This changes the replication protocol so that the server does not send down `RDATA` for rows that happened before the client connected. Instead, the server will send a `POSITION` and clients then query the database (or master out of band) to get up to date.

* Pull Sentinel out of LoggingContext

... and drop a few unnecessary references to it

* Factor out LoggingContext.current_context

move `current_context` and `set_context` out to top-level functions.

Mostly this means that I can more easily trace what's actually referring to
LoggingContext, but I think it's generally neater.

* move copy-to-parent into `stop`

this really just makes `start` and `stop` more symetric. It also means that it
behaves correctly if you manually `set_log_context` rather than using the
context manager.

* Replace `LoggingContext.alive` with `finished`

Turn `alive` into `finished` and make it a bit better defined.

This just helps keep the rows closer to their streams, so that it's easier to
see what the format of each stream is.

Attempts to clarify the sample config for databases, and add some stuff about
tcp keepalives to `postgres.md`.

It was originally implemented by pulling the full auth chain of all
state sets out of the database and doing set comparison. However, that
can take a lot work if the state and auth chains are large.

Instead, lets try and fetch the auth chains at the same time and
calculate the difference on the fly, allowing us to bail early if all
the auth chains converge. Assuming that the auth chains do converge more
often than not, this should improve performance. Hopefully.

Extends #5794 etc to the SimpleHttpClient so that it also applies to non-federation requests.

Fixes #7092.

This reverts commit 54dd2862, reversing
changes made to 6640460d.

* Break down monthly active users by appservice_id and emit via prometheus.

Co-authored-by: Brendan Abolivier <babolivier@matrix.org>

This is a precursor to giving EventBase objects the knowledge of which room version they belong to.

Fix #6910

Fix #6910 

to stop the federationhandler trying to do master stuff

When we get an invite over federation, store the room version in the rooms table.

The general idea here is that, when we pull the invite out again, we'll want to know what room_version it belongs to (so that we can later redact it if need be). So we need to store it somewhere...

Ensure 'deactivated' parameter is a boolean on user admin API, Fix error handling of call to deactivate user (#6990)

Ensure good comprehension hygiene using flake8-comprehensions.

The state res v2 algorithm only cares about the difference between auth
chains, so we can pass in the known common state to the `get_auth_chain`
storage function so that it can ignore those events.

it's not in the spec yet, so needs to be unstable. Also add a feature flag for it. Also add a test for admin users.

As per
https://github.com/matrix-org/matrix-doc/pull/2432#pullrequestreview-360566830,
make room alias lists accessible to users outside world_readable rooms.

these were getting a bit unwieldy, so let's combine `check_joined_room` and
`check_user_was_in_room` into a single `check_user_in_room`.

per matrix-org/matrix-doc#2432

Stop sending events when creating or deleting associations (room aliases). Send an updated canonical alias event if one of the alt_aliases is deleted.