Batched background migrations

Version history

There can be risks when disabling released features. Refer to this feature’s version history for more details.

To update database tables in batches, GitLab can use batched background migrations. These migrations are created by GitLab developers and run automatically on upgrade. However, such migrations are limited in scope to help with migrating some integer database columns to bigint. This is needed to prevent integer overflow for some tables.

Check the status of background migrations

All migrations must have a Finished status before updating GitLab. To check the status of the existing migrations:

  1. On the top bar, select Menu > Admin.
  2. On the left sidebar, select Monitoring > Background Migrations.

    queued batched background migrations table

Enable or disable batched background migrations

Batched background migrations are under development but ready for production use. It is deployed behind a feature flag that is enabled by default. GitLab administrators with access to the GitLab Rails console can opt to disable it.

To enable it:

Feature.enable(:execute_batched_migrations_on_schedule)

To disable it:

Feature.disable(:execute_batched_migrations_on_schedule)

Automatic batch size optimization

Version history

There can be risks when disabling released features. Refer to this feature’s version history for more details.

To maximize throughput of batched background migrations (in terms of the number of tuples updated per time unit), batch sizes are automatically adjusted based on how long the previous batches took to complete.

Enable or disable automatic batch size optimization

Automatic batch size optimization for batched background migrations is under development but ready for production use. It is deployed behind a feature flag that is enabled by default. GitLab administrators with access to the GitLab Rails console can opt to disable it.

To enable it:

Feature.enable(:optimize_batched_migrations)

To disable it:

Feature.disable(:optimize_batched_migrations)

Troubleshooting

Database migrations failing because of batched background migration not finished

When updating to GitLab 14.2 or later there might be a database migration failing with a message like:

StandardError: An error has occurred, all later migrations canceled:

Expected batched background migration for the given configuration to be marked as 'finished', but it is 'active':
  {:job_class_name=>"CopyColumnUsingBackgroundMigrationJob", :table_name=>"push_event_payloads", :column_name=>"event_id", :job_arguments=>[["event_id"], ["event_id_convert_to_bigint"]]}

To fix this error:

  1. Update to either 14.0.5 or 14.1.
  2. Check the status of the batched background migration from the error message, and make sure it is listed as finished. If it is still active, either wait until it is done, or finalize it manually using the command suggested in the error, for example:
sudo gitlab-rake gitlab:background_migrations:finalize[CopyColumnUsingBackgroundMigrationJob,push_event_payloads,event_id,'[["event_id"]\, ["event_id_convert_to_bigint"]]']
  1. You can now update to GitLab 14.2 or higher.