mash-playbook/docs/services/postgres.md

Postgres

PostgreSQL is a powerful, open source object-relational database system with over 35 years of active development that has earned it a strong reputation for reliability, feature robustness, and performance.

Many of the services installed by this playbook require a Postgres database.

Enabling the Postgres database service will automatically wire all other services which require such a database to use it.

Configuration

To enable this service, add the following configuration to your vars.yml file and re-run the installation process:

########################################################################
#                                                                      #
# postgres                                                             #
#                                                                      #
########################################################################

postgres_enabled: true

# Put a strong password below, generated with `pwgen -s 64 1` or in another way
postgres_connection_password: ''

########################################################################
#                                                                      #
# /postgres                                                            #
#                                                                      #
########################################################################

Importing

Importing an existing Postgres database from another installation (optional)

Follow this section if you'd like to import your database from a previous installation.

Prerequisites

The playbook supports importing Postgres dump files in text (e.g. pg_dump > dump.sql) or gzipped formats (e.g. pg_dump | gzip -c > dump.sql.gz).

Importing multiple databases (as dumped by pg_dumpall) is also supported.

Before doing the actual import, you need to upload your Postgres dump file to the server (any path is okay).

Importing a dump file

To import, run this command (make sure to replace SERVER_PATH_TO_POSTGRES_DUMP_FILE with a file path on your server):

just run-tags import-postgres \
--extra-vars=server_path_postgres_dump=SERVER_PATH_TO_POSTGRES_DUMP_FILE \
--extra-vars=postgres_default_import_database=main

Notes:

• SERVER_PATH_TO_POSTGRES_DUMP_FILE must be a file path to a Postgres dump file on the server (not on your local machine!)
• postgres_default_import_database defaults to main, which is useful for importing multiple databases (for dumps made with pg_dumpall). If you're importing a single database (e.g. miniflux), consider changing postgres_default_import_database to the name of the database (e.g. miniflux)
• after importing a large database, it's a good idea to run an ANALYZE operation to make Postgres rebuild its database statistics and optimize its query planner. You can easily do this via the playbook by running just run-tags run-postgres-vacuum -e postgres_vacuum_preset=analyze (see Vacuuming PostgreSQL for more details).

Maintenance

This section shows you how to perform various maintenance tasks related to the Postgres database server used by various components of this playbook.

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.

• Tuning PostgreSQL to make it run faster

Getting a database terminal

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

By default, this tool puts you in the main database, which contains nothing.

To see the available databases, run \list (or just \l).

To change to another database (for example miniflux), run \connect miniflux (or just \c miniflux).

You can then proceed to write queries. Example: SELECT COUNT(*) FROM users;

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.

Vacuuming PostgreSQL

Deleting lots data from Postgres does not make it release disk space, until you perform a VACUUM operation.

You can run different VACUUM operations via the playbook, with the default preset being vacuum-complete:

• (default) vacuum-complete: stops all services temporarily and runs VACUUM FULL VERBOSE ANALYZE.
• vacuum-full: stops all services temporarily and runs VACUUM FULL VERBOSE
• vacuum: runs VACUUM VERBOSE without stopping any services
• vacuum-analyze runs VACUUM VERBOSE ANALYZE without stopping any services
• analyze runs ANALYZE VERBOSE without stopping any services (this is just ANALYZE without doing a vacuum, so it's faster)

Note: for the vacuum-complete and vacuum-full presets, you'll need plenty of available disk space in your Postgres data directory (usually /mash/postgres/data). These presets also stop all services while the vacuum operation is running.

Example playbook invocations:

• just run-tags run-postgres-vacuum: runs the default vacuum-complete preset and restarts all services
• just run-tags run-postgres-vacuum -e postgres_vacuum_preset=analyze: runs the analyze preset with all services remaining operational at all times

Backing up PostgreSQL

To automatically make Postgres database backups on a fixed schedule, consider enabling the Postgres Backup service.

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:

/usr/bin/docker exec \
--env-file=/mash/postgres/env-postgres-psql \
mash-postgres \
/usr/local/bin/pg_dumpall -h mash-postgres \
| gzip -c \
> /mash/postgres.sql.gz

Restoring a backup made this way can be done by importing it.

Upgrading PostgreSQL

Once this playbook installs Postgres for you, it 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:

just run-tags upgrade-postgres

The old Postgres data directory is backed up automatically, by renaming it to /mash/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/mash-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"

To save disk space in /tmp, the dump file is gzipped on the fly at the expense of CPU usage. 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=mash-postgres-dump.sql"

All databases, roles, etc. on the Postgres server are migrated.

Tuning PostgreSQL

PostgreSQL can be tuned to make it run faster. This is done by passing extra arguments to the Postgres process.

The Postgres Ansible role already does some tuning by default, which matches the tuning logic 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.

Most users should be fine with the automatically-done tuning. However, you may wish to:

• adjust the automatically-deterimned tuning parameters manually: change the values for the tuning variables defined in the Postgres role's default configuration file (see postgres_max_connections, postgres_data_storage etc). These variables are ultimately passed to Postgres via a postgres_postgres_process_extra_arguments_auto variable

• turn automatically-performed tuning off: override it like this: postgres_postgres_process_extra_arguments_auto: []

• 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 for inspiration

Recommended other services

You may also wish to look into:

• Postgres Backup for backing up your Postgres database

• Prometheus, prometheus-postgres-exporter and Grafana for monitoring your Postgres database