This adds quite a lot of OpenTracing decoration for database activity. Specifically it adds tracing at four different levels:

 * emit a span for each "interaction" - ie, the top level database function that we tend to call "transaction", but isn't really, because it can end up as multiple transactions.
 * emit a span while we hold a database connection open
 * emit a span for each database transaction - actual actual transaction.
 * emit a span for each database query.

I'm aware this might be quite a lot of overhead, but even just running it on a local Synapse it looks really interesting, and I hope the overhead can be offset just by turning down the sampling frequency and finding other ways of tracing requests of interest (eg, the `force_tracing_for_users` setting).

The existing tracing reports an error each time there is a timeout, which isn't
really representative.

Additionally, we log things about the way `wait_for_events` works
(eg, the result of the callback) to the *parent* span, which is confusing.

So that they render nicely in mdbook (see #10086), and so that we no longer have a mix of structured text languages in our documentation (excluding files outside of `docs/`).

[MSC2432](https://github.com/matrix-org/matrix-doc/pull/2432) added this endpoint originally but it has since been included in the spec for nearly a year. 

This is progress towards https://github.com/matrix-org/synapse/issues/8334

Related to: #6681, #5956, #10040

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

... using the script from matrix-org/sytest#1052

c.f. https://github.com/matrix-org/synapse/pull/9617 and https://github.com/matrix-org/matrix-doc/blob/master/proposals/2858-Multiple-SSO-Identity-Providers.md

Fixes #9627.

Empirically, this helped my server considerably when handling gaps in Matrix HQ. The problem was that we would repeatedly call have_seen_events for the same set of (50K or so) auth_events, each of which would take many minutes to complete, even though it's only an index scan.

Signed-off-by: Brad Murray <brad@beeper.com>

Fixes #10087.

... because tags on spans which aren't being sampled get thrown away.

Split out from https://github.com/matrix-org/synapse/pull/9247

Strings:

 - `parse_string`
 - `parse_string_from_args`
 - `parse_strings_from_args`

For comparison with ints:

 - `parse_integer`
 - `parse_integer_from_args`

Previous discussions:

 - https://github.com/matrix-org/synapse/pull/9247#discussion_r573195687
 - https://github.com/matrix-org/synapse/pull/9247#discussion_r574214156
 - https://github.com/matrix-org/synapse/pull/9247#discussion_r573264791



Signed-off-by: Eric Eastwood <erice@element.io>

Implements MSC2414: https://github.com/matrix-org/matrix-doc/pull/2414


See #8551 

Signed-off-by: Callum Brown <callum@calcuode.com>

Synapse 1.35.0rc2 (2021-05-27)
==============================

Bugfixes
--------

- Fix a bug introduced in v1.35.0rc1 when calling the spaces summary API via a GET request. ([\#10079](https://github.com/matrix-org/synapse/issues/10079))

Fixes #10068

Fixes a bug due to conflicting PRs which were merged. (One added a new caller to
a method, the other added a new parameter to the same method.)