Using Postgres
--------------

Set up database
===============

The PostgreSQL database used *must* have the correct encoding set, otherwise
would not be able to store UTF8 strings. To create a database with the correct
encoding use, e.g.::

 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 exist).

Set up client
=============

Postgres support depends on the postgres python connector ``psycopg2``. In the
virtual env::

    sudo apt-get install libpq-dev
    pip install psycopg2


Synapse config
==============

When you are ready to start using PostgreSQL, add the following line to your
config file::

    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 ``port_from_sqlite_to_postgres.py`` 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

Assuming your new config file (as described in the section *Synapse config*)
is named ``homeserver-postgres.yaml`` and the SQLite snapshot is at
``homeserver.db.snapshot`` then simply run::

    python scripts/port_from_sqlite_to_postgres.py \
        --sqlite-database homeserver.db.snapshot \
        --postgres-config database_config.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::

    python scripts/port_from_sqlite_to_postgres.py \
        --sqlite-database homeserver.db \
        --postgres-config database_config.yaml

Once that has completed, change the synapse config to point at the PostgreSQL
database configuration file using the ``database_config`` parameter (see
`Synapse Config`_) and restart synapse. Synapse should now be running against
PostgreSQL.