drop unused table event_labels

[richvdh]

We seem to have a table called event_labels which is wholly unused

[clokep]

We filter on it at:

synapse/synapse/storage/databases/main/stream.py

Lines 1242 to 1252 in 79dadf7

	if event_filter and event_filter.labels:
	# If we're not filtering on a label, then joining on event_labels will
	# return as many row for a single event as the number of labels it has. To
	# avoid this, only join if we're filtering on at least one label.
	join_clause += """
	LEFT JOIN event_labels
	USING (event_id, room_id, topological_ordering)
	"""
	if len(event_filter.labels) > 1:
	# Multiple labels could cause the same event to appear multiple times.
	needs_distinct = True

And we insert into it at:

synapse/synapse/storage/databases/main/events.py

Lines 1579 to 1584 in 586bfc6

	# Store the labels for this event.
	labels = event.content.get(EventContentFields.LABELS)
	if labels:
	self.insert_labels_for_event_txn(
	txn, event.event_id, labels, event.room_id, event.depth
	)

Note that this is from MSC2326 (but not behind an experimental flag, since it has been there a long time).

[squahtx]

In #1207 @H-Shay, notes that it comes from an implementation of MSC2326. Which I believe has been completely superseded by threading?

I'm in favour of removing it all.

[richvdh]

oh, hrm. I assumed it was unused because it's empty on matrix.org. I'm inclined to rip it out rather than leave essentially-unused code sitting around.

[clokep]

Which I believe has been completely superseded by threading?

I don't really think it has been superseded by threading, but there is an overlap. 🤷 (That conversation likely belongs on the MSC though!)