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Diffstat (limited to 'doc/development/migration_style_guide.md')
| -rw-r--r-- | doc/development/migration_style_guide.md | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/doc/development/migration_style_guide.md b/doc/development/migration_style_guide.md index 71191d1d871..84679a78545 100644 --- a/doc/development/migration_style_guide.md +++ b/doc/development/migration_style_guide.md @@ -1,3 +1,9 @@ +--- +stage: none +group: unassigned +info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers +--- + # Migration Style Guide When writing migrations for GitLab, you have to take into account that @@ -376,8 +382,7 @@ Example changes: - `change_column_default` - `create_table` / `drop_table` -NOTE: **Note:** -`with_lock_retries` method **cannot** be used within the `change` method, you must manually define the `up` and `down` methods to make the migration reversible. +The `with_lock_retries` method **cannot** be used within the `change` method, you must manually define the `up` and `down` methods to make the migration reversible. ### How the helper method works @@ -437,7 +442,6 @@ the `with_multiple_threads` block, instead of re-using the global connection pool. This ensures each thread has its own connection object, and won't time out when trying to obtain one. -NOTE: **Note:** PostgreSQL has a maximum amount of connections that it allows. This limit can vary from installation to installation. As a result, it's recommended you do not use more than 32 threads in a single migration. Usually, 4-8 threads @@ -474,6 +478,12 @@ For a small table (such as an empty one or one with less than `1,000` records), it is recommended to use `remove_index` in a single-transaction migration, combining it with other operations that don't require `disable_ddl_transaction!`. +### Disabling an index + +There are certain situations in which you might want to disable an index before removing it. +See the [maintenance operations guide](database/maintenance_operations.md#disabling-an-index) +for more details. + ## Adding indexes Before adding an index, consider if this one is necessary. There are situations in which an index @@ -612,7 +622,6 @@ Before PostgreSQL 11, adding a column with a default was problematic as it would have caused a full table rewrite. The corresponding helper `add_column_with_default` has been deprecated and will be removed in a later release. -NOTE: **Note:** If a backport adding a column with a default value is needed for %12.9 or earlier versions, it should use `add_column_with_default` helper. If a [large table](https://gitlab.com/gitlab-org/gitlab/-/blob/master/rubocop/rubocop-migrations.yml#L3) is involved, backporting to %12.9 is contraindicated. @@ -958,7 +967,6 @@ in a previous migration. ### Example: Add a column `my_column` to the users table -NOTE: **Note:** It is important not to leave out the `User.reset_column_information` command, in order to ensure that the old schema is dropped from the cache and ActiveRecord loads the updated schema information. ```ruby |