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Diffstat (limited to 'doc/development/migration_style_guide.md')
| -rw-r--r-- | doc/development/migration_style_guide.md | 14 |
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diff --git a/doc/development/migration_style_guide.md b/doc/development/migration_style_guide.md index c9b59ba66b5..e0e21319f47 100644 --- a/doc/development/migration_style_guide.md +++ b/doc/development/migration_style_guide.md @@ -90,6 +90,14 @@ Keep in mind that all durations should be measured against GitLab.com. | Post-deployment migrations | `<= 10 minutes` | A valid exception are schema changes, since they must not happen in background migrations. | | Background migrations | `> 10 minutes` | Since these are suitable for larger tables, it's not possible to set a precise timing guideline, however, any single query must stay below [`1 second` execution time](query_performance.md#timing-guidelines-for-queries) with cold caches. | +## Decide which database to target + +GitLab connects to two different Postgres databases: `main` and `ci`. This split can affect migrations +as they may run on either or both of these databases. + +Read [Migrations for Multiple databases](database/migrations_for_multiple_databases.md) to understand if or how +a migration you add should account for this. + ## Create a regular schema migration To create a migration you can use the following Rails generator: @@ -569,6 +577,12 @@ class MyMigration < Gitlab::Database::Migration[2.0] end ``` +Verify the index is not being used anymore with this Thanos query: + +```sql +sum(rate(pg_stat_user_indexes_idx_tup_read{env="gprd", indexrelname="index_ci_name", type="patroni-ci"}[5m])) +``` + Note that it is not necessary to check if the index exists prior to removing it, however it is required to specify the name of the index that is being removed. This can be done either by passing the name |