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113 lines
7.0 KiB
Markdown
113 lines
7.0 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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- [Tuning PostgreSQL](#tuning-postgresql) to make it run faster
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## Getting a database terminal
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You can use the `/matrix/postgres/bin/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. 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](https://www.postgresql.org/docs/current/sql-vacuum.html).
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You can run different `VACUUM` operations via the playbook, with the default preset being `vacuum-complete`:
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- (default) `vacuum-complete`: stops all services temporarily and runs `VACUUM FULL VERBOSE ANALYZE`.
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- `vacuum-full`: stops all services temporarily and runs `VACUUM FULL VERBOSE`
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- `vacuum`: runs `VACUUM VERBOSE` without stopping any services
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- `vacuum-analyze` runs `VACUUM VERBOSE ANALYZE` without stopping any services
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- `analyze` runs `ANALYZE VERBOSE` without stopping any services (this is just [ANALYZE](https://www.postgresql.org/docs/current/sql-analyze.html) without doing a vacuum, so it's faster)
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**Note**: for the `vacuum-complete` and `vacuum-full` presets, you'll need plenty of available disk space in your Postgres data directory (usually `/matrix/postgres/data`). These presets also stop all services (e.g. Synapse, etc.) while the vacuum operation is running.
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Example playbook invocations:
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- `just run-tags run-postgres-vacuum`: runs the default `vacuum-complete` preset and restarts all services
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- `just run-tags run-postgres-vacuum -e postgres_vacuum_preset=analyze`: runs the `analyze` preset with all services remaining operational at all times
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## Backing up PostgreSQL
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To automatically make Postgres database backups on a fixed schedule, see [Setting up postgres backup](configuring-playbook-postgres-backup.md).
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To make a one off 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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/usr/bin/docker exec \
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--env-file=/matrix/postgres/env-postgres-psql \
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matrix-postgres \
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/usr/local/bin/pg_dumpall -h matrix-postgres \
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| gzip -c \
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> /matrix/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 neither the credentials file (`/matrix/postgres/env-postgres-psql`), nor the `matrix-postgres` container is available.
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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. 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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```sh
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just run-tags upgrade-postgres
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```
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**The old Postgres data directory is backed up** automatically, by renaming it to `/matrix/postgres/data-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"`
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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. 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`. 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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## Tuning PostgreSQL
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PostgreSQL can be [tuned](https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server) to make it run faster. This is done by passing extra arguments to the Postgres process.
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The [Postgres Ansible role](https://github.com/mother-of-all-self-hosting/ansible-role-postgres) **already does some tuning by default**, which matches the [tuning logic](https://github.com/le0pard/pgtune/blob/master/src/features/configuration/configurationSlice.js) done by websites like https://pgtune.leopard.in.ua/. You can manually influence some of the tuning variables. These parameters (variables) are injected via the `postgres_postgres_process_extra_arguments_auto` variable.
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Most users should be fine with the automatically-done tuning. However, you may wish to:
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- **adjust the automatically-determined tuning parameters manually**: change the values for the tuning variables defined in the Postgres role's [default configuration file](https://github.com/mother-of-all-self-hosting/ansible-role-postgres/blob/main/defaults/main.yml) (see `postgres_max_connections`, `postgres_data_storage` etc). These variables are ultimately passed to Postgres via a `postgres_postgres_process_extra_arguments_auto` variable
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- **turn automatically-performed tuning off**: override it like this: `postgres_postgres_process_extra_arguments_auto: []`
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- **add additional tuning parameters**: define your additional Postgres configuration parameters in `postgres_postgres_process_extra_arguments_custom`. See `postgres_postgres_process_extra_arguments_auto` defined in the Postgres role's [default configuration file](https://github.com/mother-of-all-self-hosting/ansible-role-postgres/blob/main/defaults/main.yml) for inspiration
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