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diff --git a/doc/development/redis.md b/doc/development/redis.md index 5073d9350e8..ebc7c0271a1 100644 --- a/doc/development/redis.md +++ b/doc/development/redis.md @@ -285,3 +285,48 @@ This is used by the [`RepositorySetCache`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/repository_set_cache.rb) to provide a convenient way to use sets to cache repository data like branch names. + +## Background migration + +Redis-based migrations involve using the `SCAN` command to scan the entire Redis instance for certain key patterns. +For large Redis instances, the migration might [exceed the time limit](migration_style_guide.md#how-long-a-migration-should-take) +for regular or post-deployment migrations. [`RedisMigrationWorker`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/workers/redis_migration_worker.rb) +performs long-running Redis migrations as a background migration. + +To perform a background migration by creating a class: + +```ruby +module Gitlab + module BackgroundMigration + module Redis + class BackfillCertainKey + def perform(keys) + # implement logic to clean up or backfill keys + end + + def scan_match_pattern + # define the match pattern for the `SCAN` command + end + + def redis + # define the exact Redis instance + end + end + end + end +end +``` + +To trigger the worker through a post-deployment migration: + +```ruby +class ExampleBackfill < Gitlab::Database::Migration[2.1] + disable_ddl_transaction! + + MIGRATION='BackfillCertainKey' + + def up + queue_redis_migration_job(MIGRATION) + end +end +``` |