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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.
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