synapse-product/synapse/storage/events.py

# -*- coding: utf-8 -*-
# Copyright 2014, 2015 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from _base import SQLBaseStore, _RollbackButIsFineException

from twisted.internet import defer, reactor

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

from synapse.util.logcontext import preserve_context_over_deferred
from synapse.util.logutils import log_function
from synapse.api.constants import EventTypes

from canonicaljson import encode_canonical_json
from contextlib import contextmanager

import logging
import math
import ujson as json

logger = logging.getLogger(__name__)


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

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


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

        if backfilled:
            if not self.min_token_deferred.called:
                yield self.min_token_deferred
            start = self.min_token - 1
            self.min_token -= len(events_and_contexts) + 1
            stream_orderings = range(start, self.min_token, -1)

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

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

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

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

    @defer.inlineCallbacks
    @log_function
    def persist_event(self, event, context, backfilled=False,
                      is_new_state=True, current_state=None):
        stream_ordering = None
        if backfilled:
            if not self.min_token_deferred.called:
                yield self.min_token_deferred
            self.min_token -= 1
            stream_ordering = self.min_token

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

            event_map[event.event_id] = event

            if event.event_id not in have_persisted:
                continue

            to_remove.add(event)

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

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

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

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

                self._update_extremeties(txn, [event])

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

        if not events_and_contexts:
            return

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

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

        for event, _ in events_and_contexts:
            if event.type == EventTypes.Name:
                self._store_room_name_txn(txn, event)
            elif event.type == EventTypes.Topic:
                self._store_room_topic_txn(txn, event)
            elif event.type == EventTypes.Redaction:
                self._store_redaction(txn, event)

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

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

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

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

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

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

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

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

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

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

            state_values.append(vals)

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

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

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

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

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

        return

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

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

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

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

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

            return res

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

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

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

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

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

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

        event_map.update(missing_events)

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

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

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

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

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

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

        event_map.update(missing_events)

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

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

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

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

        return events[0] if events else None

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

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

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

        return event_map

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

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

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

                rows = self._new_transaction(
                    conn, "do_fetch", [], self._fetch_event_rows, event_ids
                )

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

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

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

                if event_list:
                    reactor.callFromThread(fire, event_list)

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

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

            self._event_fetch_lock.notify()

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

        if should_start:
            self.runWithConnection(
                self._do_fetch
            )

        rows = yield preserve_context_over_deferred(events_d)

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

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

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

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

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

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

        return rows

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

        rows = self._fetch_event_rows(
            txn, events,
        )

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

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

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

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

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

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

        if check_redacted and redacted:
            ev = prune_event(ev)

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

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

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

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

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

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

        defer.returnValue(ev)

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

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

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

        if check_redacted and redacted:
            ev = prune_event(ev)

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

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

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

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

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

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

        return ev

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

        return self._get_events_txn(txn, event_ids)

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

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

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

            txn.execute(
                "SELECT stream_ordering"
                " FROM events"
                " ORDER BY stream_ordering DESC"
                " LIMIT 1"
            )
            now_reporting = self.cursor_to_dict(txn)
            if not now_reporting:
                return None
            now_reporting = now_reporting[0]["stream_ordering"]

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

            if not last_reported:
                return None

            # Close enough to correct for our purposes.
            yesterday = (now - 24 * 60 * 60)
            if math.fabs(yesterday - last_reported[0]["reported_time"]) > 60 * 60:
                return None

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

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