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Diffstat (limited to 'doc/development/what_requires_downtime.md')
| -rw-r--r-- | doc/development/what_requires_downtime.md | 36 |
1 files changed, 6 insertions, 30 deletions
diff --git a/doc/development/what_requires_downtime.md b/doc/development/what_requires_downtime.md index 8ea9f70fc7a..407899b23d5 100644 --- a/doc/development/what_requires_downtime.md +++ b/doc/development/what_requires_downtime.md @@ -130,12 +130,12 @@ class CleanupUsersUpdatedAtRename < ActiveRecord::Migration[4.2] end ``` -NOTE: **Note:** If you're renaming a [large table](https://gitlab.com/gitlab-org/gitlab/-/blob/master/rubocop/migration_helpers.rb#L9), please carefully consider the state when the first migration has run but the second cleanup migration hasn't been run yet. +NOTE: **Note:** If you're renaming a [large table](https://gitlab.com/gitlab-org/gitlab/-/blob/master/rubocop/rubocop-migrations.yml#L3), please carefully consider the state when the first migration has run but the second cleanup migration hasn't been run yet. With [Canary](https://about.gitlab.com/handbook/engineering/infrastructure/library/canary/) it is possible that the system runs in this state for a significant amount of time. ## Changing Column Constraints -Adding or removing a NOT NULL clause (or another constraint) can typically be +Adding or removing a `NOT NULL` clause (or another constraint) can typically be done without requiring downtime. However, this does require that any application changes are deployed _first_. Thus, changing the constraints of a column should happen in a post-deployment migration. @@ -143,35 +143,11 @@ happen in a post-deployment migration. NOTE: Avoid using `change_column` as it produces an inefficient query because it re-defines the whole column type. -To add a NOT NULL constraint, use the `add_not_null_constraint` migration helper: +You can check the following guides for each specific use case: -```ruby -# A post-deployment migration in db/post_migrate -class AddNotNull < ActiveRecord::Migration[4.2] - include Gitlab::Database::MigrationHelpers - - disable_ddl_transaction! - - def up - add_not_null_constraint :users, :username - end - - def down - remove_not_null_constraint :users, :username - end -end -``` - -If the column to be updated requires cleaning first (e.g. there are `NULL` values), you should: - -1. Add the `NOT NULL` constraint with `validate: false` - - `add_not_null_constraint :users, :username, validate: false` - -1. Clean up the data with a data migration -1. Validate the `NOT NULL` constraint with a followup migration - - `validate_not_null_constraint :users, :username` +- [Adding foreign-key constraints](migration_style_guide.md#adding-foreign-key-constraints) +- [Adding `NOT NULL` constraints](database/not_null_constraints.md) +- [Adding limits to text columns](database/strings_and_the_text_data_type.md) ## Changing Column Types |