Autocommit means that we don't wrap the functions in transactions, and instead get executed directly. Introduced in #8456. This will help:
1. reduce the number of `could not serialize access due to concurrent delete` errors that we see (though there are a few functions that often cause serialization errors that we don't fix here);
2. improve the DB performance, as it no longer needs to deal with the overhead of `REPEATABLE READ` isolation levels; and
3. improve wall clock speed of these functions, as we no longer need to send `BEGIN` and `COMMIT` to the DB.
Some notes about the differences between autocommit mode and our default `REPEATABLE READ` transactions:
1. Currently `autocommit` only applies when using PostgreSQL, and is ignored when using SQLite (due to silliness with [Twisted DB classes](https://twistedmatrix.com/trac/ticket/9998)).
2. Autocommit functions may get retried on error, which means they can get applied *twice* (or more) to the DB (since they are not in a transaction the previous call would not get rolled back). This means that the functions need to be idempotent (or otherwise not care about being called multiple times). Read queries, simple deletes, and updates/upserts that replace rows (rather than generating new values from existing rows) are all idempotent.
3. Autocommit functions no longer get executed in [`REPEATABLE READ`](https://www.postgresql.org/docs/current/transaction-iso.html) isolation level, and so data can change queries, which is fine for single statement queries.
We asserted that the IDs returned by postgres sequence was greater than
any we had seen, however this is technically racey as we may update the
current positions out of order.
We now assert that the sequences are correct on startup, so the
assertion is no longer really required, so we remove them.
* Fix outbound federaion with multiple event persisters.
We incorrectly notified federation senders that the minimum persisted
stream position had advanced when we got an `RDATA` from an event
persister.
Notifying of federation senders already correctly happens in the
notifier, so we just delete the offending line.
* Change some interfaces to use RoomStreamToken.
By enforcing use of `RoomStreamTokens` we make it less likely that
people pass in random ints that they got from somewhere random.
Currently background proccesses stream the events stream use the "minimum persisted position" (i.e. `get_current_token()`) rather than the vector clock style tokens. This is broadly fine as it doesn't matter if the background processes lag a small amount. However, in extreme cases (i.e. SyTests) where we only write to one event persister the background processes will never make progress.
This PR changes it so that the `MultiWriterIDGenerator` keeps the current position of a given instance as up to date as possible (i.e using the latest token it sees if its not in the process of persisting anything), and then periodically announces that over replication. This then allows the "minimum persisted position" to advance, albeit with a small lag.
This PR allows Synapse modules making use of the `ModuleApi` to create and send non-membership events into a room. This can useful to have modules send messages, or change power levels in a room etc. Note that they must send event through a user that's already in the room.
The non-membership event limitation is currently arbitrary, as it's another chunk of work and not necessary at the moment.
==============================
Bugfixes
--------
- Fix duplication of events on high traffic servers, caused by PostgreSQL `could not serialize access due to concurrent update` errors. ([\#8456](https://github.com/matrix-org/synapse/issues/8456))
Internal Changes
----------------
- Add Groovy Gorilla to the list of distributions we build `.deb`s for. ([\#8475](https://github.com/matrix-org/synapse/issues/8475))
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Merge tag 'v1.21.0rc3' into develop
Synapse 1.21.0rc3 (2020-10-08)
==============================
Bugfixes
--------
- Fix duplication of events on high traffic servers, caused by PostgreSQL `could not serialize access due to concurrent update` errors. ([\#8456](https://github.com/matrix-org/synapse/issues/8456))
Internal Changes
----------------
- Add Groovy Gorilla to the list of distributions we build `.deb`s for. ([\#8475](https://github.com/matrix-org/synapse/issues/8475))
We call `_update_stream_positions_table_txn` a lot, which is an UPSERT
that can conflict in `REPEATABLE READ` isolation level. Instead of doing
a transaction consisting of a single query we may as well run it outside
of a transaction.
We call `_update_stream_positions_table_txn` a lot, which is an UPSERT
that can conflict in `REPEATABLE READ` isolation level. Instead of doing
a transaction consisting of a single query we may as well run it outside
of a transaction.
Currently when using multiple event persisters we (in the worst case) don't tell clients about events until all event persisters have persisted new events after the original event. This is a suboptimal, especially if one of the event persisters goes down.
To handle this, we encode the position of each event persister in the room tokens so that we can send events to clients immediately. To reduce the size of the token we do two things:
1. We create a unique immutable persistent mapping between instance names and a generated small integer ID, which we can encode in the tokens instead of the instance name; and
2. We encode the "persisted upto position" of the room token and then only explicitly include instances that have positions strictly greater than that.
The new tokens look something like: `m3478~1.3488~2.3489`, where the first number is the min position, and the subsequent `-` separated pairs are the instance ID to positions map. (We use `.` and `~` as separators as they're URL safe and not already used by `StreamToken`).
Lots of different module apis is not easy to maintain.
Rather than adding yet another ModuleApi(hs, hs.get_auth_handler()) incantation, first add an hs.get_module_api() method and use it where possible.
* Optimise and test state fetching for 3p event rules
Getting all the events at once is much more efficient than getting them
individually
* Test that 3p event rules can modify events
PR #8292 tried to maintain backwards compat with modules which don't provide a
`check_visibility_can_be_modified` method, but the tests weren't being run,
and the check didn't work.
