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PostgreSQL maintenance

This document shows you how to perform various maintenance tasks related to the Postgres database server used by Matrix.

Table of contents:

Getting a database terminal, for when you wish to execute SQL queries
Vacuuming PostgreSQL, for when you wish to run a Postgres VACUUM (optimizing disk space)
Backing up PostgreSQL, for when you wish to make a backup
Upgrading PostgreSQL, for upgrading to new major versions of PostgreSQL. Such manual upgrades are sometimes required.

Getting a database terminal

You can use the /usr/local/bin/matrix-postgres-cli tool to get interactive terminal access (psql) to the PostgreSQL server.

If you are using an external Postgres server, the above tool will not be available.

Vacuuming PostgreSQL

To perform a FULL Postgres VACUUM, run the playbook with --tags=run-postgres-vacuum.

Example:

ansible-playbook -i inventory/hosts setup.yml --tags=run-postgres-vacuum,start

Note: this will automatically stop Synapse temporarily and restart it later. You'll also need plenty of available disk space in your Postgres data directory (usually /matrix/postgres/data).

Backing up PostgreSQL

To make a back up of the current PostgreSQL database, make sure it's running and then execute a command like this on the server:

docker run \
--rm \
--network matrix \
--env-file=/matrix/postgres/env-postgres-psql \
postgres:12.0-alpine \
pg_dump -h matrix-postgres \
| gzip -c \
> /postgres.sql.gz

If you are using an external Postgres server, the above command will not work, because the credentials file (/matrix/postgres/env-postgres-psql) is not available.

Upgrading PostgreSQL

Unless you are using an external Postgres server, this playbook initially installs Postgres for you.

Once installed, the playbook attempts to preserve the Postgres version it starts with. This is because newer Postgres versions cannot start with data generated by older Postgres versions.

Upgrades must be performed manually.

This playbook can upgrade your existing Postgres setup with the following command:

ansible-playbook -i inventory/hosts setup.yml --tags=upgrade-postgres

The old Postgres data directory is backed up automatically, by renaming to /matrix/postgres-auto-upgrade-backup. To rename to a different path, pass some extra flags to the command above, like this: --extra-vars="postgres_auto_upgrade_backup_data_path=/another/disk/matrix-postgres-before-upgrade"

The auto-upgrade-backup directory stays around forever, until you manually decide to delete it.

As part of the upgrade, the database is dumped to /tmp, an upgraded and empty Postgres server is started, and then the dump is restored into the new server. To use a different directory for the dump, pass some extra flags to the command above, like this: --extra-vars="postgres_dump_dir=/directory/to/dump/here"

ONLY one database is migrated (the one specified in matrix_postgres_db_name, named homeserver by default). If you've created other databases in that database instance (something this playbook never does and never advises), data will be lost.

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