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diff --git a/doc/development/deleting_migrations.md b/doc/development/deleting_migrations.md new file mode 100644 index 00000000000..438e8c9f5e9 --- /dev/null +++ b/doc/development/deleting_migrations.md @@ -0,0 +1,33 @@ +# Delete existing migrations + +When removing existing migrations from the GitLab project, you have to take into account +the possibility of the migration already been included in past releases or in the current release, and thus already executed on GitLab.com and/or in self-hosted instances. + +Because of it, it's not possible to delete existing migrations, as that could lead to: + +- Schema inconsistency, as changes introduced into the database were not rollbacked properly. +- Leaving a record on the `schema_versions` table, that points out to migration that no longer exists on the codebase. + +Instead of deleting we can opt for disabling the migration. + +## Pre-requisites to disable a migration + +Migrations can be disabled if: + +- They caused a timeout or general issue on GitLab.com. +- They are obsoleted, e.g. changes are not necessary due to a feature change. +- Migration is a data migration only, i.e. the migration does not change the database schema. + +## How to disable a data migration? + +In order to disable a migration, the following steps apply to all types of migrations: + +1. Turn the migration into a noop by removing the code inside `#up`, `#down` + or `#perform` methods, and adding `#no-op` comment instead. +1. Add a comment explaining why the code is gone. + +Disabling migrations requires explicit approval of Database Maintainer. + +## Examples + +- [Disable scheduling of productivity analytics](https://gitlab.com/gitlab-org/gitlab/merge_requests/17253) |