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98 lines
4.5 KiB
Markdown
98 lines
4.5 KiB
Markdown
# PostgreSQL maintenance
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This document shows you how to perform various maintenance tasks related to the Postgres database server used by Matrix.
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Table of contents:
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- [Getting a database terminal](#getting-a-database-terminal), for when you wish to execute SQL queries
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- [Vacuuming PostgreSQL](#vacuuming-postgresql), for when you wish to run a Postgres [VACUUM](https://www.postgresql.org/docs/current/sql-vacuum.html) (optimizing disk space)
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- [Backing up PostgreSQL](#backing-up-postgresql), for when you wish to make a backup
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- [Upgrading PostgreSQL](#upgrading-postgresql), for upgrading to new major versions of PostgreSQL. Such **manual upgrades are sometimes required**.
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## Getting a database terminal
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You can use the `/usr/local/bin/matrix-postgres-cli` tool to get interactive terminal access ([psql](https://www.postgresql.org/docs/11/app-psql.html)) to the PostgreSQL server.
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If you are using an [external Postgres server](configuring-playbook-external-postgres.md), the above tool will not be available.
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By default, this tool puts you in the `matrix` database, which contains nothing.
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To see the available databases, run `\list` (or just `\l`).
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To change to another database (for example `synapse`), run `\connect synapse` (or just `\c synapse`).
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You can then proceed to write queries. Example: `SELECT COUNT(*) FROM users;`
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**Be careful**. Modifying the database directly (especially as services are running) is dangerous and may lead to irreversible database corruption.
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When in doubt, consider [making a backup](#backing-up-postgresql).
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## Vacuuming PostgreSQL
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Deleting lots data from Postgres does not make it release disk space, until you perform a `VACUUM` operation.
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To perform a `FULL` Postgres [VACUUM](https://www.postgresql.org/docs/current/sql-vacuum.html), run the playbook with `--tags=run-postgres-vacuum`.
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Example:
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```bash
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ansible-playbook -i inventory/hosts setup.yml --tags=run-postgres-vacuum,start
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```
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**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`).
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## Backing up PostgreSQL
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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:
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```bash
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docker run \
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--rm \
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--log-driver=none \
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--network=matrix \
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--env-file=/matrix/postgres/env-postgres-psql \
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docker.io/postgres:13.1-alpine \
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pg_dumpall -h matrix-postgres \
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> /postgres.sql.gz
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```
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If you are using an [external Postgres server](configuring-playbook-external-postgres.md), the above command will not work, because the credentials file (`/matrix/postgres/env-postgres-psql`) is not available.
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If your server is on the ARM32 [architecture](alternative-architectures.md), you may need to remove the `-alpine` suffix from the image name in the command above.
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Restoring a backup made this way can be done by [importing it](importing-postgres.md).
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## Upgrading PostgreSQL
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Unless you are using an [external Postgres server](configuring-playbook-external-postgres.md), this playbook initially installs Postgres for you.
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Once installed, the playbook attempts to preserve the Postgres version it starts with.
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This is because newer Postgres versions cannot start with data generated by older Postgres versions.
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Upgrades must be performed manually.
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This playbook can upgrade your existing Postgres setup with the following command:
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ansible-playbook -i inventory/hosts setup.yml --tags=upgrade-postgres
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**The old Postgres data directory is backed up** automatically, by renaming it to `/matrix/postgres/data-auto-upgrade-backup`.
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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"`
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The auto-upgrade-backup directory stays around forever, until you **manually decide to delete it**.
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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.
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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"`
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To save disk space in `/tmp`, the dump file is gzipped on the fly at the expense of CPU usage.
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If you have plenty of space in `/tmp` and would rather avoid gzipping, you can explicitly pass a dump filename which doesn't end in `.gz`.
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Example: `--extra-vars="postgres_dump_name=matrix-postgres-dump.sql"`
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**All databases, roles, etc. on the Postgres server are migrated**.
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