summaryrefslogtreecommitdiffstats
path: root/database/engine/rrdengineapi.c
blob: c6b1fa2dde4944a9da2fe94df03a88fd26d9c9c8 (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
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
// SPDX-License-Identifier: GPL-3.0-or-later
#include "rrdengine.h"

/* Default global database instance */
struct rrdengine_instance multidb_ctx_storage_tier0;
struct rrdengine_instance multidb_ctx_storage_tier1;
struct rrdengine_instance multidb_ctx_storage_tier2;
struct rrdengine_instance multidb_ctx_storage_tier3;
struct rrdengine_instance multidb_ctx_storage_tier4;

#define mrg_metric_ctx(metric) (struct rrdengine_instance *)mrg_metric_section(main_mrg, metric)

#if RRD_STORAGE_TIERS != 5
#error RRD_STORAGE_TIERS is not 5 - you need to add allocations here
#endif
struct rrdengine_instance *multidb_ctx[RRD_STORAGE_TIERS];
uint8_t tier_page_type[RRD_STORAGE_TIERS] = {PAGE_METRICS, PAGE_TIER, PAGE_TIER, PAGE_TIER, PAGE_TIER};

#if defined(ENV32BIT)
size_t tier_page_size[RRD_STORAGE_TIERS] = {2048, 1024, 192, 192, 192};
#else
size_t tier_page_size[RRD_STORAGE_TIERS] = {4096, 2048, 384, 384, 384};
#endif

#if PAGE_TYPE_MAX != 1
#error PAGE_TYPE_MAX is not 1 - you need to add allocations here
#endif
size_t page_type_size[256] = {sizeof(storage_number), sizeof(storage_number_tier1_t)};

__attribute__((constructor)) void initialize_multidb_ctx(void) {
    multidb_ctx[0] = &multidb_ctx_storage_tier0;
    multidb_ctx[1] = &multidb_ctx_storage_tier1;
    multidb_ctx[2] = &multidb_ctx_storage_tier2;
    multidb_ctx[3] = &multidb_ctx_storage_tier3;
    multidb_ctx[4] = &multidb_ctx_storage_tier4;
}

int db_engine_journal_check = 0;
int default_rrdeng_disk_quota_mb = 256;
int default_multidb_disk_quota_mb = 256;

#if defined(ENV32BIT)
int default_rrdeng_page_cache_mb = 16;
int default_rrdeng_extent_cache_mb = 0;
#else
int default_rrdeng_page_cache_mb = 32;
int default_rrdeng_extent_cache_mb = 0;
#endif

// ----------------------------------------------------------------------------
// metrics groups

static inline void rrdeng_page_alignment_acquire(struct pg_alignment *pa) {
    if(unlikely(!pa)) return;
    __atomic_add_fetch(&pa->refcount, 1, __ATOMIC_SEQ_CST);
}

static inline bool rrdeng_page_alignment_release(struct pg_alignment *pa) {
    if(unlikely(!pa)) return true;

    if(__atomic_sub_fetch(&pa->refcount, 1, __ATOMIC_SEQ_CST) == 0) {
        freez(pa);
        return true;
    }

    return false;
}

// charts call this
STORAGE_METRICS_GROUP *rrdeng_metrics_group_get(STORAGE_INSTANCE *db_instance __maybe_unused, uuid_t *uuid __maybe_unused) {
    struct pg_alignment *pa = callocz(1, sizeof(struct pg_alignment));
    rrdeng_page_alignment_acquire(pa);
    return (STORAGE_METRICS_GROUP *)pa;
}

// charts call this
void rrdeng_metrics_group_release(STORAGE_INSTANCE *db_instance __maybe_unused, STORAGE_METRICS_GROUP *smg) {
    if(unlikely(!smg)) return;

    struct pg_alignment *pa = (struct pg_alignment *)smg;
    rrdeng_page_alignment_release(pa);
}

// ----------------------------------------------------------------------------
// metric handle for legacy dbs

/* This UUID is not unique across hosts */
void rrdeng_generate_legacy_uuid(const char *dim_id, const char *chart_id, uuid_t *ret_uuid)
{
    EVP_MD_CTX *evpctx;
    unsigned char hash_value[EVP_MAX_MD_SIZE];
    unsigned int hash_len;

    evpctx = EVP_MD_CTX_create();
    EVP_DigestInit_ex(evpctx, EVP_sha256(), NULL);
    EVP_DigestUpdate(evpctx, dim_id, strlen(dim_id));
    EVP_DigestUpdate(evpctx, chart_id, strlen(chart_id));
    EVP_DigestFinal_ex(evpctx, hash_value, &hash_len);
    EVP_MD_CTX_destroy(evpctx);
    fatal_assert(hash_len > sizeof(uuid_t));
    memcpy(ret_uuid, hash_value, sizeof(uuid_t));
}

static METRIC *rrdeng_metric_get_legacy(STORAGE_INSTANCE *db_instance, const char *rd_id, const char *st_id) {
    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
    uuid_t legacy_uuid;
    rrdeng_generate_legacy_uuid(rd_id, st_id, &legacy_uuid);
    return mrg_metric_get_and_acquire(main_mrg, &legacy_uuid, (Word_t) ctx);
}

// ----------------------------------------------------------------------------
// metric handle

void rrdeng_metric_release(STORAGE_METRIC_HANDLE *db_metric_handle) {
    METRIC *metric = (METRIC *)db_metric_handle;
    mrg_metric_release(main_mrg, metric);
}

STORAGE_METRIC_HANDLE *rrdeng_metric_dup(STORAGE_METRIC_HANDLE *db_metric_handle) {
    METRIC *metric = (METRIC *)db_metric_handle;
    return (STORAGE_METRIC_HANDLE *) mrg_metric_dup(main_mrg, metric);
}

STORAGE_METRIC_HANDLE *rrdeng_metric_get(STORAGE_INSTANCE *db_instance, uuid_t *uuid) {
    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
    return (STORAGE_METRIC_HANDLE *) mrg_metric_get_and_acquire(main_mrg, uuid, (Word_t) ctx);
}

static METRIC *rrdeng_metric_create(STORAGE_INSTANCE *db_instance, uuid_t *uuid) {
    internal_fatal(!db_instance, "DBENGINE: db_instance is NULL");

    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
    MRG_ENTRY entry = {
            .uuid = uuid,
            .section = (Word_t)ctx,
            .first_time_s = 0,
            .last_time_s = 0,
            .latest_update_every_s = 0,
    };

    METRIC *metric = mrg_metric_add_and_acquire(main_mrg, entry, NULL);
    return metric;
}

STORAGE_METRIC_HANDLE *rrdeng_metric_get_or_create(RRDDIM *rd, STORAGE_INSTANCE *db_instance) {
    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
    METRIC *metric;

    metric = mrg_metric_get_and_acquire(main_mrg, &rd->metric_uuid, (Word_t) ctx);

    if(unlikely(!metric)) {
        if(unlikely(ctx->config.legacy)) {
            // this is a single host database
            // generate uuid from the chart and dimensions ids
            // and overwrite the one supplied by rrddim
            metric = rrdeng_metric_get_legacy(db_instance, rrddim_id(rd), rrdset_id(rd->rrdset));
            if (metric)
                uuid_copy(rd->metric_uuid, *mrg_metric_uuid(main_mrg, metric));
        }

        if(likely(!metric))
            metric = rrdeng_metric_create(db_instance, &rd->metric_uuid);
    }

#ifdef NETDATA_INTERNAL_CHECKS
    if(uuid_memcmp(&rd->metric_uuid, mrg_metric_uuid(main_mrg, metric)) != 0) {
        char uuid1[UUID_STR_LEN + 1];
        char uuid2[UUID_STR_LEN + 1];

        uuid_unparse(rd->metric_uuid, uuid1);
        uuid_unparse(*mrg_metric_uuid(main_mrg, metric), uuid2);
        fatal("DBENGINE: uuids do not match, asked for metric '%s', but got metric '%s'", uuid1, uuid2);
    }

    if(mrg_metric_ctx(metric) != ctx)
        fatal("DBENGINE: mixed up db instances, asked for metric from %p, got from %p",
              ctx, mrg_metric_ctx(metric));
#endif

    return (STORAGE_METRIC_HANDLE *)metric;
}


// ----------------------------------------------------------------------------
// collect ops

static inline void check_and_fix_mrg_update_every(struct rrdeng_collect_handle *handle) {
    if(unlikely((time_t)(handle->update_every_ut / USEC_PER_SEC) != mrg_metric_get_update_every_s(main_mrg, handle->metric))) {
        internal_error(true, "DBENGINE: collection handle has update every %ld, but the metric registry has %ld. Fixing it.",
              (time_t)(handle->update_every_ut / USEC_PER_SEC), mrg_metric_get_update_every_s(main_mrg, handle->metric));

        if(unlikely(!handle->update_every_ut))
            handle->update_every_ut = (usec_t)mrg_metric_get_update_every_s(main_mrg, handle->metric) * USEC_PER_SEC;
        else
            mrg_metric_set_update_every(main_mrg, handle->metric, (time_t)(handle->update_every_ut / USEC_PER_SEC));
    }
}

static inline bool check_completed_page_consistency(struct rrdeng_collect_handle *handle __maybe_unused) {
#ifdef NETDATA_INTERNAL_CHECKS
    if (unlikely(!handle->page || !handle->page_entries_max || !handle->page_position || !handle->page_end_time_ut))
        return false;

    struct rrdengine_instance *ctx = mrg_metric_ctx(handle->metric);

    uuid_t *uuid = mrg_metric_uuid(main_mrg, handle->metric);
    time_t start_time_s = pgc_page_start_time_s(handle->page);
    time_t end_time_s = pgc_page_end_time_s(handle->page);
    time_t update_every_s = pgc_page_update_every_s(handle->page);
    size_t page_length = handle->page_position * CTX_POINT_SIZE_BYTES(ctx);
    size_t entries = handle->page_position;
    time_t overwrite_zero_update_every_s = (time_t)(handle->update_every_ut / USEC_PER_SEC);

    if(end_time_s > max_acceptable_collected_time())
        handle->page_flags |= RRDENG_PAGE_COMPLETED_IN_FUTURE;

    VALIDATED_PAGE_DESCRIPTOR vd = validate_page(
            uuid,
            start_time_s,
            end_time_s,
            update_every_s,
            page_length,
            ctx->config.page_type,
            entries,
            0, // do not check for future timestamps - we inherit the timestamps of the children
            overwrite_zero_update_every_s,
            false,
            "collected",
            handle->page_flags);

    return vd.is_valid;
#else
    return true;
#endif
}

/*
 * Gets a handle for storing metrics to the database.
 * The handle must be released with rrdeng_store_metric_final().
 */
STORAGE_COLLECT_HANDLE *rrdeng_store_metric_init(STORAGE_METRIC_HANDLE *db_metric_handle, uint32_t update_every, STORAGE_METRICS_GROUP *smg) {
    METRIC *metric = (METRIC *)db_metric_handle;
    struct rrdengine_instance *ctx = mrg_metric_ctx(metric);

    bool is_1st_metric_writer = true;
    if(!mrg_metric_set_writer(main_mrg, metric)) {
        is_1st_metric_writer = false;
        char uuid[UUID_STR_LEN + 1];
        uuid_unparse(*mrg_metric_uuid(main_mrg, metric), uuid);
        netdata_log_error("DBENGINE: metric '%s' is already collected and should not be collected twice - expect gaps on the charts", uuid);
    }

    metric = mrg_metric_dup(main_mrg, metric);

    struct rrdeng_collect_handle *handle;

    handle = callocz(1, sizeof(struct rrdeng_collect_handle));
    handle->common.backend = STORAGE_ENGINE_BACKEND_DBENGINE;
    handle->metric = metric;
    handle->page = NULL;
    handle->data = NULL;
    handle->data_size = 0;
    handle->page_position = 0;
    handle->page_entries_max = 0;
    handle->update_every_ut = (usec_t)update_every * USEC_PER_SEC;
    handle->options = is_1st_metric_writer ? RRDENG_1ST_METRIC_WRITER : 0;

    __atomic_add_fetch(&ctx->atomic.collectors_running, 1, __ATOMIC_RELAXED);
    if(!is_1st_metric_writer)
        __atomic_add_fetch(&ctx->atomic.collectors_running_duplicate, 1, __ATOMIC_RELAXED);

    mrg_metric_set_update_every(main_mrg, metric, update_every);

    handle->alignment = (struct pg_alignment *)smg;
    rrdeng_page_alignment_acquire(handle->alignment);

    // this is important!
    // if we don't set the page_end_time_ut during the first collection
    // data collection may be able to go back in time and during the addition of new pages
    // clean pages may be found matching ours!

    time_t db_first_time_s, db_last_time_s, db_update_every_s;
    mrg_metric_get_retention(main_mrg, metric, &db_first_time_s, &db_last_time_s, &db_update_every_s);
    handle->page_end_time_ut = (usec_t)db_last_time_s * USEC_PER_SEC;

    return (STORAGE_COLLECT_HANDLE *)handle;
}

/* The page must be populated and referenced */
static bool page_has_only_empty_metrics(struct rrdeng_collect_handle *handle) {
    switch(handle->type) {
        case PAGE_METRICS: {
            size_t slots = handle->page_position;
            storage_number *array = (storage_number *)pgc_page_data(handle->page);
            for (size_t i = 0 ; i < slots; ++i) {
                if(does_storage_number_exist(array[i]))
                    return false;
            }
        }
        break;

        case PAGE_TIER: {
            size_t slots = handle->page_position;
            storage_number_tier1_t *array = (storage_number_tier1_t *)pgc_page_data(handle->page);
            for (size_t i = 0 ; i < slots; ++i) {
                if(fpclassify(array[i].sum_value) != FP_NAN)
                    return false;
            }
        }
        break;

        default: {
            static bool logged = false;
            if(!logged) {
                netdata_log_error("DBENGINE: cannot check page for nulls on unknown page type id %d", (mrg_metric_ctx(handle->metric))->config.page_type);
                logged = true;
            }
            return false;
        }
    }

    return true;
}

void rrdeng_store_metric_flush_current_page(STORAGE_COLLECT_HANDLE *collection_handle) {
    struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;

    if (unlikely(!handle->page))
        return;

    if(!handle->page_position || page_has_only_empty_metrics(handle))
        pgc_page_to_clean_evict_or_release(main_cache, handle->page);

    else {
        check_completed_page_consistency(handle);
        mrg_metric_set_clean_latest_time_s(main_mrg, handle->metric, pgc_page_end_time_s(handle->page));
        pgc_page_hot_to_dirty_and_release(main_cache, handle->page);
    }

    mrg_metric_set_hot_latest_time_s(main_mrg, handle->metric, 0);

    handle->page = NULL;
    handle->page_flags = 0;
    handle->page_position = 0;
    handle->page_entries_max = 0;
    handle->data = NULL;
    handle->data_size = 0;

    // important!
    // we should never zero page end time ut, because this will allow
    // collection to go back in time
    // handle->page_end_time_ut = 0;
    // handle->page_start_time_ut;

    check_and_fix_mrg_update_every(handle);

    timing_step(TIMING_STEP_DBENGINE_FLUSH_PAGE);
}

static void rrdeng_store_metric_create_new_page(struct rrdeng_collect_handle *handle,
                struct rrdengine_instance *ctx,
                usec_t point_in_time_ut,
                void *data,
                size_t data_size) {
    time_t point_in_time_s = (time_t)(point_in_time_ut / USEC_PER_SEC);
    const time_t update_every_s = (time_t)(handle->update_every_ut / USEC_PER_SEC);

    PGC_ENTRY page_entry = {
            .section = (Word_t) ctx,
            .metric_id = mrg_metric_id(main_mrg, handle->metric),
            .start_time_s = point_in_time_s,
            .end_time_s = point_in_time_s,
            .size = data_size,
            .data = data,
            .update_every_s = (uint32_t) update_every_s,
            .hot = true
    };

    size_t conflicts = 0;
    bool added = true;
    PGC_PAGE *page = pgc_page_add_and_acquire(main_cache, page_entry, &added);
    while (unlikely(!added)) {
        conflicts++;

        char uuid[UUID_STR_LEN + 1];
        uuid_unparse(*mrg_metric_uuid(main_mrg, handle->metric), uuid);

#ifdef NETDATA_INTERNAL_CHECKS
        internal_error(true,
#else
        error_limit_static_global_var(erl, 1, 0);
        error_limit(&erl,
#endif
              "DBENGINE: metric '%s' new page from %ld to %ld, update every %ld, has a conflict in main cache "
              "with existing %s%s page from %ld to %ld, update every %ld - "
              "is it collected more than once?",
              uuid,
              page_entry.start_time_s, page_entry.end_time_s, (time_t)page_entry.update_every_s,
              pgc_is_page_hot(page) ? "hot" : "not-hot",
              pgc_page_data(page) == DBENGINE_EMPTY_PAGE ? " gap" : "",
              pgc_page_start_time_s(page), pgc_page_end_time_s(page), pgc_page_update_every_s(page)
              );

        pgc_page_release(main_cache, page);

        point_in_time_ut -= handle->update_every_ut;
        point_in_time_s = (time_t)(point_in_time_ut / USEC_PER_SEC);
        page_entry.start_time_s = point_in_time_s;
        page_entry.end_time_s = point_in_time_s;
        page = pgc_page_add_and_acquire(main_cache, page_entry, &added);
    }

    handle->page_entries_max = data_size / CTX_POINT_SIZE_BYTES(ctx);
    handle->page_start_time_ut = point_in_time_ut;
    handle->page_end_time_ut = point_in_time_ut;
    handle->page_position = 1; // zero is already in our data
    handle->page = page;
    handle->page_flags = conflicts? RRDENG_PAGE_CONFLICT : 0;

    if(point_in_time_s > max_acceptable_collected_time())
        handle->page_flags |= RRDENG_PAGE_CREATED_IN_FUTURE;

    check_and_fix_mrg_update_every(handle);

    timing_step(TIMING_STEP_DBENGINE_CREATE_NEW_PAGE);
}

static size_t aligned_allocation_entries(size_t max_slots, size_t target_slot, time_t now_s) {
    size_t slots = target_slot;
    size_t pos = (now_s % max_slots);

    if(pos > slots)
        slots += max_slots - pos;

    else if(pos < slots)
        slots -= pos;

    else
        slots = max_slots;

    return slots;
}

static void *rrdeng_alloc_new_metric_data(struct rrdeng_collect_handle *handle, size_t *data_size, usec_t point_in_time_ut) {
    struct rrdengine_instance *ctx = mrg_metric_ctx(handle->metric);

    size_t max_size = tier_page_size[ctx->config.tier];
    size_t max_slots = max_size / CTX_POINT_SIZE_BYTES(ctx);

    size_t slots = aligned_allocation_entries(
            max_slots,
            indexing_partition((Word_t) handle->alignment, max_slots),
            (time_t) (point_in_time_ut / USEC_PER_SEC)
    );

    if(slots < max_slots / 3)
        slots = max_slots / 3;

    if(slots < 3)
        slots = 3;

    size_t size = slots * CTX_POINT_SIZE_BYTES(ctx);

    // internal_error(true, "PAGE ALLOC %zu bytes (%zu max)", size, max_size);

    internal_fatal(slots < 3 || slots > max_slots, "ooops! wrong distribution of metrics across time");
    internal_fatal(size > tier_page_size[ctx->config.tier] || size < CTX_POINT_SIZE_BYTES(ctx) * 2, "ooops! wrong page size");

    *data_size = size;
    void *d = dbengine_page_alloc(size);

    timing_step(TIMING_STEP_DBENGINE_PAGE_ALLOC);

    return d;
}

static void rrdeng_store_metric_append_point(STORAGE_COLLECT_HANDLE *collection_handle,
                                             const usec_t point_in_time_ut,
                                             const NETDATA_DOUBLE n,
                                             const NETDATA_DOUBLE min_value,
                                             const NETDATA_DOUBLE max_value,
                                             const uint16_t count,
                                             const uint16_t anomaly_count,
                                             const SN_FLAGS flags)
{
    struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;
    struct rrdengine_instance *ctx = mrg_metric_ctx(handle->metric);

    if(unlikely(!handle->data))
        handle->data = rrdeng_alloc_new_metric_data(handle, &handle->data_size, point_in_time_ut);

    timing_step(TIMING_STEP_DBENGINE_CHECK_DATA);

    if(likely(ctx->config.page_type == PAGE_METRICS)) {
        storage_number *tier0_metric_data = handle->data;
        tier0_metric_data[handle->page_position] = pack_storage_number(n, flags);
    }
    else if(likely(ctx->config.page_type == PAGE_TIER)) {
        storage_number_tier1_t *tier12_metric_data = handle->data;
        storage_number_tier1_t number_tier1;
        number_tier1.sum_value = (float) n;
        number_tier1.min_value = (float) min_value;
        number_tier1.max_value = (float) max_value;
        number_tier1.anomaly_count = anomaly_count;
        number_tier1.count = count;
        tier12_metric_data[handle->page_position] = number_tier1;
    }
    else
        fatal("DBENGINE: cannot store metric on unknown page type id %d", ctx->config.page_type);

    timing_step(TIMING_STEP_DBENGINE_PACK);

    if(unlikely(!handle->page)){
        rrdeng_store_metric_create_new_page(handle, ctx, point_in_time_ut, handle->data, handle->data_size);
        // handle->position is set to 1 already
    }
    else {
        // update an existing page
        pgc_page_hot_set_end_time_s(main_cache, handle->page, (time_t) (point_in_time_ut / USEC_PER_SEC));
        handle->page_end_time_ut = point_in_time_ut;

        if(unlikely(++handle->page_position >= handle->page_entries_max)) {
            internal_fatal(handle->page_position > handle->page_entries_max, "DBENGINE: exceeded page max number of points");
            handle->page_flags |= RRDENG_PAGE_FULL;
            rrdeng_store_metric_flush_current_page(collection_handle);
        }
    }

    timing_step(TIMING_STEP_DBENGINE_PAGE_FIN);

    // update the metric information
    mrg_metric_set_hot_latest_time_s(main_mrg, handle->metric, (time_t) (point_in_time_ut / USEC_PER_SEC));

    timing_step(TIMING_STEP_DBENGINE_MRG_UPDATE);
}

static void store_metric_next_error_log(struct rrdeng_collect_handle *handle, usec_t point_in_time_ut, const char *msg) {
    time_t point_in_time_s = (time_t)(point_in_time_ut / USEC_PER_SEC);
    char uuid[UUID_STR_LEN + 1];
    uuid_unparse(*mrg_metric_uuid(main_mrg, handle->metric), uuid);

    BUFFER *wb = NULL;
    if(handle->page && handle->page_flags) {
        wb = buffer_create(0, NULL);
        collect_page_flags_to_buffer(wb, handle->page_flags);
    }

    error_limit_static_global_var(erl, 1, 0);
    error_limit(&erl,
                "DBENGINE: metric '%s' collected point at %ld, %s last collection at %ld, "
                "update every %ld, %s page from %ld to %ld, position %u (of %u), flags: %s",
                uuid,
                point_in_time_s,
                msg,
                (time_t)(handle->page_end_time_ut / USEC_PER_SEC),
                (time_t)(handle->update_every_ut / USEC_PER_SEC),
                handle->page ? "current" : "*LAST*",
                (time_t)(handle->page_start_time_ut / USEC_PER_SEC),
                (time_t)(handle->page_end_time_ut / USEC_PER_SEC),
                handle->page_position, handle->page_entries_max,
                wb ? buffer_tostring(wb) : ""
    );

    buffer_free(wb);
}

void rrdeng_store_metric_next(STORAGE_COLLECT_HANDLE *collection_handle,
                              const usec_t point_in_time_ut,
                              const NETDATA_DOUBLE n,
                              const NETDATA_DOUBLE min_value,
                              const NETDATA_DOUBLE max_value,
                              const uint16_t count,
                              const uint16_t anomaly_count,
                              const SN_FLAGS flags)
{
    timing_step(TIMING_STEP_RRDSET_STORE_METRIC);

    struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;

#ifdef NETDATA_INTERNAL_CHECKS
    if(unlikely(point_in_time_ut > (usec_t)max_acceptable_collected_time() * USEC_PER_SEC))
        handle->page_flags |= RRDENG_PAGE_FUTURE_POINT;
#endif

    usec_t delta_ut = point_in_time_ut - handle->page_end_time_ut;

    if(likely(delta_ut == handle->update_every_ut)) {
        // happy path
        ;
    }
    else if(unlikely(point_in_time_ut > handle->page_end_time_ut)) {
        if(handle->page) {
            if (unlikely(delta_ut < handle->update_every_ut)) {
                handle->page_flags |= RRDENG_PAGE_STEP_TOO_SMALL;
                rrdeng_store_metric_flush_current_page(collection_handle);
            }
            else if (unlikely(delta_ut % handle->update_every_ut)) {
                handle->page_flags |= RRDENG_PAGE_STEP_UNALIGNED;
                rrdeng_store_metric_flush_current_page(collection_handle);
            }
            else {
                size_t points_gap = delta_ut / handle->update_every_ut;
                size_t page_remaining_points = handle->page_entries_max - handle->page_position;

                if (points_gap >= page_remaining_points) {
                    handle->page_flags |= RRDENG_PAGE_BIG_GAP;
                    rrdeng_store_metric_flush_current_page(collection_handle);
                }
                else {
                    // loop to fill the gap
                    handle->page_flags |= RRDENG_PAGE_GAP;

                    usec_t stop_ut = point_in_time_ut - handle->update_every_ut;
                    for (usec_t this_ut = handle->page_end_time_ut + handle->update_every_ut;
                         this_ut <= stop_ut;
                         this_ut = handle->page_end_time_ut + handle->update_every_ut) {
                        rrdeng_store_metric_append_point(
                                collection_handle,
                                this_ut,
                                NAN, NAN, NAN,
                                1, 0,
                                SN_EMPTY_SLOT);
                    }
                }
            }
        }
    }
    else if(unlikely(point_in_time_ut < handle->page_end_time_ut)) {
        handle->page_flags |= RRDENG_PAGE_PAST_COLLECTION;
        store_metric_next_error_log(handle, point_in_time_ut, "is older than the");
        return;
    }

    else /* if(unlikely(point_in_time_ut == handle->page_end_time_ut)) */ {
        handle->page_flags |= RRDENG_PAGE_REPEATED_COLLECTION;
        store_metric_next_error_log(handle, point_in_time_ut, "is at the same time as the");
        return;
    }

    timing_step(TIMING_STEP_DBENGINE_FIRST_CHECK);

    rrdeng_store_metric_append_point(collection_handle,
                                     point_in_time_ut,
                                     n, min_value, max_value,
                                     count, anomaly_count,
                                     flags);
}

/*
 * Releases the database reference from the handle for storing metrics.
 * Returns 1 if it's safe to delete the dimension.
 */
int rrdeng_store_metric_finalize(STORAGE_COLLECT_HANDLE *collection_handle) {
    struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;
    struct rrdengine_instance *ctx = mrg_metric_ctx(handle->metric);

    handle->page_flags |= RRDENG_PAGE_COLLECT_FINALIZE;
    rrdeng_store_metric_flush_current_page(collection_handle);
    rrdeng_page_alignment_release(handle->alignment);

    __atomic_sub_fetch(&ctx->atomic.collectors_running, 1, __ATOMIC_RELAXED);
    if(!(handle->options & RRDENG_1ST_METRIC_WRITER))
        __atomic_sub_fetch(&ctx->atomic.collectors_running_duplicate, 1, __ATOMIC_RELAXED);

    if((handle->options & RRDENG_1ST_METRIC_WRITER) && !mrg_metric_clear_writer(main_mrg, handle->metric))
        internal_fatal(true, "DBENGINE: metric is already released");

    time_t first_time_s, last_time_s, update_every_s;
    mrg_metric_get_retention(main_mrg, handle->metric, &first_time_s, &last_time_s, &update_every_s);

    mrg_metric_release(main_mrg, handle->metric);
    freez(handle);

    if(!first_time_s && !last_time_s)
        return 1;

    return 0;
}

void rrdeng_store_metric_change_collection_frequency(STORAGE_COLLECT_HANDLE *collection_handle, int update_every) {
    struct rrdeng_collect_handle *handle = (struct rrdeng_collect_handle *)collection_handle;
    check_and_fix_mrg_update_every(handle);

    METRIC *metric = handle->metric;
    usec_t update_every_ut = (usec_t)update_every * USEC_PER_SEC;

    if(update_every_ut == handle->update_every_ut)
        return;

    handle->page_flags |= RRDENG_PAGE_UPDATE_EVERY_CHANGE;
    rrdeng_store_metric_flush_current_page(collection_handle);
    mrg_metric_set_update_every(main_mrg, metric, update_every);
    handle->update_every_ut = update_every_ut;
}

// ----------------------------------------------------------------------------
// query ops

#ifdef NETDATA_INTERNAL_CHECKS
SPINLOCK global_query_handle_spinlock = NETDATA_SPINLOCK_INITIALIZER;
static struct rrdeng_query_handle *global_query_handle_ll = NULL;
static void register_query_handle(struct rrdeng_query_handle *handle) {
    handle->query_pid = gettid();
    handle->started_time_s = now_realtime_sec();

    spinlock_lock(&global_query_handle_spinlock);
    DOUBLE_LINKED_LIST_APPEND_ITEM_UNSAFE(global_query_handle_ll, handle, prev, next);
    spinlock_unlock(&global_query_handle_spinlock);
}
static void unregister_query_handle(struct rrdeng_query_handle *handle) {
    spinlock_lock(&global_query_handle_spinlock);
    DOUBLE_LINKED_LIST_REMOVE_ITEM_UNSAFE(global_query_handle_ll, handle, prev, next);
    spinlock_unlock(&global_query_handle_spinlock);
}
#else
static void register_query_handle(struct rrdeng_query_handle *handle __maybe_unused) {
    ;
}
static void unregister_query_handle(struct rrdeng_query_handle *handle __maybe_unused) {
    ;
}
#endif

/*
 * Gets a handle for loading metrics from the database.
 * The handle must be released with rrdeng_load_metric_final().
 */
void rrdeng_load_metric_init(STORAGE_METRIC_HANDLE *db_metric_handle,
                             struct storage_engine_query_handle *rrddim_handle,
                             time_t start_time_s,
                             time_t end_time_s,
                             STORAGE_PRIORITY priority)
{
    usec_t started_ut = now_monotonic_usec();

    netdata_thread_disable_cancelability();

    METRIC *metric = (METRIC *)db_metric_handle;
    struct rrdengine_instance *ctx = mrg_metric_ctx(metric);
    struct rrdeng_query_handle *handle;

    handle = rrdeng_query_handle_get();
    register_query_handle(handle);

    if (unlikely(priority < STORAGE_PRIORITY_HIGH))
        priority = STORAGE_PRIORITY_HIGH;
    else if (unlikely(priority >= STORAGE_PRIORITY_INTERNAL_MAX_DONT_USE))
        priority = STORAGE_PRIORITY_INTERNAL_MAX_DONT_USE - 1;

    handle->ctx = ctx;
    handle->metric = metric;
    handle->priority = priority;

    // IMPORTANT!
    // It is crucial not to exceed the db boundaries, because dbengine
    // now has gap caching, so when a gap is detected a negative page
    // is inserted into the main cache, to avoid scanning the journals
    // again for pages matching the gap.

    time_t db_first_time_s, db_last_time_s, db_update_every_s;
    mrg_metric_get_retention(main_mrg, metric, &db_first_time_s, &db_last_time_s, &db_update_every_s);

    if(is_page_in_time_range(start_time_s, end_time_s, db_first_time_s, db_last_time_s) == PAGE_IS_IN_RANGE) {
        handle->start_time_s = MAX(start_time_s, db_first_time_s);
        handle->end_time_s = MIN(end_time_s, db_last_time_s);
        handle->now_s = handle->start_time_s;

        handle->dt_s = db_update_every_s;
        if (!handle->dt_s) {
            handle->dt_s = default_rrd_update_every;
            mrg_metric_set_update_every_s_if_zero(main_mrg, metric, default_rrd_update_every);
        }

        rrddim_handle->handle = (STORAGE_QUERY_HANDLE *) handle;
        rrddim_handle->start_time_s = handle->start_time_s;
        rrddim_handle->end_time_s = handle->end_time_s;
        rrddim_handle->priority = priority;
        rrddim_handle->backend = STORAGE_ENGINE_BACKEND_DBENGINE;

        pg_cache_preload(handle);

        __atomic_add_fetch(&rrdeng_cache_efficiency_stats.query_time_init, now_monotonic_usec() - started_ut, __ATOMIC_RELAXED);
    }
    else {
        handle->start_time_s = start_time_s;
        handle->end_time_s = end_time_s;
        handle->now_s = start_time_s;
        handle->dt_s = db_update_every_s;

        rrddim_handle->handle = (STORAGE_QUERY_HANDLE *) handle;
        rrddim_handle->start_time_s = handle->start_time_s;
        rrddim_handle->end_time_s = 0;
        rrddim_handle->priority = priority;
        rrddim_handle->backend = STORAGE_ENGINE_BACKEND_DBENGINE;
    }
}

static bool rrdeng_load_page_next(struct storage_engine_query_handle *rrddim_handle, bool debug_this __maybe_unused) {
    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrddim_handle->handle;
    struct rrdengine_instance *ctx = handle->ctx;

    if (likely(handle->page)) {
        // we have a page to release
        pgc_page_release(main_cache, handle->page);
        handle->page = NULL;
    }

    if (unlikely(handle->now_s > rrddim_handle->end_time_s))
        return false;

    size_t entries;
    handle->page = pg_cache_lookup_next(ctx, handle->pdc, handle->now_s, handle->dt_s, &entries);
    if (unlikely(!handle->page))
        return false;

    internal_fatal(pgc_page_data(handle->page) == DBENGINE_EMPTY_PAGE, "Empty page returned");

    time_t page_start_time_s = pgc_page_start_time_s(handle->page);
    time_t page_end_time_s = pgc_page_end_time_s(handle->page);
    time_t page_update_every_s = pgc_page_update_every_s(handle->page);

    unsigned position;
    if(likely(handle->now_s >= page_start_time_s && handle->now_s <= page_end_time_s)) {

        if(unlikely(entries == 1 || page_start_time_s == page_end_time_s || !page_update_every_s)) {
            position = 0;
            handle->now_s = page_start_time_s;
        }
        else {
            position = (handle->now_s - page_start_time_s) * (entries - 1) / (page_end_time_s - page_start_time_s);
            time_t point_end_time_s = page_start_time_s + position * page_update_every_s;
            while(point_end_time_s < handle->now_s && position + 1 < entries) {
                // https://github.com/netdata/netdata/issues/14411
                // we really need a while() here, because the delta may be
                // 2 points at higher tiers
                position++;
                point_end_time_s = page_start_time_s + position * page_update_every_s;
            }
            handle->now_s = point_end_time_s;
        }

        internal_fatal(position >= entries, "DBENGINE: wrong page position calculation");
    }
    else if(handle->now_s < page_start_time_s) {
        handle->now_s = page_start_time_s;
        position = 0;
    }
    else {
        internal_fatal(true, "DBENGINE: this page is entirely in our past and should not be accepted for this query in the first place");
        handle->now_s = page_end_time_s;
        position = entries - 1;
    }

    handle->entries = entries;
    handle->position = position;
    handle->metric_data = pgc_page_data((PGC_PAGE *)handle->page);
    handle->dt_s = page_update_every_s;
    return true;
}

// Returns the metric and sets its timestamp into current_time
// IT IS REQUIRED TO **ALWAYS** SET ALL RETURN VALUES (current_time, end_time, flags)
// IT IS REQUIRED TO **ALWAYS** KEEP TRACK OF TIME, EVEN OUTSIDE THE DATABASE BOUNDARIES
STORAGE_POINT rrdeng_load_metric_next(struct storage_engine_query_handle *rrddim_handle) {
    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrddim_handle->handle;
    STORAGE_POINT sp;

    if (unlikely(handle->now_s > rrddim_handle->end_time_s)) {
        storage_point_empty(sp, handle->now_s - handle->dt_s, handle->now_s);
        goto prepare_for_next_iteration;
    }

    if (unlikely(!handle->page || handle->position >= handle->entries)) {
        // We need to get a new page

        if (!rrdeng_load_page_next(rrddim_handle, false)) {
            handle->now_s = rrddim_handle->end_time_s;
            storage_point_empty(sp, handle->now_s - handle->dt_s, handle->now_s);
            goto prepare_for_next_iteration;
        }
    }

    sp.start_time_s = handle->now_s - handle->dt_s;
    sp.end_time_s = handle->now_s;

    switch(handle->ctx->config.page_type) {
        case PAGE_METRICS: {
            storage_number n = handle->metric_data[handle->position];
            sp.min = sp.max = sp.sum = unpack_storage_number(n);
            sp.flags = n & SN_USER_FLAGS;
            sp.count = 1;
            sp.anomaly_count = is_storage_number_anomalous(n) ? 1 : 0;
        }
        break;

        case PAGE_TIER: {
            storage_number_tier1_t tier1_value = ((storage_number_tier1_t *)handle->metric_data)[handle->position];
            sp.flags = tier1_value.anomaly_count ? SN_FLAG_NONE : SN_FLAG_NOT_ANOMALOUS;
            sp.count = tier1_value.count;
            sp.anomaly_count = tier1_value.anomaly_count;
            sp.min = tier1_value.min_value;
            sp.max = tier1_value.max_value;
            sp.sum = tier1_value.sum_value;
        }
        break;

        // we don't know this page type
        default: {
            static bool logged = false;
            if(!logged) {
                netdata_log_error("DBENGINE: unknown page type %d found. Cannot decode it. Ignoring its metrics.", handle->ctx->config.page_type);
                logged = true;
            }
            storage_point_empty(sp, sp.start_time_s, sp.end_time_s);
        }
        break;
    }

prepare_for_next_iteration:
    internal_fatal(sp.end_time_s < rrddim_handle->start_time_s, "DBENGINE: this point is too old for this query");
    internal_fatal(sp.end_time_s < handle->now_s, "DBENGINE: this point is too old for this point in time");

    handle->now_s += handle->dt_s;
    handle->position++;

    return sp;
}

int rrdeng_load_metric_is_finished(struct storage_engine_query_handle *rrddim_handle) {
    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrddim_handle->handle;
    return (handle->now_s > rrddim_handle->end_time_s);
}

/*
 * Releases the database reference from the handle for loading metrics.
 */
void rrdeng_load_metric_finalize(struct storage_engine_query_handle *rrddim_handle)
{
    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrddim_handle->handle;

    if (handle->page)
        pgc_page_release(main_cache, handle->page);

    if(!pdc_release_and_destroy_if_unreferenced(handle->pdc, false, false))
        __atomic_store_n(&handle->pdc->workers_should_stop, true, __ATOMIC_RELAXED);

    unregister_query_handle(handle);
    rrdeng_query_handle_release(handle);
    rrddim_handle->handle = NULL;
    netdata_thread_enable_cancelability();
}

time_t rrdeng_load_align_to_optimal_before(struct storage_engine_query_handle *rrddim_handle) {
    struct rrdeng_query_handle *handle = (struct rrdeng_query_handle *)rrddim_handle->handle;

    if(handle->pdc) {
        rrdeng_prep_wait(handle->pdc);
        if (handle->pdc->optimal_end_time_s > rrddim_handle->end_time_s)
            rrddim_handle->end_time_s = handle->pdc->optimal_end_time_s;
    }

    return rrddim_handle->end_time_s;
}

time_t rrdeng_metric_latest_time(STORAGE_METRIC_HANDLE *db_metric_handle) {
    METRIC *metric = (METRIC *)db_metric_handle;
    time_t latest_time_s = 0;

    if (metric)
        latest_time_s = mrg_metric_get_latest_time_s(main_mrg, metric);

    return latest_time_s;
}

time_t rrdeng_metric_oldest_time(STORAGE_METRIC_HANDLE *db_metric_handle) {
    METRIC *metric = (METRIC *)db_metric_handle;

    time_t oldest_time_s = 0;
    if (metric)
        oldest_time_s = mrg_metric_get_first_time_s(main_mrg, metric);

    return oldest_time_s;
}

bool rrdeng_metric_retention_by_uuid(STORAGE_INSTANCE *db_instance, uuid_t *dim_uuid, time_t *first_entry_s, time_t *last_entry_s)
{
    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
    if (unlikely(!ctx)) {
        netdata_log_error("DBENGINE: invalid STORAGE INSTANCE to %s()", __FUNCTION__);
        return false;
    }

    METRIC *metric = mrg_metric_get_and_acquire(main_mrg, dim_uuid, (Word_t) ctx);
    if (unlikely(!metric))
        return false;

    time_t update_every_s;
    mrg_metric_get_retention(main_mrg, metric, first_entry_s, last_entry_s, &update_every_s);

    mrg_metric_release(main_mrg, metric);

    return true;
}

size_t rrdeng_disk_space_max(STORAGE_INSTANCE *db_instance) {
    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
    return ctx->config.max_disk_space;
}

size_t rrdeng_disk_space_used(STORAGE_INSTANCE *db_instance) {
    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
    return __atomic_load_n(&ctx->atomic.current_disk_space, __ATOMIC_RELAXED);
}

time_t rrdeng_global_first_time_s(STORAGE_INSTANCE *db_instance) {
    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;

    time_t t = __atomic_load_n(&ctx->atomic.first_time_s, __ATOMIC_RELAXED);
    if(t == LONG_MAX || t < 0)
        t = 0;

    return t;
}

size_t rrdeng_currently_collected_metrics(STORAGE_INSTANCE *db_instance) {
    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
    return __atomic_load_n(&ctx->atomic.collectors_running, __ATOMIC_RELAXED);
}

/*
 * Gathers Database Engine statistics.
 * Careful when modifying this function.
 * You must not change the indices of the statistics or user code will break.
 * You must not exceed RRDENG_NR_STATS or it will crash.
 */
void rrdeng_get_37_statistics(struct rrdengine_instance *ctx, unsigned long long *array)
{
    if (ctx == NULL)
        return;

    array[0] = (uint64_t)__atomic_load_n(&ctx->atomic.collectors_running, __ATOMIC_RELAXED); // API producers
    array[1] = (uint64_t)__atomic_load_n(&ctx->atomic.inflight_queries, __ATOMIC_RELAXED);   // API consumers
    array[2] = 0;
    array[3] = 0;
    array[4] = 0;
    array[5] = 0; // (uint64_t)ctx->stats.pg_cache_insertions;
    array[6] = 0; // (uint64_t)ctx->stats.pg_cache_deletions;
    array[7] = 0; // (uint64_t)ctx->stats.pg_cache_hits;
    array[8] = 0; // (uint64_t)ctx->stats.pg_cache_misses;
    array[9] = 0; // (uint64_t)ctx->stats.pg_cache_backfills;
    array[10] = 0; // (uint64_t)ctx->stats.pg_cache_evictions;
    array[11] = (uint64_t)__atomic_load_n(&ctx->stats.before_compress_bytes, __ATOMIC_RELAXED); // used
    array[12] = (uint64_t)__atomic_load_n(&ctx->stats.after_compress_bytes, __ATOMIC_RELAXED); // used
    array[13] = (uint64_t)__atomic_load_n(&ctx->stats.before_decompress_bytes, __ATOMIC_RELAXED);
    array[14] = (uint64_t)__atomic_load_n(&ctx->stats.after_decompress_bytes, __ATOMIC_RELAXED);
    array[15] = (uint64_t)__atomic_load_n(&ctx->stats.io_write_bytes, __ATOMIC_RELAXED); // used
    array[16] = (uint64_t)__atomic_load_n(&ctx->stats.io_write_requests, __ATOMIC_RELAXED); // used
    array[17] = (uint64_t)__atomic_load_n(&ctx->stats.io_read_bytes, __ATOMIC_RELAXED);
    array[18] = (uint64_t)__atomic_load_n(&ctx->stats.io_read_requests, __ATOMIC_RELAXED); // used
    array[19] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.io_write_extent_bytes, __ATOMIC_RELAXED);
    array[20] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.io_write_extents, __ATOMIC_RELAXED);
    array[21] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.io_read_extent_bytes, __ATOMIC_RELAXED);
    array[22] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.io_read_extents, __ATOMIC_RELAXED);
    array[23] = (uint64_t)__atomic_load_n(&ctx->stats.datafile_creations, __ATOMIC_RELAXED);
    array[24] = (uint64_t)__atomic_load_n(&ctx->stats.datafile_deletions, __ATOMIC_RELAXED);
    array[25] = (uint64_t)__atomic_load_n(&ctx->stats.journalfile_creations, __ATOMIC_RELAXED);
    array[26] = (uint64_t)__atomic_load_n(&ctx->stats.journalfile_deletions, __ATOMIC_RELAXED);
    array[27] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.page_cache_descriptors, __ATOMIC_RELAXED);
    array[28] = (uint64_t)__atomic_load_n(&ctx->stats.io_errors, __ATOMIC_RELAXED);
    array[29] = (uint64_t)__atomic_load_n(&ctx->stats.fs_errors, __ATOMIC_RELAXED);
    array[30] = (uint64_t)__atomic_load_n(&global_io_errors, __ATOMIC_RELAXED); // used
    array[31] = (uint64_t)__atomic_load_n(&global_fs_errors, __ATOMIC_RELAXED); // used
    array[32] = (uint64_t)__atomic_load_n(&rrdeng_reserved_file_descriptors, __ATOMIC_RELAXED); // used
    array[33] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.pg_cache_over_half_dirty_events, __ATOMIC_RELAXED);
    array[34] = (uint64_t)__atomic_load_n(&global_pg_cache_over_half_dirty_events, __ATOMIC_RELAXED); // used
    array[35] = 0; // (uint64_t)__atomic_load_n(&ctx->stats.flushing_pressure_page_deletions, __ATOMIC_RELAXED);
    array[36] = (uint64_t)__atomic_load_n(&global_flushing_pressure_page_deletions, __ATOMIC_RELAXED); // used
    array[37] = 0; //(uint64_t)pg_cache->active_descriptors;

    fatal_assert(RRDENG_NR_STATS == 38);
}

static void rrdeng_populate_mrg(struct rrdengine_instance *ctx) {
    uv_rwlock_rdlock(&ctx->datafiles.rwlock);
    size_t datafiles = 0;
    for(struct rrdengine_datafile *df = ctx->datafiles.first; df ;df = df->next)
        datafiles++;
    uv_rwlock_rdunlock(&ctx->datafiles.rwlock);

    ssize_t cpus = (ssize_t)get_netdata_cpus() / (ssize_t)storage_tiers;
    if(cpus > (ssize_t)datafiles)
        cpus = (ssize_t)datafiles;

    if(cpus > (ssize_t)libuv_worker_threads)
        cpus = (ssize_t)libuv_worker_threads;

    if(cpus >= (ssize_t)get_netdata_cpus() / 2)
        cpus = (ssize_t)(get_netdata_cpus() / 2 - 1);

    if(cpus < 1)
        cpus = 1;

    netdata_log_info("DBENGINE: populating retention to MRG from %zu journal files of tier %d, using %zd threads...", datafiles, ctx->config.tier, cpus);

    if(datafiles > 2) {
        struct rrdengine_datafile *datafile;

        datafile = ctx->datafiles.first->prev;
        if(!(datafile->journalfile->v2.flags & JOURNALFILE_FLAG_IS_AVAILABLE))
            datafile = datafile->prev;

        if(datafile->journalfile->v2.flags & JOURNALFILE_FLAG_IS_AVAILABLE) {
            journalfile_v2_populate_retention_to_mrg(ctx, datafile->journalfile);
            datafile->populate_mrg.populated = true;
        }

        datafile = ctx->datafiles.first;
        if(datafile->journalfile->v2.flags & JOURNALFILE_FLAG_IS_AVAILABLE) {
            journalfile_v2_populate_retention_to_mrg(ctx, datafile->journalfile);
            datafile->populate_mrg.populated = true;
        }
    }

    ctx->loading.populate_mrg.size = cpus;
    ctx->loading.populate_mrg.array = callocz(ctx->loading.populate_mrg.size, sizeof(struct completion));

    for (size_t i = 0; i < ctx->loading.populate_mrg.size; i++) {
        completion_init(&ctx->loading.populate_mrg.array[i]);
        rrdeng_enq_cmd(ctx, RRDENG_OPCODE_CTX_POPULATE_MRG, NULL, &ctx->loading.populate_mrg.array[i],
                       STORAGE_PRIORITY_INTERNAL_DBENGINE, NULL, NULL);
    }
}

void rrdeng_readiness_wait(struct rrdengine_instance *ctx) {
    for (size_t i = 0; i < ctx->loading.populate_mrg.size; i++) {
        completion_wait_for(&ctx->loading.populate_mrg.array[i]);
        completion_destroy(&ctx->loading.populate_mrg.array[i]);
    }

    freez(ctx->loading.populate_mrg.array);
    ctx->loading.populate_mrg.array = NULL;
    ctx->loading.populate_mrg.size = 0;

    netdata_log_info("DBENGINE: tier %d is ready for data collection and queries", ctx->config.tier);
}

bool rrdeng_is_legacy(STORAGE_INSTANCE *db_instance) {
    struct rrdengine_instance *ctx = (struct rrdengine_instance *)db_instance;
    return ctx->config.legacy;
}

void rrdeng_exit_mode(struct rrdengine_instance *ctx) {
    __atomic_store_n(&ctx->quiesce.exit_mode, true, __ATOMIC_RELAXED);
}
/*
 * Returns 0 on success, negative on error
 */
int rrdeng_init(struct rrdengine_instance **ctxp, const char *dbfiles_path,
                unsigned disk_space_mb, size_t tier) {
    struct rrdengine_instance *ctx;
    uint32_t max_open_files;

    max_open_files = rlimit_nofile.rlim_cur / 4;

    /* reserve RRDENG_FD_BUDGET_PER_INSTANCE file descriptors for this instance */
    rrd_stat_atomic_add(&rrdeng_reserved_file_descriptors, RRDENG_FD_BUDGET_PER_INSTANCE);
    if (rrdeng_reserved_file_descriptors > max_open_files) {
        netdata_log_error(
            "Exceeded the budget of available file descriptors (%u/%u), cannot create new dbengine instance.",
            (unsigned)rrdeng_reserved_file_descriptors,
            (unsigned)max_open_files);

        rrd_stat_atomic_add(&global_fs_errors, 1);
        rrd_stat_atomic_add(&rrdeng_reserved_file_descriptors, -RRDENG_FD_BUDGET_PER_INSTANCE);
        return UV_EMFILE;
    }

    if(NULL == ctxp) {
        ctx = multidb_ctx[tier];
        memset(ctx, 0, sizeof(*ctx));
        ctx->config.legacy = false;
    }
    else {
        *ctxp = ctx = callocz(1, sizeof(*ctx));
        ctx->config.legacy = true;
    }

    ctx->config.tier = (int)tier;
    ctx->config.page_type = tier_page_type[tier];
    ctx->config.global_compress_alg = RRD_LZ4;
    if (disk_space_mb < RRDENG_MIN_DISK_SPACE_MB)
        disk_space_mb = RRDENG_MIN_DISK_SPACE_MB;
    ctx->config.max_disk_space = disk_space_mb * 1048576LLU;
    strncpyz(ctx->config.dbfiles_path, dbfiles_path, sizeof(ctx->config.dbfiles_path) - 1);
    ctx->config.dbfiles_path[sizeof(ctx->config.dbfiles_path) - 1] = '\0';

    ctx->atomic.transaction_id = 1;
    ctx->quiesce.enabled = false;

    rw_spinlock_init(&ctx->njfv2idx.spinlock);
    ctx->atomic.first_time_s = LONG_MAX;

    if (rrdeng_dbengine_spawn(ctx) && !init_rrd_files(ctx)) {
        // success - we run this ctx too
        rrdeng_populate_mrg(ctx);
        return 0;
    }

    if (ctx->config.legacy) {
        freez(ctx);
        if (ctxp)
            *ctxp = NULL;
    }

    rrd_stat_atomic_add(&rrdeng_reserved_file_descriptors, -RRDENG_FD_BUDGET_PER_INSTANCE);
    return UV_EIO;
}

size_t rrdeng_collectors_running(struct rrdengine_instance *ctx) {
    return __atomic_load_n(&ctx->atomic.collectors_running, __ATOMIC_RELAXED);
}

/*
 * Returns 0 on success, 1 on error
 */
int rrdeng_exit(struct rrdengine_instance *ctx) {
    if (NULL == ctx)
        return 1;

    // FIXME - ktsaou - properly cleanup ctx
    // 1. make sure all collectors are stopped
    // 2. make new queries will not be accepted (this is quiesce that has already run)
    // 3. flush this section of the main cache
    // 4. then wait for completion

    bool logged = false;
    while(__atomic_load_n(&ctx->atomic.collectors_running, __ATOMIC_RELAXED) && !unittest_running) {
        if(!logged) {
            netdata_log_info("DBENGINE: waiting for collectors to finish on tier %d...", (ctx->config.legacy) ? -1 : ctx->config.tier);
            logged = true;
        }
        sleep_usec(100 * USEC_PER_MS);
    }

    netdata_log_info("DBENGINE: flushing main cache for tier %d", (ctx->config.legacy) ? -1 : ctx->config.tier);
    pgc_flush_all_hot_and_dirty_pages(main_cache, (Word_t)ctx);

    netdata_log_info("DBENGINE: shutting down tier %d", (ctx->config.legacy) ? -1 : ctx->config.tier);
    struct completion completion = {};
    completion_init(&completion);
    rrdeng_enq_cmd(ctx, RRDENG_OPCODE_CTX_SHUTDOWN, NULL, &completion, STORAGE_PRIORITY_BEST_EFFORT, NULL, NULL);
    completion_wait_for(&completion);
    completion_destroy(&completion);

    finalize_rrd_files(ctx);

    if(ctx->config.legacy)
        freez(ctx);

    rrd_stat_atomic_add(&rrdeng_reserved_file_descriptors, -RRDENG_FD_BUDGET_PER_INSTANCE);
    return 0;
}

void rrdeng_prepare_exit(struct rrdengine_instance *ctx) {
    if (NULL == ctx)
        return;

    // FIXME - ktsaou - properly cleanup ctx
    // 1. make sure all collectors are stopped

    completion_init(&ctx->quiesce.completion);
    rrdeng_enq_cmd(ctx, RRDENG_OPCODE_CTX_QUIESCE, NULL, NULL, STORAGE_PRIORITY_INTERNAL_DBENGINE, NULL, NULL);
}

static void populate_v2_statistics(struct rrdengine_datafile *datafile, RRDENG_SIZE_STATS *stats)
{
    struct journal_v2_header *j2_header = journalfile_v2_data_acquire(datafile->journalfile, NULL, 0, 0);
    void *data_start = (void *)j2_header;

    if(unlikely(!j2_header))
        return;

    stats->extents += j2_header->extent_count;

    unsigned entries;
    struct journal_extent_list *extent_list = (void *) (data_start + j2_header->extent_offset);
    for (entries = 0; entries < j2_header->extent_count; entries++) {
        stats->extents_compressed_bytes += extent_list->datafile_size;
        stats->extents_pages += extent_list->pages;
        extent_list++;
    }

    struct journal_metric_list *metric = (void *) (data_start + j2_header->metric_offset);
    time_t journal_start_time_s = (time_t) (j2_header->start_time_ut / USEC_PER_SEC);

    stats->metrics += j2_header->metric_count;
    for (entries = 0; entries < j2_header->metric_count; entries++) {

        struct journal_page_header *metric_list_header = (void *) (data_start + metric->page_offset);
        stats->metrics_pages += metric_list_header->entries;
        struct journal_page_list *descr =  (void *) (data_start + metric->page_offset + sizeof(struct journal_page_header));
        for (uint32_t idx=0; idx < metric_list_header->entries; idx++) {

            time_t update_every_s;

            size_t points = descr->page_length / CTX_POINT_SIZE_BYTES(datafile->ctx);

            time_t start_time_s = journal_start_time_s + descr->delta_start_s;
            time_t end_time_s = journal_start_time_s + descr->delta_end_s;

            if(likely(points > 1))
                update_every_s = (time_t) ((end_time_s - start_time_s) / (points - 1));
            else {
                update_every_s = (time_t) (default_rrd_update_every * get_tier_grouping(datafile->ctx->config.tier));
                stats->single_point_pages++;
            }

            time_t duration_s = (time_t)((end_time_s - start_time_s + update_every_s));

            stats->pages_uncompressed_bytes += descr->page_length;
            stats->pages_duration_secs += duration_s;
            stats->points += points;

            stats->page_types[descr->type].pages++;
            stats->page_types[descr->type].pages_uncompressed_bytes += descr->page_length;
            stats->page_types[descr->type].pages_duration_secs += duration_s;
            stats->page_types[descr->type].points += points;

            if(!stats->first_time_s || (start_time_s - update_every_s) < stats->first_time_s)
                stats->first_time_s = (start_time_s - update_every_s);

            if(!stats->last_time_s || end_time_s > stats->last_time_s)
                stats->last_time_s = end_time_s;

            descr++;
        }
        metric++;
    }

    journalfile_v2_data_release(datafile->journalfile);
}

RRDENG_SIZE_STATS rrdeng_size_statistics(struct rrdengine_instance *ctx) {
    RRDENG_SIZE_STATS stats = { 0 };

    uv_rwlock_rdlock(&ctx->datafiles.rwlock);
    for(struct rrdengine_datafile *df = ctx->datafiles.first; df ;df = df->next) {
        stats.datafiles++;
        populate_v2_statistics(df, &stats);
    }
    uv_rwlock_rdunlock(&ctx->datafiles.rwlock);

    stats.currently_collected_metrics = __atomic_load_n(&ctx->atomic.collectors_running, __ATOMIC_RELAXED);

    internal_error(stats.metrics_pages != stats.extents_pages + stats.currently_collected_metrics,
                   "DBENGINE: metrics pages is %zu, but extents pages is %zu and API consumers is %zu",
                   stats.metrics_pages, stats.extents_pages, stats.currently_collected_metrics);

    stats.disk_space = ctx_current_disk_space_get(ctx);
    stats.max_disk_space = ctx->config.max_disk_space;

    stats.database_retention_secs = (time_t)(stats.last_time_s - stats.first_time_s);

    if(stats.extents_pages)
        stats.average_page_size_bytes = (double)stats.pages_uncompressed_bytes / (double)stats.extents_pages;

    if(stats.pages_uncompressed_bytes > 0)
        stats.average_compression_savings = 100.0 - ((double)stats.extents_compressed_bytes * 100.0 / (double)stats.pages_uncompressed_bytes);

    if(stats.points)
        stats.average_point_duration_secs = (double)stats.pages_duration_secs / (double)stats.points;

    if(stats.metrics) {
        stats.average_metric_retention_secs = (double)stats.pages_duration_secs / (double)stats.metrics;

        if(stats.database_retention_secs) {
            double metric_coverage = stats.average_metric_retention_secs / (double)stats.database_retention_secs;
            double db_retention_days = (double)stats.database_retention_secs / 86400.0;

            stats.estimated_concurrently_collected_metrics = stats.metrics * metric_coverage;

            stats.ephemeral_metrics_per_day_percent = ((double)stats.metrics * 100.0 / (double)stats.estimated_concurrently_collected_metrics - 100.0) / (double)db_retention_days;
        }
    }

//    stats.sizeof_metric = 0;
    stats.sizeof_datafile = struct_natural_alignment(sizeof(struct rrdengine_datafile)) + struct_natural_alignment(sizeof(struct rrdengine_journalfile));
    stats.sizeof_page_in_cache = 0; // struct_natural_alignment(sizeof(struct page_cache_descr));
    stats.sizeof_point_data = page_type_size[ctx->config.page_type];
    stats.sizeof_page_data = tier_page_size[ctx->config.tier];
    stats.pages_per_extent = rrdeng_pages_per_extent;

//    stats.sizeof_metric_in_index = 40;
//    stats.sizeof_page_in_index = 24;

    stats.default_granularity_secs = (size_t)default_rrd_update_every * get_tier_grouping(ctx->config.tier);

    return stats;
}

struct rrdeng_cache_efficiency_stats rrdeng_get_cache_efficiency_stats(void) {
    // FIXME - make cache efficiency stats atomic
    return rrdeng_cache_efficiency_stats;
}