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Synapse |support| |development| |documentation| |license| |pypi| |python|
=========================================================================
Synapse is an open-source `Matrix <https://matrix.org/>`_ homeserver written and
maintained by the Matrix.org Foundation. We began rapid development began in 2014,
reaching v1.0.0 in 2019. Development on Synapse and the Matrix protocol itself continues
in earnest today.
Briefly, Matrix is an open standard for communications on the internet, supporting
federation, encryption and VoIP. Matrix.org has more to say about the `goals of the
Matrix project <https://matrix.org/docs/guides/introduction>`_, and the `formal specification
<https://spec.matrix.org/>`_ describes the technical details.
.. contents::
Introduction
============
Installing and configuration
============================
Matrix is an ambitious new ecosystem for open federated Instant Messaging and
VoIP. The basics you need to know to get up and running are:
- Everything in Matrix happens in a room. Rooms are distributed and do not
exist on any single server. Rooms can be located using convenience aliases
like ``#matrix:matrix.org`` or ``#test:localhost:8448``.
- Matrix user IDs look like ``@matthew:matrix.org`` (although in the future
you will normally refer to yourself and others using a third party identifier
(3PID): email address, phone number, etc rather than manipulating Matrix user IDs)
The overall architecture is::
client <----> homeserver <=====================> homeserver <----> client
https://somewhere.org/_matrix https://elsewhere.net/_matrix
``#matrix:matrix.org`` is the official support room for Matrix, and can be
accessed by any client from https://matrix.org/docs/projects/try-matrix-now.html or
via IRC bridge at irc://irc.libera.chat/matrix.
Synapse is currently in rapid development, but as of version 0.5 we believe it
is sufficiently stable to be run as an internet-facing service for real usage!
About Matrix
============
Matrix specifies a set of pragmatic RESTful HTTP JSON APIs as an open standard,
which handle:
- Creating and managing fully distributed chat rooms with no
single points of control or failure
- Eventually-consistent cryptographically secure synchronisation of room
state across a global open network of federated servers and services
- Sending and receiving extensible messages in a room with (optional)
end-to-end encryption
- Inviting, joining, leaving, kicking, banning room members
- Managing user accounts (registration, login, logout)
- Using 3rd Party IDs (3PIDs) such as email addresses, phone numbers,
Facebook accounts to authenticate, identify and discover users on Matrix.
- Placing 1:1 VoIP and Video calls
These APIs are intended to be implemented on a wide range of servers, services
and clients, letting developers build messaging and VoIP functionality on top
of the entirely open Matrix ecosystem rather than using closed or proprietary
solutions. The hope is for Matrix to act as the building blocks for a new
generation of fully open and interoperable messaging and VoIP apps for the
internet.
Synapse is a Matrix "homeserver" implementation developed by the matrix.org core
team, written in Python 3/Twisted.
In Matrix, every user runs one or more Matrix clients, which connect through to
a Matrix homeserver. The homeserver stores all their personal chat history and
user account information - much as a mail client connects through to an
IMAP/SMTP server. Just like email, you can either run your own Matrix
homeserver and control and own your own communications and history or use one
hosted by someone else (e.g. matrix.org) - there is no single point of control
or mandatory service provider in Matrix, unlike WhatsApp, Facebook, Hangouts,
etc.
We'd like to invite you to join #matrix:matrix.org (via
https://matrix.org/docs/projects/try-matrix-now.html), run a homeserver, take a look
at the `Matrix spec <https://matrix.org/docs/spec>`_, and experiment with the
`APIs <https://matrix.org/docs/api>`_ and `Client SDKs
<https://matrix.org/docs/projects/try-matrix-now.html#client-sdks>`_.
Thanks for using Matrix!
Support
=======
For support installing or managing Synapse, please join |room|_ (from a matrix.org
account if necessary) and ask questions there. We do not use GitHub issues for
support requests, only for bug reports and feature requests.
Synapse's documentation is `nicely rendered on GitHub Pages <https://matrix-org.github.io/synapse>`_,
with its source available in |docs|_.
.. |room| replace:: ``#synapse:matrix.org``
.. _room: https://matrix.to/#/#synapse:matrix.org
.. |docs| replace:: ``docs``
.. _docs: docs
Synapse Installation
====================
The Synapse documentation describes `how to install Synapse <https://matrix-org.github.io/synapse/latest/setup/installation.html>`_. We recommend using
`Docker images <https://matrix-org.github.io/synapse/latest/setup/installation.html#docker-images-and-ansible-playbooks>`_ or `Debian packages from Matrix.org
<https://matrix-org.github.io/synapse/latest/setup/installation.html#matrixorg-packages>`_.
.. _federation:
* For details on how to install synapse, see
`Installation Instructions <https://matrix-org.github.io/synapse/latest/setup/installation.html>`_.
* For specific details on how to configure Synapse for federation see `docs/federate.md <docs/federate.md>`_
Synapse has a variety of `config options
<https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html>`_
which can be used to customise its behaviour after installation.
There are additional details on how to `configure Synapse for federation here
<https://matrix-org.github.io/synapse/latest/federate.html>`_.
.. _reverse-proxy:
Using a reverse proxy with Synapse
----------------------------------
It is recommended to put a reverse proxy such as
`nginx <https://nginx.org/en/docs/http/ngx_http_proxy_module.html>`_,
`Apache <https://httpd.apache.org/docs/current/mod/mod_proxy_http.html>`_,
`Caddy <https://caddyserver.com/docs/quick-starts/reverse-proxy>`_,
`HAProxy <https://www.haproxy.org/>`_ or
`relayd <https://man.openbsd.org/relayd.8>`_ in front of Synapse. One advantage of
doing so is that it means that you can expose the default https port (443) to
Matrix clients without needing to run Synapse with root privileges.
For information on configuring one, see `the reverse proxy docs
<https://matrix-org.github.io/synapse/latest/reverse_proxy.html>`_.
Upgrading an existing Synapse
-----------------------------
The instructions for upgrading Synapse are in `the upgrade notes`_.
Please check these instructions as upgrading may require extra steps for some
versions of Synapse.
.. _the upgrade notes: https://matrix-org.github.io/synapse/develop/upgrade.html
Connecting to Synapse from a client
===================================
Platform dependencies
---------------------
The easiest way to try out your new Synapse installation is by connecting to it
from a web client.
Synapse uses a number of platform dependencies such as Python and PostgreSQL,
and aims to follow supported upstream versions. See the
`deprecation policy <https://matrix-org.github.io/synapse/latest/deprecation_policy.html>`_
for more details.
Unless you are running a test instance of Synapse on your local machine, in
general, you will need to enable TLS support before you can successfully
connect from a client: see
`TLS certificates <https://matrix-org.github.io/synapse/latest/setup/installation.html#tls-certificates>`_.
An easy way to get started is to login or register via Element at
https://app.element.io/#/login or https://app.element.io/#/register respectively.
You will need to change the server you are logging into from ``matrix.org``
and instead specify a Homeserver URL of ``https://<server_name>:8448``
(or just ``https://<server_name>`` if you are using a reverse proxy).
If you prefer to use another client, refer to our
`client breakdown <https://matrix.org/docs/projects/clients-matrix>`_.
If all goes well you should at least be able to log in, create a room, and
start sending messages.
.. _`client-user-reg`:
Registering a new user from a client
------------------------------------
By default, registration of new users via Matrix clients is disabled. To enable
it, specify ``enable_registration: true`` in ``homeserver.yaml``. (It is then
recommended to also set up CAPTCHA - see `<docs/CAPTCHA_SETUP.md>`_.)
Once ``enable_registration`` is set to ``true``, it is possible to register a
user via a Matrix client.
Your new user name will be formed partly from the ``server_name``, and partly
from a localpart you specify when you create the account. Your name will take
the form of::
@localpart:my.domain.name
(pronounced "at localpart on my dot domain dot name").
As when logging in, you will need to specify a "Custom server". Specify your
desired ``localpart`` in the 'User name' box.
Security note
=============
-------------
Matrix serves raw, user-supplied data in some APIs -- specifically the `content
repository endpoints`_.
@ -187,30 +105,76 @@ Following this advice ensures that even if an XSS is found in Synapse, the
impact to other applications will be minimal.
Upgrading an existing Synapse
=============================
Testing a new installation
==========================
The instructions for upgrading synapse are in `the upgrade notes`_.
Please check these instructions as upgrading may require extra steps for some
versions of synapse.
The easiest way to try out your new Synapse installation is by connecting to it
from a web client.
.. _the upgrade notes: https://matrix-org.github.io/synapse/develop/upgrade.html
Unless you are running a test instance of Synapse on your local machine, in
general, you will need to enable TLS support before you can successfully
connect from a client: see
`TLS certificates <https://matrix-org.github.io/synapse/latest/setup/installation.html#tls-certificates>`_.
.. _reverse-proxy:
An easy way to get started is to login or register via Element at
https://app.element.io/#/login or https://app.element.io/#/register respectively.
You will need to change the server you are logging into from ``matrix.org``
and instead specify a Homeserver URL of ``https://<server_name>:8448``
(or just ``https://<server_name>`` if you are using a reverse proxy).
If you prefer to use another client, refer to our
`client breakdown <https://matrix.org/docs/projects/clients-matrix>`_.
Using a reverse proxy with Synapse
==================================
If all goes well you should at least be able to log in, create a room, and
start sending messages.
It is recommended to put a reverse proxy such as
`nginx <https://nginx.org/en/docs/http/ngx_http_proxy_module.html>`_,
`Apache <https://httpd.apache.org/docs/current/mod/mod_proxy_http.html>`_,
`Caddy <https://caddyserver.com/docs/quick-starts/reverse-proxy>`_,
`HAProxy <https://www.haproxy.org/>`_ or
`relayd <https://man.openbsd.org/relayd.8>`_ in front of Synapse. One advantage of
doing so is that it means that you can expose the default https port (443) to
Matrix clients without needing to run Synapse with root privileges.
.. _`client-user-reg`:
For information on configuring one, see `<docs/reverse_proxy.md>`_.
Registering a new user from a client
------------------------------------
By default, registration of new users via Matrix clients is disabled. To enable
it:
1. In the
`registration config section <https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#registration>`_
set ``enable_registration: true`` in ``homeserver.yaml``.
2. Then **either**:
a. set up a `CAPTCHA <https://matrix-org.github.io/synapse/latest/CAPTCHA_SETUP.html>`_, or
b. set ``enable_registration_without_verification: true`` in ``homeserver.yaml``.
We **strongly** recommend using a CAPTCHA, particularly if your homeserver is exposed to
the public internet. Without it, anyone can freely register accounts on your homeserver.
This can be exploited by attackers to create spambots targetting the rest of the Matrix
federation.
Your new user name will be formed partly from the ``server_name``, and partly
from a localpart you specify when you create the account. Your name will take
the form of::
@localpart:my.domain.name
(pronounced "at localpart on my dot domain dot name").
As when logging in, you will need to specify a "Custom server". Specify your
desired ``localpart`` in the 'User name' box.
Troubleshooting and support
===========================
The `Admin FAQ <https://matrix-org.github.io/synapse/latest/usage/administration/admin_faq.html>`_
includes tips on dealing with some common problems. For more details, see
`Synapse's wider documentation <https://matrix-org.github.io/synapse/latest/>`_.
For additional support installing or managing Synapse, please ask in the community
support room |room|_ (from a matrix.org account if necessary). We do not use GitHub
issues for support requests, only for bug reports and feature requests.
.. |room| replace:: ``#synapse:matrix.org``
.. _room: https://matrix.to/#/#synapse:matrix.org
.. |docs| replace:: ``docs``
.. _docs: docs
Identity Servers
================
@ -242,34 +206,15 @@ an email address with your account, or send an invite to another user via their
email address.
Password reset
==============
Users can reset their password through their client. Alternatively, a server admin
can reset a users password using the `admin API <docs/admin_api/user_admin_api.md#reset-password>`_
or by directly editing the database as shown below.
First calculate the hash of the new password::
$ ~/synapse/env/bin/hash_password
Password:
Confirm password:
$2a$12$xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Then update the ``users`` table in the database::
UPDATE users SET password_hash='$2a$12$xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
WHERE name='@test:test.com';
Synapse Development
===================
Development
===========
We welcome contributions to Synapse from the community!
The best place to get started is our
`guide for contributors <https://matrix-org.github.io/synapse/latest/development/contributing_guide.html>`_.
This is part of our larger `documentation <https://matrix-org.github.io/synapse/latest>`_, which includes
information for synapse developers as well as synapse administrators.
information for Synapse developers as well as Synapse administrators.
Developers might be particularly interested in:
* `Synapse's database schema <https://matrix-org.github.io/synapse/latest/development/database_schema.html>`_,
@ -280,187 +225,6 @@ Alongside all that, join our developer community on Matrix:
`#synapse-dev:matrix.org <https://matrix.to/#/#synapse-dev:matrix.org>`_, featuring real humans!
Quick start
-----------
Before setting up a development environment for synapse, make sure you have the
system dependencies (such as the python header files) installed - see
`Platform-specific prerequisites <https://matrix-org.github.io/synapse/latest/setup/installation.html#platform-specific-prerequisites>`_.
To check out a synapse for development, clone the git repo into a working
directory of your choice::
git clone https://github.com/matrix-org/synapse.git
cd synapse
Synapse has a number of external dependencies. We maintain a fixed development
environment using `Poetry <https://python-poetry.org/>`_. First, install poetry. We recommend::
pip install --user pipx
pipx install poetry
as described `here <https://python-poetry.org/docs/#installing-with-pipx>`_.
(See `poetry's installation docs <https://python-poetry.org/docs/#installation>`_
for other installation methods.) Then ask poetry to create a virtual environment
from the project and install Synapse's dependencies::
poetry install --extras "all test"
This will run a process of downloading and installing all the needed
dependencies into a virtual env.
We recommend using the demo which starts 3 federated instances running on ports `8080` - `8082`::
poetry run ./demo/start.sh
(to stop, you can use ``poetry run ./demo/stop.sh``)
See the `demo documentation <https://matrix-org.github.io/synapse/develop/development/demo.html>`_
for more information.
If you just want to start a single instance of the app and run it directly::
# Create the homeserver.yaml config once
poetry run synapse_homeserver \
--server-name my.domain.name \
--config-path homeserver.yaml \
--generate-config \
--report-stats=[yes|no]
# Start the app
poetry run synapse_homeserver --config-path homeserver.yaml
Running the unit tests
----------------------
After getting up and running, you may wish to run Synapse's unit tests to
check that everything is installed correctly::
poetry run trial tests
This should end with a 'PASSED' result (note that exact numbers will
differ)::
Ran 1337 tests in 716.064s
PASSED (skips=15, successes=1322)
For more tips on running the unit tests, like running a specific test or
to see the logging output, see the `CONTRIBUTING doc <CONTRIBUTING.md#run-the-unit-tests>`_.
Running the Integration Tests
-----------------------------
Synapse is accompanied by `SyTest <https://github.com/matrix-org/sytest>`_,
a Matrix homeserver integration testing suite, which uses HTTP requests to
access the API as a Matrix client would. It is able to run Synapse directly from
the source tree, so installation of the server is not required.
Testing with SyTest is recommended for verifying that changes related to the
Client-Server API are functioning correctly. See the `SyTest installation
instructions <https://github.com/matrix-org/sytest#installing>`_ for details.
Platform dependencies
=====================
Synapse uses a number of platform dependencies such as Python and PostgreSQL,
and aims to follow supported upstream versions. See the
`<docs/deprecation_policy.md>`_ document for more details.
Troubleshooting
===============
Need help? Join our community support room on Matrix:
`#synapse:matrix.org <https://matrix.to/#/#synapse:matrix.org>`_
Running out of File Handles
---------------------------
If synapse runs out of file handles, it typically fails badly - live-locking
at 100% CPU, and/or failing to accept new TCP connections (blocking the
connecting client). Matrix currently can legitimately use a lot of file handles,
thanks to busy rooms like #matrix:matrix.org containing hundreds of participating
servers. The first time a server talks in a room it will try to connect
simultaneously to all participating servers, which could exhaust the available
file descriptors between DNS queries & HTTPS sockets, especially if DNS is slow
to respond. (We need to improve the routing algorithm used to be better than
full mesh, but as of March 2019 this hasn't happened yet).
If you hit this failure mode, we recommend increasing the maximum number of
open file handles to be at least 4096 (assuming a default of 1024 or 256).
This is typically done by editing ``/etc/security/limits.conf``
Separately, Synapse may leak file handles if inbound HTTP requests get stuck
during processing - e.g. blocked behind a lock or talking to a remote server etc.
This is best diagnosed by matching up the 'Received request' and 'Processed request'
log lines and looking for any 'Processed request' lines which take more than
a few seconds to execute. Please let us know at #synapse:matrix.org if
you see this failure mode so we can help debug it, however.
Help!! Synapse is slow and eats all my RAM/CPU!
-----------------------------------------------
First, ensure you are running the latest version of Synapse, using Python 3
with a PostgreSQL database.
Synapse's architecture is quite RAM hungry currently - we deliberately
cache a lot of recent room data and metadata in RAM in order to speed up
common requests. We'll improve this in the future, but for now the easiest
way to either reduce the RAM usage (at the risk of slowing things down)
is to set the almost-undocumented ``SYNAPSE_CACHE_FACTOR`` environment
variable. The default is 0.5, which can be decreased to reduce RAM usage
in memory constrained enviroments, or increased if performance starts to
degrade.
However, degraded performance due to a low cache factor, common on
machines with slow disks, often leads to explosions in memory use due
backlogged requests. In this case, reducing the cache factor will make
things worse. Instead, try increasing it drastically. 2.0 is a good
starting value.
Using `libjemalloc <http://jemalloc.net/>`_ can also yield a significant
improvement in overall memory use, and especially in terms of giving back
RAM to the OS. To use it, the library must simply be put in the
LD_PRELOAD environment variable when launching Synapse. On Debian, this
can be done by installing the ``libjemalloc1`` package and adding this
line to ``/etc/default/matrix-synapse``::
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.1
This can make a significant difference on Python 2.7 - it's unclear how
much of an improvement it provides on Python 3.x.
If you're encountering high CPU use by the Synapse process itself, you
may be affected by a bug with presence tracking that leads to a
massive excess of outgoing federation requests (see `discussion
<https://github.com/matrix-org/synapse/issues/3971>`_). If metrics
indicate that your server is also issuing far more outgoing federation
requests than can be accounted for by your users' activity, this is a
likely cause. The misbehavior can be worked around by setting
the following in the Synapse config file:
.. code-block:: yaml
presence:
enabled: false
People can't accept room invitations from me
--------------------------------------------
The typical failure mode here is that you send an invitation to someone
to join a room or direct chat, but when they go to accept it, they get an
error (typically along the lines of "Invalid signature"). They might see
something like the following in their logs::
2019-09-11 19:32:04,271 - synapse.federation.transport.server - 288 - WARNING - GET-11752 - authenticate_request failed: 401: Invalid signature for server <server> with key ed25519:a_EqML: Unable to verify signature for <server>
This is normally caused by a misconfiguration in your reverse-proxy. See
`<docs/reverse_proxy.md>`_ and double-check that your settings are correct.
.. |support| image:: https://img.shields.io/matrix/synapse:matrix.org?label=support&logo=matrix
:alt: (get support on #synapse:matrix.org)
:target: https://matrix.to/#/#synapse:matrix.org

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@ -0,0 +1 @@
Tidy up Synapse's README.

90
docs/usage/administration/admin_faq.md
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@ -2,9 +2,9 @@
How do I become a server admin?
---
If your server already has an admin account you should use the user admin API to promote other accounts to become admins. See [User Admin API](../../admin_api/user_admin_api.md#Change-whether-a-user-is-a-server-administrator-or-not)
If your server already has an admin account you should use the [User Admin API](../../admin_api/user_admin_api.md#Change-whether-a-user-is-a-server-administrator-or-not) to promote other accounts to become admins.
If you don't have any admin accounts yet you won't be able to use the admin API so you'll have to edit the database manually. Manually editing the database is generally not recommended so once you have an admin account, use the admin APIs to make further changes.
If you don't have any admin accounts yet you won't be able to use the admin API, so you'll have to edit the database manually. Manually editing the database is generally not recommended so once you have an admin account: use the admin APIs to make further changes.
```sql
UPDATE users SET admin = 1 WHERE name = '@foo:bar.com';
@ -32,9 +32,11 @@ What users are registered on my server?
SELECT NAME from users;
```
Manually resetting passwords:
Manually resetting passwords
---
See https://github.com/matrix-org/synapse/blob/master/README.rst#password-reset
Users can reset their password through their client. Alternatively, a server admin
can reset a user's password using the [admin API](../../admin_api/user_admin_api.md#reset-password).
I have a problem with my server. Can I just delete my database and start again?
---
@ -101,3 +103,83 @@ LIMIT 10;
You can also use the [List Room API](../../admin_api/rooms.md#list-room-api)
and `order_by` `state_events`.
People can't accept room invitations from me
---
The typical failure mode here is that you send an invitation to someone
to join a room or direct chat, but when they go to accept it, they get an
error (typically along the lines of "Invalid signature"). They might see
something like the following in their logs:
2019-09-11 19:32:04,271 - synapse.federation.transport.server - 288 - WARNING - GET-11752 - authenticate_request failed: 401: Invalid signature for server <server> with key ed25519:a_EqML: Unable to verify signature for <server>
This is normally caused by a misconfiguration in your reverse-proxy. See [the reverse proxy docs](docs/reverse_proxy.md) and double-check that your settings are correct.
Help!! Synapse is slow and eats all my RAM/CPU!
-----------------------------------------------
First, ensure you are running the latest version of Synapse, using Python 3
with a [PostgreSQL database](../../postgres.md).
Synapse's architecture is quite RAM hungry currently - we deliberately
cache a lot of recent room data and metadata in RAM in order to speed up
common requests. We'll improve this in the future, but for now the easiest
way to either reduce the RAM usage (at the risk of slowing things down)
is to set the almost-undocumented ``SYNAPSE_CACHE_FACTOR`` environment
variable. The default is 0.5, which can be decreased to reduce RAM usage
in memory constrained environments, or increased if performance starts to
degrade.
However, degraded performance due to a low cache factor, common on
machines with slow disks, often leads to explosions in memory use due
backlogged requests. In this case, reducing the cache factor will make
things worse. Instead, try increasing it drastically. 2.0 is a good
starting value.
Using [libjemalloc](https://jemalloc.net) can also yield a significant
improvement in overall memory use, and especially in terms of giving back
RAM to the OS. To use it, the library must simply be put in the
LD_PRELOAD environment variable when launching Synapse. On Debian, this
can be done by installing the `libjemalloc1` package and adding this
line to `/etc/default/matrix-synapse`:
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.1
This made a significant difference on Python 2.7 - it's unclear how
much of an improvement it provides on Python 3.x.
If you're encountering high CPU use by the Synapse process itself, you
may be affected by a bug with presence tracking that leads to a
massive excess of outgoing federation requests (see [discussion](https://github.com/matrix-org/synapse/issues/3971)). If metrics
indicate that your server is also issuing far more outgoing federation
requests than can be accounted for by your users' activity, this is a
likely cause. The misbehavior can be worked around by disabling presence
in the Synapse config file: [see here](../configuration/config_documentation.md#presence).
Running out of File Handles
---------------------------
If Synapse runs out of file handles, it typically fails badly - live-locking
at 100% CPU, and/or failing to accept new TCP connections (blocking the
connecting client). Matrix currently can legitimately use a lot of file handles,
thanks to busy rooms like `#matrix:matrix.org` containing hundreds of participating
servers. The first time a server talks in a room it will try to connect
simultaneously to all participating servers, which could exhaust the available
file descriptors between DNS queries & HTTPS sockets, especially if DNS is slow
to respond. (We need to improve the routing algorithm used to be better than
full mesh, but as of March 2019 this hasn't happened yet).
If you hit this failure mode, we recommend increasing the maximum number of
open file handles to be at least 4096 (assuming a default of 1024 or 256).
This is typically done by editing ``/etc/security/limits.conf``
Separately, Synapse may leak file handles if inbound HTTP requests get stuck
during processing - e.g. blocked behind a lock or talking to a remote server etc.
This is best diagnosed by matching up the 'Received request' and 'Processed request'
log lines and looking for any 'Processed request' lines which take more than
a few seconds to execute. Please let us know at [`#synapse:matrix.org`](https://matrix.to/#/#synapse-dev:matrix.org) if
you see this failure mode so we can help debug it, however.