summary refs log tree commit diff
path: root/synapse/storage/events.py
blob: c6ed54721ce75a684e1bd0a7f1bdfb0b9e9fbd0e (plain) (blame)
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
# -*- coding: utf-8 -*-
# Copyright 2014-2016 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from _base import SQLBaseStore, _RollbackButIsFineException

from twisted.internet import defer, reactor

from synapse.events import FrozenEvent, USE_FROZEN_DICTS
from synapse.events.utils import prune_event

from synapse.util.logcontext import preserve_fn, PreserveLoggingContext
from synapse.util.logutils import log_function
from synapse.api.constants import EventTypes

from canonicaljson import encode_canonical_json
from contextlib import contextmanager

import logging
import math
import ujson as json

logger = logging.getLogger(__name__)


def encode_json(json_object):
    if USE_FROZEN_DICTS:
        # ujson doesn't like frozen_dicts
        return encode_canonical_json(json_object)
    else:
        return json.dumps(json_object, ensure_ascii=False)

# These values are used in the `enqueus_event` and `_do_fetch` methods to
# control how we batch/bulk fetch events from the database.
# The values are plucked out of thing air to make initial sync run faster
# on jki.re
# TODO: Make these configurable.
EVENT_QUEUE_THREADS = 3  # Max number of threads that will fetch events
EVENT_QUEUE_ITERATIONS = 3  # No. times we block waiting for requests for events
EVENT_QUEUE_TIMEOUT_S = 0.1  # Timeout when waiting for requests for events


class EventsStore(SQLBaseStore):
    EVENT_ORIGIN_SERVER_TS_NAME = "event_origin_server_ts"

    def __init__(self, hs):
        super(EventsStore, self).__init__(hs)
        self.register_background_update_handler(
            self.EVENT_ORIGIN_SERVER_TS_NAME, self._background_reindex_origin_server_ts
        )

    @defer.inlineCallbacks
    def persist_events(self, events_and_contexts, backfilled=False,
                       is_new_state=True):
        if not events_and_contexts:
            return

        if backfilled:
            start = self.min_stream_token - 1
            self.min_stream_token -= len(events_and_contexts) + 1
            stream_orderings = range(start, self.min_stream_token, -1)

            @contextmanager
            def stream_ordering_manager():
                yield stream_orderings
            stream_ordering_manager = stream_ordering_manager()
        else:
            stream_ordering_manager = yield self._stream_id_gen.get_next_mult(
                self, len(events_and_contexts)
            )

        with stream_ordering_manager as stream_orderings:
            for (event, _), stream in zip(events_and_contexts, stream_orderings):
                event.internal_metadata.stream_ordering = stream

            chunks = [
                events_and_contexts[x:x + 100]
                for x in xrange(0, len(events_and_contexts), 100)
            ]

            for chunk in chunks:
                # We can't easily parallelize these since different chunks
                # might contain the same event. :(
                yield self.runInteraction(
                    "persist_events",
                    self._persist_events_txn,
                    events_and_contexts=chunk,
                    backfilled=backfilled,
                    is_new_state=is_new_state,
                )

    @defer.inlineCallbacks
    @log_function
    def persist_event(self, event, context, backfilled=False,
                      is_new_state=True, current_state=None):
        stream_ordering = None
        if backfilled:
            self.min_stream_token -= 1
            stream_ordering = self.min_stream_token

        if stream_ordering is None:
            stream_ordering_manager = yield self._stream_id_gen.get_next(self)
        else:
            @contextmanager
            def stream_ordering_manager():
                yield stream_ordering
            stream_ordering_manager = stream_ordering_manager()

        try:
            with stream_ordering_manager as stream_ordering:
                event.internal_metadata.stream_ordering = stream_ordering
                yield self.runInteraction(
                    "persist_event",
                    self._persist_event_txn,
                    event=event,
                    context=context,
                    backfilled=backfilled,
                    is_new_state=is_new_state,
                    current_state=current_state,
                )
        except _RollbackButIsFineException:
            pass

        max_persisted_id = yield self._stream_id_gen.get_max_token(self)
        defer.returnValue((stream_ordering, max_persisted_id))

    @defer.inlineCallbacks
    def get_event(self, event_id, check_redacted=True,
                  get_prev_content=False, allow_rejected=False,
                  allow_none=False):
        """Get an event from the database by event_id.

        Args:
            event_id (str): The event_id of the event to fetch
            check_redacted (bool): If True, check if event has been redacted
                and redact it.
            get_prev_content (bool): If True and event is a state event,
                include the previous states content in the unsigned field.
            allow_rejected (bool): If True return rejected events.
            allow_none (bool): If True, return None if no event found, if
                False throw an exception.

        Returns:
            Deferred : A FrozenEvent.
        """
        events = yield self._get_events(
            [event_id],
            check_redacted=check_redacted,
            get_prev_content=get_prev_content,
            allow_rejected=allow_rejected,
        )

        if not events and not allow_none:
            raise RuntimeError("Could not find event %s" % (event_id,))

        defer.returnValue(events[0] if events else None)

    @log_function
    def _persist_event_txn(self, txn, event, context, backfilled,
                           is_new_state=True, current_state=None):
        # We purposefully do this first since if we include a `current_state`
        # key, we *want* to update the `current_state_events` table
        if current_state:
            txn.call_after(self.get_current_state_for_key.invalidate_all)
            txn.call_after(self.get_rooms_for_user.invalidate_all)
            txn.call_after(self.get_users_in_room.invalidate, (event.room_id,))
            txn.call_after(self.get_joined_hosts_for_room.invalidate, (event.room_id,))
            txn.call_after(self.get_room_name_and_aliases, event.room_id)

            self._simple_delete_txn(
                txn,
                table="current_state_events",
                keyvalues={"room_id": event.room_id},
            )

            for s in current_state:
                self._simple_insert_txn(
                    txn,
                    "current_state_events",
                    {
                        "event_id": s.event_id,
                        "room_id": s.room_id,
                        "type": s.type,
                        "state_key": s.state_key,
                    }
                )

        return self._persist_events_txn(
            txn,
            [(event, context)],
            backfilled=backfilled,
            is_new_state=is_new_state,
        )

    @log_function
    def _persist_events_txn(self, txn, events_and_contexts, backfilled,
                            is_new_state=True):

        # Remove the any existing cache entries for the event_ids
        for event, _ in events_and_contexts:
            txn.call_after(self._invalidate_get_event_cache, event.event_id)

            if not backfilled:
                txn.call_after(
                    self._events_stream_cache.entity_has_changed,
                    event.room_id, event.internal_metadata.stream_ordering,
                )

        depth_updates = {}
        for event, _ in events_and_contexts:
            if event.internal_metadata.is_outlier():
                continue
            depth_updates[event.room_id] = max(
                event.depth, depth_updates.get(event.room_id, event.depth)
            )

        for room_id, depth in depth_updates.items():
            self._update_min_depth_for_room_txn(txn, room_id, depth)

        txn.execute(
            "SELECT event_id, outlier FROM events WHERE event_id in (%s)" % (
                ",".join(["?"] * len(events_and_contexts)),
            ),
            [event.event_id for event, _ in events_and_contexts]
        )
        have_persisted = {
            event_id: outlier
            for event_id, outlier in txn.fetchall()
        }

        event_map = {}
        to_remove = set()
        for event, context in events_and_contexts:
            # Handle the case of the list including the same event multiple
            # times. The tricky thing here is when they differ by whether
            # they are an outlier.
            if event.event_id in event_map:
                other = event_map[event.event_id]

                if not other.internal_metadata.is_outlier():
                    to_remove.add(event)
                    continue
                elif not event.internal_metadata.is_outlier():
                    to_remove.add(event)
                    continue
                else:
                    to_remove.add(other)

            event_map[event.event_id] = event

            if event.event_id not in have_persisted:
                continue

            to_remove.add(event)

            outlier_persisted = have_persisted[event.event_id]
            if not event.internal_metadata.is_outlier() and outlier_persisted:
                self._store_state_groups_txn(
                    txn, event, context,
                )

                metadata_json = encode_json(
                    event.internal_metadata.get_dict()
                ).decode("UTF-8")

                sql = (
                    "UPDATE event_json SET internal_metadata = ?"
                    " WHERE event_id = ?"
                )
                txn.execute(
                    sql,
                    (metadata_json, event.event_id,)
                )

                sql = (
                    "UPDATE events SET outlier = ?"
                    " WHERE event_id = ?"
                )
                txn.execute(
                    sql,
                    (False, event.event_id,)
                )

                self._update_extremeties(txn, [event])

        events_and_contexts = filter(
            lambda ec: ec[0] not in to_remove,
            events_and_contexts
        )

        if not events_and_contexts:
            return

        self._store_mult_state_groups_txn(txn, [
            (event, context)
            for event, context in events_and_contexts
            if not event.internal_metadata.is_outlier()
        ])

        self._handle_mult_prev_events(
            txn,
            events=[event for event, _ in events_and_contexts],
        )

        for event, _ in events_and_contexts:
            if event.type == EventTypes.Name:
                self._store_room_name_txn(txn, event)
            elif event.type == EventTypes.Topic:
                self._store_room_topic_txn(txn, event)
            elif event.type == EventTypes.Message:
                self._store_room_message_txn(txn, event)
            elif event.type == EventTypes.Redaction:
                self._store_redaction(txn, event)
            elif event.type == EventTypes.RoomHistoryVisibility:
                self._store_history_visibility_txn(txn, event)
            elif event.type == EventTypes.GuestAccess:
                self._store_guest_access_txn(txn, event)

        self._store_room_members_txn(
            txn,
            [
                event
                for event, _ in events_and_contexts
                if event.type == EventTypes.Member
            ]
        )

        def event_dict(event):
            return {
                k: v
                for k, v in event.get_dict().items()
                if k not in [
                    "redacted",
                    "redacted_because",
                ]
            }

        self._simple_insert_many_txn(
            txn,
            table="event_json",
            values=[
                {
                    "event_id": event.event_id,
                    "room_id": event.room_id,
                    "internal_metadata": encode_json(
                        event.internal_metadata.get_dict()
                    ).decode("UTF-8"),
                    "json": encode_json(event_dict(event)).decode("UTF-8"),
                }
                for event, _ in events_and_contexts
            ],
        )

        self._simple_insert_many_txn(
            txn,
            table="events",
            values=[
                {
                    "stream_ordering": event.internal_metadata.stream_ordering,
                    "topological_ordering": event.depth,
                    "depth": event.depth,
                    "event_id": event.event_id,
                    "room_id": event.room_id,
                    "type": event.type,
                    "processed": True,
                    "outlier": event.internal_metadata.is_outlier(),
                    "content": encode_json(event.content).decode("UTF-8"),
                    "origin_server_ts": int(event.origin_server_ts),
                }
                for event, _ in events_and_contexts
            ],
        )

        if context.rejected:
            self._store_rejections_txn(
                txn, event.event_id, context.rejected
            )

        self._simple_insert_many_txn(
            txn,
            table="event_auth",
            values=[
                {
                    "event_id": event.event_id,
                    "room_id": event.room_id,
                    "auth_id": auth_id,
                }
                for event, _ in events_and_contexts
                for auth_id, _ in event.auth_events
            ],
        )

        self._store_event_reference_hashes_txn(
            txn, [event for event, _ in events_and_contexts]
        )

        state_events_and_contexts = filter(
            lambda i: i[0].is_state(),
            events_and_contexts,
        )

        state_values = []
        for event, context in state_events_and_contexts:
            vals = {
                "event_id": event.event_id,
                "room_id": event.room_id,
                "type": event.type,
                "state_key": event.state_key,
            }

            # TODO: How does this work with backfilling?
            if hasattr(event, "replaces_state"):
                vals["prev_state"] = event.replaces_state

            state_values.append(vals)

        self._simple_insert_many_txn(
            txn,
            table="state_events",
            values=state_values,
        )

        self._simple_insert_many_txn(
            txn,
            table="event_edges",
            values=[
                {
                    "event_id": event.event_id,
                    "prev_event_id": prev_id,
                    "room_id": event.room_id,
                    "is_state": True,
                }
                for event, _ in state_events_and_contexts
                for prev_id, _ in event.prev_state
            ],
        )

        if is_new_state:
            for event, _ in state_events_and_contexts:
                if not context.rejected:
                    txn.call_after(
                        self.get_current_state_for_key.invalidate,
                        (event.room_id, event.type, event.state_key,)
                    )

                    if event.type in [EventTypes.Name, EventTypes.Aliases]:
                        txn.call_after(
                            self.get_room_name_and_aliases.invalidate,
                            (event.room_id,)
                        )

                    self._simple_upsert_txn(
                        txn,
                        "current_state_events",
                        keyvalues={
                            "room_id": event.room_id,
                            "type": event.type,
                            "state_key": event.state_key,
                        },
                        values={
                            "event_id": event.event_id,
                        }
                    )

        return

    def _store_redaction(self, txn, event):
        # invalidate the cache for the redacted event
        txn.call_after(self._invalidate_get_event_cache, event.redacts)
        txn.execute(
            "INSERT INTO redactions (event_id, redacts) VALUES (?,?)",
            (event.event_id, event.redacts)
        )

    def have_events(self, event_ids):
        """Given a list of event ids, check if we have already processed them.

        Returns:
            dict: Has an entry for each event id we already have seen. Maps to
            the rejected reason string if we rejected the event, else maps to
            None.
        """
        if not event_ids:
            return defer.succeed({})

        def f(txn):
            sql = (
                "SELECT e.event_id, reason FROM events as e "
                "LEFT JOIN rejections as r ON e.event_id = r.event_id "
                "WHERE e.event_id = ?"
            )

            res = {}
            for event_id in event_ids:
                txn.execute(sql, (event_id,))
                row = txn.fetchone()
                if row:
                    _, rejected = row
                    res[event_id] = rejected

            return res

        return self.runInteraction(
            "have_events", f,
        )

    @defer.inlineCallbacks
    def _get_events(self, event_ids, check_redacted=True,
                    get_prev_content=False, allow_rejected=False):
        if not event_ids:
            defer.returnValue([])

        event_map = self._get_events_from_cache(
            event_ids,
            check_redacted=check_redacted,
            get_prev_content=get_prev_content,
            allow_rejected=allow_rejected,
        )

        missing_events_ids = [e for e in event_ids if e not in event_map]

        if not missing_events_ids:
            defer.returnValue([
                event_map[e_id] for e_id in event_ids
                if e_id in event_map and event_map[e_id]
            ])

        missing_events = yield self._enqueue_events(
            missing_events_ids,
            check_redacted=check_redacted,
            get_prev_content=get_prev_content,
            allow_rejected=allow_rejected,
        )

        event_map.update(missing_events)

        defer.returnValue([
            event_map[e_id] for e_id in event_ids
            if e_id in event_map and event_map[e_id]
        ])

    def _get_events_txn(self, txn, event_ids, check_redacted=True,
                        get_prev_content=False, allow_rejected=False):
        if not event_ids:
            return []

        event_map = self._get_events_from_cache(
            event_ids,
            check_redacted=check_redacted,
            get_prev_content=get_prev_content,
            allow_rejected=allow_rejected,
        )

        missing_events_ids = [e for e in event_ids if e not in event_map]

        if not missing_events_ids:
            return [
                event_map[e_id] for e_id in event_ids
                if e_id in event_map and event_map[e_id]
            ]

        missing_events = self._fetch_events_txn(
            txn,
            missing_events_ids,
            check_redacted=check_redacted,
            get_prev_content=get_prev_content,
            allow_rejected=allow_rejected,
        )

        event_map.update(missing_events)

        return [
            event_map[e_id] for e_id in event_ids
            if e_id in event_map and event_map[e_id]
        ]

    def _invalidate_get_event_cache(self, event_id):
        for check_redacted in (False, True):
            for get_prev_content in (False, True):
                self._get_event_cache.invalidate(
                    (event_id, check_redacted, get_prev_content)
                )

    def _get_event_txn(self, txn, event_id, check_redacted=True,
                       get_prev_content=False, allow_rejected=False):

        events = self._get_events_txn(
            txn, [event_id],
            check_redacted=check_redacted,
            get_prev_content=get_prev_content,
            allow_rejected=allow_rejected,
        )

        return events[0] if events else None

    def _get_events_from_cache(self, events, check_redacted, get_prev_content,
                               allow_rejected):
        event_map = {}

        for event_id in events:
            try:
                ret = self._get_event_cache.get(
                    (event_id, check_redacted, get_prev_content,)
                )

                if allow_rejected or not ret.rejected_reason:
                    event_map[event_id] = ret
                else:
                    event_map[event_id] = None
            except KeyError:
                pass

        return event_map

    def _do_fetch(self, conn):
        """Takes a database connection and waits for requests for events from
        the _event_fetch_list queue.
        """
        event_list = []
        i = 0
        while True:
            try:
                with self._event_fetch_lock:
                    event_list = self._event_fetch_list
                    self._event_fetch_list = []

                    if not event_list:
                        single_threaded = self.database_engine.single_threaded
                        if single_threaded or i > EVENT_QUEUE_ITERATIONS:
                            self._event_fetch_ongoing -= 1
                            return
                        else:
                            self._event_fetch_lock.wait(EVENT_QUEUE_TIMEOUT_S)
                            i += 1
                            continue
                    i = 0

                event_id_lists = zip(*event_list)[0]
                event_ids = [
                    item for sublist in event_id_lists for item in sublist
                ]

                rows = self._new_transaction(
                    conn, "do_fetch", [], None, self._fetch_event_rows, event_ids
                )

                row_dict = {
                    r["event_id"]: r
                    for r in rows
                }

                # We only want to resolve deferreds from the main thread
                def fire(lst, res):
                    for ids, d in lst:
                        if not d.called:
                            try:
                                with PreserveLoggingContext():
                                    d.callback([
                                        res[i]
                                        for i in ids
                                        if i in res
                                    ])
                            except:
                                logger.exception("Failed to callback")
                with PreserveLoggingContext():
                    reactor.callFromThread(fire, event_list, row_dict)
            except Exception as e:
                logger.exception("do_fetch")

                # We only want to resolve deferreds from the main thread
                def fire(evs):
                    for _, d in evs:
                        if not d.called:
                            with PreserveLoggingContext():
                                d.errback(e)

                if event_list:
                    with PreserveLoggingContext():
                        reactor.callFromThread(fire, event_list)

    @defer.inlineCallbacks
    def _enqueue_events(self, events, check_redacted=True,
                        get_prev_content=False, allow_rejected=False):
        """Fetches events from the database using the _event_fetch_list. This
        allows batch and bulk fetching of events - it allows us to fetch events
        without having to create a new transaction for each request for events.
        """
        if not events:
            defer.returnValue({})

        events_d = defer.Deferred()
        with self._event_fetch_lock:
            self._event_fetch_list.append(
                (events, events_d)
            )

            self._event_fetch_lock.notify()

            if self._event_fetch_ongoing < EVENT_QUEUE_THREADS:
                self._event_fetch_ongoing += 1
                should_start = True
            else:
                should_start = False

        if should_start:
            with PreserveLoggingContext():
                self.runWithConnection(
                    self._do_fetch
                )

        with PreserveLoggingContext():
            rows = yield events_d

        if not allow_rejected:
            rows[:] = [r for r in rows if not r["rejects"]]

        res = yield defer.gatherResults(
            [
                preserve_fn(self._get_event_from_row)(
                    row["internal_metadata"], row["json"], row["redacts"],
                    check_redacted=check_redacted,
                    get_prev_content=get_prev_content,
                    rejected_reason=row["rejects"],
                )
                for row in rows
            ],
            consumeErrors=True
        )

        defer.returnValue({
            e.event_id: e
            for e in res if e
        })

    def _fetch_event_rows(self, txn, events):
        rows = []
        N = 200
        for i in range(1 + len(events) / N):
            evs = events[i * N:(i + 1) * N]
            if not evs:
                break

            sql = (
                "SELECT "
                " e.event_id as event_id, "
                " e.internal_metadata,"
                " e.json,"
                " r.redacts as redacts,"
                " rej.event_id as rejects "
                " FROM event_json as e"
                " LEFT JOIN rejections as rej USING (event_id)"
                " LEFT JOIN redactions as r ON e.event_id = r.redacts"
                " WHERE e.event_id IN (%s)"
            ) % (",".join(["?"] * len(evs)),)

            txn.execute(sql, evs)
            rows.extend(self.cursor_to_dict(txn))

        return rows

    def _fetch_events_txn(self, txn, events, check_redacted=True,
                          get_prev_content=False, allow_rejected=False):
        if not events:
            return {}

        rows = self._fetch_event_rows(
            txn, events,
        )

        if not allow_rejected:
            rows[:] = [r for r in rows if not r["rejects"]]

        res = [
            self._get_event_from_row_txn(
                txn,
                row["internal_metadata"], row["json"], row["redacts"],
                check_redacted=check_redacted,
                get_prev_content=get_prev_content,
                rejected_reason=row["rejects"],
            )
            for row in rows
        ]

        return {
            r.event_id: r
            for r in res
        }

    @defer.inlineCallbacks
    def _get_event_from_row(self, internal_metadata, js, redacted,
                            check_redacted=True, get_prev_content=False,
                            rejected_reason=None):
        d = json.loads(js)
        internal_metadata = json.loads(internal_metadata)

        if rejected_reason:
            rejected_reason = yield self._simple_select_one_onecol(
                table="rejections",
                keyvalues={"event_id": rejected_reason},
                retcol="reason",
                desc="_get_event_from_row",
            )

        ev = FrozenEvent(
            d,
            internal_metadata_dict=internal_metadata,
            rejected_reason=rejected_reason,
        )

        if check_redacted and redacted:
            ev = prune_event(ev)

            redaction_id = yield self._simple_select_one_onecol(
                table="redactions",
                keyvalues={"redacts": ev.event_id},
                retcol="event_id",
                desc="_get_event_from_row",
            )

            ev.unsigned["redacted_by"] = redaction_id
            # Get the redaction event.

            because = yield self.get_event(
                redaction_id,
                check_redacted=False,
                allow_none=True,
            )

            if because:
                # It's fine to do add the event directly, since get_pdu_json
                # will serialise this field correctly
                ev.unsigned["redacted_because"] = because

        if get_prev_content and "replaces_state" in ev.unsigned:
            prev = yield self.get_event(
                ev.unsigned["replaces_state"],
                get_prev_content=False,
                allow_none=True,
            )
            if prev:
                ev.unsigned["prev_content"] = prev.content
                ev.unsigned["prev_sender"] = prev.sender

        self._get_event_cache.prefill(
            (ev.event_id, check_redacted, get_prev_content), ev
        )

        defer.returnValue(ev)

    def _get_event_from_row_txn(self, txn, internal_metadata, js, redacted,
                                check_redacted=True, get_prev_content=False,
                                rejected_reason=None):
        d = json.loads(js)
        internal_metadata = json.loads(internal_metadata)

        if rejected_reason:
            rejected_reason = self._simple_select_one_onecol_txn(
                txn,
                table="rejections",
                keyvalues={"event_id": rejected_reason},
                retcol="reason",
            )

        ev = FrozenEvent(
            d,
            internal_metadata_dict=internal_metadata,
            rejected_reason=rejected_reason,
        )

        if check_redacted and redacted:
            ev = prune_event(ev)

            redaction_id = self._simple_select_one_onecol_txn(
                txn,
                table="redactions",
                keyvalues={"redacts": ev.event_id},
                retcol="event_id",
            )

            ev.unsigned["redacted_by"] = redaction_id
            # Get the redaction event.

            because = self._get_event_txn(
                txn,
                redaction_id,
                check_redacted=False
            )

            if because:
                ev.unsigned["redacted_because"] = because

        if get_prev_content and "replaces_state" in ev.unsigned:
            prev = self._get_event_txn(
                txn,
                ev.unsigned["replaces_state"],
                get_prev_content=False,
            )
            if prev:
                ev.unsigned["prev_content"] = prev.content
                ev.unsigned["prev_sender"] = prev.sender

        self._get_event_cache.prefill(
            (ev.event_id, check_redacted, get_prev_content), ev
        )

        return ev

    def _parse_events_txn(self, txn, rows):
        event_ids = [r["event_id"] for r in rows]

        return self._get_events_txn(txn, event_ids)

    @defer.inlineCallbacks
    def count_daily_messages(self):
        """
        Returns an estimate of the number of messages sent in the last day.

        If it has been significantly less or more than one day since the last
        call to this function, it will return None.
        """
        def _count_messages(txn):
            now = self.hs.get_clock().time()

            txn.execute(
                "SELECT reported_stream_token, reported_time FROM stats_reporting"
            )
            last_reported = self.cursor_to_dict(txn)

            txn.execute(
                "SELECT stream_ordering"
                " FROM events"
                " ORDER BY stream_ordering DESC"
                " LIMIT 1"
            )
            now_reporting = self.cursor_to_dict(txn)
            if not now_reporting:
                logger.info("Calculating daily messages skipped; no now_reporting")
                return None
            now_reporting = now_reporting[0]["stream_ordering"]

            txn.execute("DELETE FROM stats_reporting")
            txn.execute(
                "INSERT INTO stats_reporting"
                " (reported_stream_token, reported_time)"
                " VALUES (?, ?)",
                (now_reporting, now,)
            )

            if not last_reported:
                logger.info("Calculating daily messages skipped; no last_reported")
                return None

            # Close enough to correct for our purposes.
            yesterday = (now - 24 * 60 * 60)
            since_yesterday_seconds = yesterday - last_reported[0]["reported_time"]
            any_since_yesterday = math.fabs(since_yesterday_seconds) > 60 * 60
            if any_since_yesterday:
                logger.info(
                    "Calculating daily messages skipped; since_yesterday_seconds: %d" %
                    (since_yesterday_seconds,)
                )
                return None

            txn.execute(
                "SELECT COUNT(*) as messages"
                " FROM events NATURAL JOIN event_json"
                " WHERE json like '%m.room.message%'"
                " AND stream_ordering > ?"
                " AND stream_ordering <= ?",
                (
                    last_reported[0]["reported_stream_token"],
                    now_reporting,
                )
            )
            rows = self.cursor_to_dict(txn)
            if not rows:
                logger.info("Calculating daily messages skipped; messages count missing")
                return None
            return rows[0]["messages"]

        ret = yield self.runInteraction("count_messages", _count_messages)
        defer.returnValue(ret)

    @defer.inlineCallbacks
    def _background_reindex_origin_server_ts(self, progress, batch_size):
        target_min_stream_id = progress["target_min_stream_id_inclusive"]
        max_stream_id = progress["max_stream_id_exclusive"]
        rows_inserted = progress.get("rows_inserted", 0)

        INSERT_CLUMP_SIZE = 1000

        def reindex_search_txn(txn):
            sql = (
                "SELECT stream_ordering, event_id FROM events"
                " WHERE ? <= stream_ordering AND stream_ordering < ?"
                " ORDER BY stream_ordering DESC"
                " LIMIT ?"
            )

            txn.execute(sql, (target_min_stream_id, max_stream_id, batch_size))

            rows = txn.fetchall()
            if not rows:
                return 0

            min_stream_id = rows[-1][0]
            event_ids = [row[1] for row in rows]

            events = self._get_events_txn(txn, event_ids)

            rows = []
            for event in events:
                try:
                    event_id = event.event_id
                    origin_server_ts = event.origin_server_ts
                except (KeyError, AttributeError):
                    # If the event is missing a necessary field then
                    # skip over it.
                    continue

                rows.append((origin_server_ts, event_id))

            sql = (
                "UPDATE events SET origin_server_ts = ? WHERE event_id = ?"
            )

            for index in range(0, len(rows), INSERT_CLUMP_SIZE):
                clump = rows[index:index + INSERT_CLUMP_SIZE]
                txn.executemany(sql, clump)

            progress = {
                "target_min_stream_id_inclusive": target_min_stream_id,
                "max_stream_id_exclusive": min_stream_id,
                "rows_inserted": rows_inserted + len(rows)
            }

            self._background_update_progress_txn(
                txn, self.EVENT_ORIGIN_SERVER_TS_NAME, progress
            )

            return len(rows)

        result = yield self.runInteraction(
            self.EVENT_ORIGIN_SERVER_TS_NAME, reindex_search_txn
        )

        if not result:
            yield self._end_background_update(self.EVENT_ORIGIN_SERVER_TS_NAME)

        defer.returnValue(result)