Due to the table locks taken out by the naive upsert, the table
statistics may be out of date. During deduplication it is important that
the correct index is used as otherwise a full table scan may be
incorrectly used, which can end up thrashing the database badly.
The background update to remove duplicate rows naively deleted and
reinserted the duplicates. For large tables with a large number of
duplicates this causes a lot of bloat (with postgres), as the inserted
rows are appended to the table, since deleted rows will not be
overwritten until a VACUUM has happened.
This should hopefully also help ensure that the query in the last batch
uses the correct index, as inserting a large number of new rows without
analyzing will upset the query planner.
Add more tables to the list of tables which need a background update to
complete before we can upsert into them, which fixes a race against the
background updates.
Currently they're stored as non-outliers even though the server isn't in
the room, which can be problematic in places where the code assumes it
has the state for all non outlier events.
In particular, there is an edge case where persisting the leave event
triggers a state resolution, which requires looking up the room version
from state. Since the server doesn't have the state, this causes an
exception to be thrown.
Currently we only have the one event format version defined, but this
adds the necessary infrastructure to persist and fetch the format
versions alongside the events.
We specify the format version rather than the room version as:
1. We don't necessarily know the room version, existing events may be
either v1 or v2.
2. We'd need to be careful to prevent/handle correctly if different
events in the same room reported to be of different versions, which
sounds annoying.
This was caused by accidentally overwritting a `last_seen` variable
in a for loop, causing the wrong value to be written to the progress
table. The result of which was that we didn't scan sections of the table
when searching for duplicates, and so some duplicates did not get
deleted.
