Move storage classes into a main "data store".

This is in preparation for having multiple data stores that offer
different functionality, e.g. splitting out state or event storage.

1 files changed, 0 insertions, 2489 deletions

diff --git a/synapse/storage/events.py b/synapse/storage/events.py
deleted file mode 100644
index ee49ef235d..0000000000
--- a/synapse/storage/events.py
+++ /dev/null
@@ -1,2489 +0,0 @@
-# -*- coding: utf-8 -*-
-# Copyright 2014-2016 OpenMarket 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.
-
-import itertools
-import logging
-from collections import Counter as c_counter, OrderedDict, deque, namedtuple
-from functools import wraps
-
-from six import iteritems, text_type
-from six.moves import range
-
-from canonicaljson import json
-from prometheus_client import Counter, Histogram
-
-from twisted.internet import defer
-
-import synapse.metrics
-from synapse.api.constants import EventTypes
-from synapse.api.errors import SynapseError
-from synapse.events import EventBase  # noqa: F401
-from synapse.events.snapshot import EventContext  # noqa: F401
-from synapse.events.utils import prune_event_dict
-from synapse.logging.context import PreserveLoggingContext, make_deferred_yieldable
-from synapse.logging.utils import log_function
-from synapse.metrics import BucketCollector
-from synapse.metrics.background_process_metrics import run_as_background_process
-from synapse.state import StateResolutionStore
-from synapse.storage._base import make_in_list_sql_clause
-from synapse.storage.background_updates import BackgroundUpdateStore
-from synapse.storage.event_federation import EventFederationStore
-from synapse.storage.events_worker import EventsWorkerStore
-from synapse.storage.state import StateGroupWorkerStore
-from synapse.types import RoomStreamToken, get_domain_from_id
-from synapse.util import batch_iter
-from synapse.util.async_helpers import ObservableDeferred
-from synapse.util.caches.descriptors import cached, cachedInlineCallbacks
-from synapse.util.frozenutils import frozendict_json_encoder
-from synapse.util.metrics import Measure
-
-logger = logging.getLogger(__name__)
-
-persist_event_counter = Counter("synapse_storage_events_persisted_events", "")
-event_counter = Counter(
-    "synapse_storage_events_persisted_events_sep",
-    "",
-    ["type", "origin_type", "origin_entity"],
-)
-
-# The number of times we are recalculating the current state
-state_delta_counter = Counter("synapse_storage_events_state_delta", "")
-
-# The number of times we are recalculating state when there is only a
-# single forward extremity
-state_delta_single_event_counter = Counter(
-    "synapse_storage_events_state_delta_single_event", ""
-)
-
-# The number of times we are reculating state when we could have resonably
-# calculated the delta when we calculated the state for an event we were
-# persisting.
-state_delta_reuse_delta_counter = Counter(
-    "synapse_storage_events_state_delta_reuse_delta", ""
-)
-
-# The number of forward extremities for each new event.
-forward_extremities_counter = Histogram(
-    "synapse_storage_events_forward_extremities_persisted",
-    "Number of forward extremities for each new event",
-    buckets=(1, 2, 3, 5, 7, 10, 15, 20, 50, 100, 200, 500, "+Inf"),
-)
-
-# The number of stale forward extremities for each new event. Stale extremities
-# are those that were in the previous set of extremities as well as the new.
-stale_forward_extremities_counter = Histogram(
-    "synapse_storage_events_stale_forward_extremities_persisted",
-    "Number of unchanged forward extremities for each new event",
-    buckets=(0, 1, 2, 3, 5, 7, 10, 15, 20, 50, 100, 200, 500, "+Inf"),
-)
-
-
-def encode_json(json_object):
-    """
-    Encode a Python object as JSON and return it in a Unicode string.
-    """
-    out = frozendict_json_encoder.encode(json_object)
-    if isinstance(out, bytes):
-        out = out.decode("utf8")
-    return out
-
-
-class _EventPeristenceQueue(object):
-    """Queues up events so that they can be persisted in bulk with only one
-    concurrent transaction per room.
-    """
-
-    _EventPersistQueueItem = namedtuple(
-        "_EventPersistQueueItem", ("events_and_contexts", "backfilled", "deferred")
-    )
-
-    def __init__(self):
-        self._event_persist_queues = {}
-        self._currently_persisting_rooms = set()
-
-    def add_to_queue(self, room_id, events_and_contexts, backfilled):
-        """Add events to the queue, with the given persist_event options.
-
-        NB: due to the normal usage pattern of this method, it does *not*
-        follow the synapse logcontext rules, and leaves the logcontext in
-        place whether or not the returned deferred is ready.
-
-        Args:
-            room_id (str):
-            events_and_contexts (list[(EventBase, EventContext)]):
-            backfilled (bool):
-
-        Returns:
-            defer.Deferred: a deferred which will resolve once the events are
-                persisted. Runs its callbacks *without* a logcontext.
-        """
-        queue = self._event_persist_queues.setdefault(room_id, deque())
-        if queue:
-            # if the last item in the queue has the same `backfilled` setting,
-            # we can just add these new events to that item.
-            end_item = queue[-1]
-            if end_item.backfilled == backfilled:
-                end_item.events_and_contexts.extend(events_and_contexts)
-                return end_item.deferred.observe()
-
-        deferred = ObservableDeferred(defer.Deferred(), consumeErrors=True)
-
-        queue.append(
-            self._EventPersistQueueItem(
-                events_and_contexts=events_and_contexts,
-                backfilled=backfilled,
-                deferred=deferred,
-            )
-        )
-
-        return deferred.observe()
-
-    def handle_queue(self, room_id, per_item_callback):
-        """Attempts to handle the queue for a room if not already being handled.
-
-        The given callback will be invoked with for each item in the queue,
-        of type _EventPersistQueueItem. The per_item_callback will continuously
-        be called with new items, unless the queue becomnes empty. The return
-        value of the function will be given to the deferreds waiting on the item,
-        exceptions will be passed to the deferreds as well.
-
-        This function should therefore be called whenever anything is added
-        to the queue.
-
-        If another callback is currently handling the queue then it will not be
-        invoked.
-        """
-
-        if room_id in self._currently_persisting_rooms:
-            return
-
-        self._currently_persisting_rooms.add(room_id)
-
-        @defer.inlineCallbacks
-        def handle_queue_loop():
-            try:
-                queue = self._get_drainining_queue(room_id)
-                for item in queue:
-                    try:
-                        ret = yield per_item_callback(item)
-                    except Exception:
-                        with PreserveLoggingContext():
-                            item.deferred.errback()
-                    else:
-                        with PreserveLoggingContext():
-                            item.deferred.callback(ret)
-            finally:
-                queue = self._event_persist_queues.pop(room_id, None)
-                if queue:
-                    self._event_persist_queues[room_id] = queue
-                self._currently_persisting_rooms.discard(room_id)
-
-        # set handle_queue_loop off in the background
-        run_as_background_process("persist_events", handle_queue_loop)
-
-    def _get_drainining_queue(self, room_id):
-        queue = self._event_persist_queues.setdefault(room_id, deque())
-
-        try:
-            while True:
-                yield queue.popleft()
-        except IndexError:
-            # Queue has been drained.
-            pass
-
-
-_EventCacheEntry = namedtuple("_EventCacheEntry", ("event", "redacted_event"))
-
-
-def _retry_on_integrity_error(func):
-    """Wraps a database function so that it gets retried on IntegrityError,
-    with `delete_existing=True` passed in.
-
-    Args:
-        func: function that returns a Deferred and accepts a `delete_existing` arg
-    """
-
-    @wraps(func)
-    @defer.inlineCallbacks
-    def f(self, *args, **kwargs):
-        try:
-            res = yield func(self, *args, **kwargs)
-        except self.database_engine.module.IntegrityError:
-            logger.exception("IntegrityError, retrying.")
-            res = yield func(self, *args, delete_existing=True, **kwargs)
-        return res
-
-    return f
-
-
-# inherits from EventFederationStore so that we can call _update_backward_extremities
-# and _handle_mult_prev_events (though arguably those could both be moved in here)
-class EventsStore(
-    StateGroupWorkerStore,
-    EventFederationStore,
-    EventsWorkerStore,
-    BackgroundUpdateStore,
-):
-    def __init__(self, db_conn, hs):
-        super(EventsStore, self).__init__(db_conn, hs)
-
-        self._event_persist_queue = _EventPeristenceQueue()
-        self._state_resolution_handler = hs.get_state_resolution_handler()
-
-        # Collect metrics on the number of forward extremities that exist.
-        # Counter of number of extremities to count
-        self._current_forward_extremities_amount = c_counter()
-
-        BucketCollector(
-            "synapse_forward_extremities",
-            lambda: self._current_forward_extremities_amount,
-            buckets=[1, 2, 3, 5, 7, 10, 15, 20, 50, 100, 200, 500, "+Inf"],
-        )
-
-        # Read the extrems every 60 minutes
-        def read_forward_extremities():
-            # run as a background process to make sure that the database transactions
-            # have a logcontext to report to
-            return run_as_background_process(
-                "read_forward_extremities", self._read_forward_extremities
-            )
-
-        hs.get_clock().looping_call(read_forward_extremities, 60 * 60 * 1000)
-
-        def _censor_redactions():
-            return run_as_background_process(
-                "_censor_redactions", self._censor_redactions
-            )
-
-        if self.hs.config.redaction_retention_period is not None:
-            hs.get_clock().looping_call(_censor_redactions, 5 * 60 * 1000)
-
-    @defer.inlineCallbacks
-    def _read_forward_extremities(self):
-        def fetch(txn):
-            txn.execute(
-                """
-                select count(*) c from event_forward_extremities
-                group by room_id
-                """
-            )
-            return txn.fetchall()
-
-        res = yield self.runInteraction("read_forward_extremities", fetch)
-        self._current_forward_extremities_amount = c_counter(list(x[0] for x in res))
-
-    @defer.inlineCallbacks
-    def persist_events(self, events_and_contexts, backfilled=False):
-        """
-        Write events to the database
-        Args:
-            events_and_contexts: list of tuples of (event, context)
-            backfilled (bool): Whether the results are retrieved from federation
-                via backfill or not. Used to determine if they're "new" events
-                which might update the current state etc.
-
-        Returns:
-            Deferred[int]: the stream ordering of the latest persisted event
-        """
-        partitioned = {}
-        for event, ctx in events_and_contexts:
-            partitioned.setdefault(event.room_id, []).append((event, ctx))
-
-        deferreds = []
-        for room_id, evs_ctxs in iteritems(partitioned):
-            d = self._event_persist_queue.add_to_queue(
-                room_id, evs_ctxs, backfilled=backfilled
-            )
-            deferreds.append(d)
-
-        for room_id in partitioned:
-            self._maybe_start_persisting(room_id)
-
-        yield make_deferred_yieldable(
-            defer.gatherResults(deferreds, consumeErrors=True)
-        )
-
-        max_persisted_id = yield self._stream_id_gen.get_current_token()
-
-        return max_persisted_id
-
-    @defer.inlineCallbacks
-    @log_function
-    def persist_event(self, event, context, backfilled=False):
-        """
-
-        Args:
-            event (EventBase):
-            context (EventContext):
-            backfilled (bool):
-
-        Returns:
-            Deferred: resolves to (int, int): the stream ordering of ``event``,
-            and the stream ordering of the latest persisted event
-        """
-        deferred = self._event_persist_queue.add_to_queue(
-            event.room_id, [(event, context)], backfilled=backfilled
-        )
-
-        self._maybe_start_persisting(event.room_id)
-
-        yield make_deferred_yieldable(deferred)
-
-        max_persisted_id = yield self._stream_id_gen.get_current_token()
-        return (event.internal_metadata.stream_ordering, max_persisted_id)
-
-    def _maybe_start_persisting(self, room_id):
-        @defer.inlineCallbacks
-        def persisting_queue(item):
-            with Measure(self._clock, "persist_events"):
-                yield self._persist_events(
-                    item.events_and_contexts, backfilled=item.backfilled
-                )
-
-        self._event_persist_queue.handle_queue(room_id, persisting_queue)
-
-    @_retry_on_integrity_error
-    @defer.inlineCallbacks
-    def _persist_events(
-        self, events_and_contexts, backfilled=False, delete_existing=False
-    ):
-        """Persist events to db
-
-        Args:
-            events_and_contexts (list[(EventBase, EventContext)]):
-            backfilled (bool):
-            delete_existing (bool):
-
-        Returns:
-            Deferred: resolves when the events have been persisted
-        """
-        if not events_and_contexts:
-            return
-
-        chunks = [
-            events_and_contexts[x : x + 100]
-            for x in range(0, len(events_and_contexts), 100)
-        ]
-
-        for chunk in chunks:
-            # We can't easily parallelize these since different chunks
-            # might contain the same event. :(
-
-            # NB: Assumes that we are only persisting events for one room
-            # at a time.
-
-            # map room_id->list[event_ids] giving the new forward
-            # extremities in each room
-            new_forward_extremeties = {}
-
-            # map room_id->(type,state_key)->event_id tracking the full
-            # state in each room after adding these events.
-            # This is simply used to prefill the get_current_state_ids
-            # cache
-            current_state_for_room = {}
-
-            # map room_id->(to_delete, to_insert) where to_delete is a list
-            # of type/state keys to remove from current state, and to_insert
-            # is a map (type,key)->event_id giving the state delta in each
-            # room
-            state_delta_for_room = {}
-
-            if not backfilled:
-                with Measure(self._clock, "_calculate_state_and_extrem"):
-                    # Work out the new "current state" for each room.
-                    # We do this by working out what the new extremities are and then
-                    # calculating the state from that.
-                    events_by_room = {}
-                    for event, context in chunk:
-                        events_by_room.setdefault(event.room_id, []).append(
-                            (event, context)
-                        )
-
-                    for room_id, ev_ctx_rm in iteritems(events_by_room):
-                        latest_event_ids = yield self.get_latest_event_ids_in_room(
-                            room_id
-                        )
-                        new_latest_event_ids = yield self._calculate_new_extremities(
-                            room_id, ev_ctx_rm, latest_event_ids
-                        )
-
-                        latest_event_ids = set(latest_event_ids)
-                        if new_latest_event_ids == latest_event_ids:
-                            # No change in extremities, so no change in state
-                            continue
-
-                        # there should always be at least one forward extremity.
-                        # (except during the initial persistence of the send_join
-                        # results, in which case there will be no existing
-                        # extremities, so we'll `continue` above and skip this bit.)
-                        assert new_latest_event_ids, "No forward extremities left!"
-
-                        new_forward_extremeties[room_id] = new_latest_event_ids
-
-                        len_1 = (
-                            len(latest_event_ids) == 1
-                            and len(new_latest_event_ids) == 1
-                        )
-                        if len_1:
-                            all_single_prev_not_state = all(
-                                len(event.prev_event_ids()) == 1
-                                and not event.is_state()
-                                for event, ctx in ev_ctx_rm
-                            )
-                            # Don't bother calculating state if they're just
-                            # a long chain of single ancestor non-state events.
-                            if all_single_prev_not_state:
-                                continue
-
-                        state_delta_counter.inc()
-                        if len(new_latest_event_ids) == 1:
-                            state_delta_single_event_counter.inc()
-
-                            # This is a fairly handwavey check to see if we could
-                            # have guessed what the delta would have been when
-                            # processing one of these events.
-                            # What we're interested in is if the latest extremities
-                            # were the same when we created the event as they are
-                            # now. When this server creates a new event (as opposed
-                            # to receiving it over federation) it will use the
-                            # forward extremities as the prev_events, so we can
-                            # guess this by looking at the prev_events and checking
-                            # if they match the current forward extremities.
-                            for ev, _ in ev_ctx_rm:
-                                prev_event_ids = set(ev.prev_event_ids())
-                                if latest_event_ids == prev_event_ids:
-                                    state_delta_reuse_delta_counter.inc()
-                                    break
-
-                        logger.info("Calculating state delta for room %s", room_id)
-                        with Measure(
-                            self._clock, "persist_events.get_new_state_after_events"
-                        ):
-                            res = yield self._get_new_state_after_events(
-                                room_id,
-                                ev_ctx_rm,
-                                latest_event_ids,
-                                new_latest_event_ids,
-                            )
-                            current_state, delta_ids = res
-
-                        # If either are not None then there has been a change,
-                        # and we need to work out the delta (or use that
-                        # given)
-                        if delta_ids is not None:
-                            # If there is a delta we know that we've
-                            # only added or replaced state, never
-                            # removed keys entirely.
-                            state_delta_for_room[room_id] = ([], delta_ids)
-                        elif current_state is not None:
-                            with Measure(
-                                self._clock, "persist_events.calculate_state_delta"
-                            ):
-                                delta = yield self._calculate_state_delta(
-                                    room_id, current_state
-                                )
-                            state_delta_for_room[room_id] = delta
-
-                        # If we have the current_state then lets prefill
-                        # the cache with it.
-                        if current_state is not None:
-                            current_state_for_room[room_id] = current_state
-
-            # We want to calculate the stream orderings as late as possible, as
-            # we only notify after all events with a lesser stream ordering have
-            # been persisted. I.e. if we spend 10s inside the with block then
-            # that will delay all subsequent events from being notified about.
-            # Hence why we do it down here rather than wrapping the entire
-            # function.
-            #
-            # Its safe to do this after calculating the state deltas etc as we
-            # only need to protect the *persistence* of the events. This is to
-            # ensure that queries of the form "fetch events since X" don't
-            # return events and stream positions after events that are still in
-            # flight, as otherwise subsequent requests "fetch event since Y"
-            # will not return those events.
-            #
-            # Note: Multiple instances of this function cannot be in flight at
-            # the same time for the same room.
-            if backfilled:
-                stream_ordering_manager = self._backfill_id_gen.get_next_mult(
-                    len(chunk)
-                )
-            else:
-                stream_ordering_manager = self._stream_id_gen.get_next_mult(len(chunk))
-
-            with stream_ordering_manager as stream_orderings:
-                for (event, context), stream in zip(chunk, stream_orderings):
-                    event.internal_metadata.stream_ordering = stream
-
-                yield self.runInteraction(
-                    "persist_events",
-                    self._persist_events_txn,
-                    events_and_contexts=chunk,
-                    backfilled=backfilled,
-                    delete_existing=delete_existing,
-                    state_delta_for_room=state_delta_for_room,
-                    new_forward_extremeties=new_forward_extremeties,
-                )
-                persist_event_counter.inc(len(chunk))
-
-                if not backfilled:
-                    # backfilled events have negative stream orderings, so we don't
-                    # want to set the event_persisted_position to that.
-                    synapse.metrics.event_persisted_position.set(
-                        chunk[-1][0].internal_metadata.stream_ordering
-                    )
-
-                for event, context in chunk:
-                    if context.app_service:
-                        origin_type = "local"
-                        origin_entity = context.app_service.id
-                    elif self.hs.is_mine_id(event.sender):
-                        origin_type = "local"
-                        origin_entity = "*client*"
-                    else:
-                        origin_type = "remote"
-                        origin_entity = get_domain_from_id(event.sender)
-
-                    event_counter.labels(event.type, origin_type, origin_entity).inc()
-
-                for room_id, new_state in iteritems(current_state_for_room):
-                    self.get_current_state_ids.prefill((room_id,), new_state)
-
-                for room_id, latest_event_ids in iteritems(new_forward_extremeties):
-                    self.get_latest_event_ids_in_room.prefill(
-                        (room_id,), list(latest_event_ids)
-                    )
-
-    @defer.inlineCallbacks
-    def _calculate_new_extremities(self, room_id, event_contexts, latest_event_ids):
-        """Calculates the new forward extremities for a room given events to
-        persist.
-
-        Assumes that we are only persisting events for one room at a time.
-        """
-
-        # we're only interested in new events which aren't outliers and which aren't
-        # being rejected.
-        new_events = [
-            event
-            for event, ctx in event_contexts
-            if not event.internal_metadata.is_outlier()
-            and not ctx.rejected
-            and not event.internal_metadata.is_soft_failed()
-        ]
-
-        latest_event_ids = set(latest_event_ids)
-
-        # start with the existing forward extremities
-        result = set(latest_event_ids)
-
-        # add all the new events to the list
-        result.update(event.event_id for event in new_events)
-
-        # Now remove all events which are prev_events of any of the new events
-        result.difference_update(
-            e_id for event in new_events for e_id in event.prev_event_ids()
-        )
-
-        # Remove any events which are prev_events of any existing events.
-        existing_prevs = yield self._get_events_which_are_prevs(result)
-        result.difference_update(existing_prevs)
-
-        # Finally handle the case where the new events have soft-failed prev
-        # events. If they do we need to remove them and their prev events,
-        # otherwise we end up with dangling extremities.
-        existing_prevs = yield self._get_prevs_before_rejected(
-            e_id for event in new_events for e_id in event.prev_event_ids()
-        )
-        result.difference_update(existing_prevs)
-
-        # We only update metrics for events that change forward extremities
-        # (e.g. we ignore backfill/outliers/etc)
-        if result != latest_event_ids:
-            forward_extremities_counter.observe(len(result))
-            stale = latest_event_ids & result
-            stale_forward_extremities_counter.observe(len(stale))
-
-        return result
-
-    @defer.inlineCallbacks
-    def _get_events_which_are_prevs(self, event_ids):
-        """Filter the supplied list of event_ids to get those which are prev_events of
-        existing (non-outlier/rejected) events.
-
-        Args:
-            event_ids (Iterable[str]): event ids to filter
-
-        Returns:
-            Deferred[List[str]]: filtered event ids
-        """
-        results = []
-
-        def _get_events_which_are_prevs_txn(txn, batch):
-            sql = """
-            SELECT prev_event_id, internal_metadata
-            FROM event_edges
-                INNER JOIN events USING (event_id)
-                LEFT JOIN rejections USING (event_id)
-                LEFT JOIN event_json USING (event_id)
-            WHERE
-                NOT events.outlier
-                AND rejections.event_id IS NULL
-                AND
-            """
-
-            clause, args = make_in_list_sql_clause(
-                self.database_engine, "prev_event_id", batch
-            )
-
-            txn.execute(sql + clause, args)
-            results.extend(r[0] for r in txn if not json.loads(r[1]).get("soft_failed"))
-
-        for chunk in batch_iter(event_ids, 100):
-            yield self.runInteraction(
-                "_get_events_which_are_prevs", _get_events_which_are_prevs_txn, chunk
-            )
-
-        return results
-
-    @defer.inlineCallbacks
-    def _get_prevs_before_rejected(self, event_ids):
-        """Get soft-failed ancestors to remove from the extremities.
-
-        Given a set of events, find all those that have been soft-failed or
-        rejected. Returns those soft failed/rejected events and their prev
-        events (whether soft-failed/rejected or not), and recurses up the
-        prev-event graph until it finds no more soft-failed/rejected events.
-
-        This is used to find extremities that are ancestors of new events, but
-        are separated by soft failed events.
-
-        Args:
-            event_ids (Iterable[str]): Events to find prev events for. Note
-                that these must have already been persisted.
-
-        Returns:
-            Deferred[set[str]]
-        """
-
-        # The set of event_ids to return. This includes all soft-failed events
-        # and their prev events.
-        existing_prevs = set()
-
-        def _get_prevs_before_rejected_txn(txn, batch):
-            to_recursively_check = batch
-
-            while to_recursively_check:
-                sql = """
-                SELECT
-                    event_id, prev_event_id, internal_metadata,
-                    rejections.event_id IS NOT NULL
-                FROM event_edges
-                    INNER JOIN events USING (event_id)
-                    LEFT JOIN rejections USING (event_id)
-                    LEFT JOIN event_json USING (event_id)
-                WHERE
-                    NOT events.outlier
-                    AND
-                """
-
-                clause, args = make_in_list_sql_clause(
-                    self.database_engine, "event_id", to_recursively_check
-                )
-
-                txn.execute(sql + clause, args)
-                to_recursively_check = []
-
-                for event_id, prev_event_id, metadata, rejected in txn:
-                    if prev_event_id in existing_prevs:
-                        continue
-
-                    soft_failed = json.loads(metadata).get("soft_failed")
-                    if soft_failed or rejected:
-                        to_recursively_check.append(prev_event_id)
-                        existing_prevs.add(prev_event_id)
-
-        for chunk in batch_iter(event_ids, 100):
-            yield self.runInteraction(
-                "_get_prevs_before_rejected", _get_prevs_before_rejected_txn, chunk
-            )
-
-        return existing_prevs
-
-    @defer.inlineCallbacks
-    def _get_new_state_after_events(
-        self, room_id, events_context, old_latest_event_ids, new_latest_event_ids
-    ):
-        """Calculate the current state dict after adding some new events to
-        a room
-
-        Args:
-            room_id (str):
-                room to which the events are being added. Used for logging etc
-
-            events_context (list[(EventBase, EventContext)]):
-                events and contexts which are being added to the room
-
-            old_latest_event_ids (iterable[str]):
-                the old forward extremities for the room.
-
-            new_latest_event_ids (iterable[str]):
-                the new forward extremities for the room.
-
-        Returns:
-            Deferred[tuple[dict[(str,str), str]|None, dict[(str,str), str]|None]]:
-            Returns a tuple of two state maps, the first being the full new current
-            state and the second being the delta to the existing current state.
-            If both are None then there has been no change.
-
-            If there has been a change then we only return the delta if its
-            already been calculated. Conversely if we do know the delta then
-            the new current state is only returned if we've already calculated
-            it.
-        """
-        # map from state_group to ((type, key) -> event_id) state map
-        state_groups_map = {}
-
-        # Map from (prev state group, new state group) -> delta state dict
-        state_group_deltas = {}
-
-        for ev, ctx in events_context:
-            if ctx.state_group is None:
-                # This should only happen for outlier events.
-                if not ev.internal_metadata.is_outlier():
-                    raise Exception(
-                        "Context for new event %s has no state "
-                        "group" % (ev.event_id,)
-                    )
-                continue
-
-            if ctx.state_group in state_groups_map:
-                continue
-
-            # We're only interested in pulling out state that has already
-            # been cached in the context. We'll pull stuff out of the DB later
-            # if necessary.
-            current_state_ids = ctx.get_cached_current_state_ids()
-            if current_state_ids is not None:
-                state_groups_map[ctx.state_group] = current_state_ids
-
-            if ctx.prev_group:
-                state_group_deltas[(ctx.prev_group, ctx.state_group)] = ctx.delta_ids
-
-        # We need to map the event_ids to their state groups. First, let's
-        # check if the event is one we're persisting, in which case we can
-        # pull the state group from its context.
-        # Otherwise we need to pull the state group from the database.
-
-        # Set of events we need to fetch groups for. (We know none of the old
-        # extremities are going to be in events_context).
-        missing_event_ids = set(old_latest_event_ids)
-
-        event_id_to_state_group = {}
-        for event_id in new_latest_event_ids:
-            # First search in the list of new events we're adding.
-            for ev, ctx in events_context:
-                if event_id == ev.event_id and ctx.state_group is not None:
-                    event_id_to_state_group[event_id] = ctx.state_group
-                    break
-            else:
-                # If we couldn't find it, then we'll need to pull
-                # the state from the database
-                missing_event_ids.add(event_id)
-
-        if missing_event_ids:
-            # Now pull out the state groups for any missing events from DB
-            event_to_groups = yield self._get_state_group_for_events(missing_event_ids)
-            event_id_to_state_group.update(event_to_groups)
-
-        # State groups of old_latest_event_ids
-        old_state_groups = set(
-            event_id_to_state_group[evid] for evid in old_latest_event_ids
-        )
-
-        # State groups of new_latest_event_ids
-        new_state_groups = set(
-            event_id_to_state_group[evid] for evid in new_latest_event_ids
-        )
-
-        # If they old and new groups are the same then we don't need to do
-        # anything.
-        if old_state_groups == new_state_groups:
-            return None, None
-
-        if len(new_state_groups) == 1 and len(old_state_groups) == 1:
-            # If we're going from one state group to another, lets check if
-            # we have a delta for that transition. If we do then we can just
-            # return that.
-
-            new_state_group = next(iter(new_state_groups))
-            old_state_group = next(iter(old_state_groups))
-
-            delta_ids = state_group_deltas.get((old_state_group, new_state_group), None)
-            if delta_ids is not None:
-                # We have a delta from the existing to new current state,
-                # so lets just return that. If we happen to already have
-                # the current state in memory then lets also return that,
-                # but it doesn't matter if we don't.
-                new_state = state_groups_map.get(new_state_group)
-                return new_state, delta_ids
-
-        # Now that we have calculated new_state_groups we need to get
-        # their state IDs so we can resolve to a single state set.
-        missing_state = new_state_groups - set(state_groups_map)
-        if missing_state:
-            group_to_state = yield self._get_state_for_groups(missing_state)
-            state_groups_map.update(group_to_state)
-
-        if len(new_state_groups) == 1:
-            # If there is only one state group, then we know what the current
-            # state is.
-            return state_groups_map[new_state_groups.pop()], None
-
-        # Ok, we need to defer to the state handler to resolve our state sets.
-
-        state_groups = {sg: state_groups_map[sg] for sg in new_state_groups}
-
-        events_map = {ev.event_id: ev for ev, _ in events_context}
-
-        # We need to get the room version, which is in the create event.
-        # Normally that'd be in the database, but its also possible that we're
-        # currently trying to persist it.
-        room_version = None
-        for ev, _ in events_context:
-            if ev.type == EventTypes.Create and ev.state_key == "":
-                room_version = ev.content.get("room_version", "1")
-                break
-
-        if not room_version:
-            room_version = yield self.get_room_version(room_id)
-
-        logger.debug("calling resolve_state_groups from preserve_events")
-        res = yield self._state_resolution_handler.resolve_state_groups(
-            room_id,
-            room_version,
-            state_groups,
-            events_map,
-            state_res_store=StateResolutionStore(self),
-        )
-
-        return res.state, None
-
-    @defer.inlineCallbacks
-    def _calculate_state_delta(self, room_id, current_state):
-        """Calculate the new state deltas for a room.
-
-        Assumes that we are only persisting events for one room at a time.
-
-        Returns:
-            tuple[list, dict] (to_delete, to_insert): where to_delete are the
-            type/state_keys to remove from current_state_events and `to_insert`
-            are the updates to current_state_events.
-        """
-        existing_state = yield self.get_current_state_ids(room_id)
-
-        to_delete = [key for key in existing_state if key not in current_state]
-
-        to_insert = {
-            key: ev_id
-            for key, ev_id in iteritems(current_state)
-            if ev_id != existing_state.get(key)
-        }
-
-        return to_delete, to_insert
-
-    @log_function
-    def _persist_events_txn(
-        self,
-        txn,
-        events_and_contexts,
-        backfilled,
-        delete_existing=False,
-        state_delta_for_room={},
-        new_forward_extremeties={},
-    ):
-        """Insert some number of room events into the necessary database tables.
-
-        Rejected events are only inserted into the events table, the events_json table,
-        and the rejections table. Things reading from those table will need to check
-        whether the event was rejected.
-
-        Args:
-            txn (twisted.enterprise.adbapi.Connection): db connection
-            events_and_contexts (list[(EventBase, EventContext)]):
-                events to persist
-            backfilled (bool): True if the events were backfilled
-            delete_existing (bool): True to purge existing table rows for the
-                events from the database. This is useful when retrying due to
-                IntegrityError.
-            state_delta_for_room (dict[str, (list, dict)]):
-                The current-state delta for each room. For each room, a tuple
-                (to_delete, to_insert), being a list of type/state keys to be
-                removed from the current state, and a state set to be added to
-                the current state.
-            new_forward_extremeties (dict[str, list[str]]):
-                The new forward extremities for each room. For each room, a
-                list of the event ids which are the forward extremities.
-
-        """
-        all_events_and_contexts = events_and_contexts
-
-        min_stream_order = events_and_contexts[0][0].internal_metadata.stream_ordering
-        max_stream_order = events_and_contexts[-1][0].internal_metadata.stream_ordering
-
-        self._update_forward_extremities_txn(
-            txn,
-            new_forward_extremities=new_forward_extremeties,
-            max_stream_order=max_stream_order,
-        )
-
-        # Ensure that we don't have the same event twice.
-        events_and_contexts = self._filter_events_and_contexts_for_duplicates(
-            events_and_contexts
-        )
-
-        self._update_room_depths_txn(
-            txn, events_and_contexts=events_and_contexts, backfilled=backfilled
-        )
-
-        # _update_outliers_txn filters out any events which have already been
-        # persisted, and returns the filtered list.
-        events_and_contexts = self._update_outliers_txn(
-            txn, events_and_contexts=events_and_contexts
-        )
-
-        # From this point onwards the events are only events that we haven't
-        # seen before.
-
-        if delete_existing:
-            # For paranoia reasons, we go and delete all the existing entries
-            # for these events so we can reinsert them.
-            # This gets around any problems with some tables already having
-            # entries.
-            self._delete_existing_rows_txn(txn, events_and_contexts=events_and_contexts)
-
-        self._store_event_txn(txn, events_and_contexts=events_and_contexts)
-
-        # Insert into event_to_state_groups.
-        self._store_event_state_mappings_txn(txn, events_and_contexts)
-
-        # We want to store event_auth mappings for rejected events, as they're
-        # used in state res v2.
-        # This is only necessary if the rejected event appears in an accepted
-        # event's auth chain, but its easier for now just to store them (and
-        # it doesn't take much storage compared to storing the entire event
-        # anyway).
-        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_event_ids()
-                if event.is_state()
-            ],
-        )
-
-        # _store_rejected_events_txn filters out any events which were
-        # rejected, and returns the filtered list.
-        events_and_contexts = self._store_rejected_events_txn(
-            txn, events_and_contexts=events_and_contexts
-        )
-
-        # From this point onwards the events are only ones that weren't
-        # rejected.
-
-        self._update_metadata_tables_txn(
-            txn,
-            events_and_contexts=events_and_contexts,
-            all_events_and_contexts=all_events_and_contexts,
-            backfilled=backfilled,
-        )
-
-        # We call this last as it assumes we've inserted the events into
-        # room_memberships, where applicable.
-        self._update_current_state_txn(txn, state_delta_for_room, min_stream_order)
-
-    def _update_current_state_txn(self, txn, state_delta_by_room, stream_id):
-        for room_id, current_state_tuple in iteritems(state_delta_by_room):
-            to_delete, to_insert = current_state_tuple
-
-            # First we add entries to the current_state_delta_stream. We
-            # do this before updating the current_state_events table so
-            # that we can use it to calculate the `prev_event_id`. (This
-            # allows us to not have to pull out the existing state
-            # unnecessarily).
-            #
-            # The stream_id for the update is chosen to be the minimum of the stream_ids
-            # for the batch of the events that we are persisting; that means we do not
-            # end up in a situation where workers see events before the
-            # current_state_delta updates.
-            #
-            sql = """
-                INSERT INTO current_state_delta_stream
-                (stream_id, room_id, type, state_key, event_id, prev_event_id)
-                SELECT ?, ?, ?, ?, ?, (
-                    SELECT event_id FROM current_state_events
-                    WHERE room_id = ? AND type = ? AND state_key = ?
-                )
-            """
-            txn.executemany(
-                sql,
-                (
-                    (
-                        stream_id,
-                        room_id,
-                        etype,
-                        state_key,
-                        None,
-                        room_id,
-                        etype,
-                        state_key,
-                    )
-                    for etype, state_key in to_delete
-                    # We sanity check that we're deleting rather than updating
-                    if (etype, state_key) not in to_insert
-                ),
-            )
-            txn.executemany(
-                sql,
-                (
-                    (
-                        stream_id,
-                        room_id,
-                        etype,
-                        state_key,
-                        ev_id,
-                        room_id,
-                        etype,
-                        state_key,
-                    )
-                    for (etype, state_key), ev_id in iteritems(to_insert)
-                ),
-            )
-
-            # Now we actually update the current_state_events table
-
-            txn.executemany(
-                "DELETE FROM current_state_events"
-                " WHERE room_id = ? AND type = ? AND state_key = ?",
-                (
-                    (room_id, etype, state_key)
-                    for etype, state_key in itertools.chain(to_delete, to_insert)
-                ),
-            )
-
-            # We include the membership in the current state table, hence we do
-            # a lookup when we insert. This assumes that all events have already
-            # been inserted into room_memberships.
-            txn.executemany(
-                """INSERT INTO current_state_events
-                    (room_id, type, state_key, event_id, membership)
-                VALUES (?, ?, ?, ?, (SELECT membership FROM room_memberships WHERE event_id = ?))
-                """,
-                [
-                    (room_id, key[0], key[1], ev_id, ev_id)
-                    for key, ev_id in iteritems(to_insert)
-                ],
-            )
-
-            txn.call_after(
-                self._curr_state_delta_stream_cache.entity_has_changed,
-                room_id,
-                stream_id,
-            )
-
-            # Invalidate the various caches
-
-            # Figure out the changes of membership to invalidate the
-            # `get_rooms_for_user` cache.
-            # We find out which membership events we may have deleted
-            # and which we have added, then we invlidate the caches for all
-            # those users.
-            members_changed = set(
-                state_key
-                for ev_type, state_key in itertools.chain(to_delete, to_insert)
-                if ev_type == EventTypes.Member
-            )
-
-            for member in members_changed:
-                txn.call_after(
-                    self.get_rooms_for_user_with_stream_ordering.invalidate, (member,)
-                )
-
-            self._invalidate_state_caches_and_stream(txn, room_id, members_changed)
-
-    def _update_forward_extremities_txn(
-        self, txn, new_forward_extremities, max_stream_order
-    ):
-        for room_id, new_extrem in iteritems(new_forward_extremities):
-            self._simple_delete_txn(
-                txn, table="event_forward_extremities", keyvalues={"room_id": room_id}
-            )
-            txn.call_after(self.get_latest_event_ids_in_room.invalidate, (room_id,))
-
-        self._simple_insert_many_txn(
-            txn,
-            table="event_forward_extremities",
-            values=[
-                {"event_id": ev_id, "room_id": room_id}
-                for room_id, new_extrem in iteritems(new_forward_extremities)
-                for ev_id in new_extrem
-            ],
-        )
-        # We now insert into stream_ordering_to_exterm a mapping from room_id,
-        # new stream_ordering to new forward extremeties in the room.
-        # This allows us to later efficiently look up the forward extremeties
-        # for a room before a given stream_ordering
-        self._simple_insert_many_txn(
-            txn,
-            table="stream_ordering_to_exterm",
-            values=[
-                {
-                    "room_id": room_id,
-                    "event_id": event_id,
-                    "stream_ordering": max_stream_order,
-                }
-                for room_id, new_extrem in iteritems(new_forward_extremities)
-                for event_id in new_extrem
-            ],
-        )
-
-    @classmethod
-    def _filter_events_and_contexts_for_duplicates(cls, events_and_contexts):
-        """Ensure that we don't have the same event twice.
-
-        Pick the earliest non-outlier if there is one, else the earliest one.
-
-        Args:
-            events_and_contexts (list[(EventBase, EventContext)]):
-        Returns:
-            list[(EventBase, EventContext)]: filtered list
-        """
-        new_events_and_contexts = OrderedDict()
-        for event, context in events_and_contexts:
-            prev_event_context = new_events_and_contexts.get(event.event_id)
-            if prev_event_context:
-                if not event.internal_metadata.is_outlier():
-                    if prev_event_context[0].internal_metadata.is_outlier():
-                        # To ensure correct ordering we pop, as OrderedDict is
-                        # ordered by first insertion.
-                        new_events_and_contexts.pop(event.event_id, None)
-                        new_events_and_contexts[event.event_id] = (event, context)
-            else:
-                new_events_and_contexts[event.event_id] = (event, context)
-        return list(new_events_and_contexts.values())
-
-    def _update_room_depths_txn(self, txn, events_and_contexts, backfilled):
-        """Update min_depth for each room
-
-        Args:
-            txn (twisted.enterprise.adbapi.Connection): db connection
-            events_and_contexts (list[(EventBase, EventContext)]): events
-                we are persisting
-            backfilled (bool): True if the events were backfilled
-        """
-        depth_updates = {}
-        for event, context in events_and_contexts:
-            # Remove the any existing cache entries for the event_ids
-            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,
-                )
-
-            if not event.internal_metadata.is_outlier() and not context.rejected:
-                depth_updates[event.room_id] = max(
-                    event.depth, depth_updates.get(event.room_id, event.depth)
-                )
-
-        for room_id, depth in iteritems(depth_updates):
-            self._update_min_depth_for_room_txn(txn, room_id, depth)
-
-    def _update_outliers_txn(self, txn, events_and_contexts):
-        """Update any outliers with new event info.
-
-        This turns outliers into ex-outliers (unless the new event was
-        rejected).
-
-        Args:
-            txn (twisted.enterprise.adbapi.Connection): db connection
-            events_and_contexts (list[(EventBase, EventContext)]): events
-                we are persisting
-
-        Returns:
-            list[(EventBase, EventContext)] new list, without events which
-            are already in the events table.
-        """
-        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}
-
-        to_remove = set()
-        for event, context in events_and_contexts:
-            if event.event_id not in have_persisted:
-                continue
-
-            to_remove.add(event)
-
-            if context.rejected:
-                # If the event is rejected then we don't care if the event
-                # was an outlier or not.
-                continue
-
-            outlier_persisted = have_persisted[event.event_id]
-            if not event.internal_metadata.is_outlier() and outlier_persisted:
-                # We received a copy of an event that we had already stored as
-                # an outlier in the database. We now have some state at that
-                # so we need to update the state_groups table with that state.
-
-                # insert into event_to_state_groups.
-                try:
-                    self._store_event_state_mappings_txn(txn, ((event, context),))
-                except Exception:
-                    logger.exception("")
-                    raise
-
-                metadata_json = encode_json(event.internal_metadata.get_dict())
-
-                sql = (
-                    "UPDATE event_json SET internal_metadata = ?" " WHERE event_id = ?"
-                )
-                txn.execute(sql, (metadata_json, event.event_id))
-
-                # Add an entry to the ex_outlier_stream table to replicate the
-                # change in outlier status to our workers.
-                stream_order = event.internal_metadata.stream_ordering
-                state_group_id = context.state_group
-                self._simple_insert_txn(
-                    txn,
-                    table="ex_outlier_stream",
-                    values={
-                        "event_stream_ordering": stream_order,
-                        "event_id": event.event_id,
-                        "state_group": state_group_id,
-                    },
-                )
-
-                sql = "UPDATE events SET outlier = ?" " WHERE event_id = ?"
-                txn.execute(sql, (False, event.event_id))
-
-                # Update the event_backward_extremities table now that this
-                # event isn't an outlier any more.
-                self._update_backward_extremeties(txn, [event])
-
-        return [ec for ec in events_and_contexts if ec[0] not in to_remove]
-
-    @classmethod
-    def _delete_existing_rows_txn(cls, txn, events_and_contexts):
-        if not events_and_contexts:
-            # nothing to do here
-            return
-
-        logger.info("Deleting existing")
-
-        for table in (
-            "events",
-            "event_auth",
-            "event_json",
-            "event_edges",
-            "event_forward_extremities",
-            "event_reference_hashes",
-            "event_search",
-            "event_to_state_groups",
-            "local_invites",
-            "state_events",
-            "rejections",
-            "redactions",
-            "room_memberships",
-        ):
-            txn.executemany(
-                "DELETE FROM %s WHERE event_id = ?" % (table,),
-                [(ev.event_id,) for ev, _ in events_and_contexts],
-            )
-
-        for table in ("event_push_actions",):
-            txn.executemany(
-                "DELETE FROM %s WHERE room_id = ? AND event_id = ?" % (table,),
-                [(ev.room_id, ev.event_id) for ev, _ in events_and_contexts],
-            )
-
-    def _store_event_txn(self, txn, events_and_contexts):
-        """Insert new events into the event and event_json tables
-
-        Args:
-            txn (twisted.enterprise.adbapi.Connection): db connection
-            events_and_contexts (list[(EventBase, EventContext)]): events
-                we are persisting
-        """
-
-        if not events_and_contexts:
-            # nothing to do here
-            return
-
-        def event_dict(event):
-            d = event.get_dict()
-            d.pop("redacted", None)
-            d.pop("redacted_because", None)
-            return d
-
-        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()
-                    ),
-                    "json": encode_json(event_dict(event)),
-                    "format_version": event.format_version,
-                }
-                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(),
-                    "origin_server_ts": int(event.origin_server_ts),
-                    "received_ts": self._clock.time_msec(),
-                    "sender": event.sender,
-                    "contains_url": (
-                        "url" in event.content
-                        and isinstance(event.content["url"], text_type)
-                    ),
-                }
-                for event, _ in events_and_contexts
-            ],
-        )
-
-        for event, _ in events_and_contexts:
-            if not event.internal_metadata.is_redacted():
-                # If we're persisting an unredacted event we go and ensure
-                # that we mark any redactions that reference this event as
-                # requiring censoring.
-                self._simple_update_txn(
-                    txn,
-                    table="redactions",
-                    keyvalues={"redacts": event.event_id},
-                    updatevalues={"have_censored": False},
-                )
-
-    def _store_rejected_events_txn(self, txn, events_and_contexts):
-        """Add rows to the 'rejections' table for received events which were
-        rejected
-
-        Args:
-            txn (twisted.enterprise.adbapi.Connection): db connection
-            events_and_contexts (list[(EventBase, EventContext)]): events
-                we are persisting
-
-        Returns:
-            list[(EventBase, EventContext)] new list, without the rejected
-                events.
-        """
-        # Remove the rejected events from the list now that we've added them
-        # to the events table and the events_json table.
-        to_remove = set()
-        for event, context in events_and_contexts:
-            if context.rejected:
-                # Insert the event_id into the rejections table
-                self._store_rejections_txn(txn, event.event_id, context.rejected)
-                to_remove.add(event)
-
-        return [ec for ec in events_and_contexts if ec[0] not in to_remove]
-
-    def _update_metadata_tables_txn(
-        self, txn, events_and_contexts, all_events_and_contexts, backfilled
-    ):
-        """Update all the miscellaneous tables for new events
-
-        Args:
-            txn (twisted.enterprise.adbapi.Connection): db connection
-            events_and_contexts (list[(EventBase, EventContext)]): events
-                we are persisting
-            all_events_and_contexts (list[(EventBase, EventContext)]): all
-                events that we were going to persist. This includes events
-                we've already persisted, etc, that wouldn't appear in
-                events_and_context.
-            backfilled (bool): True if the events were backfilled
-        """
-
-        # Insert all the push actions into the event_push_actions table.
-        self._set_push_actions_for_event_and_users_txn(
-            txn,
-            events_and_contexts=events_and_contexts,
-            all_events_and_contexts=all_events_and_contexts,
-        )
-
-        if not events_and_contexts:
-            # nothing to do here
-            return
-
-        for event, context in events_and_contexts:
-            if event.type == EventTypes.Redaction and event.redacts is not None:
-                # Remove the entries in the event_push_actions table for the
-                # redacted event.
-                self._remove_push_actions_for_event_id_txn(
-                    txn, event.room_id, event.redacts
-                )
-
-                # Remove from relations table.
-                self._handle_redaction(txn, event.redacts)
-
-        # Update the event_forward_extremities, event_backward_extremities and
-        # event_edges tables.
-        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:
-                # Insert into the event_search table.
-                self._store_room_name_txn(txn, event)
-            elif event.type == EventTypes.Topic:
-                # Insert into the event_search table.
-                self._store_room_topic_txn(txn, event)
-            elif event.type == EventTypes.Message:
-                # Insert into the event_search table.
-                self._store_room_message_txn(txn, event)
-            elif event.type == EventTypes.Redaction:
-                # Insert into the redactions table.
-                self._store_redaction(txn, event)
-
-            self._handle_event_relations(txn, event)
-
-        # Insert into the room_memberships table.
-        self._store_room_members_txn(
-            txn,
-            [
-                event
-                for event, _ in events_and_contexts
-                if event.type == EventTypes.Member
-            ],
-            backfilled=backfilled,
-        )
-
-        # Insert event_reference_hashes table.
-        self._store_event_reference_hashes_txn(
-            txn, [event for event, _ in events_and_contexts]
-        )
-
-        state_events_and_contexts = [
-            ec for ec in events_and_contexts if ec[0].is_state()
-        ]
-
-        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)
-
-        # Prefill the event cache
-        self._add_to_cache(txn, events_and_contexts)
-
-    def _add_to_cache(self, txn, events_and_contexts):
-        to_prefill = []
-
-        rows = []
-        N = 200
-        for i in range(0, len(events_and_contexts), N):
-            ev_map = {e[0].event_id: e[0] for e in events_and_contexts[i : i + N]}
-            if not ev_map:
-                break
-
-            sql = (
-                "SELECT "
-                " e.event_id as event_id, "
-                " r.redacts as redacts,"
-                " rej.event_id as rejects "
-                " FROM events as e"
-                " LEFT JOIN rejections as rej USING (event_id)"
-                " LEFT JOIN redactions as r ON e.event_id = r.redacts"
-                " WHERE "
-            )
-
-            clause, args = make_in_list_sql_clause(
-                self.database_engine, "e.event_id", list(ev_map)
-            )
-
-            txn.execute(sql + clause, args)
-            rows = self.cursor_to_dict(txn)
-            for row in rows:
-                event = ev_map[row["event_id"]]
-                if not row["rejects"] and not row["redacts"]:
-                    to_prefill.append(
-                        _EventCacheEntry(event=event, redacted_event=None)
-                    )
-
-        def prefill():
-            for cache_entry in to_prefill:
-                self._get_event_cache.prefill((cache_entry[0].event_id,), cache_entry)
-
-        txn.call_after(prefill)
-
-    def _store_redaction(self, txn, event):
-        # invalidate the cache for the redacted event
-        txn.call_after(self._invalidate_get_event_cache, event.redacts)
-
-        self._simple_insert_txn(
-            txn,
-            table="redactions",
-            values={
-                "event_id": event.event_id,
-                "redacts": event.redacts,
-                "received_ts": self._clock.time_msec(),
-            },
-        )
-
-    @defer.inlineCallbacks
-    def _censor_redactions(self):
-        """Censors all redactions older than the configured period that haven't
-        been censored yet.
-
-        By censor we mean update the event_json table with the redacted event.
-
-        Returns:
-            Deferred
-        """
-
-        if self.hs.config.redaction_retention_period is None:
-            return
-
-        before_ts = self._clock.time_msec() - self.hs.config.redaction_retention_period
-
-        # We fetch all redactions that:
-        #   1. point to an event we have,
-        #   2. has a received_ts from before the cut off, and
-        #   3. we haven't yet censored.
-        #
-        # This is limited to 100 events to ensure that we don't try and do too
-        # much at once. We'll get called again so this should eventually catch
-        # up.
-        sql = """
-            SELECT redactions.event_id, redacts FROM redactions
-            LEFT JOIN events AS original_event ON (
-                redacts = original_event.event_id
-            )
-            WHERE NOT have_censored
-            AND redactions.received_ts <= ?
-            ORDER BY redactions.received_ts ASC
-            LIMIT ?
-        """
-
-        rows = yield self._execute(
-            "_censor_redactions_fetch", None, sql, before_ts, 100
-        )
-
-        updates = []
-
-        for redaction_id, event_id in rows:
-            redaction_event = yield self.get_event(redaction_id, allow_none=True)
-            original_event = yield self.get_event(
-                event_id, allow_rejected=True, allow_none=True
-            )
-
-            # The SQL above ensures that we have both the redaction and
-            # original event, so if the `get_event` calls return None it
-            # means that the redaction wasn't allowed. Either way we know that
-            # the result won't change so we mark the fact that we've checked.
-            if (
-                redaction_event
-                and original_event
-                and original_event.internal_metadata.is_redacted()
-            ):
-                # Redaction was allowed
-                pruned_json = encode_json(prune_event_dict(original_event.get_dict()))
-            else:
-                # Redaction wasn't allowed
-                pruned_json = None
-
-            updates.append((redaction_id, event_id, pruned_json))
-
-        def _update_censor_txn(txn):
-            for redaction_id, event_id, pruned_json in updates:
-                if pruned_json:
-                    self._simple_update_one_txn(
-                        txn,
-                        table="event_json",
-                        keyvalues={"event_id": event_id},
-                        updatevalues={"json": pruned_json},
-                    )
-
-                self._simple_update_one_txn(
-                    txn,
-                    table="redactions",
-                    keyvalues={"event_id": redaction_id},
-                    updatevalues={"have_censored": True},
-                )
-
-        yield self.runInteraction("_update_censor_txn", _update_censor_txn)
-
-    @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):
-            sql = """
-                SELECT COALESCE(COUNT(*), 0) FROM events
-                WHERE type = 'm.room.message'
-                AND stream_ordering > ?
-            """
-            txn.execute(sql, (self.stream_ordering_day_ago,))
-            count, = txn.fetchone()
-            return count
-
-        ret = yield self.runInteraction("count_messages", _count_messages)
-        return ret
-
-    @defer.inlineCallbacks
-    def count_daily_sent_messages(self):
-        def _count_messages(txn):
-            # This is good enough as if you have silly characters in your own
-            # hostname then thats your own fault.
-            like_clause = "%:" + self.hs.hostname
-
-            sql = """
-                SELECT COALESCE(COUNT(*), 0) FROM events
-                WHERE type = 'm.room.message'
-                    AND sender LIKE ?
-                AND stream_ordering > ?
-            """
-
-            txn.execute(sql, (like_clause, self.stream_ordering_day_ago))
-            count, = txn.fetchone()
-            return count
-
-        ret = yield self.runInteraction("count_daily_sent_messages", _count_messages)
-        return ret
-
-    @defer.inlineCallbacks
-    def count_daily_active_rooms(self):
-        def _count(txn):
-            sql = """
-                SELECT COALESCE(COUNT(DISTINCT room_id), 0) FROM events
-                WHERE type = 'm.room.message'
-                AND stream_ordering > ?
-            """
-            txn.execute(sql, (self.stream_ordering_day_ago,))
-            count, = txn.fetchone()
-            return count
-
-        ret = yield self.runInteraction("count_daily_active_rooms", _count)
-        return ret
-
-    def get_current_backfill_token(self):
-        """The current minimum token that backfilled events have reached"""
-        return -self._backfill_id_gen.get_current_token()
-
-    def get_current_events_token(self):
-        """The current maximum token that events have reached"""
-        return self._stream_id_gen.get_current_token()
-
-    def get_all_new_forward_event_rows(self, last_id, current_id, limit):
-        if last_id == current_id:
-            return defer.succeed([])
-
-        def get_all_new_forward_event_rows(txn):
-            sql = (
-                "SELECT e.stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts, relates_to_id"
-                " FROM events AS e"
-                " LEFT JOIN redactions USING (event_id)"
-                " LEFT JOIN state_events USING (event_id)"
-                " LEFT JOIN event_relations USING (event_id)"
-                " WHERE ? < stream_ordering AND stream_ordering <= ?"
-                " ORDER BY stream_ordering ASC"
-                " LIMIT ?"
-            )
-            txn.execute(sql, (last_id, current_id, limit))
-            new_event_updates = txn.fetchall()
-
-            if len(new_event_updates) == limit:
-                upper_bound = new_event_updates[-1][0]
-            else:
-                upper_bound = current_id
-
-            sql = (
-                "SELECT event_stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts, relates_to_id"
-                " FROM events AS e"
-                " INNER JOIN ex_outlier_stream USING (event_id)"
-                " LEFT JOIN redactions USING (event_id)"
-                " LEFT JOIN state_events USING (event_id)"
-                " LEFT JOIN event_relations USING (event_id)"
-                " WHERE ? < event_stream_ordering"
-                " AND event_stream_ordering <= ?"
-                " ORDER BY event_stream_ordering DESC"
-            )
-            txn.execute(sql, (last_id, upper_bound))
-            new_event_updates.extend(txn)
-
-            return new_event_updates
-
-        return self.runInteraction(
-            "get_all_new_forward_event_rows", get_all_new_forward_event_rows
-        )
-
-    def get_all_new_backfill_event_rows(self, last_id, current_id, limit):
-        if last_id == current_id:
-            return defer.succeed([])
-
-        def get_all_new_backfill_event_rows(txn):
-            sql = (
-                "SELECT -e.stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts, relates_to_id"
-                " FROM events AS e"
-                " LEFT JOIN redactions USING (event_id)"
-                " LEFT JOIN state_events USING (event_id)"
-                " LEFT JOIN event_relations USING (event_id)"
-                " WHERE ? > stream_ordering AND stream_ordering >= ?"
-                " ORDER BY stream_ordering ASC"
-                " LIMIT ?"
-            )
-            txn.execute(sql, (-last_id, -current_id, limit))
-            new_event_updates = txn.fetchall()
-
-            if len(new_event_updates) == limit:
-                upper_bound = new_event_updates[-1][0]
-            else:
-                upper_bound = current_id
-
-            sql = (
-                "SELECT -event_stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts, relates_to_id"
-                " FROM events AS e"
-                " INNER JOIN ex_outlier_stream USING (event_id)"
-                " LEFT JOIN redactions USING (event_id)"
-                " LEFT JOIN state_events USING (event_id)"
-                " LEFT JOIN event_relations USING (event_id)"
-                " WHERE ? > event_stream_ordering"
-                " AND event_stream_ordering >= ?"
-                " ORDER BY event_stream_ordering DESC"
-            )
-            txn.execute(sql, (-last_id, -upper_bound))
-            new_event_updates.extend(txn.fetchall())
-
-            return new_event_updates
-
-        return self.runInteraction(
-            "get_all_new_backfill_event_rows", get_all_new_backfill_event_rows
-        )
-
-    @cached(num_args=5, max_entries=10)
-    def get_all_new_events(
-        self,
-        last_backfill_id,
-        last_forward_id,
-        current_backfill_id,
-        current_forward_id,
-        limit,
-    ):
-        """Get all the new events that have arrived at the server either as
-        new events or as backfilled events"""
-        have_backfill_events = last_backfill_id != current_backfill_id
-        have_forward_events = last_forward_id != current_forward_id
-
-        if not have_backfill_events and not have_forward_events:
-            return defer.succeed(AllNewEventsResult([], [], [], [], []))
-
-        def get_all_new_events_txn(txn):
-            sql = (
-                "SELECT e.stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts"
-                " FROM events AS e"
-                " LEFT JOIN redactions USING (event_id)"
-                " LEFT JOIN state_events USING (event_id)"
-                " WHERE ? < stream_ordering AND stream_ordering <= ?"
-                " ORDER BY stream_ordering ASC"
-                " LIMIT ?"
-            )
-            if have_forward_events:
-                txn.execute(sql, (last_forward_id, current_forward_id, limit))
-                new_forward_events = txn.fetchall()
-
-                if len(new_forward_events) == limit:
-                    upper_bound = new_forward_events[-1][0]
-                else:
-                    upper_bound = current_forward_id
-
-                sql = (
-                    "SELECT event_stream_ordering, event_id, state_group"
-                    " FROM ex_outlier_stream"
-                    " WHERE ? > event_stream_ordering"
-                    " AND event_stream_ordering >= ?"
-                    " ORDER BY event_stream_ordering DESC"
-                )
-                txn.execute(sql, (last_forward_id, upper_bound))
-                forward_ex_outliers = txn.fetchall()
-            else:
-                new_forward_events = []
-                forward_ex_outliers = []
-
-            sql = (
-                "SELECT -e.stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts"
-                " FROM events AS e"
-                " LEFT JOIN redactions USING (event_id)"
-                " LEFT JOIN state_events USING (event_id)"
-                " WHERE ? > stream_ordering AND stream_ordering >= ?"
-                " ORDER BY stream_ordering DESC"
-                " LIMIT ?"
-            )
-            if have_backfill_events:
-                txn.execute(sql, (-last_backfill_id, -current_backfill_id, limit))
-                new_backfill_events = txn.fetchall()
-
-                if len(new_backfill_events) == limit:
-                    upper_bound = new_backfill_events[-1][0]
-                else:
-                    upper_bound = current_backfill_id
-
-                sql = (
-                    "SELECT -event_stream_ordering, event_id, state_group"
-                    " FROM ex_outlier_stream"
-                    " WHERE ? > event_stream_ordering"
-                    " AND event_stream_ordering >= ?"
-                    " ORDER BY event_stream_ordering DESC"
-                )
-                txn.execute(sql, (-last_backfill_id, -upper_bound))
-                backward_ex_outliers = txn.fetchall()
-            else:
-                new_backfill_events = []
-                backward_ex_outliers = []
-
-            return AllNewEventsResult(
-                new_forward_events,
-                new_backfill_events,
-                forward_ex_outliers,
-                backward_ex_outliers,
-            )
-
-        return self.runInteraction("get_all_new_events", get_all_new_events_txn)
-
-    def purge_history(self, room_id, token, delete_local_events):
-        """Deletes room history before a certain point
-
-        Args:
-            room_id (str):
-
-            token (str): A topological token to delete events before
-
-            delete_local_events (bool):
-                if True, we will delete local events as well as remote ones
-                (instead of just marking them as outliers and deleting their
-                state groups).
-        """
-
-        return self.runInteraction(
-            "purge_history",
-            self._purge_history_txn,
-            room_id,
-            token,
-            delete_local_events,
-        )
-
-    def _purge_history_txn(self, txn, room_id, token_str, delete_local_events):
-        token = RoomStreamToken.parse(token_str)
-
-        # Tables that should be pruned:
-        #     event_auth
-        #     event_backward_extremities
-        #     event_edges
-        #     event_forward_extremities
-        #     event_json
-        #     event_push_actions
-        #     event_reference_hashes
-        #     event_search
-        #     event_to_state_groups
-        #     events
-        #     rejections
-        #     room_depth
-        #     state_groups
-        #     state_groups_state
-
-        # we will build a temporary table listing the events so that we don't
-        # have to keep shovelling the list back and forth across the
-        # connection. Annoyingly the python sqlite driver commits the
-        # transaction on CREATE, so let's do this first.
-        #
-        # furthermore, we might already have the table from a previous (failed)
-        # purge attempt, so let's drop the table first.
-
-        txn.execute("DROP TABLE IF EXISTS events_to_purge")
-
-        txn.execute(
-            "CREATE TEMPORARY TABLE events_to_purge ("
-            "    event_id TEXT NOT NULL,"
-            "    should_delete BOOLEAN NOT NULL"
-            ")"
-        )
-
-        # First ensure that we're not about to delete all the forward extremeties
-        txn.execute(
-            "SELECT e.event_id, e.depth FROM events as e "
-            "INNER JOIN event_forward_extremities as f "
-            "ON e.event_id = f.event_id "
-            "AND e.room_id = f.room_id "
-            "WHERE f.room_id = ?",
-            (room_id,),
-        )
-        rows = txn.fetchall()
-        max_depth = max(row[1] for row in rows)
-
-        if max_depth < token.topological:
-            # We need to ensure we don't delete all the events from the database
-            # otherwise we wouldn't be able to send any events (due to not
-            # having any backwards extremeties)
-            raise SynapseError(
-                400, "topological_ordering is greater than forward extremeties"
-            )
-
-        logger.info("[purge] looking for events to delete")
-
-        should_delete_expr = "state_key IS NULL"
-        should_delete_params = ()
-        if not delete_local_events:
-            should_delete_expr += " AND event_id NOT LIKE ?"
-
-            # We include the parameter twice since we use the expression twice
-            should_delete_params += ("%:" + self.hs.hostname, "%:" + self.hs.hostname)
-
-        should_delete_params += (room_id, token.topological)
-
-        # Note that we insert events that are outliers and aren't going to be
-        # deleted, as nothing will happen to them.
-        txn.execute(
-            "INSERT INTO events_to_purge"
-            " SELECT event_id, %s"
-            " FROM events AS e LEFT JOIN state_events USING (event_id)"
-            " WHERE (NOT outlier OR (%s)) AND e.room_id = ? AND topological_ordering < ?"
-            % (should_delete_expr, should_delete_expr),
-            should_delete_params,
-        )
-
-        # We create the indices *after* insertion as that's a lot faster.
-
-        # create an index on should_delete because later we'll be looking for
-        # the should_delete / shouldn't_delete subsets
-        txn.execute(
-            "CREATE INDEX events_to_purge_should_delete"
-            " ON events_to_purge(should_delete)"
-        )
-
-        # We do joins against events_to_purge for e.g. calculating state
-        # groups to purge, etc., so lets make an index.
-        txn.execute("CREATE INDEX events_to_purge_id" " ON events_to_purge(event_id)")
-
-        txn.execute("SELECT event_id, should_delete FROM events_to_purge")
-        event_rows = txn.fetchall()
-        logger.info(
-            "[purge] found %i events before cutoff, of which %i can be deleted",
-            len(event_rows),
-            sum(1 for e in event_rows if e[1]),
-        )
-
-        logger.info("[purge] Finding new backward extremities")
-
-        # We calculate the new entries for the backward extremeties by finding
-        # events to be purged that are pointed to by events we're not going to
-        # purge.
-        txn.execute(
-            "SELECT DISTINCT e.event_id FROM events_to_purge AS e"
-            " INNER JOIN event_edges AS ed ON e.event_id = ed.prev_event_id"
-            " LEFT JOIN events_to_purge AS ep2 ON ed.event_id = ep2.event_id"
-            " WHERE ep2.event_id IS NULL"
-        )
-        new_backwards_extrems = txn.fetchall()
-
-        logger.info("[purge] replacing backward extremities: %r", new_backwards_extrems)
-
-        txn.execute(
-            "DELETE FROM event_backward_extremities WHERE room_id = ?", (room_id,)
-        )
-
-        # Update backward extremeties
-        txn.executemany(
-            "INSERT INTO event_backward_extremities (room_id, event_id)"
-            " VALUES (?, ?)",
-            [(room_id, event_id) for event_id, in new_backwards_extrems],
-        )
-
-        logger.info("[purge] finding redundant state groups")
-
-        # Get all state groups that are referenced by events that are to be
-        # deleted. We then go and check if they are referenced by other events
-        # or state groups, and if not we delete them.
-        txn.execute(
-            """
-            SELECT DISTINCT state_group FROM events_to_purge
-            INNER JOIN event_to_state_groups USING (event_id)
-        """
-        )
-
-        referenced_state_groups = set(sg for sg, in txn)
-        logger.info(
-            "[purge] found %i referenced state groups", len(referenced_state_groups)
-        )
-
-        logger.info("[purge] finding state groups that can be deleted")
-
-        _ = self._find_unreferenced_groups_during_purge(txn, referenced_state_groups)
-        state_groups_to_delete, remaining_state_groups = _
-
-        logger.info(
-            "[purge] found %i state groups to delete", len(state_groups_to_delete)
-        )
-
-        logger.info(
-            "[purge] de-delta-ing %i remaining state groups",
-            len(remaining_state_groups),
-        )
-
-        # Now we turn the state groups that reference to-be-deleted state
-        # groups to non delta versions.
-        for sg in remaining_state_groups:
-            logger.info("[purge] de-delta-ing remaining state group %s", sg)
-            curr_state = self._get_state_groups_from_groups_txn(txn, [sg])
-            curr_state = curr_state[sg]
-
-            self._simple_delete_txn(
-                txn, table="state_groups_state", keyvalues={"state_group": sg}
-            )
-
-            self._simple_delete_txn(
-                txn, table="state_group_edges", keyvalues={"state_group": sg}
-            )
-
-            self._simple_insert_many_txn(
-                txn,
-                table="state_groups_state",
-                values=[
-                    {
-                        "state_group": sg,
-                        "room_id": room_id,
-                        "type": key[0],
-                        "state_key": key[1],
-                        "event_id": state_id,
-                    }
-                    for key, state_id in iteritems(curr_state)
-                ],
-            )
-
-        logger.info("[purge] removing redundant state groups")
-        txn.executemany(
-            "DELETE FROM state_groups_state WHERE state_group = ?",
-            ((sg,) for sg in state_groups_to_delete),
-        )
-        txn.executemany(
-            "DELETE FROM state_groups WHERE id = ?",
-            ((sg,) for sg in state_groups_to_delete),
-        )
-
-        logger.info("[purge] removing events from event_to_state_groups")
-        txn.execute(
-            "DELETE FROM event_to_state_groups "
-            "WHERE event_id IN (SELECT event_id from events_to_purge)"
-        )
-        for event_id, _ in event_rows:
-            txn.call_after(self._get_state_group_for_event.invalidate, (event_id,))
-
-        # Delete all remote non-state events
-        for table in (
-            "events",
-            "event_json",
-            "event_auth",
-            "event_edges",
-            "event_forward_extremities",
-            "event_reference_hashes",
-            "event_search",
-            "rejections",
-        ):
-            logger.info("[purge] removing events from %s", table)
-
-            txn.execute(
-                "DELETE FROM %s WHERE event_id IN ("
-                "    SELECT event_id FROM events_to_purge WHERE should_delete"
-                ")" % (table,)
-            )
-
-        # event_push_actions lacks an index on event_id, and has one on
-        # (room_id, event_id) instead.
-        for table in ("event_push_actions",):
-            logger.info("[purge] removing events from %s", table)
-
-            txn.execute(
-                "DELETE FROM %s WHERE room_id = ? AND event_id IN ("
-                "    SELECT event_id FROM events_to_purge WHERE should_delete"
-                ")" % (table,),
-                (room_id,),
-            )
-
-        # Mark all state and own events as outliers
-        logger.info("[purge] marking remaining events as outliers")
-        txn.execute(
-            "UPDATE events SET outlier = ?"
-            " WHERE event_id IN ("
-            "    SELECT event_id FROM events_to_purge "
-            "    WHERE NOT should_delete"
-            ")",
-            (True,),
-        )
-
-        # synapse tries to take out an exclusive lock on room_depth whenever it
-        # persists events (because upsert), and once we run this update, we
-        # will block that for the rest of our transaction.
-        #
-        # So, let's stick it at the end so that we don't block event
-        # persistence.
-        #
-        # We do this by calculating the minimum depth of the backwards
-        # extremities. However, the events in event_backward_extremities
-        # are ones we don't have yet so we need to look at the events that
-        # point to it via event_edges table.
-        txn.execute(
-            """
-            SELECT COALESCE(MIN(depth), 0)
-            FROM event_backward_extremities AS eb
-            INNER JOIN event_edges AS eg ON eg.prev_event_id = eb.event_id
-            INNER JOIN events AS e ON e.event_id = eg.event_id
-            WHERE eb.room_id = ?
-        """,
-            (room_id,),
-        )
-        min_depth, = txn.fetchone()
-
-        logger.info("[purge] updating room_depth to %d", min_depth)
-
-        txn.execute(
-            "UPDATE room_depth SET min_depth = ? WHERE room_id = ?",
-            (min_depth, room_id),
-        )
-
-        # finally, drop the temp table. this will commit the txn in sqlite,
-        # so make sure to keep this actually last.
-        txn.execute("DROP TABLE events_to_purge")
-
-        logger.info("[purge] done")
-
-    def _find_unreferenced_groups_during_purge(self, txn, state_groups):
-        """Used when purging history to figure out which state groups can be
-        deleted and which need to be de-delta'ed (due to one of its prev groups
-        being scheduled for deletion).
-
-        Args:
-            txn
-            state_groups (set[int]): Set of state groups referenced by events
-                that are going to be deleted.
-
-        Returns:
-            tuple[set[int], set[int]]: The set of state groups that can be
-            deleted and the set of state groups that need to be de-delta'ed
-        """
-        # Graph of state group -> previous group
-        graph = {}
-
-        # Set of events that we have found to be referenced by events
-        referenced_groups = set()
-
-        # Set of state groups we've already seen
-        state_groups_seen = set(state_groups)
-
-        # Set of state groups to handle next.
-        next_to_search = set(state_groups)
-        while next_to_search:
-            # We bound size of groups we're looking up at once, to stop the
-            # SQL query getting too big
-            if len(next_to_search) < 100:
-                current_search = next_to_search
-                next_to_search = set()
-            else:
-                current_search = set(itertools.islice(next_to_search, 100))
-                next_to_search -= current_search
-
-            # Check if state groups are referenced
-            sql = """
-                SELECT DISTINCT state_group FROM event_to_state_groups
-                LEFT JOIN events_to_purge AS ep USING (event_id)
-                WHERE ep.event_id IS NULL AND
-            """
-            clause, args = make_in_list_sql_clause(
-                txn.database_engine, "state_group", current_search
-            )
-            txn.execute(sql + clause, list(args))
-
-            referenced = set(sg for sg, in txn)
-            referenced_groups |= referenced
-
-            # We don't continue iterating up the state group graphs for state
-            # groups that are referenced.
-            current_search -= referenced
-
-            rows = self._simple_select_many_txn(
-                txn,
-                table="state_group_edges",
-                column="prev_state_group",
-                iterable=current_search,
-                keyvalues={},
-                retcols=("prev_state_group", "state_group"),
-            )
-
-            prevs = set(row["state_group"] for row in rows)
-            # We don't bother re-handling groups we've already seen
-            prevs -= state_groups_seen
-            next_to_search |= prevs
-            state_groups_seen |= prevs
-
-            for row in rows:
-                # Note: Each state group can have at most one prev group
-                graph[row["state_group"]] = row["prev_state_group"]
-
-        to_delete = state_groups_seen - referenced_groups
-
-        to_dedelta = set()
-        for sg in referenced_groups:
-            prev_sg = graph.get(sg)
-            if prev_sg and prev_sg in to_delete:
-                to_dedelta.add(sg)
-
-        return to_delete, to_dedelta
-
-    def purge_room(self, room_id):
-        """Deletes all record of a room
-
-        Args:
-            room_id (str):
-        """
-
-        return self.runInteraction("purge_room", self._purge_room_txn, room_id)
-
-    def _purge_room_txn(self, txn, room_id):
-        # first we have to delete the state groups states
-        logger.info("[purge] removing %s from state_groups_state", room_id)
-
-        txn.execute(
-            """
-            DELETE FROM state_groups_state WHERE state_group IN (
-              SELECT state_group FROM events JOIN event_to_state_groups USING(event_id)
-              WHERE events.room_id=?
-            )
-            """,
-            (room_id,),
-        )
-
-        # ... and the state group edges
-        logger.info("[purge] removing %s from state_group_edges", room_id)
-
-        txn.execute(
-            """
-            DELETE FROM state_group_edges WHERE state_group IN (
-              SELECT state_group FROM events JOIN event_to_state_groups USING(event_id)
-              WHERE events.room_id=?
-            )
-            """,
-            (room_id,),
-        )
-
-        # ... and the state groups
-        logger.info("[purge] removing %s from state_groups", room_id)
-
-        txn.execute(
-            """
-            DELETE FROM state_groups WHERE id IN (
-              SELECT state_group FROM events JOIN event_to_state_groups USING(event_id)
-              WHERE events.room_id=?
-            )
-            """,
-            (room_id,),
-        )
-
-        # and then tables which lack an index on room_id but have one on event_id
-        for table in (
-            "event_auth",
-            "event_edges",
-            "event_push_actions_staging",
-            "event_reference_hashes",
-            "event_relations",
-            "event_to_state_groups",
-            "redactions",
-            "rejections",
-            "state_events",
-        ):
-            logger.info("[purge] removing %s from %s", room_id, table)
-
-            txn.execute(
-                """
-                DELETE FROM %s WHERE event_id IN (
-                  SELECT event_id FROM events WHERE room_id=?
-                )
-                """
-                % (table,),
-                (room_id,),
-            )
-
-        # and finally, the tables with an index on room_id (or no useful index)
-        for table in (
-            "current_state_events",
-            "event_backward_extremities",
-            "event_forward_extremities",
-            "event_json",
-            "event_push_actions",
-            "event_search",
-            "events",
-            "group_rooms",
-            "public_room_list_stream",
-            "receipts_graph",
-            "receipts_linearized",
-            "room_aliases",
-            "room_depth",
-            "room_memberships",
-            "room_stats_state",
-            "room_stats_current",
-            "room_stats_historical",
-            "room_stats_earliest_token",
-            "rooms",
-            "stream_ordering_to_exterm",
-            "topics",
-            "users_in_public_rooms",
-            "users_who_share_private_rooms",
-            # no useful index, but let's clear them anyway
-            "appservice_room_list",
-            "e2e_room_keys",
-            "event_push_summary",
-            "pusher_throttle",
-            "group_summary_rooms",
-            "local_invites",
-            "room_account_data",
-            "room_tags",
-        ):
-            logger.info("[purge] removing %s from %s", room_id, table)
-            txn.execute("DELETE FROM %s WHERE room_id=?" % (table,), (room_id,))
-
-        # Other tables we do NOT need to clear out:
-        #
-        #  - blocked_rooms
-        #    This is important, to make sure that we don't accidentally rejoin a blocked
-        #    room after it was purged
-        #
-        #  - user_directory
-        #    This has a room_id column, but it is unused
-        #
-
-        # Other tables that we might want to consider clearing out include:
-        #
-        #  - event_reports
-        #       Given that these are intended for abuse management my initial
-        #       inclination is to leave them in place.
-        #
-        #  - current_state_delta_stream
-        #  - ex_outlier_stream
-        #  - room_tags_revisions
-        #       The problem with these is that they are largeish and there is no room_id
-        #       index on them. In any case we should be clearing out 'stream' tables
-        #       periodically anyway (#5888)
-
-        # TODO: we could probably usefully do a bunch of cache invalidation here
-
-        logger.info("[purge] done")
-
-    @defer.inlineCallbacks
-    def is_event_after(self, event_id1, event_id2):
-        """Returns True if event_id1 is after event_id2 in the stream
-        """
-        to_1, so_1 = yield self._get_event_ordering(event_id1)
-        to_2, so_2 = yield self._get_event_ordering(event_id2)
-        return (to_1, so_1) > (to_2, so_2)
-
-    @cachedInlineCallbacks(max_entries=5000)
-    def _get_event_ordering(self, event_id):
-        res = yield self._simple_select_one(
-            table="events",
-            retcols=["topological_ordering", "stream_ordering"],
-            keyvalues={"event_id": event_id},
-            allow_none=True,
-        )
-
-        if not res:
-            raise SynapseError(404, "Could not find event %s" % (event_id,))
-
-        return (int(res["topological_ordering"]), int(res["stream_ordering"]))
-
-    def get_all_updated_current_state_deltas(self, from_token, to_token, limit):
-        def get_all_updated_current_state_deltas_txn(txn):
-            sql = """
-                SELECT stream_id, room_id, type, state_key, event_id
-                FROM current_state_delta_stream
-                WHERE ? < stream_id AND stream_id <= ?
-                ORDER BY stream_id ASC LIMIT ?
-            """
-            txn.execute(sql, (from_token, to_token, limit))
-            return txn.fetchall()
-
-        return self.runInteraction(
-            "get_all_updated_current_state_deltas",
-            get_all_updated_current_state_deltas_txn,
-        )
-
-
-AllNewEventsResult = namedtuple(
-    "AllNewEventsResult",
-    [
-        "new_forward_events",
-        "new_backfill_events",
-        "forward_ex_outliers",
-        "backward_ex_outliers",
-    ],
-)