When figuring out which topological token to start a purge job at, we
need to do the following:
1. Figure out a timestamp before which events will be purged
2. Select the first stream ordering after that timestamp
3. Select info about the first event after that stream ordering
4. Build a topological token from that info
In some situations (e.g. quiet rooms with a short max_lifetime), there
might not be an event after the stream ordering at step 3, therefore we
abort the purge with the error `No event found`. To mitigate that, this
patch fetches the first event _before_ the stream ordering, instead of
after.
PaginationHandler.get_messages is only called by RoomMessageListRestServlet,
which is async.
Chase the code path down from there:
- FederationHandler.maybe_backfill (and nested try_backfill)
- FederationHandler.backfill
If no `from` param is specified we calculate and use the "current
token" that inlcuded typing, presence, etc. These are unused during
pagination and are not available on workers, so we simply don't
calculate them.
Currently when fetching state groups from the data store we make two
hits two the database: once for members and once for non-members (unless
request is filtered to one or the other). This adds needless load to the
datbase, so this PR refactors the lookup to make only a single database
hit.
don't filter membership events based on history visibility
as we will already have filtered the messages in the timeline, and state events
are always visible.
and because @erikjohnston said so.
