section = (Word_t) ctx,
+                        .metric_id = metric_id,
+                        .start_time_s = page_first_time_s,
+                        .end_time_s = page_last_time_s,
+                        .update_every_s = page_update_every_s,
+                        .data = datafile,
+                        .size = 0,
+                        .custom_data = (uint8_t *) &ei,
+                }, &added);
+
+                if(!added)
+                    datafile_release(datafile, DATAFILE_ACQUIRE_OPEN_CACHE);
+
+                callback(page, callback_data);
+
+                pgc_page_release(open_cache, page);
+
+                pages_found++;
+            }
+        }
+
+        journalfile_v2_data_release(datafile->journalfile);
+    }
+
+    return pages_found;
+}
+
+void add_page_details_from_journal_v2(PGC_PAGE *page, void *JudyL_pptr) {
+    struct rrdengine_datafile *datafile = pgc_page_data(page);
+
+    if(!datafile_acquire(datafile, DATAFILE_ACQUIRE_PAGE_DETAILS)) // for pd
+        return;
+
+    Pvoid_t *PValue = PDCJudyLIns(JudyL_pptr, pgc_page_start_time_s(page), PJE0);
+    if (!PValue || PValue == PJERR)
+        fatal("DBENGINE: corrupted judy array");
+
+    if (unlikely(*PValue)) {
+        datafile_release(datafile, DATAFILE_ACQUIRE_PAGE_DETAILS);
+        return;
+    }
+
+    Word_t metric_id = pgc_page_metric(page);
+
+    // let's add it to the judy
+    struct extent_io_data *ei = pgc_page_custom_data(open_cache, page);
+    struct page_details *pd = page_details_get();
+    *PValue = pd;
+
+    pd->datafile.extent.pos = ei->pos;
+    pd->datafile.extent.bytes = ei->bytes;
+    pd->datafile.file = ei->file;
+    pd->datafile.fileno = ei->fileno;
+    pd->first_time_s = pgc_page_start_time_s(page);
+    pd->last_time_s = pgc_page_end_time_s(page);
+    pd->datafile.ptr = datafile;
+    pd->update_every_s = (uint32_t) pgc_page_update_every_s(page);
+    pd->metric_id = metric_id;
+    pd->status |= PDC_PAGE_DISK_PENDING | PDC_PAGE_SOURCE_JOURNAL_V2 | PDC_PAGE_DATAFILE_ACQUIRED;
+}
+
+// Return a judyL will all pages that have start_time_ut and end_time_ut
+// Pvalue of the judy will be the end time for that page
+// DBENGINE2:
+#define time_delta(finish, pass) do { if(pass) { usec_t t = pass; (pass) = (finish) - (pass); (finish) = t; } } while(0)
+static Pvoid_t get_page_list(
+        struct rrdengine_instance *ctx,
+        METRIC *metric,
+        usec_t start_time_ut,
+        usec_t end_time_ut,
+        time_t *optimal_end_time_s,
+        size_t *pages_to_load_from_disk,
+        PDC_PAGE_STATUS *common_status
+) {
+    *optimal_end_time_s = 0;
+    *pages_to_load_from_disk = 0;
+    *common_status = 0;
+
+    Pvoid_t JudyL_page_array = (Pvoid_t) NULL;
+
+    time_t wanted_start_time_s = (time_t)(start_time_ut / USEC_PER_SEC);
+    time_t wanted_end_time_s = (time_t)(end_time_ut / USEC_PER_SEC);
+
+    size_t  pages_found_in_main_cache = 0,
+            pages_found_in_open_cache = 0,
+            pages_found_in_journals_v2 = 0,
+            pages_found_pass4 = 0,
+            pages_overlapping = 0,
+            pages_total = 0;
+
+    size_t cache_gaps = 0, query_gaps = 0;
+    bool done_v2 = false, done_open = false;
+
+    usec_t pass1_ut = 0, pass2_ut = 0, pass3_ut = 0, pass4_ut = 0, finish_ut = 0;
+
+    // --------------------------------------------------------------
+    // PASS 1: Check what the main page cache has available
+
+    pass1_ut = now_monotonic_usec();
+    size_t pages_pass1 = get_page_list_from_pgc(main_cache, metric, ctx, wanted_start_time_s, wanted_end_time_s,
+                                                &JudyL_page_array, &cache_gaps,
+                                                false, PDC_PAGE_SOURCE_MAIN_CACHE);
+    query_gaps += cache_gaps;
+    pages_found_in_main_cache += pages_pass1;
+    pages_total += pages_pass1;
+
+    if(pages_found_in_main_cache && !cache_gaps) {
+        query_gaps = list_has_time_gaps(ctx, metric, JudyL_page_array, wanted_start_time_s, wanted_end_time_s,
+                                        &pages_total, &pages_found_pass4, pages_to_load_from_disk, &pages_overlapping,
+                                        optimal_end_time_s, false, common_status);
+
+        if (pages_total && !query_gaps)
+            goto we_are_done;
+    }
+
+    // --------------------------------------------------------------
+    // PASS 2: Check what the open journal page cache has available
+    //         these will be loaded from disk
+
+    pass2_ut = now_monotonic_usec();
+    size_t pages_pass2 = get_page_list_from_pgc(open_cache, metric, ctx, wanted_start_time_s, wanted_end_time_s,
+                                                &JudyL_page_array, &cache_gaps,
+                                                true, PDC_PAGE_SOURCE_OPEN_CACHE);
+    query_gaps += cache_gaps;
+    pages_found_in_open_cache += pages_pass2;
+    pages_total += pages_pass2;
+    done_open = true;
+
+    if(pages_found_in_open_cache) {
+        query_gaps = list_has_time_gaps(ctx, metric, JudyL_page_array, wanted_start_time_s, wanted_end_time_s,
+                                        &pages_total, &pages_found_pass4, pages_to_load_from_disk, &pages_overlapping,
+                                        optimal_end_time_s, false, common_status);
+
+        if (pages_total && !query_gaps)
+            goto we_are_done;
+    }
+
+    // --------------------------------------------------------------
+    // PASS 3: Check Journal v2 to fill the gaps
+
+    pass3_ut = now_monotonic_usec();
+    size_t pages_pass3 = get_page_list_from_journal_v2(ctx, metric, start_time_ut, end_time_ut,
+                                                       add_page_details_from_journal_v2, &JudyL_page_array);
+    pages_found_in_journals_v2 += pages_pass3;
+    pages_total += pages_pass3;
+    done_v2 = true;
+
+    // --------------------------------------------------------------
+    // PASS 4: Check the cache again
+    //         and calculate the time gaps in the query
+    //         THIS IS REQUIRED AFTER JOURNAL V2 LOOKUP
+
+    pass4_ut = now_monotonic_usec();
+    query_gaps = list_has_time_gaps(ctx, metric, JudyL_page_array, wanted_start_time_s, wanted_end_time_s,
+                                    &pages_total, &pages_found_pass4, pages_to_load_from_disk, &pages_overlapping,
+                                    optimal_end_time_s, true, common_status);
+
+we_are_done:
+    finish_ut = now_monotonic_usec();
+    time_delta(finish_ut, pass4_ut);
+    time_delta(finish_ut, pass3_ut);
+    time_delta(finish_ut, pass2_ut);
+    time_delta(finish_ut, pass1_ut);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.prep_time_in_main_cache_lookup, pass1_ut, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.prep_time_in_open_cache_lookup, pass2_ut, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.prep_time_in_journal_v2_lookup, pass3_ut, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.prep_time_in_pass4_lookup, pass4_ut, __ATOMIC_RELAXED);
+
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.queries, 1, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.queries_planned_with_gaps, (query_gaps) ? 1 : 0, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.queries_open, done_open ? 1 : 0, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.queries_journal_v2, done_v2 ? 1 : 0, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_total, pages_total, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_meta_source_main_cache, pages_found_in_main_cache, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_meta_source_open_cache, pages_found_in_open_cache, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_meta_source_journal_v2, pages_found_in_journals_v2, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_data_source_main_cache, pages_found_in_main_cache, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_data_source_main_cache_at_pass4, pages_found_pass4, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_to_load_from_disk, *pages_to_load_from_disk, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_overlapping_skipped, pages_overlapping, __ATOMIC_RELAXED);
+
+    return JudyL_page_array;
+}
+
+inline void rrdeng_prep_wait(PDC *pdc) {
+    if (unlikely(pdc && !pdc->prep_done)) {
+        usec_t started_ut = now_monotonic_usec();
+        completion_wait_for(&pdc->prep_completion);
+        pdc->prep_done = true;
+        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.query_time_wait_for_prep, now_monotonic_usec() - started_ut, __ATOMIC_RELAXED);
+    }
+}
+
+void rrdeng_prep_query(struct page_details_control *pdc, bool worker) {
+    if(worker)
+        worker_is_busy(UV_EVENT_DBENGINE_QUERY);
+
+    pdc->page_list_JudyL = get_page_list(pdc->ctx, pdc->metric,
+                                                 pdc->start_time_s * USEC_PER_SEC,
+                                                 pdc->end_time_s * USEC_PER_SEC,
+                                                 &pdc->optimal_end_time_s,
+                                                 &pdc->pages_to_load_from_disk,
+                                                 &pdc->common_status);
+
+    internal_fatal(pdc->pages_to_load_from_disk && !(pdc->common_status & PDC_PAGE_DISK_PENDING),
+                   "DBENGINE: PDC reports there are %zu pages to load from disk, "
+                   "but none of the pages has the PDC_PAGE_DISK_PENDING flag",
+                   pdc->pages_to_load_from_disk);
+
+    internal_fatal(!pdc->pages_to_load_from_disk && (pdc->common_status & PDC_PAGE_DISK_PENDING),
+                   "DBENGINE: PDC reports there are no pages to load from disk, "
+                   "but one or more pages have the PDC_PAGE_DISK_PENDING flag");
+
+    if (pdc->pages_to_load_from_disk && pdc->page_list_JudyL) {
+        pdc_acquire(pdc); // we get 1 for the 1st worker in the chain: do_read_page_list_work()
+        usec_t start_ut = now_monotonic_usec();
+        if(likely(pdc->priority == STORAGE_PRIORITY_SYNCHRONOUS))
+            pdc_route_synchronously(pdc->ctx, pdc);
+        else
+            pdc_route_asynchronously(pdc->ctx, pdc);
+        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.prep_time_to_route, now_monotonic_usec() - start_ut, __ATOMIC_RELAXED);
+    }
+    else
+        completion_mark_complete(&pdc->page_completion);
+
+    completion_mark_complete(&pdc->prep_completion);
+
+    pdc_release_and_destroy_if_unreferenced(pdc, true, true);
+
+    if(worker)
+        worker_is_idle();
+}
+
+/**
+ * Searches for pages in a time range and triggers disk I/O if necessary and possible.
+ * @param ctx DB context
+ * @param handle query handle as initialized
+ * @param start_time_ut inclusive starting time in usec
+ * @param end_time_ut inclusive ending time in usec
+ * @return 1 / 0 (pages found or not found)
+ */
+void pg_cache_preload(struct rrdeng_query_handle *handle) {
+    if (unlikely(!handle || !handle->metric))
+        return;
+
+    __atomic_add_fetch(&handle->ctx->atomic.inflight_queries, 1, __ATOMIC_RELAXED);
+    __atomic_add_fetch(&rrdeng_cache_efficiency_stats.currently_running_queries, 1, __ATOMIC_RELAXED);
+    handle->pdc = pdc_get();
+    handle->pdc->metric = mrg_metric_dup(main_mrg, handle->metric);
+    handle->pdc->start_time_s = handle->start_time_s;
+    handle->pdc->end_time_s = handle->end_time_s;
+    handle->pdc->priority = handle->priority;
+    handle->pdc->optimal_end_time_s = handle->end_time_s;
+    handle->pdc->ctx = handle->ctx;
+    handle->pdc->refcount = 1;
+    spinlock_init(&handle->pdc->refcount_spinlock);
+    completion_init(&handle->pdc->prep_completion);
+    completion_init(&handle->pdc->page_completion);
+
+    if(ctx_is_available_for_queries(handle->ctx)) {
+        handle->pdc->refcount++; // we get 1 for the query thread and 1 for the prep thread
+
+        if(unlikely(handle->pdc->priority == STORAGE_PRIORITY_SYNCHRONOUS))
+            rrdeng_prep_query(handle->pdc, false);
+        else
+            rrdeng_enq_cmd(handle->ctx, RRDENG_OPCODE_QUERY, handle->pdc, NULL, handle->priority, NULL, NULL);
+    }
+    else {
+        completion_mark_complete(&handle->pdc->prep_completion);
+        completion_mark_complete(&handle->pdc->page_completion);
+    }
+}
+
+/*
+ * Searches for the first page between start_time and end_time and gets a reference.
+ * start_time and end_time are inclusive.
+ * If index is NULL lookup by UUID (id).
+ */
+struct pgc_page *pg_cache_lookup_next(
+        struct rrdengine_instance *ctx,
+        PDC *pdc,
+        time_t now_s,
+        uint32_t last_update_every_s,
+        size_t *entries
+) {
+    if (unlikely(!pdc))
+        return NULL;
+
+    rrdeng_prep_wait(pdc);
+
+    if (unlikely(!pdc->page_list_JudyL))
+        return NULL;
+
+    usec_t start_ut = now_monotonic_usec();
+    size_t gaps = 0;
+    bool waited = false, preloaded;
+    PGC_PAGE *page = NULL;
+
+    while(!page) {
+        bool page_from_pd = false;
+        preloaded = false;
+        struct page_details *pd = pdc_find_page_for_time(
+                pdc->page_list_JudyL, now_s, &gaps,
+                PDC_PAGE_PROCESSED, PDC_PAGE_EMPTY);
+
+        if (!pd)
+            break;
+
+        page = pd->page;
+        page_from_pd = true;
+        preloaded = pdc_page_status_check(pd, PDC_PAGE_PRELOADED);
+        if(!page) {
+            if(!completion_is_done(&pdc->page_completion)) {
+                page = pgc_page_get_and_acquire(main_cache, (Word_t)ctx,
+                                                pd->metric_id, pd->first_time_s, PGC_SEARCH_EXACT);
+                page_from_pd = false;
+                preloaded = pdc_page_status_check(pd, PDC_PAGE_PRELOADED);
+            }
+
+            if(!page) {
+                pdc->completed_jobs =
+                        completion_wait_for_a_job(&pdc->page_completion, pdc->completed_jobs);
+
+                page = pd->page;
+                page_from_pd = true;
+                preloaded = pdc_page_status_check(pd, PDC_PAGE_PRELOADED);
+                waited = true;
+            }
+        }
+
+        if(page && pgd_is_empty(pgc_page_data(page)))
+                pdc_page_status_set(pd, PDC_PAGE_EMPTY);
+
+        if(!page || pdc_page_status_check(pd, PDC_PAGE_QUERY_GLOBAL_SKIP_LIST | PDC_PAGE_EMPTY)) {
+            page = NULL;
+            continue;
+        }
+
+        // we now have page and is not empty
+
+        time_t page_start_time_s = pgc_page_start_time_s(page);
+        time_t page_end_time_s = pgc_page_end_time_s(page);
+        uint32_t page_update_every_s = pgc_page_update_every_s(page);
+
+        if(unlikely(page_start_time_s == INVALID_TIME || page_end_time_s == INVALID_TIME)) {
+            __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_zero_time_skipped, 1, __ATOMIC_RELAXED);
+            pgc_page_to_clean_evict_or_release(main_cache, page);
+            pdc_page_status_set(pd, PDC_PAGE_INVALID | PDC_PAGE_RELEASED);
+            pd->page = page = NULL;
+            continue;
+        }
+        else {
+            if (unlikely(page_update_every_s <= 0 || page_update_every_s > 86400)) {
+                __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_invalid_update_every_fixed, 1, __ATOMIC_RELAXED);
+                page_update_every_s = pgc_page_fix_update_every(page, last_update_every_s);
+                pd->update_every_s = page_update_every_s;
+            }
+
+            size_t entries_by_size = pgd_slots_used(pgc_page_data(page));
+            size_t entries_by_time = page_entries_by_time(page_start_time_s, page_end_time_s, page_update_every_s);
+            if(unlikely(entries_by_size < entries_by_time)) {
+                time_t fixed_page_end_time_s = (time_t)(page_start_time_s + (entries_by_size - 1) * page_update_every_s);
+                pd->last_time_s = page_end_time_s = pgc_page_fix_end_time_s(page, fixed_page_end_time_s);
+                entries_by_time = (page_end_time_s - (page_start_time_s - page_update_every_s)) / page_update_every_s;
+
+                internal_fatal(entries_by_size != entries_by_time, "DBENGINE: wrong entries by time again!");
+
+                __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_invalid_entries_fixed, 1, __ATOMIC_RELAXED);
+            }
+            *entries = entries_by_time;
+        }
+
+        if(unlikely(page_end_time_s < now_s)) {
+            __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_past_time_skipped, 1, __ATOMIC_RELAXED);
+            pgc_page_release(main_cache, page);
+            pdc_page_status_set(pd, PDC_PAGE_SKIP | PDC_PAGE_RELEASED);
+            pd->page = page = NULL;
+            continue;
+        }
+
+        if(page_from_pd)
+            // PDC_PAGE_RELEASED is for pdc_destroy() to not release the page twice - the caller will release it
+            pdc_page_status_set(pd, PDC_PAGE_RELEASED | PDC_PAGE_PROCESSED);
+        else
+            pdc_page_status_set(pd, PDC_PAGE_PROCESSED);
+    }
+
+    if(gaps && !pdc->executed_with_gaps)
+        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.queries_executed_with_gaps, 1, __ATOMIC_RELAXED);
+    pdc->executed_with_gaps = +gaps;
+
+    if(page) {
+        if(waited)
+            __atomic_add_fetch(&rrdeng_cache_efficiency_stats.page_next_wait_loaded, 1, __ATOMIC_RELAXED);
+        else
+            __atomic_add_fetch(&rrdeng_cache_efficiency_stats.page_next_nowait_loaded, 1, __ATOMIC_RELAXED);
+    }
+    else {
+        if(waited)
+            __atomic_add_fetch(&rrdeng_cache_efficiency_stats.page_next_wait_failed, 1, __ATOMIC_RELAXED);
+        else
+            __atomic_add_fetch(&rrdeng_cache_efficiency_stats.page_next_nowait_failed, 1, __ATOMIC_RELAXED);
+    }
+
+    if(waited) {
+        if(preloaded)
+            __atomic_add_fetch(&rrdeng_cache_efficiency_stats.query_time_to_slow_preload_next_page, now_monotonic_usec() - start_ut, __ATOMIC_RELAXED);
+        else
+            __atomic_add_fetch(&rrdeng_cache_efficiency_stats.query_time_to_slow_disk_next_page, now_monotonic_usec() - start_ut, __ATOMIC_RELAXED);
+    }
+    else {
+        if(preloaded)
+            __atomic_add_fetch(&rrdeng_cache_efficiency_stats.query_time_to_fast_preload_next_page, now_monotonic_usec() - start_ut, __ATOMIC_RELAXED);
+        else
+            __atomic_add_fetch(&rrdeng_cache_efficiency_stats.query_time_to_fast_disk_next_page, now_monotonic_usec() - start_ut, __ATOMIC_RELAXED);
+    }
+
+    return page;
+}
+
+void pgc_open_add_hot_page(Word_t section, Word_t metric_id, time_t start_time_s, time_t end_time_s, uint32_t update_every_s,
+           struct rrdengine_datafile *datafile, uint64_t extent_offset, unsigned extent_size, uint32_t page_length) {
+
+    if(!datafile_acquire(datafile, DATAFILE_ACQUIRE_OPEN_CACHE)) // for open cache item
+        fatal("DBENGINE: cannot acquire datafile to put page in open cache");
+
+    struct extent_io_data ext_io_data = {
+            .file  = datafile->file,
+            .fileno = datafile->fileno,
+            .pos = extent_offset,
+            .bytes = extent_size,
+            .page_length = page_length
+    };
+
+    PGC_ENTRY page_entry = {
+            .hot = true,
+            .section = section,
+            .metric_id = metric_id,
+            .start_time_s = start_time_s,
+            .end_time_s =  end_time_s,
+            .update_every_s = update_every_s,
+            .size = 0,
+            .data = datafile,
+            .custom_data = (uint8_t *) &ext_io_data,
+    };
+
+    internal_fatal(!datafile->fileno, "DBENGINE: datafile supplied does not have a number");
+
+    bool added = true;
+    PGC_PAGE *page = pgc_page_add_and_acquire(open_cache, page_entry, &added);
+    int tries = 100;
+    while(!added && page_entry.end_time_s > pgc_page_end_time_s(page) && tries--) {
+        pgc_page_to_clean_evict_or_release(open_cache, page);
+        page = pgc_page_add_and_acquire(open_cache, page_entry, &added);
+    }
+
+    if(!added) {
+        datafile_release(datafile, DATAFILE_ACQUIRE_OPEN_CACHE);
+
+        internal_fatal(page_entry.end_time_s > pgc_page_end_time_s(page),
+                       "DBENGINE: cannot add longer page to open cache");
+    }
+
+    pgc_page_release(open_cache, (PGC_PAGE *)page);
+}
+
+size_t dynamic_open_cache_size(void) {
+    size_t main_cache_size = pgc_get_wanted_cache_size(main_cache);
+    size_t target_size = main_cache_size / 100 * 5;
+
+    if(target_size < 2 * 1024 * 1024)
+        target_size = 2 * 1024 * 1024;
+
+    return target_size;
+}
+
+size_t dynamic_extent_cache_size(void) {
+    size_t main_cache_size = pgc_get_wanted_cache_size(main_cache);
+    size_t target_size = main_cache_size / 100 * 5;
+
+    if(target_size < 3 * 1024 * 1024)
+        target_size = 3 * 1024 * 1024;
+
+    return target_size;
+}
+
+void pgc_and_mrg_initialize(void)
+{
+    main_mrg = mrg_create(0);
+
+    size_t target_cache_size = (size_t)default_rrdeng_page_cache_mb * 1024ULL * 1024ULL;
+    size_t main_cache_size = (target_cache_size / 100) * 95;
+    size_t open_cache_size = 0;
+    size_t extent_cache_size = (target_cache_size / 100) * 5;
+
+    if(extent_cache_size < 3 * 1024 * 1024) {
+        extent_cache_size = 3 * 1024 * 1024;
+        main_cache_size = target_cache_size - extent_cache_size;
+    }
+
+    extent_cache_size += (size_t)(default_rrdeng_extent_cache_mb * 1024ULL * 1024ULL);
+
+    main_cache = pgc_create(
+            "main_cache",
+            main_cache_size,
+            main_cache_free_clean_page_callback,
+            (size_t) rrdeng_pages_per_extent,
+            main_cache_flush_dirty_page_init_callback,
+            main_cache_flush_dirty_page_callback,
+            10,
+            10240,                                      // if there are that many threads, evict so many at once!
+            1000,                           //
+            5,                                          // don't delay too much other threads
+            PGC_OPTIONS_AUTOSCALE,                               // AUTOSCALE = 2x max hot pages
+            0,                                                 // 0 = as many as the system cpus
+            0
+    );
+
+    open_cache = pgc_create(
+            "open_cache",
+            open_cache_size,                             // the default is 1MB
+            open_cache_free_clean_page_callback,
+            1,
+            NULL,
+            open_cache_flush_dirty_page_callback,
+            10,
+            10240,                                      // if there are that many threads, evict that many at once!
+            1000,                           //
+            3,                                          // don't delay too much other threads
+            PGC_OPTIONS_AUTOSCALE | PGC_OPTIONS_EVICT_PAGES_INLINE | PGC_OPTIONS_FLUSH_PAGES_INLINE,
+            0,                                                 // 0 = as many as the system cpus
+            sizeof(struct extent_io_data)
+    );
+    pgc_set_dynamic_target_cache_size_callback(open_cache, dynamic_open_cache_size);
+
+    extent_cache = pgc_create(
+            "extent_cache",
+            extent_cache_size,
+            extent_cache_free_clean_page_callback,
+            1,
+            NULL,
+            extent_cache_flush_dirty_page_callback,
+            5,
+            10,                                         // it will lose up to that extents at once!
+            100,                            //
+            2,                                          // don't delay too much other threads
+            PGC_OPTIONS_AUTOSCALE | PGC_OPTIONS_EVICT_PAGES_INLINE | PGC_OPTIONS_FLUSH_PAGES_INLINE,
+            0,                                                 // 0 = as many as the system cpus
+            0
+    );
+    pgc_set_dynamic_target_cache_size_callback(extent_cache, dynamic_extent_cache_size);
+}