Managing PostgreSQL extensions

This guide documents how to manage PostgreSQL extensions for installations with an external PostgreSQL database.

GitLab requires certain extensions to be installed into the GitLab database. For example, GitLab relies on pg_trgm and the btree_gist extensions.

In order to install extensions, PostgreSQL requires the user to have superuser privileges. Typically, the GitLab database user is not a superuser. Therefore, regular database migrations cannot be used in installing extensions and instead, extensions have to be installed manually prior to upgrading GitLab to a newer version.

Installing PostgreSQL extensions manually

In order to install a PostgreSQL extension, this procedure should be followed:

Connect to the GitLab PostgreSQL database using a superuser, for example:
```
sudo gitlab-psql -d gitlabhq_production
```
Install the extension (btree_gist in this example) using CREATE EXTENSION:
```
CREATE EXTENSION IF NOT EXISTS btree_gist
```

Verify installed extensions:

 gitlabhq_production=# \dx
                                     List of installed extensions
     Name    | Version |   Schema   |                            Description
 ------------+---------+------------+-------------------------------------------------------------------
 btree_gist | 1.5     | public     | support for indexing common datatypes in GiST
 pg_trgm    | 1.4     | public     | text similarity measurement and index searching based on trigrams
 plpgsql    | 1.0     | pg_catalog | PL/pgSQL procedural language
 (3 rows)

On some systems you may need to install an additional package (for example, postgresql-contrib) for certain extensions to become available.

A typical migration failure scenario

The following is an example of a situation when the extension hasn't been installed before running migrations. In this scenario, the database migration fails to create the extension btree_gist because of insufficient privileges.

== 20200515152649 EnableBtreeGistExtension: migrating =========================
-- execute("CREATE EXTENSION IF NOT EXISTS btree_gist")

GitLab requires the PostgreSQL extension 'btree_gist' installed in database 'gitlabhq_production', but
the database user is not allowed to install the extension.

You can either install the extension manually using a database superuser:

  CREATE EXTENSION IF NOT EXISTS btree_gist

Or, you can solve this by logging in to the GitLab database (gitlabhq_production) using a superuser and running:

    ALTER regular WITH SUPERUSER

This query will grant the user superuser permissions, ensuring any database extensions
can be installed through migrations.

In order to recover from this situation, the extension needs to be installed manually using a superuser, and the database migration (or GitLab upgrade) can be retried afterwards.