event_push_actions.py

# -*- coding: utf-8 -*-
# Copyright 2015 OpenMarket Ltd
# Copyright 2018 New Vector 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.

import logging

from six import iteritems

from canonicaljson import json

from twisted.internet import defer

from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.storage._base import LoggingTransaction, SQLBaseStore
from synapse.storage.database import Database
from synapse.util.caches.descriptors import cachedInlineCallbacks

logger = logging.getLogger(__name__)


DEFAULT_NOTIF_ACTION = ["notify", {"set_tweak": "highlight", "value": False}]
DEFAULT_HIGHLIGHT_ACTION = [
    "notify",
    {"set_tweak": "sound", "value": "default"},
    {"set_tweak": "highlight"},
]


def _serialize_action(actions, is_highlight):
    """Custom serializer for actions. This allows us to "compress" common actions.

    We use the fact that most users have the same actions for notifs (and for
    highlights).
    We store these default actions as the empty string rather than the full JSON.
    Since the empty string isn't valid JSON there is no risk of this clashing with
    any real JSON actions
    """
    if is_highlight:
        if actions == DEFAULT_HIGHLIGHT_ACTION:
            return ""  # We use empty string as the column is non-NULL
    else:
        if actions == DEFAULT_NOTIF_ACTION:
            return ""
    return json.dumps(actions)


def _deserialize_action(actions, is_highlight):
    """Custom deserializer for actions. This allows us to "compress" common actions
    """
    if actions:
        return json.loads(actions)

    if is_highlight:
        return DEFAULT_HIGHLIGHT_ACTION
    else:
        return DEFAULT_NOTIF_ACTION


class EventPushActionsWorkerStore(SQLBaseStore):
    def __init__(self, database: Database, db_conn, hs):
        super(EventPushActionsWorkerStore, self).__init__(database, db_conn, hs)

        # These get correctly set by _find_stream_orderings_for_times_txn
        self.stream_ordering_month_ago = None
        self.stream_ordering_day_ago = None

        cur = LoggingTransaction(
            db_conn.cursor(),
            name="_find_stream_orderings_for_times_txn",
            database_engine=self.database_engine,
        )
        self._find_stream_orderings_for_times_txn(cur)
        cur.close()

        self.find_stream_orderings_looping_call = self._clock.looping_call(
            self._find_stream_orderings_for_times, 10 * 60 * 1000
        )
        self._rotate_delay = 3
        self._rotate_count = 10000

    @cachedInlineCallbacks(num_args=3, tree=True, max_entries=5000)
    def get_unread_event_push_actions_by_room_for_user(
        self, room_id, user_id, last_read_event_id
    ):
        ret = yield self.db.runInteraction(
            "get_unread_event_push_actions_by_room",
            self._get_unread_counts_by_receipt_txn,
            room_id,
            user_id,
            last_read_event_id,
        )
        return ret

    def _get_unread_counts_by_receipt_txn(
        self, txn, room_id, user_id, last_read_event_id
    ):
        sql = (
            "SELECT stream_ordering"
            " FROM events"
            " WHERE room_id = ? AND event_id = ?"
        )
        txn.execute(sql, (room_id, last_read_event_id))
        results = txn.fetchall()
        if len(results) == 0:
            return {"notify_count": 0, "highlight_count": 0}

        stream_ordering = results[0][0]

        return self._get_unread_counts_by_pos_txn(
            txn, room_id, user_id, stream_ordering
        )

    def _get_unread_counts_by_pos_txn(self, txn, room_id, user_id, stream_ordering):

        # First get number of notifications.
        # We don't need to put a notif=1 clause as all rows always have
        # notif=1
        sql = (
            "SELECT count(*)"
            " FROM event_push_actions ea"
            " WHERE"
            " user_id = ?"
            " AND room_id = ?"
            " AND stream_ordering > ?"
        )

        txn.execute(sql, (user_id, room_id, stream_ordering))
        row = txn.fetchone()
        notify_count = row[0] if row else 0

        txn.execute(
            """
            SELECT notif_count FROM event_push_summary
            WHERE room_id = ? AND user_id = ? AND stream_ordering > ?
        """,
            (room_id, user_id, stream_ordering),
        )
        rows = txn.fetchall()
        if rows:
            notify_count += rows[0][0]

        # Now get the number of highlights
        sql = (
            "SELECT count(*)"
            " FROM event_push_actions ea"
            " WHERE"
            " highlight = 1"
            " AND user_id = ?"
            " AND room_id = ?"
            " AND stream_ordering > ?"
        )

        txn.execute(sql, (user_id, room_id, stream_ordering))
        row = txn.fetchone()
        highlight_count = row[0] if row else 0

        return {"notify_count": notify_count, "highlight_count": highlight_count}

    @defer.inlineCallbacks
    def get_push_action_users_in_range(self, min_stream_ordering, max_stream_ordering):
        def f(txn):
            sql = (
                "SELECT DISTINCT(user_id) FROM event_push_actions WHERE"
                " stream_ordering >= ? AND stream_ordering <= ?"
            )
            txn.execute(sql, (min_stream_ordering, max_stream_ordering))
            return [r[0] for r in txn]

        ret = yield self.db.runInteraction("get_push_action_users_in_range", f)
        return ret

    @defer.inlineCallbacks
    def get_unread_push_actions_for_user_in_range_for_http(
        self, user_id, min_stream_ordering, max_stream_ordering, limit=20
    ):
        """Get a list of the most recent unread push actions for a given user,
        within the given stream ordering range. Called by the httppusher.

        Args:
            user_id (str): The user to fetch push actions for.
            min_stream_ordering(int): The exclusive lower bound on the
                stream ordering of event push actions to fetch.
            max_stream_ordering(int): The inclusive upper bound on the
                stream ordering of event push actions to fetch.
            limit (int): The maximum number of rows to return.
        Returns:
            A promise which resolves to a list of dicts with the keys "event_id",
            "room_id", "stream_ordering", "actions".
            The list will be ordered by ascending stream_ordering.
            The list will have between 0~limit entries.
        """
        # find rooms that have a read receipt in them and return the next
        # push actions
        def get_after_receipt(txn):
            # find rooms that have a read receipt in them and return the next
            # push actions
            sql = (
                "SELECT ep.event_id, ep.room_id, ep.stream_ordering, ep.actions,"
                "   ep.highlight "
                " FROM ("
                "   SELECT room_id,"
                "       MAX(stream_ordering) as stream_ordering"
                "   FROM events"
                "   INNER JOIN receipts_linearized USING (room_id, event_id)"
                "   WHERE receipt_type = 'm.read' AND user_id = ?"
                "   GROUP BY room_id"
                ") AS rl,"
                " event_push_actions AS ep"
                " WHERE"
                "   ep.room_id = rl.room_id"
                "   AND ep.stream_ordering > rl.stream_ordering"
                "   AND ep.user_id = ?"
                "   AND ep.stream_ordering > ?"
                "   AND ep.stream_ordering <= ?"
                " ORDER BY ep.stream_ordering ASC LIMIT ?"
            )
            args = [user_id, user_id, min_stream_ordering, max_stream_ordering, limit]
            txn.execute(sql, args)
            return txn.fetchall()

        after_read_receipt = yield self.db.runInteraction(
            "get_unread_push_actions_for_user_in_range_http_arr", get_after_receipt
        )

        # There are rooms with push actions in them but you don't have a read receipt in
        # them e.g. rooms you've been invited to, so get push actions for rooms which do
        # not have read receipts in them too.
        def get_no_receipt(txn):
            sql = (
                "SELECT ep.event_id, ep.room_id, ep.stream_ordering, ep.actions,"
                "   ep.highlight "
                " FROM event_push_actions AS ep"
                " INNER JOIN events AS e USING (room_id, event_id)"
                " WHERE"
                "   ep.room_id NOT IN ("
                "     SELECT room_id FROM receipts_linearized"
                "       WHERE receipt_type = 'm.read' AND user_id = ?"
                "       GROUP BY room_id"
                "   )"
                "   AND ep.user_id = ?"
                "   AND ep.stream_ordering > ?"
                "   AND ep.stream_ordering <= ?"
                " ORDER BY ep.stream_ordering ASC LIMIT ?"
            )
            args = [user_id, user_id, min_stream_ordering, max_stream_ordering, limit]
            txn.execute(sql, args)
            return txn.fetchall()

        no_read_receipt = yield self.db.runInteraction(
            "get_unread_push_actions_for_user_in_range_http_nrr", get_no_receipt
        )

        notifs = [
            {
                "event_id": row[0],
                "room_id": row[1],
                "stream_ordering": row[2],
                "actions": _deserialize_action(row[3], row[4]),
            }
            for row in after_read_receipt + no_read_receipt
        ]

        # Now sort it so it's ordered correctly, since currently it will
        # contain results from the first query, correctly ordered, followed
        # by results from the second query, but we want them all ordered
        # by stream_ordering, oldest first.
        notifs.sort(key=lambda r: r["stream_ordering"])

        # Take only up to the limit. We have to stop at the limit because
        # one of the subqueries may have hit the limit.
        return notifs[:limit]

    @defer.inlineCallbacks
    def get_unread_push_actions_for_user_in_range_for_email(
        self, user_id, min_stream_ordering, max_stream_ordering, limit=20
    ):
        """Get a list of the most recent unread push actions for a given user,
        within the given stream ordering range. Called by the emailpusher

        Args:
            user_id (str): The user to fetch push actions for.
            min_stream_ordering(int): The exclusive lower bound on the
                stream ordering of event push actions to fetch.
            max_stream_ordering(int): The inclusive upper bound on the
                stream ordering of event push actions to fetch.
            limit (int): The maximum number of rows to return.
        Returns:
            A promise which resolves to a list of dicts with the keys "event_id",
            "room_id", "stream_ordering", "actions", "received_ts".
            The list will be ordered by descending received_ts.
            The list will have between 0~limit entries.
        """
        # find rooms that have a read receipt in them and return the most recent
        # push actions
        def get_after_receipt(txn):
            sql = (
                "SELECT ep.event_id, ep.room_id, ep.stream_ordering, ep.actions,"
                "  ep.highlight, e.received_ts"
                " FROM ("
                "   SELECT room_id,"
                "       MAX(stream_ordering) as stream_ordering"
                "   FROM events"
                "   INNER JOIN receipts_linearized USING (room_id, event_id)"
                "   WHERE receipt_type = 'm.read' AND user_id = ?"
                "   GROUP BY room_id"
                ") AS rl,"
                " event_push_actions AS ep"
                " INNER JOIN events AS e USING (room_id, event_id)"
                " WHERE"
                "   ep.room_id = rl.room_id"
                "   AND ep.stream_ordering > rl.stream_ordering"
                "   AND ep.user_id = ?"
                "   AND ep.stream_ordering > ?"
                "   AND ep.stream_ordering <= ?"
                " ORDER BY ep.stream_ordering DESC LIMIT ?"
            )
            args = [user_id, user_id, min_stream_ordering, max_stream_ordering, limit]
            txn.execute(sql, args)
            return txn.fetchall()

        after_read_receipt = yield self.db.runInteraction(
            "get_unread_push_actions_for_user_in_range_email_arr", get_after_receipt
        )

        # There are rooms with push actions in them but you don't have a read receipt in
        # them e.g. rooms you've been invited to, so get push actions for rooms which do
        # not have read receipts in them too.
        def get_no_receipt(txn):
            sql = (
                "SELECT ep.event_id, ep.room_id, ep.stream_ordering, ep.actions,"
                "   ep.highlight, e.received_ts"
                " FROM event_push_actions AS ep"
                " INNER JOIN events AS e USING (room_id, event_id)"
                " WHERE"
                "   ep.room_id NOT IN ("
                "     SELECT room_id FROM receipts_linearized"
                "       WHERE receipt_type = 'm.read' AND user_id = ?"
                "       GROUP BY room_id"
                "   )"
                "   AND ep.user_id = ?"
                "   AND ep.stream_ordering > ?"
                "   AND ep.stream_ordering <= ?"
                " ORDER BY ep.stream_ordering DESC LIMIT ?"
            )
            args = [user_id, user_id, min_stream_ordering, max_stream_ordering, limit]
            txn.execute(sql, args)
            return txn.fetchall()

        no_read_receipt = yield self.db.runInteraction(
            "get_unread_push_actions_for_user_in_range_email_nrr", get_no_receipt
        )

        # Make a list of dicts from the two sets of results.
        notifs = [
            {
                "event_id": row[0],
                "room_id": row[1],
                "stream_ordering": row[2],
                "actions": _deserialize_action(row[3], row[4]),
                "received_ts": row[5],
            }
            for row in after_read_receipt + no_read_receipt
        ]

        # Now sort it so it's ordered correctly, since currently it will
        # contain results from the first query, correctly ordered, followed
        # by results from the second query, but we want them all ordered
        # by received_ts (most recent first)
        notifs.sort(key=lambda r: -(r["received_ts"] or 0))

        # Now return the first `limit`
        return notifs[:limit]

    def get_if_maybe_push_in_range_for_user(self, user_id, min_stream_ordering):
        """A fast check to see if there might be something to push for the
        user since the given stream ordering. May return false positives.

        Useful to know whether to bother starting a pusher on start up or not.

        Args:
            user_id (str)
            min_stream_ordering (int)

        Returns:
            Deferred[bool]: True if there may be push to process, False if
            there definitely isn't.
        """

        def _get_if_maybe_push_in_range_for_user_txn(txn):
            sql = """
                SELECT 1 FROM event_push_actions
                WHERE user_id = ? AND stream_ordering > ?
                LIMIT 1
            """

            txn.execute(sql, (user_id, min_stream_ordering))
            return bool(txn.fetchone())

        return self.db.runInteraction(
            "get_if_maybe_push_in_range_for_user",
            _get_if_maybe_push_in_range_for_user_txn,
        )

    def add_push_actions_to_staging(self, event_id, user_id_actions):
        """Add the push actions for the event to the push action staging area.

        Args:
            event_id (str)
            user_id_actions (dict[str, list[dict|str])]): A dictionary mapping
                user_id to list of push actions, where an action can either be
                a string or dict.

        Returns:
            Deferred
        """

        if not user_id_actions:
            return

        # This is a helper function for generating the necessary tuple that
        # can be used to inert into the `event_push_actions_staging` table.
        def _gen_entry(user_id, actions):
            is_highlight = 1 if _action_has_highlight(actions) else 0
            return (
                event_id,  # event_id column
                user_id,  # user_id column
                _serialize_action(actions, is_highlight),  # actions column
                1,  # notif column
                is_highlight,  # highlight column
            )

        def _add_push_actions_to_staging_txn(txn):
            # We don't use simple_insert_many here to avoid the overhead
            # of generating lists of dicts.

            sql = """
                INSERT INTO event_push_actions_staging
                    (event_id, user_id, actions, notif, highlight)
                VALUES (?, ?, ?, ?, ?)
            """

            txn.executemany(
                sql,
                (
                    _gen_entry(user_id, actions)
                    for user_id, actions in iteritems(user_id_actions)
                ),
            )

        return self.db.runInteraction(
            "add_push_actions_to_staging", _add_push_actions_to_staging_txn
        )

    @defer.inlineCallbacks
    def remove_push_actions_from_staging(self, event_id):
        """Called if we failed to persist the event to ensure that stale push
        actions don't build up in the DB

        Args:
            event_id (str)
        """

        try:
            res = yield self.db.simple_delete(
                table="event_push_actions_staging",
                keyvalues={"event_id": event_id},
                desc="remove_push_actions_from_staging",
            )
            return res
        except Exception:
            # this method is called from an exception handler, so propagating
            # another exception here really isn't helpful - there's nothing
            # the caller can do about it. Just log the exception and move on.
            logger.exception(
                "Error removing push actions after event persistence failure"
            )

    def _find_stream_orderings_for_times(self):
        return run_as_background_process(
            "event_push_action_stream_orderings",
            self.db.runInteraction,
            "_find_stream_orderings_for_times",
            self._find_stream_orderings_for_times_txn,
        )

    def _find_stream_orderings_for_times_txn(self, txn):
        logger.info("Searching for stream ordering 1 month ago")
        self.stream_ordering_month_ago = self._find_first_stream_ordering_after_ts_txn(
            txn, self._clock.time_msec() - 30 * 24 * 60 * 60 * 1000
        )
        logger.info(
            "Found stream ordering 1 month ago: it's %d", self.stream_ordering_month_ago
        )
        logger.info("Searching for stream ordering 1 day ago")
        self.stream_ordering_day_ago = self._find_first_stream_ordering_after_ts_txn(
            txn, self._clock.time_msec() - 24 * 60 * 60 * 1000
        )
        logger.info(
            "Found stream ordering 1 day ago: it's %d", self.stream_ordering_day_ago
        )

    def find_first_stream_ordering_after_ts(self, ts):
        """Gets the stream ordering corresponding to a given timestamp.

        Specifically, finds the stream_ordering of the first event that was
        received on or after the timestamp. This is done by a binary search on
        the events table, since there is no index on received_ts, so is
        relatively slow.

        Args:
            ts (int): timestamp in millis

        Returns:
            Deferred[int]: stream ordering of the first event received on/after
                the timestamp
        """
        return self.db.runInteraction(
            "_find_first_stream_ordering_after_ts_txn",
            self._find_first_stream_ordering_after_ts_txn,
            ts,
        )

    @staticmethod
    def _find_first_stream_ordering_after_ts_txn(txn, ts):
        """
        Find the stream_ordering of the first event that was received on or
        after a given timestamp. This is relatively slow as there is no index
        on received_ts but we can then use this to delete push actions before
        this.

        received_ts must necessarily be in the same order as stream_ordering
        and stream_ordering is indexed, so we manually binary search using
        stream_ordering

        Args:
            txn (twisted.enterprise.adbapi.Transaction):
            ts (int): timestamp to search for

        Returns:
            int: stream ordering
        """
        txn.execute("SELECT MAX(stream_ordering) FROM events")
        max_stream_ordering = txn.fetchone()[0]

        if max_stream_ordering is None:
            return 0

        # We want the first stream_ordering in which received_ts is greater
        # than or equal to ts. Call this point X.
        #
        # We maintain the invariants:
        #
        #   range_start <= X <= range_end
        #
        range_start = 0
        range_end = max_stream_ordering + 1

        # Given a stream_ordering, look up the timestamp at that
        # stream_ordering.
        #
        # The array may be sparse (we may be missing some stream_orderings).
        # We treat the gaps as the same as having the same value as the
        # preceding entry, because we will pick the lowest stream_ordering
        # which satisfies our requirement of received_ts >= ts.
        #
        # For example, if our array of events indexed by stream_ordering is
        # [10, <none>, 20], we should treat this as being equivalent to
        # [10, 10, 20].
        #
        sql = (
            "SELECT received_ts FROM events"
            " WHERE stream_ordering <= ?"
            " ORDER BY stream_ordering DESC"
            " LIMIT 1"
        )

        while range_end - range_start > 0:
            middle = (range_end + range_start) // 2
            txn.execute(sql, (middle,))
            row = txn.fetchone()
            if row is None:
                # no rows with stream_ordering<=middle
                range_start = middle + 1
                continue

            middle_ts = row[0]
            if ts > middle_ts:
                # we got a timestamp lower than the one we were looking for.
                # definitely need to look higher: X > middle.
                range_start = middle + 1
            else:
                # we got a timestamp higher than (or the same as) the one we
                # were looking for. We aren't yet sure about the point we
                # looked up, but we can be sure that X <= middle.
                range_end = middle

        return range_end

    @defer.inlineCallbacks
    def get_time_of_last_push_action_before(self, stream_ordering):
        def f(txn):
            sql = (
                "SELECT e.received_ts"
                " FROM event_push_actions AS ep"
                " JOIN events e ON ep.room_id = e.room_id AND ep.event_id = e.event_id"
                " WHERE ep.stream_ordering > ?"
                " ORDER BY ep.stream_ordering ASC"
                " LIMIT 1"
            )
            txn.execute(sql, (stream_ordering,))
            return txn.fetchone()

        result = yield self.db.runInteraction("get_time_of_last_push_action_before", f)
        return result[0] if result else None


class EventPushActionsStore(EventPushActionsWorkerStore):
    EPA_HIGHLIGHT_INDEX = "epa_highlight_index"

    def __init__(self, database: Database, db_conn, hs):
        super(EventPushActionsStore, self).__init__(database, db_conn, hs)

        self.db.updates.register_background_index_update(
            self.EPA_HIGHLIGHT_INDEX,
            index_name="event_push_actions_u_highlight",
            table="event_push_actions",
            columns=["user_id", "stream_ordering"],
        )

        self.db.updates.register_background_index_update(
            "event_push_actions_highlights_index",
            index_name="event_push_actions_highlights_index",
            table="event_push_actions",
            columns=["user_id", "room_id", "topological_ordering", "stream_ordering"],
            where_clause="highlight=1",
        )

        self._doing_notif_rotation = False
        self._rotate_notif_loop = self._clock.looping_call(
            self._start_rotate_notifs, 30 * 60 * 1000
        )

    def _set_push_actions_for_event_and_users_txn(
        self, txn, events_and_contexts, all_events_and_contexts
    ):
        """Handles moving push actions from staging table to main
        event_push_actions table for all events in `events_and_contexts`.

        Also ensures that all events in `all_events_and_contexts` are removed
        from the push action staging area.

        Args:
            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.
        """

        sql = """
            INSERT INTO event_push_actions (
                room_id, event_id, user_id, actions, stream_ordering,
                topological_ordering, notif, highlight
            )
            SELECT ?, event_id, user_id, actions, ?, ?, notif, highlight
            FROM event_push_actions_staging
            WHERE event_id = ?
        """

        if events_and_contexts:
            txn.executemany(
                sql,
                (
                    (
                        event.room_id,
                        event.internal_metadata.stream_ordering,
                        event.depth,
                        event.event_id,
                    )
                    for event, _ in events_and_contexts
                ),
            )

        for event, _ in events_and_contexts:
            user_ids = self.db.simple_select_onecol_txn(
                txn,
                table="event_push_actions_staging",
                keyvalues={"event_id": event.event_id},
                retcol="user_id",
            )

            for uid in user_ids:
                txn.call_after(
                    self.get_unread_event_push_actions_by_room_for_user.invalidate_many,
                    (event.room_id, uid),
                )

        # Now we delete the staging area for *all* events that were being
        # persisted.
        txn.executemany(
            "DELETE FROM event_push_actions_staging WHERE event_id = ?",
            ((event.event_id,) for event, _ in all_events_and_contexts),
        )

    @defer.inlineCallbacks
    def get_push_actions_for_user(
        self, user_id, before=None, limit=50, only_highlight=False
    ):
        def f(txn):
            before_clause = ""
            if before:
                before_clause = "AND epa.stream_ordering < ?"
                args = [user_id, before, limit]
            else:
                args = [user_id, limit]

            if only_highlight:
                if len(before_clause) > 0:
                    before_clause += " "
                before_clause += "AND epa.highlight = 1"

            # NB. This assumes event_ids are globally unique since
            # it makes the query easier to index
            sql = (
                "SELECT epa.event_id, epa.room_id,"
                " epa.stream_ordering, epa.topological_ordering,"
                " epa.actions, epa.highlight, epa.profile_tag, e.received_ts"
                " FROM event_push_actions epa, events e"
                " WHERE epa.event_id = e.event_id"
                " AND epa.user_id = ? %s"
                " ORDER BY epa.stream_ordering DESC"
                " LIMIT ?" % (before_clause,)
            )
            txn.execute(sql, args)
            return self.db.cursor_to_dict(txn)

        push_actions = yield self.db.runInteraction("get_push_actions_for_user", f)
        for pa in push_actions:
            pa["actions"] = _deserialize_action(pa["actions"], pa["highlight"])
        return push_actions

    @defer.inlineCallbacks
    def get_latest_push_action_stream_ordering(self):
        def f(txn):
            txn.execute("SELECT MAX(stream_ordering) FROM event_push_actions")
            return txn.fetchone()

        result = yield self.db.runInteraction(
            "get_latest_push_action_stream_ordering", f
        )
        return result[0] or 0

    def _remove_push_actions_for_event_id_txn(self, txn, room_id, event_id):
        # Sad that we have to blow away the cache for the whole room here
        txn.call_after(
            self.get_unread_event_push_actions_by_room_for_user.invalidate_many,
            (room_id,),
        )
        txn.execute(
            "DELETE FROM event_push_actions WHERE room_id = ? AND event_id = ?",
            (room_id, event_id),
        )

    def _remove_old_push_actions_before_txn(
        self, txn, room_id, user_id, stream_ordering
    ):
        """
        Purges old push actions for a user and room before a given
        stream_ordering.

        We however keep a months worth of highlighted notifications, so that
        users can still get a list of recent highlights.

        Args:
            txn: The transcation
            room_id: Room ID to delete from
            user_id: user ID to delete for
            stream_ordering: The lowest stream ordering which will
                                  not be deleted.
        """
        txn.call_after(
            self.get_unread_event_push_actions_by_room_for_user.invalidate_many,
            (room_id, user_id),
        )

        # We need to join on the events table to get the received_ts for
        # event_push_actions and sqlite won't let us use a join in a delete so
        # we can't just delete where received_ts < x. Furthermore we can
        # only identify event_push_actions by a tuple of room_id, event_id
        # we we can't use a subquery.
        # Instead, we look up the stream ordering for the last event in that
        # room received before the threshold time and delete event_push_actions
        # in the room with a stream_odering before that.
        txn.execute(
            "DELETE FROM event_push_actions "
            " WHERE user_id = ? AND room_id = ? AND "
            " stream_ordering <= ?"
            " AND ((stream_ordering < ? AND highlight = 1) or highlight = 0)",
            (user_id, room_id, stream_ordering, self.stream_ordering_month_ago),
        )

        txn.execute(
            """
            DELETE FROM event_push_summary
            WHERE room_id = ? AND user_id = ? AND stream_ordering <= ?
        """,
            (room_id, user_id, stream_ordering),
        )

    def _start_rotate_notifs(self):
        return run_as_background_process("rotate_notifs", self._rotate_notifs)

    @defer.inlineCallbacks
    def _rotate_notifs(self):
        if self._doing_notif_rotation or self.stream_ordering_day_ago is None:
            return
        self._doing_notif_rotation = True

        try:
            while True:
                logger.info("Rotating notifications")

                caught_up = yield self.db.runInteraction(
                    "_rotate_notifs", self._rotate_notifs_txn
                )
                if caught_up:
                    break
                yield self.hs.get_clock().sleep(self._rotate_delay)
        finally:
            self._doing_notif_rotation = False

    def _rotate_notifs_txn(self, txn):
        """Archives older notifications into event_push_summary. Returns whether
        the archiving process has caught up or not.
        """

        old_rotate_stream_ordering = self.db.simple_select_one_onecol_txn(
            txn,
            table="event_push_summary_stream_ordering",
            keyvalues={},
            retcol="stream_ordering",
        )

        # We don't to try and rotate millions of rows at once, so we cap the
        # maximum stream ordering we'll rotate before.
        txn.execute(
            """
            SELECT stream_ordering FROM event_push_actions
            WHERE stream_ordering > ?
            ORDER BY stream_ordering ASC LIMIT 1 OFFSET ?
        """,
            (old_rotate_stream_ordering, self._rotate_count),
        )
        stream_row = txn.fetchone()
        if stream_row:
            (offset_stream_ordering,) = stream_row
            rotate_to_stream_ordering = min(
                self.stream_ordering_day_ago, offset_stream_ordering
            )
            caught_up = offset_stream_ordering >= self.stream_ordering_day_ago
        else:
            rotate_to_stream_ordering = self.stream_ordering_day_ago
            caught_up = True

        logger.info("Rotating notifications up to: %s", rotate_to_stream_ordering)

        self._rotate_notifs_before_txn(txn, rotate_to_stream_ordering)

        # We have caught up iff we were limited by `stream_ordering_day_ago`
        return caught_up

    def _rotate_notifs_before_txn(self, txn, rotate_to_stream_ordering):
        old_rotate_stream_ordering = self.db.simple_select_one_onecol_txn(
            txn,
            table="event_push_summary_stream_ordering",
            keyvalues={},
            retcol="stream_ordering",
        )

        # Calculate the new counts that should be upserted into event_push_summary
        sql = """
            SELECT user_id, room_id,
                coalesce(old.notif_count, 0) + upd.notif_count,
                upd.stream_ordering,
                old.user_id
            FROM (
                SELECT user_id, room_id, count(*) as notif_count,
                    max(stream_ordering) as stream_ordering
                FROM event_push_actions
                WHERE ? <= stream_ordering AND stream_ordering < ?
                    AND highlight = 0
                GROUP BY user_id, room_id
            ) AS upd
            LEFT JOIN event_push_summary AS old USING (user_id, room_id)
        """

        txn.execute(sql, (old_rotate_stream_ordering, rotate_to_stream_ordering))
        rows = txn.fetchall()

        logger.info("Rotating notifications, handling %d rows", len(rows))

        # If the `old.user_id` above is NULL then we know there isn't already an
        # entry in the table, so we simply insert it. Otherwise we update the
        # existing table.
        self.db.simple_insert_many_txn(
            txn,
            table="event_push_summary",
            values=[
                {
                    "user_id": row[0],
                    "room_id": row[1],
                    "notif_count": row[2],
                    "stream_ordering": row[3],
                }
                for row in rows
                if row[4] is None
            ],
        )

        txn.executemany(
            """
                UPDATE event_push_summary SET notif_count = ?, stream_ordering = ?
                WHERE user_id = ? AND room_id = ?
            """,
            ((row[2], row[3], row[0], row[1]) for row in rows if row[4] is not None),
        )

        txn.execute(
            "DELETE FROM event_push_actions"
            " WHERE ? <= stream_ordering AND stream_ordering < ? AND highlight = 0",
            (old_rotate_stream_ordering, rotate_to_stream_ordering),
        )

        logger.info("Rotating notifications, deleted %s push actions", txn.rowcount)

        txn.execute(
            "UPDATE event_push_summary_stream_ordering SET stream_ordering = ?",
            (rotate_to_stream_ordering,),
        )


def _action_has_highlight(actions):
    for action in actions:
        try:
            if action.get("set_tweak", None) == "highlight":
                return action.get("value", True)
        except AttributeError:
            pass

    return False