gitlab-org--gitlab-foss/doc/development/database/multiple_databases.md

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Multiple Databases

In order to scale GitLab, the GitLab application database will be decomposed into multiple databases.

CI Database

Support for configuring the GitLab Rails application to use a distinct database for CI tables was added in GitLab 14.1. This feature is still under development, and is not ready for production use.

By default, GitLab is configured to use only one main database. To opt-in to use a main database, and CI database, modify the config/database.yml file to have a primary and a ci database configurations. For example, given a config/database.yml like below:

development:
  adapter: postgresql
  encoding: unicode
  database: gitlabhq_development
  host: /path/to/gdk/postgresql
  pool: 10
  prepared_statements: false
  variables:
    statement_timeout: 120s

test: &test
  adapter: postgresql
  encoding: unicode
  database: gitlabhq_test
  host: /path/to/gdk/postgresql
  pool: 10
  prepared_statements: false
  variables:
    statement_timeout: 120s

Edit the config/database.yml to look like this:

development:
  primary:
    adapter: postgresql
    encoding: unicode
    database: gitlabhq_development
    host: /path/to/gdk/postgresql
    pool: 10
    prepared_statements: false
    variables:
      statement_timeout: 120s
  ci:
    adapter: postgresql
    encoding: unicode
    database: gitlabhq_development_ci
    migrations_paths: db/ci_migrate
    host: /path/to/gdk/postgresql
    pool: 10
    prepared_statements: false
    variables:
      statement_timeout: 120s

test: &test
  primary:
    adapter: postgresql
    encoding: unicode
    database: gitlabhq_test
    host: /path/to/gdk/postgresql
    pool: 10
    prepared_statements: false
    variables:
      statement_timeout: 120s
  ci:
    adapter: postgresql
    encoding: unicode
    database: gitlabhq_test_ci
    migrations_paths: db/ci_migrate
    host: /path/to/gdk/postgresql
    pool: 10
    prepared_statements: false
    variables:
      statement_timeout: 120s

Note that we use primary in the config/database.yml to refer to the main database. This is to match the default name Rails has.

Migrations

Any migrations that affect Ci::ApplicationRecord models and their tables must be placed in two directories for now:

• db/migrate
• db/ci_migrate

We aim to keep the schema for both tables the same across both databases.