Consider using the "ignored_users" database table when filtering client events

[anoadragon453]

When ignoring a user, clients modify a m.ignored_user_list key in their account data (spec). Synapse will detect if this is happening, and modify an equivalent database table named ignored_users. The idea is that the database table is faster to read from than digging the value out of account data.

The table is used when calculating bulk push rules:

synapse/synapse/push/bulk_push_rule_evaluator.py

Lines 212 to 216 in 10a88ba

	# If the event is not a state event check if any users ignore the sender.
	if not event.is_state():
	ignorers = await self.store.ignored_by(event.sender)
	else:
	ignorers = set()

synapse/synapse/storage/databases/main/account_data.py

Lines 367 to 385 in af79517

	@cached(max_entries=5000, iterable=True)
	async def ignored_by(self, user_id: str) -> Set[str]:
	"""
	Get users which ignore the given user.
	Params:
	user_id: The user ID which might be ignored.
	Return:
	The user IDs which ignore the given user.
	"""
	return set(
	await self.db_pool.simple_select_onecol(
	table="ignored_users",
	keyvalues={"ignored_user_id": user_id},
	retcol="ignorer_user_id",
	desc="ignored_by",
	)
	)

Yet it is not used when ignored users are considered while filtering events for clients (i.e. for /sync):

synapse/synapse/handlers/sync.py

Lines 1613 to 1634 in 64ec45f

	async def _get_ignored_users(self, user_id: str) -> FrozenSet[str]:
	"""Retrieve the users ignored by the given user from their global account_data.
	Returns an empty set if
	- there is no global account_data entry for ignored_users
	- there is such an entry, but it's not a JSON object.
	"""
	# TODO: Can we `SELECT ignored_user_id FROM ignored_users WHERE ignorer_user_id=?;` instead?
	ignored_account_data = (
	await self.store.get_global_account_data_by_type_for_user(
	user_id=user_id, data_type=AccountDataTypes.IGNORED_USER_LIST
	)
	)
	# If there is ignored users account data and it matches the proper type,
	# then use it.
	ignored_users: FrozenSet[str] = frozenset()
	if ignored_account_data:
	ignored_users_data = ignored_account_data.get("ignored_users", {})
	if isinstance(ignored_users_data, dict):
	ignored_users = frozenset(ignored_users_data.keys())
	return ignored_users

synapse/synapse/visibility.py

Lines 89 to 91 in 4c20965

	ignore_dict_content = await storage.main.get_global_account_data_by_type_for_user(
	user_id, AccountDataTypes.IGNORED_USER_LIST
	)

I'm not sure how much of an optimisation this would really be (as get_global_account_data_by_type_for_user is cached on key (user_id, account_data_type)). In addition, we'd need an index of the ignorer_user column, which doesn't currently exist.

On the flip side - it is a nice idea to consolidate where we pull this information from.

[clokep]

On the flip side - it is a nice idea to consolidate where we pull this information from.

I think another nice benefit is that you don't need to do the error checking (of ensuring it is a dict, etc.)

[clokep]

I'm going to look at this in light of #11753 poking a bit at ignored users too.