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

Set up client
=============
We need to have installed the postgres python connector ``psycopg2``. In the
virtual env::

    sudo apt-get install libpq-dev
    pip install psycopg2


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

Add the following line to your config file::

    database_config: <db_config_file>

Where ``<db_config_file>`` is the file name that points to a yaml file of the
following form::

    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
===================

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 PostgrSQL
   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 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 to another location. Once the copy is complete, restart synapse.

Assuming your database config file (as described in the section *Synapse
config*) is named ``database_config.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 and restart synapse. Synapse should now be running
against PostgreSQL.