summary refs log tree commit diff
path: root/synapse/storage/databases/main/stream.py
blob: 08a13a8b47b6af887aad27c12191d39464b98809 (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
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
# -*- coding: utf-8 -*-
# Copyright 2014-2016 OpenMarket Ltd
# Copyright 2017 Vector Creations Ltd
# Copyright 2018-2019 New Vector Ltd
# Copyright 2019 The Matrix.org Foundation C.I.C.
#
# 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.

""" This module is responsible for getting events from the DB for pagination
and event streaming.

The order it returns events in depend on whether we are streaming forwards or
are paginating backwards. We do this because we want to handle out of order
messages nicely, while still returning them in the correct order when we
paginate bacwards.

This is implemented by keeping two ordering columns: stream_ordering and
topological_ordering. Stream ordering is basically insertion/received order
(except for events from backfill requests). The topological_ordering is a
weak ordering of events based on the pdu graph.

This means that we have to have two different types of tokens, depending on
what sort order was used:
    - stream tokens are of the form: "s%d", which maps directly to the column
    - topological tokems: "t%d-%d", where the integers map to the topological
      and stream ordering columns respectively.
"""

import abc
import logging
from collections import namedtuple
from typing import TYPE_CHECKING, Dict, List, Optional, Set, Tuple

from twisted.internet import defer

from synapse.api.filtering import Filter
from synapse.events import EventBase
from synapse.logging.context import make_deferred_yieldable, run_in_background
from synapse.storage._base import SQLBaseStore
from synapse.storage.database import (
    DatabasePool,
    LoggingTransaction,
    make_in_list_sql_clause,
)
from synapse.storage.databases.main.events_worker import EventsWorkerStore
from synapse.storage.engines import BaseDatabaseEngine, PostgresEngine
from synapse.types import Collection, RoomStreamToken
from synapse.util.caches.stream_change_cache import StreamChangeCache

if TYPE_CHECKING:
    from synapse.server import HomeServer

logger = logging.getLogger(__name__)


MAX_STREAM_SIZE = 1000


_STREAM_TOKEN = "stream"
_TOPOLOGICAL_TOKEN = "topological"


# Used as return values for pagination APIs
_EventDictReturn = namedtuple(
    "_EventDictReturn", ("event_id", "topological_ordering", "stream_ordering")
)


def generate_pagination_where_clause(
    direction: str,
    column_names: Tuple[str, str],
    from_token: Optional[Tuple[Optional[int], int]],
    to_token: Optional[Tuple[Optional[int], int]],
    engine: BaseDatabaseEngine,
) -> str:
    """Creates an SQL expression to bound the columns by the pagination
    tokens.

    For example creates an SQL expression like:

        (6, 7) >= (topological_ordering, stream_ordering)
        AND (5, 3) < (topological_ordering, stream_ordering)

    would be generated for dir=b, from_token=(6, 7) and to_token=(5, 3).

    Note that tokens are considered to be after the row they are in, e.g. if
    a row A has a token T, then we consider A to be before T. This convention
    is important when figuring out inequalities for the generated SQL, and
    produces the following result:
        - If paginating forwards then we exclude any rows matching the from
          token, but include those that match the to token.
        - If paginating backwards then we include any rows matching the from
          token, but include those that match the to token.

    Args:
        direction: Whether we're paginating backwards("b") or forwards ("f").
        column_names: The column names to bound. Must *not* be user defined as
            these get inserted directly into the SQL statement without escapes.
        from_token: The start point for the pagination. This is an exclusive
            minimum bound if direction is "f", and an inclusive maximum bound if
            direction is "b".
        to_token: The endpoint point for the pagination. This is an inclusive
            maximum bound if direction is "f", and an exclusive minimum bound if
            direction is "b".
        engine: The database engine to generate the clauses for

    Returns:
        The sql expression
    """
    assert direction in ("b", "f")

    where_clause = []
    if from_token:
        where_clause.append(
            _make_generic_sql_bound(
                bound=">=" if direction == "b" else "<",
                column_names=column_names,
                values=from_token,
                engine=engine,
            )
        )

    if to_token:
        where_clause.append(
            _make_generic_sql_bound(
                bound="<" if direction == "b" else ">=",
                column_names=column_names,
                values=to_token,
                engine=engine,
            )
        )

    return " AND ".join(where_clause)


def _make_generic_sql_bound(
    bound: str,
    column_names: Tuple[str, str],
    values: Tuple[Optional[int], int],
    engine: BaseDatabaseEngine,
) -> str:
    """Create an SQL expression that bounds the given column names by the
    values, e.g. create the equivalent of `(1, 2) < (col1, col2)`.

    Only works with two columns.

    Older versions of SQLite don't support that syntax so we have to expand it
    out manually.

    Args:
        bound: The comparison operator to use. One of ">", "<", ">=",
            "<=", where the values are on the left and columns on the right.
        names: The column names. Must *not* be user defined
            as these get inserted directly into the SQL statement without
            escapes.
        values: The values to bound the columns by. If
            the first value is None then only creates a bound on the second
            column.
        engine: The database engine to generate the SQL for

    Returns:
        The SQL statement
    """

    assert bound in (">", "<", ">=", "<=")

    name1, name2 = column_names
    val1, val2 = values

    if val1 is None:
        val2 = int(val2)
        return "(%d %s %s)" % (val2, bound, name2)

    val1 = int(val1)
    val2 = int(val2)

    if isinstance(engine, PostgresEngine):
        # Postgres doesn't optimise ``(x < a) OR (x=a AND y<b)`` as well
        # as it optimises ``(x,y) < (a,b)`` on multicolumn indexes. So we
        # use the later form when running against postgres.
        return "((%d,%d) %s (%s,%s))" % (val1, val2, bound, name1, name2)

    # We want to generate queries of e.g. the form:
    #
    #   (val1 < name1 OR (val1 = name1 AND val2 <= name2))
    #
    # which is equivalent to (val1, val2) < (name1, name2)

    return """(
        {val1:d} {strict_bound} {name1}
        OR ({val1:d} = {name1} AND {val2:d} {bound} {name2})
    )""".format(
        name1=name1,
        val1=val1,
        name2=name2,
        val2=val2,
        strict_bound=bound[0],  # The first bound must always be strict equality here
        bound=bound,
    )


def filter_to_clause(event_filter: Optional[Filter]) -> Tuple[str, List[str]]:
    # NB: This may create SQL clauses that don't optimise well (and we don't
    # have indices on all possible clauses). E.g. it may create
    # "room_id == X AND room_id != X", which postgres doesn't optimise.

    if not event_filter:
        return "", []

    clauses = []
    args = []

    if event_filter.types:
        clauses.append("(%s)" % " OR ".join("type = ?" for _ in event_filter.types))
        args.extend(event_filter.types)

    for typ in event_filter.not_types:
        clauses.append("type != ?")
        args.append(typ)

    if event_filter.senders:
        clauses.append("(%s)" % " OR ".join("sender = ?" for _ in event_filter.senders))
        args.extend(event_filter.senders)

    for sender in event_filter.not_senders:
        clauses.append("sender != ?")
        args.append(sender)

    if event_filter.rooms:
        clauses.append("(%s)" % " OR ".join("room_id = ?" for _ in event_filter.rooms))
        args.extend(event_filter.rooms)

    for room_id in event_filter.not_rooms:
        clauses.append("room_id != ?")
        args.append(room_id)

    if event_filter.contains_url:
        clauses.append("contains_url = ?")
        args.append(event_filter.contains_url)

    # We're only applying the "labels" filter on the database query, because applying the
    # "not_labels" filter via a SQL query is non-trivial. Instead, we let
    # event_filter.check_fields apply it, which is not as efficient but makes the
    # implementation simpler.
    if event_filter.labels:
        clauses.append("(%s)" % " OR ".join("label = ?" for _ in event_filter.labels))
        args.extend(event_filter.labels)

    return " AND ".join(clauses), args


class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
    """This is an abstract base class where subclasses must implement
    `get_room_max_stream_ordering` and `get_room_min_stream_ordering`
    which can be called in the initializer.
    """

    __metaclass__ = abc.ABCMeta

    def __init__(self, database: DatabasePool, db_conn, hs: "HomeServer"):
        super(StreamWorkerStore, self).__init__(database, db_conn, hs)

        self._instance_name = hs.get_instance_name()
        self._send_federation = hs.should_send_federation()
        self._federation_shard_config = hs.config.worker.federation_shard_config

        # If we're a process that sends federation we may need to reset the
        # `federation_stream_position` table to match the current sharding
        # config. We don't do this now as otherwise two processes could conflict
        # during startup which would cause one to die.
        self._need_to_reset_federation_stream_positions = self._send_federation

        events_max = self.get_room_max_stream_ordering()
        event_cache_prefill, min_event_val = self.db_pool.get_cache_dict(
            db_conn,
            "events",
            entity_column="room_id",
            stream_column="stream_ordering",
            max_value=events_max,
        )
        self._events_stream_cache = StreamChangeCache(
            "EventsRoomStreamChangeCache",
            min_event_val,
            prefilled_cache=event_cache_prefill,
        )
        self._membership_stream_cache = StreamChangeCache(
            "MembershipStreamChangeCache", events_max
        )

        self._stream_order_on_start = self.get_room_max_stream_ordering()

    @abc.abstractmethod
    def get_room_max_stream_ordering(self) -> int:
        raise NotImplementedError()

    @abc.abstractmethod
    def get_room_min_stream_ordering(self) -> int:
        raise NotImplementedError()

    async def get_room_events_stream_for_rooms(
        self,
        room_ids: Collection[str],
        from_key: str,
        to_key: str,
        limit: int = 0,
        order: str = "DESC",
    ) -> Dict[str, Tuple[List[EventBase], str]]:
        """Get new room events in stream ordering since `from_key`.

        Args:
            room_ids
            from_key: Token from which no events are returned before
            to_key: Token from which no events are returned after. (This
                is typically the current stream token)
            limit: Maximum number of events to return
            order: Either "DESC" or "ASC". Determines which events are
                returned when the result is limited. If "DESC" then the most
                recent `limit` events are returned, otherwise returns the
                oldest `limit` events.

        Returns:
            A map from room id to a tuple containing:
                - list of recent events in the room
                - stream ordering key for the start of the chunk of events returned.
        """
        from_id = RoomStreamToken.parse_stream_token(from_key).stream

        room_ids = self._events_stream_cache.get_entities_changed(room_ids, from_id)

        if not room_ids:
            return {}

        results = {}
        room_ids = list(room_ids)
        for rm_ids in (room_ids[i : i + 20] for i in range(0, len(room_ids), 20)):
            res = await make_deferred_yieldable(
                defer.gatherResults(
                    [
                        run_in_background(
                            self.get_room_events_stream_for_room,
                            room_id,
                            from_key,
                            to_key,
                            limit,
                            order=order,
                        )
                        for room_id in rm_ids
                    ],
                    consumeErrors=True,
                )
            )
            results.update(dict(zip(rm_ids, res)))

        return results

    def get_rooms_that_changed(
        self, room_ids: Collection[str], from_key: str
    ) -> Set[str]:
        """Given a list of rooms and a token, return rooms where there may have
        been changes.

        Args:
            room_ids
            from_key: The room_key portion of a StreamToken
        """
        from_id = RoomStreamToken.parse_stream_token(from_key).stream
        return {
            room_id
            for room_id in room_ids
            if self._events_stream_cache.has_entity_changed(room_id, from_id)
        }

    async def get_room_events_stream_for_room(
        self,
        room_id: str,
        from_key: str,
        to_key: str,
        limit: int = 0,
        order: str = "DESC",
    ) -> Tuple[List[EventBase], str]:
        """Get new room events in stream ordering since `from_key`.

        Args:
            room_id
            from_key: Token from which no events are returned before
            to_key: Token from which no events are returned after. (This
                is typically the current stream token)
            limit: Maximum number of events to return
            order: Either "DESC" or "ASC". Determines which events are
                returned when the result is limited. If "DESC" then the most
                recent `limit` events are returned, otherwise returns the
                oldest `limit` events.

        Returns:
            The list of events (in ascending order) and the token from the start
            of the chunk of events returned.
        """
        if from_key == to_key:
            return [], from_key

        from_id = RoomStreamToken.parse_stream_token(from_key).stream
        to_id = RoomStreamToken.parse_stream_token(to_key).stream

        has_changed = self._events_stream_cache.has_entity_changed(room_id, from_id)

        if not has_changed:
            return [], from_key

        def f(txn):
            sql = (
                "SELECT event_id, stream_ordering FROM events WHERE"
                " room_id = ?"
                " AND not outlier"
                " AND stream_ordering > ? AND stream_ordering <= ?"
                " ORDER BY stream_ordering %s LIMIT ?"
            ) % (order,)
            txn.execute(sql, (room_id, from_id, to_id, limit))

            rows = [_EventDictReturn(row[0], None, row[1]) for row in txn]
            return rows

        rows = await self.db_pool.runInteraction("get_room_events_stream_for_room", f)

        ret = await self.get_events_as_list(
            [r.event_id for r in rows], get_prev_content=True
        )

        self._set_before_and_after(ret, rows, topo_order=from_id is None)

        if order.lower() == "desc":
            ret.reverse()

        if rows:
            key = "s%d" % min(r.stream_ordering for r in rows)
        else:
            # Assume we didn't get anything because there was nothing to
            # get.
            key = from_key

        return ret, key

    async def get_membership_changes_for_user(
        self, user_id: str, from_key: str, to_key: str
    ) -> List[EventBase]:
        from_id = RoomStreamToken.parse_stream_token(from_key).stream
        to_id = RoomStreamToken.parse_stream_token(to_key).stream

        if from_key == to_key:
            return []

        if from_id:
            has_changed = self._membership_stream_cache.has_entity_changed(
                user_id, int(from_id)
            )
            if not has_changed:
                return []

        def f(txn):
            sql = (
                "SELECT m.event_id, stream_ordering FROM events AS e,"
                " room_memberships AS m"
                " WHERE e.event_id = m.event_id"
                " AND m.user_id = ?"
                " AND e.stream_ordering > ? AND e.stream_ordering <= ?"
                " ORDER BY e.stream_ordering ASC"
            )
            txn.execute(sql, (user_id, from_id, to_id))

            rows = [_EventDictReturn(row[0], None, row[1]) for row in txn]

            return rows

        rows = await self.db_pool.runInteraction("get_membership_changes_for_user", f)

        ret = await self.get_events_as_list(
            [r.event_id for r in rows], get_prev_content=True
        )

        self._set_before_and_after(ret, rows, topo_order=False)

        return ret

    async def get_recent_events_for_room(
        self, room_id: str, limit: int, end_token: str
    ) -> Tuple[List[EventBase], str]:
        """Get the most recent events in the room in topological ordering.

        Args:
            room_id
            limit
            end_token: The stream token representing now.

        Returns:
            A list of events and a token pointing to the start of the returned
            events. The events returned are in ascending order.
        """

        rows, token = await self.get_recent_event_ids_for_room(
            room_id, limit, end_token
        )

        events = await self.get_events_as_list(
            [r.event_id for r in rows], get_prev_content=True
        )

        self._set_before_and_after(events, rows)

        return (events, token)

    async def get_recent_event_ids_for_room(
        self, room_id: str, limit: int, end_token: str
    ) -> Tuple[List[_EventDictReturn], str]:
        """Get the most recent events in the room in topological ordering.

        Args:
            room_id
            limit
            end_token: The stream token representing now.

        Returns:
            A list of _EventDictReturn and a token pointing to the start of the
            returned events. The events returned are in ascending order.
        """
        # Allow a zero limit here, and no-op.
        if limit == 0:
            return [], end_token

        parsed_end_token = RoomStreamToken.parse(end_token)

        rows, token = await self.db_pool.runInteraction(
            "get_recent_event_ids_for_room",
            self._paginate_room_events_txn,
            room_id,
            from_token=parsed_end_token,
            limit=limit,
        )

        # We want to return the results in ascending order.
        rows.reverse()

        return rows, token

    async def get_room_event_before_stream_ordering(
        self, room_id: str, stream_ordering: int
    ) -> Tuple[int, int, str]:
        """Gets details of the first event in a room at or before a stream ordering

        Args:
            room_id:
            stream_ordering:

        Returns:
            A tuple of (stream ordering, topological ordering, event_id)
        """

        def _f(txn):
            sql = (
                "SELECT stream_ordering, topological_ordering, event_id"
                " FROM events"
                " WHERE room_id = ? AND stream_ordering <= ?"
                " AND NOT outlier"
                " ORDER BY stream_ordering DESC"
                " LIMIT 1"
            )
            txn.execute(sql, (room_id, stream_ordering))
            return txn.fetchone()

        return await self.db_pool.runInteraction(
            "get_room_event_before_stream_ordering", _f
        )

    async def get_room_events_max_id(self, room_id: Optional[str] = None) -> str:
        """Returns the current token for rooms stream.

        By default, it returns the current global stream token. Specifying a
        `room_id` causes it to return the current room specific topological
        token.
        """
        token = self.get_room_max_stream_ordering()
        if room_id is None:
            return "s%d" % (token,)
        else:
            topo = await self.db_pool.runInteraction(
                "_get_max_topological_txn", self._get_max_topological_txn, room_id
            )
            return "t%d-%d" % (topo, token)

    async def get_stream_id_for_event(self, event_id: str) -> int:
        """The stream ID for an event
        Args:
            event_id: The id of the event to look up a stream token for.
        Raises:
            StoreError if the event wasn't in the database.
        Returns:
            A stream ID.
        """
        return await self.db_pool.runInteraction(
            "get_stream_id_for_event", self.get_stream_id_for_event_txn, event_id,
        )

    def get_stream_id_for_event_txn(
        self, txn: LoggingTransaction, event_id: str, allow_none=False,
    ) -> int:
        return self.db_pool.simple_select_one_onecol_txn(
            txn=txn,
            table="events",
            keyvalues={"event_id": event_id},
            retcol="stream_ordering",
            allow_none=allow_none,
        )

    async def get_stream_token_for_event(self, event_id: str) -> str:
        """The stream token for an event
        Args:
            event_id: The id of the event to look up a stream token for.
        Raises:
            StoreError if the event wasn't in the database.
        Returns:
            A "s%d" stream token.
        """
        stream_id = await self.get_stream_id_for_event(event_id)
        return "s%d" % (stream_id,)

    async def get_topological_token_for_event(self, event_id: str) -> str:
        """The stream token for an event
        Args:
            event_id: The id of the event to look up a stream token for.
        Raises:
            StoreError if the event wasn't in the database.
        Returns:
            A "t%d-%d" topological token.
        """
        row = await self.db_pool.simple_select_one(
            table="events",
            keyvalues={"event_id": event_id},
            retcols=("stream_ordering", "topological_ordering"),
            desc="get_topological_token_for_event",
        )
        return "t%d-%d" % (row["topological_ordering"], row["stream_ordering"])

    async def get_max_topological_token(self, room_id: str, stream_key: int) -> int:
        """Get the max topological token in a room before the given stream
        ordering.

        Args:
            room_id
            stream_key

        Returns:
            The maximum topological token.
        """
        sql = (
            "SELECT coalesce(max(topological_ordering), 0) FROM events"
            " WHERE room_id = ? AND stream_ordering < ?"
        )
        row = await self.db_pool.execute(
            "get_max_topological_token", None, sql, room_id, stream_key
        )
        return row[0][0] if row else 0

    def _get_max_topological_txn(self, txn: LoggingTransaction, room_id: str) -> int:
        txn.execute(
            "SELECT MAX(topological_ordering) FROM events WHERE room_id = ?",
            (room_id,),
        )

        rows = txn.fetchall()
        return rows[0][0] if rows else 0

    @staticmethod
    def _set_before_and_after(
        events: List[EventBase], rows: List[_EventDictReturn], topo_order: bool = True
    ):
        """Inserts ordering information to events' internal metadata from
        the DB rows.

        Args:
            events
            rows
            topo_order: Whether the events were ordered topologically or by stream
                ordering. If true then all rows should have a non null
                topological_ordering.
        """
        for event, row in zip(events, rows):
            stream = row.stream_ordering
            if topo_order and row.topological_ordering:
                topo = row.topological_ordering
            else:
                topo = None
            internal = event.internal_metadata
            internal.before = str(RoomStreamToken(topo, stream - 1))
            internal.after = str(RoomStreamToken(topo, stream))
            internal.order = (int(topo) if topo else 0, int(stream))

    async def get_events_around(
        self,
        room_id: str,
        event_id: str,
        before_limit: int,
        after_limit: int,
        event_filter: Optional[Filter] = None,
    ) -> dict:
        """Retrieve events and pagination tokens around a given event in a
        room.
        """

        results = await self.db_pool.runInteraction(
            "get_events_around",
            self._get_events_around_txn,
            room_id,
            event_id,
            before_limit,
            after_limit,
            event_filter,
        )

        events_before = await self.get_events_as_list(
            list(results["before"]["event_ids"]), get_prev_content=True
        )

        events_after = await self.get_events_as_list(
            list(results["after"]["event_ids"]), get_prev_content=True
        )

        return {
            "events_before": events_before,
            "events_after": events_after,
            "start": results["before"]["token"],
            "end": results["after"]["token"],
        }

    def _get_events_around_txn(
        self,
        txn: LoggingTransaction,
        room_id: str,
        event_id: str,
        before_limit: int,
        after_limit: int,
        event_filter: Optional[Filter],
    ) -> dict:
        """Retrieves event_ids and pagination tokens around a given event in a
        room.

        Args:
            room_id
            event_id
            before_limit
            after_limit
            event_filter

        Returns:
            dict
        """

        results = self.db_pool.simple_select_one_txn(
            txn,
            "events",
            keyvalues={"event_id": event_id, "room_id": room_id},
            retcols=["stream_ordering", "topological_ordering"],
        )

        # This cannot happen as `allow_none=False`.
        assert results is not None

        # Paginating backwards includes the event at the token, but paginating
        # forward doesn't.
        before_token = RoomStreamToken(
            results["topological_ordering"] - 1, results["stream_ordering"]
        )

        after_token = RoomStreamToken(
            results["topological_ordering"], results["stream_ordering"]
        )

        rows, start_token = self._paginate_room_events_txn(
            txn,
            room_id,
            before_token,
            direction="b",
            limit=before_limit,
            event_filter=event_filter,
        )
        events_before = [r.event_id for r in rows]

        rows, end_token = self._paginate_room_events_txn(
            txn,
            room_id,
            after_token,
            direction="f",
            limit=after_limit,
            event_filter=event_filter,
        )
        events_after = [r.event_id for r in rows]

        return {
            "before": {"event_ids": events_before, "token": start_token},
            "after": {"event_ids": events_after, "token": end_token},
        }

    async def get_all_new_events_stream(
        self, from_id: int, current_id: int, limit: int
    ) -> Tuple[int, List[EventBase]]:
        """Get all new events

         Returns all events with from_id < stream_ordering <= current_id.

         Args:
             from_id:  the stream_ordering of the last event we processed
             current_id:  the stream_ordering of the most recently processed event
             limit: the maximum number of events to return

         Returns:
             A tuple of (next_id, events), where `next_id` is the next value to
             pass as `from_id` (it will either be the stream_ordering of the
             last returned event, or, if fewer than `limit` events were found,
             the `current_id`).
         """

        def get_all_new_events_stream_txn(txn):
            sql = (
                "SELECT e.stream_ordering, e.event_id"
                " FROM events AS e"
                " WHERE"
                " ? < e.stream_ordering AND e.stream_ordering <= ?"
                " ORDER BY e.stream_ordering ASC"
                " LIMIT ?"
            )

            txn.execute(sql, (from_id, current_id, limit))
            rows = txn.fetchall()

            upper_bound = current_id
            if len(rows) == limit:
                upper_bound = rows[-1][0]

            return upper_bound, [row[1] for row in rows]

        upper_bound, event_ids = await self.db_pool.runInteraction(
            "get_all_new_events_stream", get_all_new_events_stream_txn
        )

        events = await self.get_events_as_list(event_ids)

        return upper_bound, events

    async def get_federation_out_pos(self, typ: str) -> int:
        if self._need_to_reset_federation_stream_positions:
            await self.db_pool.runInteraction(
                "_reset_federation_positions_txn", self._reset_federation_positions_txn
            )
            self._need_to_reset_federation_stream_positions = False

        return await self.db_pool.simple_select_one_onecol(
            table="federation_stream_position",
            retcol="stream_id",
            keyvalues={"type": typ, "instance_name": self._instance_name},
            desc="get_federation_out_pos",
        )

    async def update_federation_out_pos(self, typ: str, stream_id: int) -> None:
        if self._need_to_reset_federation_stream_positions:
            await self.db_pool.runInteraction(
                "_reset_federation_positions_txn", self._reset_federation_positions_txn
            )
            self._need_to_reset_federation_stream_positions = False

        await self.db_pool.simple_update_one(
            table="federation_stream_position",
            keyvalues={"type": typ, "instance_name": self._instance_name},
            updatevalues={"stream_id": stream_id},
            desc="update_federation_out_pos",
        )

    def _reset_federation_positions_txn(self, txn: LoggingTransaction) -> None:
        """Fiddles with the `federation_stream_position` table to make it match
        the configured federation sender instances during start up.
        """

        # The federation sender instances may have changed, so we need to
        # massage the `federation_stream_position` table to have a row per type
        # per instance sending federation. If there is a mismatch we update the
        # table with the correct rows using the *minimum* stream ID seen. This
        # may result in resending of events/EDUs to remote servers, but that is
        # preferable to dropping them.

        if not self._send_federation:
            return

        # Pull out the configured instances. If we don't have a shard config then
        # we assume that we're the only instance sending.
        configured_instances = self._federation_shard_config.instances
        if not configured_instances:
            configured_instances = [self._instance_name]
        elif self._instance_name not in configured_instances:
            return

        instances_in_table = self.db_pool.simple_select_onecol_txn(
            txn,
            table="federation_stream_position",
            keyvalues={},
            retcol="instance_name",
        )

        if set(instances_in_table) == set(configured_instances):
            # Nothing to do
            return

        sql = """
            SELECT type, MIN(stream_id) FROM federation_stream_position
            GROUP BY type
        """
        txn.execute(sql)
        min_positions = {typ: pos for typ, pos in txn}  # Map from type -> min position

        # Ensure we do actually have some values here
        assert set(min_positions) == {"federation", "events"}

        sql = """
            DELETE FROM federation_stream_position
            WHERE NOT (%s)
        """
        clause, args = make_in_list_sql_clause(
            txn.database_engine, "instance_name", configured_instances
        )
        txn.execute(sql % (clause,), args)

        for typ, stream_id in min_positions.items():
            self.db_pool.simple_upsert_txn(
                txn,
                table="federation_stream_position",
                keyvalues={"type": typ, "instance_name": self._instance_name},
                values={"stream_id": stream_id},
            )

    def has_room_changed_since(self, room_id: str, stream_id: int) -> bool:
        return self._events_stream_cache.has_entity_changed(room_id, stream_id)

    def _paginate_room_events_txn(
        self,
        txn: LoggingTransaction,
        room_id: str,
        from_token: RoomStreamToken,
        to_token: Optional[RoomStreamToken] = None,
        direction: str = "b",
        limit: int = -1,
        event_filter: Optional[Filter] = None,
    ) -> Tuple[List[_EventDictReturn], str]:
        """Returns list of events before or after a given token.

        Args:
            txn
            room_id
            from_token: The token used to stream from
            to_token: A token which if given limits the results to only those before
            direction: Either 'b' or 'f' to indicate whether we are paginating
                forwards or backwards from `from_key`.
            limit: The maximum number of events to return.
            event_filter: If provided filters the events to
                those that match the filter.

        Returns:
            A list of _EventDictReturn and a token that points to the end of the
            result set. If no events are returned then the end of the stream has
            been reached (i.e. there are no events between `from_token` and
            `to_token`), or `limit` is zero.
        """

        assert int(limit) >= 0

        # Tokens really represent positions between elements, but we use
        # the convention of pointing to the event before the gap. Hence
        # we have a bit of asymmetry when it comes to equalities.
        args = [False, room_id]
        if direction == "b":
            order = "DESC"
        else:
            order = "ASC"

        bounds = generate_pagination_where_clause(
            direction=direction,
            column_names=("topological_ordering", "stream_ordering"),
            from_token=from_token.as_tuple(),
            to_token=to_token.as_tuple() if to_token else None,
            engine=self.database_engine,
        )

        filter_clause, filter_args = filter_to_clause(event_filter)

        if filter_clause:
            bounds += " AND " + filter_clause
            args.extend(filter_args)

        args.append(int(limit))

        select_keywords = "SELECT"
        join_clause = ""
        if event_filter and event_filter.labels:
            # If we're not filtering on a label, then joining on event_labels will
            # return as many row for a single event as the number of labels it has. To
            # avoid this, only join if we're filtering on at least one label.
            join_clause = """
                LEFT JOIN event_labels
                USING (event_id, room_id, topological_ordering)
            """
            if len(event_filter.labels) > 1:
                # Using DISTINCT in this SELECT query is quite expensive, because it
                # requires the engine to sort on the entire (not limited) result set,
                # i.e. the entire events table. We only need to use it when we're
                # filtering on more than two labels, because that's the only scenario
                # in which we can possibly to get multiple times the same event ID in
                # the results.
                select_keywords += "DISTINCT"

        sql = """
            %(select_keywords)s event_id, topological_ordering, stream_ordering
            FROM events
            %(join_clause)s
            WHERE outlier = ? AND room_id = ? AND %(bounds)s
            ORDER BY topological_ordering %(order)s,
            stream_ordering %(order)s LIMIT ?
        """ % {
            "select_keywords": select_keywords,
            "join_clause": join_clause,
            "bounds": bounds,
            "order": order,
        }

        txn.execute(sql, args)

        rows = [_EventDictReturn(row[0], row[1], row[2]) for row in txn]

        if rows:
            topo = rows[-1].topological_ordering
            toke = rows[-1].stream_ordering
            if direction == "b":
                # Tokens are positions between events.
                # This token points *after* the last event in the chunk.
                # We need it to point to the event before it in the chunk
                # when we are going backwards so we subtract one from the
                # stream part.
                toke -= 1
            next_token = RoomStreamToken(topo, toke)
        else:
            # TODO (erikj): We should work out what to do here instead.
            next_token = to_token if to_token else from_token

        return rows, str(next_token)

    async def paginate_room_events(
        self,
        room_id: str,
        from_key: str,
        to_key: Optional[str] = None,
        direction: str = "b",
        limit: int = -1,
        event_filter: Optional[Filter] = None,
    ) -> Tuple[List[EventBase], str]:
        """Returns list of events before or after a given token.

        Args:
            room_id
            from_key: The token used to stream from
            to_key: A token which if given limits the results to only those before
            direction: Either 'b' or 'f' to indicate whether we are paginating
                forwards or backwards from `from_key`.
            limit: The maximum number of events to return.
            event_filter: If provided filters the events to those that match the filter.

        Returns:
            The results as a list of events and a token that points to the end
            of the result set. If no events are returned then the end of the
            stream has been reached (i.e. there are no events between `from_key`
            and `to_key`).
        """

        parsed_from_key = RoomStreamToken.parse(from_key)
        parsed_to_key = None
        if to_key:
            parsed_to_key = RoomStreamToken.parse(to_key)

        rows, token = await self.db_pool.runInteraction(
            "paginate_room_events",
            self._paginate_room_events_txn,
            room_id,
            parsed_from_key,
            parsed_to_key,
            direction,
            limit,
            event_filter,
        )

        events = await self.get_events_as_list(
            [r.event_id for r in rows], get_prev_content=True
        )

        self._set_before_and_after(events, rows)

        return (events, token)


class StreamStore(StreamWorkerStore):
    def get_room_max_stream_ordering(self) -> int:
        return self._stream_id_gen.get_current_token()

    def get_room_min_stream_ordering(self) -> int:
        return self._backfill_id_gen.get_current_token()