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synapse/docs/postgres.rst
Richard van der Hoff 1def298119
Improve Depends specs in debian package. (#5675)
This is basically a contrived way of adding a `Recommends` on `libpq5`, to fix #5653.

The way this is supposed to happen in debhelper is to run
`dh_shlibdeps`, which in turn runs `dpkg-shlibdeps`, which spits things out
into `debian/<package>.substvars` whence they can later be included by
`control`.

Previously, we had disabled `dh_shlibdeps`, mostly because `dpkg-shlibdeps`
gets confused about PIL's interdependent objects, but that's not really the
right thing to do and there is another way to work around that.

Since we don't always use postgres, we don't necessarily want a hard Depends on
libpq5, so I've actually ended up adding an explicit invocation of
`dpkg-shlibdeps` for `psycopg2`.

I've also updated the build-depends list for the package, which was missing a
couple of entries.
2019-07-17 17:47:07 +01:00

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Using Postgres
--------------
Postgres version 9.5 or later is known to work.
Install postgres client libraries
=================================
Synapse will require the python postgres client library in order to connect to
a postgres database.
* If you are using the `matrix.org debian/ubuntu
packages <../INSTALL.md#matrixorg-packages>`_,
the necessary python library will already be installed, but you will need to
ensure the low-level postgres library is installed, which you can do with
``apt install libpq5``.
* For other pre-built packages, please consult the documentation from the
relevant package.
* If you installed synapse `in a virtualenv
<../INSTALL.md#installing-from-source>`_, you can install the library with::
~/synapse/env/bin/pip install matrix-synapse[postgres]
(substituting the path to your virtualenv for ``~/synapse/env``, if you used a
different path). You will require the postgres development files. These are in
the ``libpq-dev`` package on Debian-derived distributions.
Set up database
===============
Assuming your PostgreSQL database user is called ``postgres``, create a user
``synapse_user`` with::
su - postgres
createuser --pwprompt synapse_user
Before you can authenticate with the ``synapse_user``, you must create a
database that it can access. To create a database, first connect to the database
with your database user::
su - postgres
psql
and then run::
CREATE DATABASE synapse
ENCODING 'UTF8'
LC_COLLATE='C'
LC_CTYPE='C'
template=template0
OWNER synapse_user;
This would create an appropriate database named ``synapse`` owned by the
``synapse_user`` user (which must already have been created as above).
Note that the PostgreSQL database *must* have the correct encoding set (as
shown above), otherwise it will not be able to store UTF8 strings.
You may need to enable password authentication so ``synapse_user`` can connect
to the database. See https://www.postgresql.org/docs/11/auth-pg-hba-conf.html.
Tuning Postgres
===============
The default settings should be fine for most deployments. For larger scale
deployments tuning some of the settings is recommended, details of which can be
found at https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server.
In particular, we've found tuning the following values helpful for performance:
- ``shared_buffers``
- ``effective_cache_size``
- ``work_mem``
- ``maintenance_work_mem``
- ``autovacuum_work_mem``
Note that the appropriate values for those fields depend on the amount of free
memory the database host has available.
Synapse config
==============
When you are ready to start using PostgreSQL, edit the ``database`` section in
your config file to match the following lines::
database:
name: psycopg2
args:
user: <user>
password: <pass>
database: <db>
host: <host>
cp_min: 5
cp_max: 10
All key, values in ``args`` are passed to the ``psycopg2.connect(..)``
function, except keys beginning with ``cp_``, which are consumed by the twisted
adbapi connection pool.
Porting from SQLite
===================
Overview
~~~~~~~~
The script ``synapse_port_db`` allows porting an existing synapse server
backed by SQLite to using PostgreSQL. This is done in as a two phase process:
1. Copy the existing SQLite database to a separate location (while the server
is down) and running the port script against that offline database.
2. Shut down the server. Rerun the port script to port any data that has come
in since taking the first snapshot. Restart server against the PostgreSQL
database.
The port script is designed to be run repeatedly against newer snapshots of the
SQLite database file. This makes it safe to repeat step 1 if there was a delay
between taking the previous snapshot and being ready to do step 2.
It is safe to at any time kill the port script and restart it.
Using the port script
~~~~~~~~~~~~~~~~~~~~~
Firstly, shut down the currently running synapse server and copy its database
file (typically ``homeserver.db``) to another location. Once the copy is
complete, restart synapse. For instance::
./synctl stop
cp homeserver.db homeserver.db.snapshot
./synctl start
Copy the old config file into a new config file::
cp homeserver.yaml homeserver-postgres.yaml
Edit the database section as described in the section *Synapse config* above
and with the SQLite snapshot located at ``homeserver.db.snapshot`` simply run::
synapse_port_db --sqlite-database homeserver.db.snapshot \
--postgres-config homeserver-postgres.yaml
The flag ``--curses`` displays a coloured curses progress UI.
If the script took a long time to complete, or time has otherwise passed since
the original snapshot was taken, repeat the previous steps with a newer
snapshot.
To complete the conversion shut down the synapse server and run the port
script one last time, e.g. if the SQLite database is at ``homeserver.db``
run::
synapse_port_db --sqlite-database homeserver.db \
--postgres-config homeserver-postgres.yaml
Once that has completed, change the synapse config to point at the PostgreSQL
database configuration file ``homeserver-postgres.yaml``::
./synctl stop
mv homeserver.yaml homeserver-old-sqlite.yaml
mv homeserver-postgres.yaml homeserver.yaml
./synctl start
Synapse should now be running against PostgreSQL.