Fatal 'Failed to upgrade database' error on startup

[richvdh]

As of Synapse 1.7.0, when I start synapse with an old database version, I get this rather cryptic error.

[richvdh]

I believe this only affects sqlite. I think it was introduced by #6487, which moves this code which calls prepare_database using a connection that was created with run_new_connection=False into Datastore where it is called on a connection which has had the on_new_connection method handler called.

The sqlite engine, for reasons better known to itself, calls prepare_database in its on_new_connection: https://github.com/matrix-org/synapse/blob/v1.7.0/synapse/storage/engines/sqlite.py#L62.

[richvdh]

turns out this is already fixed by #6513 on develop.