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Diffstat (limited to 'doc/development/database_review.md')
| -rw-r--r-- | doc/development/database_review.md | 16 |
1 files changed, 12 insertions, 4 deletions
diff --git a/doc/development/database_review.md b/doc/development/database_review.md index bb0bfbc759b..ba0423a1a0d 100644 --- a/doc/development/database_review.md +++ b/doc/development/database_review.md @@ -173,10 +173,11 @@ Include in the MR description: ##### Query Plans - The query plan for each raw SQL query included in the merge request along with the link to the query plan following each raw SQL snippet. -- Provide a link to the plan generated using the `explain` command in the [postgres.ai](database/database_lab.md) chatbot. - - If it's not possible to get an accurate picture in Database Lab, you may need to seed a development environment, and instead provide links - from [explain.depesz.com](https://explain.depesz.com) or [explain.dalibo.com](https://explain.dalibo.com). Be sure to paste both the plan - and the query used in the form. +- Provide a link to the plan generated using the `explain` command in the [postgres.ai](database/database_lab.md) chatbot. The `explain` command runs + `EXPLAIN ANALYZE`. + - If it's not possible to get an accurate picture in Database Lab, you may need to + seed a development environment, and instead provide output + from `EXPLAIN ANALYZE`. Create links to the plan using [explain.depesz.com](https://explain.depesz.com) or [explain.dalibo.com](https://explain.dalibo.com). Be sure to paste both the plan and the query used in the form. - When providing query plans, make sure it hits enough data: - To produce a query plan with enough data, you can use the IDs of: - The `gitlab-org` namespace (`namespace_id = 9970`), for queries involving a group. @@ -192,6 +193,13 @@ Include in the MR description: plan _before_ and _after_ the change. This helps spot differences quickly. - Include data that shows the performance improvement, preferably in the form of a benchmark. +- When evaluating a query plan, we need the final query to be + executed against the database. We don't need to analyze the intermediate + queries returned as `ActiveRecord::Relation` from finders and scopes. + PostgreSQL query plans are dependent on all the final parameters, + including limits and other things that may be added before final execution. + One way to be sure of the actual query executed is to check + `log/development.log`. #### Preparation when adding foreign keys to existing tables |