diff options
Diffstat (limited to 'synapse')
| -rw-r--r-- | synapse/storage/event_push_actions.py | 68 |
1 files changed, 53 insertions, 15 deletions
diff --git a/synapse/storage/event_push_actions.py b/synapse/storage/event_push_actions.py index 54b54dcc6a..a8c303e11e 100644 --- a/synapse/storage/event_push_actions.py +++ b/synapse/storage/event_push_actions.py @@ -493,15 +493,15 @@ class EventPushActionsWorkerStore(SQLBaseStore): """Gets the stream ordering corresponding to a given timestamp. Specifically, finds the stream_ordering of the first event that was - received after the timestamp. This is done by a binary search on the - events table, since there is no index on received_ts, so is + 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 after + Deferred[int]: stream ordering of the first event received on/after the timestamp """ return self.runInteraction( @@ -510,16 +510,24 @@ class EventPushActionsWorkerStore(SQLBaseStore): ts, ) - def _find_first_stream_ordering_after_ts_txn(self, txn, ts): + @staticmethod + def _find_first_stream_ordering_after_ts_txn(txn, ts): """ - Find the stream_ordering of the first event that was received 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 + 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] @@ -527,23 +535,53 @@ class EventPushActionsWorkerStore(SQLBaseStore): 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 - + 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" + " WHERE stream_ordering <= ?" + " ORDER BY stream_ordering DESC" " LIMIT 1" ) - while range_end - range_start > 1: - middle = int((range_end + range_start) / 2) + while range_end - range_start > 0: + middle = (range_end + range_start) // 2 txn.execute(sql, (middle,)) - middle_ts = txn.fetchone()[0] + 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: - range_start = middle + # 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 |