EventsPersistenceStorageController.persist_event is only used by test code

[anoadragon453]

The following method is only used by test code (albeit extensively):

synapse/synapse/storage/controllers/persist_events.py

Lines 441 to 474 in 6caa303

	@trace
	async def persist_event(
	self, event: EventBase, context: EventContext, backfilled: bool = False
	) -> Tuple[EventBase, PersistedEventPosition, RoomStreamToken]:
	"""
	Returns:
	The event, stream ordering of `event`, and the stream ordering of the
	latest persisted event. The returned event may not match the given
	event if it was deduplicated due to an existing event matching the
	transaction ID.
	Raises:
	PartialStateConflictError: if attempting to persist a partial state event in
	a room that has been un-partial stated.
	"""
	# add_to_queue returns a map from event ID to existing event ID if the
	# event was deduplicated. (The dict may also include other entries if
	# the event was persisted in a batch with other events.)
	replaced_events = await self._event_persist_queue.add_to_queue(
	event.room_id,
	_PersistEventsTask(
	events_and_contexts=[(event, context)], backfilled=backfilled
	),
	)
	replaced_event = replaced_events.get(event.event_id)
	if replaced_event:
	event = await self.main_store.get_event(replaced_event)
	event_stream_id = event.internal_metadata.stream_ordering
	# stream ordering should have been assigned by now
	assert event_stream_id
	pos = PersistedEventPosition(self._instance_name, event_stream_id)
	return event, pos, self.main_store.get_room_max_token()

Non-test code instead makes use of EventsPersistenceStorageController.persist_events:

synapse/synapse/storage/controllers/persist_events.py

Lines 364 to 439 in 6caa303

	@trace
	async def persist_events(
	self,
	events_and_contexts: Iterable[Tuple[EventBase, EventContext]],
	backfilled: bool = False,
	) -> Tuple[List[EventBase], RoomStreamToken]:
	"""
	Write events to the database
	Args:
	events_and_contexts: list of tuples of (event, context)
	backfilled: 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:
	List of events persisted, the current position room stream position.
	The list of events persisted may not be the same as those passed in
	if they were deduplicated due to an event already existing that
	matched the transaction ID; the existing event is returned in such
	a case.
	Raises:
	PartialStateConflictError: if attempting to persist a partial state event in
	a room that has been un-partial stated.
	"""
	event_ids: List[str] = []
	partitioned: Dict[str, List[Tuple[EventBase, EventContext]]] = {}
	for event, ctx in events_and_contexts:
	partitioned.setdefault(event.room_id, []).append((event, ctx))
	event_ids.append(event.event_id)
	set_tag(
	SynapseTags.FUNC_ARG_PREFIX + "event_ids",
	str(event_ids),
	)
	set_tag(
	SynapseTags.FUNC_ARG_PREFIX + "event_ids.length",
	str(len(event_ids)),
	)
	set_tag(SynapseTags.FUNC_ARG_PREFIX + "backfilled", str(backfilled))
	async def enqueue(
	item: Tuple[str, List[Tuple[EventBase, EventContext]]]
	) -> Dict[str, str]:
	room_id, evs_ctxs = item
	return await self._event_persist_queue.add_to_queue(
	room_id,
	_PersistEventsTask(events_and_contexts=evs_ctxs, backfilled=backfilled),
	)
	ret_vals = await yieldable_gather_results(enqueue, partitioned.items())
	# Each call to add_to_queue returns a map from event ID to existing event ID if
	# the event was deduplicated. (The dict may also include other entries if
	# the event was persisted in a batch with other events).
	#
	# Since we use `yieldable_gather_results` we need to merge the returned list
	# of dicts into one.
	replaced_events: Dict[str, str] = {}
	for d in ret_vals:
	replaced_events.update(d)
	persisted_events = []
	for event, _ in events_and_contexts:
	existing_event_id = replaced_events.get(event.event_id)
	if existing_event_id:
	persisted_events.append(
	await self.main_store.get_event(existing_event_id)
	)
	else:
	persisted_events.append(event)
	return (
	persisted_events,
	self.main_store.get_room_max_token(),
	)

It seems sensible to remove persist_event and migrate the test code to use the plural version of the method instead.

[squahtx]

Note that https://github.com/matrix-org/synapse/pull/13800/files#diff-3d4a81fcc5b115c649ae67aaba0dd4dd0c5827bb001dfcb90b00ffb1605d518eL1840-L1842 removed the last non-test usage of persist_event