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Diffstat (limited to 'doc/development/adding_database_indexes.md')
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diff --git a/doc/development/adding_database_indexes.md b/doc/development/adding_database_indexes.md index 0991c4740cc..01904d37883 100644 --- a/doc/development/adding_database_indexes.md +++ b/doc/development/adding_database_indexes.md @@ -195,3 +195,34 @@ Without an explicit name argument, Rails can return a false positive for `index_exists?`, causing a required index to not be created properly. By always requiring a name for certain types of indexes, the chance of error is greatly reduced. + +## Temporary indexes + +There may be times when an index is only needed temporarily. + +For example, in a migration, a column of a table might be conditionally +updated. To query which columns need to be updated within the +[query performance guidelines](query_performance.md), an index is needed that would otherwise +not be used. + +In these cases, a temporary index should be considered. To specify a +temporary index: + +1. Prefix the index name with `tmp_` and follow the [naming conventions](database/constraint_naming_convention.md) and [requirements for naming indexes](#requirements-for-naming-indexes) for the rest of the name. +1. Create a follow-up issue to remove the index in the next (or future) milestone. +1. Add a comment in the migration mentioning the removal issue. + +A temporary migration would look like: + +```ruby +INDEX_NAME = 'tmp_index_projects_on_owner_where_emails_disabled' + +def up + # Temporary index to be removed in 13.9 https://gitlab.com/gitlab-org/gitlab/-/issues/1234 + add_concurrent_index :projects, :creator_id, where: 'emails_disabled = false', name: INDEX_NAME +end + +def down + remove_concurrent_index_by_name :projects, INDEX_NAME +end +``` |