summaryrefslogtreecommitdiffstats
path: root/database/engine/pdc.c
blob: 7da56878740d72df07e7fb8a250ca7221755e1b0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
// SPDX-License-Identifier: GPL-3.0-or-later
#define NETDATA_RRD_INTERNALS
#include "pdc.h"

struct extent_page_details_list {
    uv_file file;
    uint64_t extent_offset;
    uint32_t extent_size;
    unsigned number_of_pages_in_JudyL;
    Pvoid_t page_details_by_metric_id_JudyL;
    struct page_details_control *pdc;
    struct rrdengine_datafile *datafile;

    struct rrdeng_cmd *cmd;
    bool head_to_datafile_extent_queries_pending_for_extent;

    struct {
        struct extent_page_details_list *prev;
        struct extent_page_details_list *next;
    } query;
};

typedef struct datafile_extent_offset_list {
    uv_file file;
    unsigned fileno;
    Pvoid_t extent_pd_list_by_extent_offset_JudyL;
} DEOL;

// ----------------------------------------------------------------------------
// PDC cache

static struct {
    struct {
        ARAL *ar;
    } pdc;

    struct {
        ARAL *ar;
    } pd;

    struct {
        ARAL *ar;
    } epdl;

    struct {
        ARAL *ar;
    } deol;
} pdc_globals = {};

void pdc_init(void) {
    pdc_globals.pdc.ar = aral_create(
            "dbengine-pdc",
            sizeof(PDC),
            0,
            65536,
            NULL,
            NULL, NULL, false, false
            );
}

PDC *pdc_get(void) {
    PDC *pdc = aral_mallocz(pdc_globals.pdc.ar);
    memset(pdc, 0, sizeof(PDC));
    return pdc;
}

static void pdc_release(PDC *pdc) {
    aral_freez(pdc_globals.pdc.ar, pdc);
}

size_t pdc_cache_size(void) {
    return aral_overhead(pdc_globals.pdc.ar) + aral_structures(pdc_globals.pdc.ar);
}

// ----------------------------------------------------------------------------
// PD cache

void page_details_init(void) {
    pdc_globals.pd.ar = aral_create(
            "dbengine-pd",
            sizeof(struct page_details),
            0,
            65536,
            NULL,
            NULL, NULL, false, false
    );
}

struct page_details *page_details_get(void) {
    struct page_details *pd = aral_mallocz(pdc_globals.pd.ar);
    memset(pd, 0, sizeof(struct page_details));
    return pd;
}

static void page_details_release(struct page_details *pd) {
    aral_freez(pdc_globals.pd.ar, pd);
}

size_t pd_cache_size(void) {
    return aral_overhead(pdc_globals.pd.ar) + aral_structures(pdc_globals.pd.ar);
}

// ----------------------------------------------------------------------------
// epdl cache

void epdl_init(void) {
    pdc_globals.epdl.ar = aral_create(
            "dbengine-epdl",
            sizeof(EPDL),
            0,
            65536,
            NULL,
            NULL, NULL, false, false
    );
}

static EPDL *epdl_get(void) {
    EPDL *epdl = aral_mallocz(pdc_globals.epdl.ar);
    memset(epdl, 0, sizeof(EPDL));
    return epdl;
}

static void epdl_release(EPDL *epdl) {
    aral_freez(pdc_globals.epdl.ar, epdl);
}

size_t epdl_cache_size(void) {
    return aral_overhead(pdc_globals.epdl.ar) + aral_structures(pdc_globals.epdl.ar);
}

// ----------------------------------------------------------------------------
// deol cache

void deol_init(void) {
    pdc_globals.deol.ar = aral_create(
            "dbengine-deol",
            sizeof(DEOL),
            0,
            65536,
            NULL,
            NULL, NULL, false, false
    );
}

static DEOL *deol_get(void) {
    DEOL *deol = aral_mallocz(pdc_globals.deol.ar);
    memset(deol, 0, sizeof(DEOL));
    return deol;
}

static void deol_release(DEOL *deol) {
    aral_freez(pdc_globals.deol.ar, deol);
}

size_t deol_cache_size(void) {
    return aral_overhead(pdc_globals.deol.ar) + aral_structures(pdc_globals.deol.ar);
}

// ----------------------------------------------------------------------------
// extent with buffer cache

static struct {
    struct {
        SPINLOCK spinlock;
        struct extent_buffer *available_items;
        size_t available;
    } protected;

    struct {
        size_t allocated;
        size_t allocated_bytes;
    } atomics;

    size_t max_size;

} extent_buffer_globals = {
        .protected = {
                .spinlock = NETDATA_SPINLOCK_INITIALIZER,
                .available_items = NULL,
                .available = 0,
        },
        .atomics = {
                .allocated = 0,
                .allocated_bytes = 0,
        },
        .max_size = MAX_PAGES_PER_EXTENT * RRDENG_BLOCK_SIZE,
};

void extent_buffer_init(void) {
    size_t max_extent_uncompressed = MAX_PAGES_PER_EXTENT * RRDENG_BLOCK_SIZE;
    size_t max_size = (size_t)LZ4_compressBound(MAX_PAGES_PER_EXTENT * RRDENG_BLOCK_SIZE);
    if(max_size < max_extent_uncompressed)
        max_size = max_extent_uncompressed;

    extent_buffer_globals.max_size = max_size;
}

void extent_buffer_cleanup1(void) {
    struct extent_buffer *item = NULL;

    if(!spinlock_trylock(&extent_buffer_globals.protected.spinlock))
        return;

    if(extent_buffer_globals.protected.available_items && extent_buffer_globals.protected.available > 1) {
        item = extent_buffer_globals.protected.available_items;
        DOUBLE_LINKED_LIST_REMOVE_ITEM_UNSAFE(extent_buffer_globals.protected.available_items, item, cache.prev, cache.next);
        extent_buffer_globals.protected.available--;
    }

    spinlock_unlock(&extent_buffer_globals.protected.spinlock);

    if(item) {
        size_t bytes = sizeof(struct extent_buffer) + item->bytes;
        freez(item);
        __atomic_sub_fetch(&extent_buffer_globals.atomics.allocated, 1, __ATOMIC_RELAXED);
        __atomic_sub_fetch(&extent_buffer_globals.atomics.allocated_bytes, bytes, __ATOMIC_RELAXED);
    }
}

struct extent_buffer *extent_buffer_get(size_t size) {
    internal_fatal(size > extent_buffer_globals.max_size, "DBENGINE: extent size is too big");

    struct extent_buffer *eb = NULL;

    if(size < extent_buffer_globals.max_size)
        size = extent_buffer_globals.max_size;

    spinlock_lock(&extent_buffer_globals.protected.spinlock);
    if(likely(extent_buffer_globals.protected.available_items)) {
        eb = extent_buffer_globals.protected.available_items;
        DOUBLE_LINKED_LIST_REMOVE_ITEM_UNSAFE(extent_buffer_globals.protected.available_items, eb, cache.prev, cache.next);
        extent_buffer_globals.protected.available--;
    }
    spinlock_unlock(&extent_buffer_globals.protected.spinlock);

    if(unlikely(eb && eb->bytes < size)) {
        size_t bytes = sizeof(struct extent_buffer) + eb->bytes;
        freez(eb);
        eb = NULL;
        __atomic_sub_fetch(&extent_buffer_globals.atomics.allocated, 1, __ATOMIC_RELAXED);
        __atomic_sub_fetch(&extent_buffer_globals.atomics.allocated_bytes, bytes, __ATOMIC_RELAXED);
    }

    if(unlikely(!eb)) {
        size_t bytes = sizeof(struct extent_buffer) + size;
        eb = mallocz(bytes);
        eb->bytes = size;
        __atomic_add_fetch(&extent_buffer_globals.atomics.allocated, 1, __ATOMIC_RELAXED);
        __atomic_add_fetch(&extent_buffer_globals.atomics.allocated_bytes, bytes, __ATOMIC_RELAXED);
    }

    return eb;
}

void extent_buffer_release(struct extent_buffer *eb) {
    if(unlikely(!eb)) return;

    spinlock_lock(&extent_buffer_globals.protected.spinlock);
    DOUBLE_LINKED_LIST_APPEND_ITEM_UNSAFE(extent_buffer_globals.protected.available_items, eb, cache.prev, cache.next);
    extent_buffer_globals.protected.available++;
    spinlock_unlock(&extent_buffer_globals.protected.spinlock);
}

size_t extent_buffer_cache_size(void) {
    return __atomic_load_n(&extent_buffer_globals.atomics.allocated_bytes, __ATOMIC_RELAXED);
}

// ----------------------------------------------------------------------------
// epdl logic

static void epdl_destroy(EPDL *epdl)
{
    Pvoid_t *pd_by_start_time_s_JudyL;
    Word_t metric_id_index = 0;
    bool metric_id_first = true;
    while ((pd_by_start_time_s_JudyL = PDCJudyLFirstThenNext(
            epdl->page_details_by_metric_id_JudyL,
            &metric_id_index, &metric_id_first)))
        PDCJudyLFreeArray(pd_by_start_time_s_JudyL, PJE0);

    PDCJudyLFreeArray(&epdl->page_details_by_metric_id_JudyL, PJE0);
    epdl_release(epdl);
}

static void epdl_mark_all_not_loaded_pages_as_failed(EPDL *epdl, PDC_PAGE_STATUS tags, size_t *statistics_counter)
{
    size_t pages_matched = 0;

    Word_t metric_id_index = 0;
    bool metric_id_first = true;
    Pvoid_t *pd_by_start_time_s_JudyL;
    while((pd_by_start_time_s_JudyL = PDCJudyLFirstThenNext(epdl->page_details_by_metric_id_JudyL, &metric_id_index, &metric_id_first))) {

        Word_t start_time_index = 0;
        bool start_time_first = true;
        Pvoid_t *PValue;
        while ((PValue = PDCJudyLFirstThenNext(*pd_by_start_time_s_JudyL, &start_time_index, &start_time_first))) {
            struct page_details *pd = *PValue;

            if(!pd->page && !pdc_page_status_check(pd, PDC_PAGE_FAILED|PDC_PAGE_READY)) {
                pdc_page_status_set(pd, PDC_PAGE_FAILED | tags);
                pages_matched++;
            }
        }
    }

    if(pages_matched && statistics_counter)
        __atomic_add_fetch(statistics_counter, pages_matched, __ATOMIC_RELAXED);
}
/*
static bool epdl_check_if_pages_are_already_in_cache(struct rrdengine_instance *ctx, EPDL *epdl, PDC_PAGE_STATUS tags)
{
    size_t count_remaining = 0;
    size_t found = 0;

    Word_t metric_id_index = 0;
    bool metric_id_first = true;
    Pvoid_t *pd_by_start_time_s_JudyL;
    while((pd_by_start_time_s_JudyL = PDCJudyLFirstThenNext(epdl->page_details_by_metric_id_JudyL, &metric_id_index, &metric_id_first))) {

        Word_t start_time_index = 0;
        bool start_time_first = true;
        Pvoid_t *PValue;
        while ((PValue = PDCJudyLFirstThenNext(*pd_by_start_time_s_JudyL, &start_time_index, &start_time_first))) {
            struct page_details *pd = *PValue;
            if (pd->page)
                continue;

            pd->page = pgc_page_get_and_acquire(main_cache, (Word_t) ctx, pd->metric_id, pd->first_time_s, PGC_SEARCH_EXACT);
            if (pd->page) {
                found++;
                pdc_page_status_set(pd, PDC_PAGE_READY | tags);
            }
            else
                count_remaining++;
        }
    }

    if(found) {
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_load_ok_preloaded, found, __ATOMIC_RELAXED);
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_data_source_main_cache, found, __ATOMIC_RELAXED);
    }

    return count_remaining == 0;
}
*/

// ----------------------------------------------------------------------------
// PDC logic

static void pdc_destroy(PDC *pdc) {
    mrg_metric_release(main_mrg, pdc->metric);
    completion_destroy(&pdc->prep_completion);
    completion_destroy(&pdc->page_completion);

    Pvoid_t *PValue;
    struct page_details *pd;
    Word_t time_index = 0;
    bool first_then_next = true;
    size_t unroutable = 0, cancelled = 0;
    while((PValue = PDCJudyLFirstThenNext(pdc->page_list_JudyL, &time_index, &first_then_next))) {
        pd = *PValue;

        // no need for atomics here - we are done...
        PDC_PAGE_STATUS status = pd->status;

        if(status & PDC_PAGE_DATAFILE_ACQUIRED) {
            datafile_release(pd->datafile.ptr, DATAFILE_ACQUIRE_PAGE_DETAILS);
            pd->datafile.ptr = NULL;
        }

        internal_fatal(pd->datafile.ptr, "DBENGINE: page details has a datafile.ptr that is not released.");

        if(!pd->page && !(status & (PDC_PAGE_READY | PDC_PAGE_FAILED | PDC_PAGE_RELEASED | PDC_PAGE_SKIP | PDC_PAGE_INVALID | PDC_PAGE_CANCELLED))) {
            // pdc_page_status_set(pd, PDC_PAGE_FAILED);
            unroutable++;
        }
        else if(!pd->page && (status & PDC_PAGE_CANCELLED))
            cancelled++;

        if(pd->page && !(status & PDC_PAGE_RELEASED)) {
            pgc_page_release(main_cache, pd->page);
            // pdc_page_status_set(pd, PDC_PAGE_RELEASED);
        }

        page_details_release(pd);
    }

    PDCJudyLFreeArray(&pdc->page_list_JudyL, PJE0);

    __atomic_sub_fetch(&rrdeng_cache_efficiency_stats.currently_running_queries, 1, __ATOMIC_RELAXED);
    __atomic_sub_fetch(&pdc->ctx->atomic.inflight_queries, 1, __ATOMIC_RELAXED);
    pdc_release(pdc);

    if(unroutable)
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_load_fail_unroutable, unroutable, __ATOMIC_RELAXED);

    if(cancelled)
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_load_fail_cancelled, cancelled, __ATOMIC_RELAXED);
}

void pdc_acquire(PDC *pdc) {
    spinlock_lock(&pdc->refcount_spinlock);

    if(pdc->refcount < 1)
        fatal("DBENGINE: pdc is not referenced and cannot be acquired");

    pdc->refcount++;
    spinlock_unlock(&pdc->refcount_spinlock);
}

bool pdc_release_and_destroy_if_unreferenced(PDC *pdc, bool worker, bool router __maybe_unused) {
    if(unlikely(!pdc))
        return true;

    spinlock_lock(&pdc->refcount_spinlock);

    if(pdc->refcount <= 0)
        fatal("DBENGINE: pdc is not referenced and cannot be released");

    pdc->refcount--;

    if (pdc->refcount <= 1 && worker) {
        // when 1 refcount is remaining, and we are a worker,
        // we can mark the job completed:
        // - if the remaining refcount is from the query caller, we will wake it up
        // - if the remaining refcount is from another worker, the query thread is already away
        completion_mark_complete(&pdc->page_completion);
    }

    if (pdc->refcount == 0) {
        spinlock_unlock(&pdc->refcount_spinlock);
        pdc_destroy(pdc);
        return true;
    }

    spinlock_unlock(&pdc->refcount_spinlock);
    return false;
}

void epdl_cmd_queued(void *epdl_ptr, struct rrdeng_cmd *cmd) {
    EPDL *epdl = epdl_ptr;
    epdl->cmd = cmd;
}

void epdl_cmd_dequeued(void *epdl_ptr) {
    EPDL *epdl = epdl_ptr;
    epdl->cmd = NULL;
}

static struct rrdeng_cmd *epdl_get_cmd(void *epdl_ptr) {
    EPDL *epdl = epdl_ptr;
    return epdl->cmd;
}

static bool epdl_pending_add(EPDL *epdl) {
    bool added_new;

    spinlock_lock(&epdl->datafile->extent_queries.spinlock);
    Pvoid_t *PValue = JudyLIns(&epdl->datafile->extent_queries.pending_epdl_by_extent_offset_judyL, epdl->extent_offset, PJE0);
    internal_fatal(!PValue || PValue == PJERR, "DBENGINE: corrupted pending extent judy");

    EPDL *base = *PValue;

    if(!base) {
        added_new = true;
        epdl->head_to_datafile_extent_queries_pending_for_extent = true;
    }
    else {
        added_new = false;
        epdl->head_to_datafile_extent_queries_pending_for_extent = false;
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_load_extent_merged, 1, __ATOMIC_RELAXED);

        if(base->pdc->priority > epdl->pdc->priority)
            rrdeng_req_cmd(epdl_get_cmd, base, epdl->pdc->priority);
    }

    DOUBLE_LINKED_LIST_APPEND_ITEM_UNSAFE(base, epdl, query.prev, query.next);
    *PValue = base;

    spinlock_unlock(&epdl->datafile->extent_queries.spinlock);

    return added_new;
}

static void epdl_pending_del(EPDL *epdl) {
    spinlock_lock(&epdl->datafile->extent_queries.spinlock);
    if(epdl->head_to_datafile_extent_queries_pending_for_extent) {
        epdl->head_to_datafile_extent_queries_pending_for_extent = false;
        int rc = JudyLDel(&epdl->datafile->extent_queries.pending_epdl_by_extent_offset_judyL, epdl->extent_offset, PJE0);
        (void) rc;
        internal_fatal(!rc, "DBENGINE: epdl not found in pending list");
    }
    spinlock_unlock(&epdl->datafile->extent_queries.spinlock);
}

void pdc_to_epdl_router(struct rrdengine_instance *ctx, PDC *pdc, execute_extent_page_details_list_t exec_first_extent_list, execute_extent_page_details_list_t exec_rest_extent_list)
{
    Pvoid_t *PValue;
    Pvoid_t *PValue1;
    Pvoid_t *PValue2;
    Word_t time_index = 0;
    struct page_details *pd = NULL;

    // this is the entire page list
    // Lets do some deduplication
    // 1. Per datafile
    // 2. Per extent
    // 3. Pages per extent will be added to the cache either as acquired or not

    Pvoid_t JudyL_datafile_list = NULL;

    DEOL *deol;
    EPDL *epdl;

    if (pdc->page_list_JudyL) {
        bool first_then_next = true;
        while((PValue = PDCJudyLFirstThenNext(pdc->page_list_JudyL, &time_index, &first_then_next))) {
            pd = *PValue;

            internal_fatal(!pd,
                           "DBENGINE: pdc page list has an empty page details entry");

            if (!(pd->status & PDC_PAGE_DISK_PENDING))
                continue;

            internal_fatal(!(pd->status & PDC_PAGE_DATAFILE_ACQUIRED),
                           "DBENGINE: page details has not acquired the datafile");

            internal_fatal((pd->status & (PDC_PAGE_READY | PDC_PAGE_FAILED)),
                           "DBENGINE: page details has disk pending flag but it is ready/failed");

            internal_fatal(pd->page,
                           "DBENGINE: page details has a page linked to it, but it is marked for loading");

            PValue1 = PDCJudyLIns(&JudyL_datafile_list, pd->datafile.fileno, PJE0);
            if (PValue1 && !*PValue1) {
                *PValue1 = deol = deol_get();
                deol->extent_pd_list_by_extent_offset_JudyL = NULL;
                deol->fileno = pd->datafile.fileno;
            }
            else
                deol = *PValue1;

            PValue2 = PDCJudyLIns(&deol->extent_pd_list_by_extent_offset_JudyL, pd->datafile.extent.pos, PJE0);
            if (PValue2 && !*PValue2) {
                *PValue2 = epdl = epdl_get();
                epdl->page_details_by_metric_id_JudyL = NULL;
                epdl->number_of_pages_in_JudyL = 0;
                epdl->file = pd->datafile.file;
                epdl->extent_offset = pd->datafile.extent.pos;
                epdl->extent_size = pd->datafile.extent.bytes;
                epdl->datafile = pd->datafile.ptr;
            }
            else
                epdl = *PValue2;

            epdl->number_of_pages_in_JudyL++;

            Pvoid_t *pd_by_first_time_s_judyL = PDCJudyLIns(&epdl->page_details_by_metric_id_JudyL, pd->metric_id, PJE0);
            Pvoid_t *pd_pptr = PDCJudyLIns(pd_by_first_time_s_judyL, pd->first_time_s, PJE0);
            *pd_pptr = pd;
        }

        size_t extent_list_no = 0;
        Word_t datafile_no = 0;
        first_then_next = true;
        while((PValue = PDCJudyLFirstThenNext(JudyL_datafile_list, &datafile_no, &first_then_next))) {
            deol = *PValue;

            bool first_then_next_extent = true;
            Word_t pos = 0;
            while ((PValue = PDCJudyLFirstThenNext(deol->extent_pd_list_by_extent_offset_JudyL, &pos, &first_then_next_extent))) {
                epdl = *PValue;
                internal_fatal(!epdl, "DBENGINE: extent_list is not populated properly");

                // The extent page list can be dispatched to a worker
                // It will need to populate the cache with "acquired" pages that are in the list (pd) only
                // the rest of the extent pages will be added to the cache butnot acquired

                pdc_acquire(pdc); // we do this for the next worker: do_read_extent_work()
                epdl->pdc = pdc;

                if(epdl_pending_add(epdl)) {
                    if (extent_list_no++ == 0)
                        exec_first_extent_list(ctx, epdl, pdc->priority);
                    else
                        exec_rest_extent_list(ctx, epdl, pdc->priority);
                }
            }
            PDCJudyLFreeArray(&deol->extent_pd_list_by_extent_offset_JudyL, PJE0);
            deol_release(deol);
        }
        PDCJudyLFreeArray(&JudyL_datafile_list, PJE0);
    }

    pdc_release_and_destroy_if_unreferenced(pdc, true, true);
}

void collect_page_flags_to_buffer(BUFFER *wb, RRDENG_COLLECT_PAGE_FLAGS flags) {
    if(flags & RRDENG_PAGE_PAST_COLLECTION)
        buffer_strcat(wb, "PAST_COLLECTION ");
    if(flags & RRDENG_PAGE_REPEATED_COLLECTION)
        buffer_strcat(wb, "REPEATED_COLLECTION ");
    if(flags & RRDENG_PAGE_BIG_GAP)
        buffer_strcat(wb, "BIG_GAP ");
    if(flags & RRDENG_PAGE_GAP)
        buffer_strcat(wb, "GAP ");
    if(flags & RRDENG_PAGE_FUTURE_POINT)
        buffer_strcat(wb, "FUTURE_POINT ");
    if(flags & RRDENG_PAGE_CREATED_IN_FUTURE)
        buffer_strcat(wb, "CREATED_IN_FUTURE ");
    if(flags & RRDENG_PAGE_COMPLETED_IN_FUTURE)
        buffer_strcat(wb, "COMPLETED_IN_FUTURE ");
    if(flags & RRDENG_PAGE_UNALIGNED)
        buffer_strcat(wb, "UNALIGNED ");
    if(flags & RRDENG_PAGE_CONFLICT)
        buffer_strcat(wb, "CONFLICT ");
    if(flags & RRDENG_PAGE_FULL)
        buffer_strcat(wb, "PAGE_FULL");
    if(flags & RRDENG_PAGE_COLLECT_FINALIZE)
        buffer_strcat(wb, "COLLECT_FINALIZE");
    if(flags & RRDENG_PAGE_UPDATE_EVERY_CHANGE)
        buffer_strcat(wb, "UPDATE_EVERY_CHANGE");
    if(flags & RRDENG_PAGE_STEP_TOO_SMALL)
        buffer_strcat(wb, "STEP_TOO_SMALL");
    if(flags & RRDENG_PAGE_STEP_UNALIGNED)
        buffer_strcat(wb, "STEP_UNALIGNED");
}

inline VALIDATED_PAGE_DESCRIPTOR validate_extent_page_descr(const struct rrdeng_extent_page_descr *descr, time_t now_s, time_t overwrite_zero_update_every_s, bool have_read_error) {
    return validate_page(
            (uuid_t *)descr->uuid,
            (time_t) (descr->start_time_ut / USEC_PER_SEC),
            (time_t) (descr->end_time_ut / USEC_PER_SEC),
            0,
            descr->page_length,
            descr->type,
            0,
            now_s,
            overwrite_zero_update_every_s,
            have_read_error,
            "loaded", 0);
}

VALIDATED_PAGE_DESCRIPTOR validate_page(
        uuid_t *uuid,
        time_t start_time_s,
        time_t end_time_s,
        time_t update_every_s,                  // can be zero, if unknown
        size_t page_length,
        uint8_t page_type,
        size_t entries,                         // can be zero, if unknown
        time_t now_s,                           // can be zero, to disable future timestamp check
        time_t overwrite_zero_update_every_s,   // can be zero, if unknown
        bool have_read_error,
        const char *msg,
        RRDENG_COLLECT_PAGE_FLAGS flags) {

    VALIDATED_PAGE_DESCRIPTOR vd = {
            .start_time_s = start_time_s,
            .end_time_s = end_time_s,
            .update_every_s = update_every_s,
            .page_length = page_length,
            .type = page_type,
            .is_valid = true,
    };

    // always calculate entries by size
    vd.point_size = page_type_size[vd.type];
    vd.entries = page_entries_by_size(vd.page_length, vd.point_size);

    // allow to be called without entries (when loading pages from disk)
    if(!entries)
        entries = vd.entries;

    // allow to be called without update every (when loading pages from disk)
    if(!update_every_s) {
        vd.update_every_s = (vd.entries > 1) ? ((vd.end_time_s - vd.start_time_s) / (time_t) (vd.entries - 1))
                                             : overwrite_zero_update_every_s;

        update_every_s = vd.update_every_s;
    }

    // another such set of checks exists in
    // update_metric_retention_and_granularity_by_uuid()

    bool updated = false;

    if( have_read_error                                         ||
        vd.page_length == 0                                     ||
        vd.page_length > RRDENG_BLOCK_SIZE                      ||
        vd.start_time_s > vd.end_time_s                         ||
        (now_s && vd.end_time_s > now_s)                        ||
        vd.start_time_s <= 0                                    ||
        vd.end_time_s <= 0                                      ||
        vd.update_every_s < 0                                   ||
        (vd.start_time_s == vd.end_time_s && vd.entries > 1)    ||
        (vd.update_every_s == 0 && vd.entries > 1)
        )
        vd.is_valid = false;

    else {
        if(unlikely(vd.entries != entries || vd.update_every_s != update_every_s))
            updated = true;

        if (likely(vd.update_every_s)) {
            size_t entries_by_time = page_entries_by_time(vd.start_time_s, vd.end_time_s, vd.update_every_s);

            if (vd.entries != entries_by_time) {
                if (overwrite_zero_update_every_s < vd.update_every_s)
                    vd.update_every_s = overwrite_zero_update_every_s;

                time_t new_end_time_s = (time_t)(vd.start_time_s + (vd.entries - 1) * vd.update_every_s);

                if(new_end_time_s <= vd.end_time_s) {
                    // end time is wrong
                    vd.end_time_s = new_end_time_s;
                }
                else {
                    // update every is wrong
                    vd.update_every_s = overwrite_zero_update_every_s;
                    vd.end_time_s = (time_t)(vd.start_time_s + (vd.entries - 1) * vd.update_every_s);
                }

                updated = true;
            }
        }
        else if(overwrite_zero_update_every_s) {
            vd.update_every_s = overwrite_zero_update_every_s;
            updated = true;
        }
    }

    if(unlikely(!vd.is_valid || updated)) {
#ifndef NETDATA_INTERNAL_CHECKS
        error_limit_static_global_var(erl, 1, 0);
#endif
        char uuid_str[UUID_STR_LEN + 1];
        uuid_unparse(*uuid, uuid_str);

        BUFFER *wb = NULL;

        if(flags) {
            wb = buffer_create(0, NULL);
            collect_page_flags_to_buffer(wb, flags);
        }

        if(!vd.is_valid) {
#ifdef NETDATA_INTERNAL_CHECKS
            internal_error(true,
#else
            error_limit(&erl,
#endif
                        "DBENGINE: metric '%s' %s invalid page of type %u "
                        "from %ld to %ld (now %ld), update every %ld, page length %zu, entries %zu (flags: %s)",
                        uuid_str, msg, vd.type,
                        vd.start_time_s, vd.end_time_s, now_s, vd.update_every_s, vd.page_length, vd.entries, wb?buffer_tostring(wb):""
            );
        }
        else {
            const char *err_valid = (vd.is_valid) ? "" : "found invalid, ";
            const char *err_start = (vd.start_time_s == start_time_s) ? "" : "start time updated, ";
            const char *err_end = (vd.end_time_s == end_time_s) ? "" : "end time updated, ";
            const char *err_update = (vd.update_every_s == update_every_s) ? "" : "update every updated, ";
            const char *err_length = (vd.page_length == page_length) ? "" : "page length updated, ";
            const char *err_entries = (vd.entries == entries) ? "" : "entries updated, ";
            const char *err_future = (now_s && vd.end_time_s <= now_s) ? "" : "future end time, ";

#ifdef NETDATA_INTERNAL_CHECKS
            internal_error(true,
#else
            error_limit(&erl,
#endif
                        "DBENGINE: metric '%s' %s page of type %u "
                        "from %ld to %ld (now %ld), update every %ld, page length %zu, entries %zu (flags: %s), "
                        "found inconsistent - the right is "
                        "from %ld to %ld, update every %ld, page length %zu, entries %zu: "
                        "%s%s%s%s%s%s%s",
                        uuid_str, msg, vd.type,
                        start_time_s, end_time_s, now_s, update_every_s, page_length, entries, wb?buffer_tostring(wb):"",
                        vd.start_time_s, vd.end_time_s, vd.update_every_s, vd.page_length, vd.entries,
                        err_valid, err_start, err_end, err_update, err_length, err_entries, err_future
            );
        }

        buffer_free(wb);
    }

    return vd;
}

static inline struct page_details *epdl_get_pd_load_link_list_from_metric_start_time(EPDL *epdl, Word_t metric_id, time_t start_time_s) {

    if(unlikely(epdl->head_to_datafile_extent_queries_pending_for_extent))
        // stop appending more pages to this epdl
        epdl_pending_del(epdl);

    struct page_details *pd_list = NULL;

    for(EPDL *ep = epdl; ep ;ep = ep->query.next) {
        Pvoid_t *pd_by_start_time_s_judyL = PDCJudyLGet(ep->page_details_by_metric_id_JudyL, metric_id, PJE0);
        internal_fatal(pd_by_start_time_s_judyL == PJERR, "DBENGINE: corrupted extent metrics JudyL");

        if (unlikely(pd_by_start_time_s_judyL && *pd_by_start_time_s_judyL)) {
            Pvoid_t *pd_pptr = PDCJudyLGet(*pd_by_start_time_s_judyL, start_time_s, PJE0);
            internal_fatal(pd_pptr == PJERR, "DBENGINE: corrupted metric page details JudyHS");

            if(likely(pd_pptr && *pd_pptr)) {
                struct page_details *pd = *pd_pptr;
                internal_fatal(metric_id != pd->metric_id, "DBENGINE: metric ids do not match");

                if(likely(!pd->page)) {
                    if (unlikely(__atomic_load_n(&ep->pdc->workers_should_stop, __ATOMIC_RELAXED)))
                        pdc_page_status_set(pd, PDC_PAGE_FAILED | PDC_PAGE_CANCELLED);
                    else
                        DOUBLE_LINKED_LIST_APPEND_ITEM_UNSAFE(pd_list, pd, load.prev, load.next);
                }
            }
        }
    }

    return pd_list;
}

static void epdl_extent_loading_error_log(struct rrdengine_instance *ctx, EPDL *epdl, struct rrdeng_extent_page_descr *descr, const char *msg) {
    char uuid[UUID_STR_LEN] = "";
    time_t start_time_s = 0;
    time_t end_time_s = 0;
    bool used_epdl = false;
    bool used_descr = false;

    if (descr) {
        start_time_s = (time_t)(descr->start_time_ut / USEC_PER_SEC);
        end_time_s = (time_t)(descr->end_time_ut / USEC_PER_SEC);
        uuid_unparse_lower(descr->uuid, uuid);
        used_descr = true;
    }
    else {
        struct page_details *pd = NULL;

        Word_t start = 0;
        Pvoid_t *pd_by_start_time_s_judyL = PDCJudyLFirst(epdl->page_details_by_metric_id_JudyL, &start, PJE0);
        if(pd_by_start_time_s_judyL) {
            start = 0;
            Pvoid_t *pd_pptr = PDCJudyLFirst(*pd_by_start_time_s_judyL, &start, PJE0);
            if(pd_pptr) {
                pd = *pd_pptr;
                start_time_s = pd->first_time_s;
                end_time_s = pd->last_time_s;
                METRIC *metric = (METRIC *)pd->metric_id;
                uuid_t *u = mrg_metric_uuid(main_mrg, metric);
                uuid_unparse_lower(*u, uuid);
                used_epdl = true;
            }
        }
    }

    if(!used_epdl && !used_descr && epdl->pdc) {
        start_time_s = epdl->pdc->start_time_s;
        end_time_s = epdl->pdc->end_time_s;
    }

    char start_time_str[LOG_DATE_LENGTH + 1] = "";
    if(start_time_s)
        log_date(start_time_str, LOG_DATE_LENGTH, start_time_s);

    char end_time_str[LOG_DATE_LENGTH + 1] = "";
    if(end_time_s)
        log_date(end_time_str, LOG_DATE_LENGTH, end_time_s);

    error_limit_static_global_var(erl, 1, 0);
    error_limit(&erl,
                "DBENGINE: error while reading extent from datafile %u of tier %d, at offset %" PRIu64 " (%u bytes) "
                "%s from %ld (%s) to %ld (%s) %s%s: "
                "%s",
                epdl->datafile->fileno, ctx->config.tier,
                epdl->extent_offset, epdl->extent_size,
                used_epdl ? "to extract page (PD)" : used_descr ? "expected page (DESCR)" : "part of a query (PDC)",
                start_time_s, start_time_str, end_time_s, end_time_str,
                used_epdl || used_descr ? " of metric " : "",
                used_epdl || used_descr ? uuid : "",
                msg);
}

static bool epdl_populate_pages_from_extent_data(
        struct rrdengine_instance *ctx,
        void *data,
        size_t data_length,
        EPDL *epdl,
        bool worker,
        PDC_PAGE_STATUS tags,
        bool cached_extent)
{
    int ret;
    unsigned i, count;
    void *uncompressed_buf = NULL;
    uint32_t payload_length, payload_offset, trailer_offset, uncompressed_payload_length = 0;
    bool have_read_error = false;
    /* persistent structures */
    struct rrdeng_df_extent_header *header;
    struct rrdeng_df_extent_trailer *trailer;
    struct extent_buffer *eb = NULL;
    uLong crc;

    bool can_use_data = true;
    if(data_length < sizeof(*header) + sizeof(header->descr[0]) + sizeof(*trailer)) {
        can_use_data = false;

        // added to satisfy the requirements of older compilers (prevent warnings)
        payload_length = 0;
        payload_offset = 0;
        trailer_offset = 0;
        count = 0;
        header = NULL;
        trailer = NULL;
    }
    else {
        header = data;
        payload_length = header->payload_length;
        count = header->number_of_pages;
        payload_offset = sizeof(*header) + sizeof(header->descr[0]) * count;
        trailer_offset = data_length - sizeof(*trailer);
        trailer = data + trailer_offset;
    }

    if( !can_use_data ||
        count < 1 ||
        count > MAX_PAGES_PER_EXTENT ||
        (header->compression_algorithm != RRD_NO_COMPRESSION && header->compression_algorithm != RRD_LZ4) ||
        (payload_length != trailer_offset - payload_offset) ||
        (data_length != payload_offset + payload_length + sizeof(*trailer))
            ) {
        epdl_extent_loading_error_log(ctx, epdl, NULL, "header is INVALID");
        return false;
    }

    crc = crc32(0L, Z_NULL, 0);
    crc = crc32(crc, data, epdl->extent_size - sizeof(*trailer));
    ret = crc32cmp(trailer->checksum, crc);
    if (unlikely(ret)) {
        ctx_io_error(ctx);
        have_read_error = true;
        epdl_extent_loading_error_log(ctx, epdl, NULL, "CRC32 checksum FAILED");
    }

    if(worker)
        worker_is_busy(UV_EVENT_DBENGINE_EXTENT_DECOMPRESSION);

    if (likely(!have_read_error && RRD_NO_COMPRESSION != header->compression_algorithm)) {
        // find the uncompressed extent size
        uncompressed_payload_length = 0;
        for (i = 0; i < count; ++i) {
            size_t page_length = header->descr[i].page_length;
            if(page_length > RRDENG_BLOCK_SIZE) {
                have_read_error = true;
                break;
            }

            uncompressed_payload_length += header->descr[i].page_length;
        }

        if(unlikely(uncompressed_payload_length > MAX_PAGES_PER_EXTENT * RRDENG_BLOCK_SIZE))
            have_read_error = true;

        if(likely(!have_read_error)) {
            eb = extent_buffer_get(uncompressed_payload_length);
            uncompressed_buf = eb->data;

            ret = LZ4_decompress_safe(data + payload_offset, uncompressed_buf,
                                      (int) payload_length, (int) uncompressed_payload_length);

            __atomic_add_fetch(&ctx->stats.before_decompress_bytes, payload_length, __ATOMIC_RELAXED);
            __atomic_add_fetch(&ctx->stats.after_decompress_bytes, ret, __ATOMIC_RELAXED);
        }
    }

    if(worker)
        worker_is_busy(UV_EVENT_DBENGINE_EXTENT_PAGE_LOOKUP);

    size_t stats_data_from_main_cache = 0;
    size_t stats_data_from_extent = 0;
    size_t stats_load_compressed = 0;
    size_t stats_load_uncompressed = 0;
    size_t stats_load_invalid_page = 0;
    size_t stats_cache_hit_while_inserting = 0;

    uint32_t page_offset = 0, page_length;
    time_t now_s = max_acceptable_collected_time();
    for (i = 0; i < count; i++, page_offset += page_length) {
        page_length = header->descr[i].page_length;
        time_t start_time_s = (time_t) (header->descr[i].start_time_ut / USEC_PER_SEC);

        if(!page_length || !start_time_s) {
            char log[200 + 1];
            snprintfz(log, 200, "page %u (out of %u) is EMPTY", i, count);
            epdl_extent_loading_error_log(ctx, epdl, &header->descr[i], log);
            continue;
        }

        METRIC *metric = mrg_metric_get_and_acquire(main_mrg, &header->descr[i].uuid, (Word_t)ctx);
        Word_t metric_id = (Word_t)metric;
        if(!metric) {
            char log[200 + 1];
            snprintfz(log, 200, "page %u (out of %u) has unknown UUID", i, count);
            epdl_extent_loading_error_log(ctx, epdl, &header->descr[i], log);
            continue;
        }
        mrg_metric_release(main_mrg, metric);

        struct page_details *pd_list = epdl_get_pd_load_link_list_from_metric_start_time(epdl, metric_id, start_time_s);
        if(likely(!pd_list))
            continue;

        VALIDATED_PAGE_DESCRIPTOR vd = validate_extent_page_descr(
                &header->descr[i], now_s,
                (pd_list) ? pd_list->update_every_s : 0,
                have_read_error);

        if(worker)
            worker_is_busy(UV_EVENT_DBENGINE_EXTENT_PAGE_ALLOCATION);

        void *page_data;

        if (unlikely(!vd.is_valid)) {
            page_data = DBENGINE_EMPTY_PAGE;
            stats_load_invalid_page++;
        }
        else {
            if (RRD_NO_COMPRESSION == header->compression_algorithm) {
                page_data = dbengine_page_alloc(vd.page_length);
                memcpy(page_data, data + payload_offset + page_offset, (size_t) vd.page_length);
                stats_load_uncompressed++;
            }
            else {
                if (unlikely(page_offset + vd.page_length > uncompressed_payload_length)) {
                    char log[200 + 1];
                    snprintfz(log, 200, "page %u (out of %u) offset %u + page length %zu, "
                                        "exceeds the uncompressed buffer size %u",
                                        i, count, page_offset, vd.page_length, uncompressed_payload_length);
                    epdl_extent_loading_error_log(ctx, epdl, &header->descr[i], log);

                    page_data = DBENGINE_EMPTY_PAGE;
                    stats_load_invalid_page++;
                }
                else {
                    page_data = dbengine_page_alloc(vd.page_length);
                    memcpy(page_data, uncompressed_buf + page_offset, vd.page_length);
                    stats_load_compressed++;
                }
            }
        }

        if(worker)
            worker_is_busy(UV_EVENT_DBENGINE_EXTENT_PAGE_POPULATION);

        PGC_ENTRY page_entry = {
                .hot = false,
                .section = (Word_t)ctx,
                .metric_id = metric_id,
                .start_time_s = vd.start_time_s,
                .end_time_s = vd.end_time_s,
                .update_every_s = (uint32_t) vd.update_every_s,
                .size = (size_t) ((page_data == DBENGINE_EMPTY_PAGE) ? 0 : vd.page_length),
                .data = page_data
        };

        bool added = true;
        PGC_PAGE *page = pgc_page_add_and_acquire(main_cache, page_entry, &added);
        if (false == added) {
            dbengine_page_free(page_data, vd.page_length);
            stats_cache_hit_while_inserting++;
            stats_data_from_main_cache++;
        }
        else
            stats_data_from_extent++;

        struct page_details *pd = pd_list;
        do {
            if(pd != pd_list)
                pgc_page_dup(main_cache, page);

            pd->page = page;
            pd->page_length = pgc_page_data_size(main_cache, page);
            pdc_page_status_set(pd, PDC_PAGE_READY | tags | ((page_data == DBENGINE_EMPTY_PAGE) ? PDC_PAGE_EMPTY : 0));

            pd = pd->load.next;
        } while(pd);

        if(worker)
            worker_is_busy(UV_EVENT_DBENGINE_EXTENT_PAGE_LOOKUP);
    }

    if(stats_data_from_main_cache)
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_data_source_main_cache, stats_data_from_main_cache, __ATOMIC_RELAXED);

    if(cached_extent)
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_data_source_extent_cache, stats_data_from_extent, __ATOMIC_RELAXED);
    else {
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_data_source_disk, stats_data_from_extent, __ATOMIC_RELAXED);
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.extents_loaded_from_disk, 1, __ATOMIC_RELAXED);
    }

    if(stats_cache_hit_while_inserting)
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_load_ok_loaded_but_cache_hit_while_inserting, stats_cache_hit_while_inserting, __ATOMIC_RELAXED);

    if(stats_load_compressed)
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_load_ok_compressed, stats_load_compressed, __ATOMIC_RELAXED);

    if(stats_load_uncompressed)
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_load_ok_uncompressed, stats_load_uncompressed, __ATOMIC_RELAXED);

    if(stats_load_invalid_page)
        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.pages_load_fail_invalid_page_in_extent, stats_load_invalid_page, __ATOMIC_RELAXED);

    if(worker)
        worker_is_idle();

    extent_buffer_release(eb);

    return true;
}

static inline void *datafile_extent_read(struct rrdengine_instance *ctx, uv_file file, unsigned pos, unsigned size_bytes)
{
    void *buffer;
    uv_fs_t request;

    unsigned real_io_size = ALIGN_BYTES_CEILING(size_bytes);
    int ret = posix_memalign(&buffer, RRDFILE_ALIGNMENT, real_io_size);
    if (unlikely(ret))
        fatal("DBENGINE: posix_memalign(): %s", strerror(ret));

    uv_buf_t iov = uv_buf_init(buffer, real_io_size);
    ret = uv_fs_read(NULL, &request, file, &iov, 1, pos, NULL);
    if (unlikely(-1 == ret)) {
        ctx_io_error(ctx);
        posix_memfree(buffer);
        buffer = NULL;
    }
    else
        ctx_io_read_op_bytes(ctx, real_io_size);

    uv_fs_req_cleanup(&request);

    return buffer;
}

static inline void datafile_extent_read_free(void *buffer) {
    posix_memfree(buffer);
}

void epdl_find_extent_and_populate_pages(struct rrdengine_instance *ctx, EPDL *epdl, bool worker) {
    if(worker)
        worker_is_busy(UV_EVENT_DBENGINE_EXTENT_CACHE_LOOKUP);

    size_t *statistics_counter = NULL;
    PDC_PAGE_STATUS not_loaded_pages_tag = 0, loaded_pages_tag = 0;

    bool should_stop = __atomic_load_n(&epdl->pdc->workers_should_stop, __ATOMIC_RELAXED);
    for(EPDL *ep = epdl->query.next; ep ;ep = ep->query.next) {
        internal_fatal(ep->datafile != epdl->datafile, "DBENGINE: datafiles do not match");
        internal_fatal(ep->extent_offset != epdl->extent_offset, "DBENGINE: extent offsets do not match");
        internal_fatal(ep->extent_size != epdl->extent_size, "DBENGINE: extent sizes do not match");
        internal_fatal(ep->file != epdl->file, "DBENGINE: files do not match");

        if(!__atomic_load_n(&ep->pdc->workers_should_stop, __ATOMIC_RELAXED)) {
            should_stop = false;
            break;
        }
    }

    if(unlikely(should_stop)) {
        statistics_counter = &rrdeng_cache_efficiency_stats.pages_load_fail_cancelled;
        not_loaded_pages_tag = PDC_PAGE_CANCELLED;
        goto cleanup;
    }

    bool extent_found_in_cache = false;

    void *extent_compressed_data = NULL;
    PGC_PAGE *extent_cache_page = pgc_page_get_and_acquire(
            extent_cache, (Word_t)ctx,
            (Word_t)epdl->datafile->fileno, (time_t)epdl->extent_offset,
            PGC_SEARCH_EXACT);

    if(extent_cache_page) {
        extent_compressed_data = pgc_page_data(extent_cache_page);
        internal_fatal(epdl->extent_size != pgc_page_data_size(extent_cache, extent_cache_page),
                       "DBENGINE: cache size does not match the expected size");

        loaded_pages_tag |= PDC_PAGE_EXTENT_FROM_CACHE;
        not_loaded_pages_tag |= PDC_PAGE_EXTENT_FROM_CACHE;
        extent_found_in_cache = true;
    }
    else {
        if(worker)
            worker_is_busy(UV_EVENT_DBENGINE_EXTENT_MMAP);

        void *extent_data = datafile_extent_read(ctx, epdl->file, epdl->extent_offset, epdl->extent_size);
        if(extent_data != NULL) {

            void *copied_extent_compressed_data = dbengine_extent_alloc(epdl->extent_size);
            memcpy(copied_extent_compressed_data, extent_data, epdl->extent_size);
            datafile_extent_read_free(extent_data);

            if(worker)
                worker_is_busy(UV_EVENT_DBENGINE_EXTENT_CACHE_LOOKUP);

            bool added = false;
            extent_cache_page = pgc_page_add_and_acquire(extent_cache, (PGC_ENTRY) {
                    .hot = false,
                    .section = (Word_t) ctx,
                    .metric_id = (Word_t) epdl->datafile->fileno,
                    .start_time_s = (time_t) epdl->extent_offset,
                    .size = epdl->extent_size,
                    .end_time_s = 0,
                    .update_every_s = 0,
                    .data = copied_extent_compressed_data,
            }, &added);

            if (!added) {
                dbengine_extent_free(copied_extent_compressed_data, epdl->extent_size);
                internal_fatal(epdl->extent_size != pgc_page_data_size(extent_cache, extent_cache_page),
                               "DBENGINE: cache size does not match the expected size");
            }

            extent_compressed_data = pgc_page_data(extent_cache_page);

            loaded_pages_tag |= PDC_PAGE_EXTENT_FROM_DISK;
            not_loaded_pages_tag |= PDC_PAGE_EXTENT_FROM_DISK;
        }
    }

    if(extent_compressed_data) {
        // Need to decompress and then process the pagelist
        bool extent_used = epdl_populate_pages_from_extent_data(
                ctx, extent_compressed_data, epdl->extent_size,
                epdl, worker, loaded_pages_tag, extent_found_in_cache);

        if(extent_used) {
            // since the extent was used, all the pages that are not
            // loaded from this extent, were not found in the extent
            not_loaded_pages_tag |= PDC_PAGE_FAILED_NOT_IN_EXTENT;
            statistics_counter = &rrdeng_cache_efficiency_stats.pages_load_fail_not_found;
        }
        else {
            not_loaded_pages_tag |= PDC_PAGE_FAILED_INVALID_EXTENT;
            statistics_counter = &rrdeng_cache_efficiency_stats.pages_load_fail_invalid_extent;
        }
    }
    else {
        not_loaded_pages_tag |= PDC_PAGE_FAILED_TO_MAP_EXTENT;
        statistics_counter = &rrdeng_cache_efficiency_stats.pages_load_fail_cant_mmap_extent;
    }

    if(extent_cache_page)
        pgc_page_release(extent_cache, extent_cache_page);

cleanup:
    // remove it from the datafile extent_queries
    // this can be called multiple times safely
    epdl_pending_del(epdl);

    // mark all pending pages as failed
    for(EPDL *ep = epdl; ep ;ep = ep->query.next) {
        epdl_mark_all_not_loaded_pages_as_failed(
                ep, not_loaded_pages_tag, statistics_counter);
    }

    for(EPDL *ep = epdl, *next = NULL; ep ; ep = next) {
        next = ep->query.next;

        completion_mark_complete_a_job(&ep->pdc->page_completion);
        pdc_release_and_destroy_if_unreferenced(ep->pdc, true, false);

        // Free the Judy that holds the requested pagelist and the extents
        epdl_destroy(ep);
    }

    if(worker)
        worker_is_idle();
}