Prepare projects and namespaces loose foreign keys

ROLLBACK steps

There is a small chance that the introduced DB triggers will cause performance degradation (slower deletion speed). If this becomes a big problem (incident), then we can mitigate it by dropping the triggers. Dropping the triggers is safe.

SET lock_timeout='3s';  -- attempt short lock waits

-- During busy hours, we might need to retry these statements a few times until they succeed:
DROP TRIGGER projects_loose_fk_trigger ON projects;
DROP TRIGGER namespaces_loose_fk_trigger ON namespaces;

What does this MR do and why?

This MR adds post-migrations for tracking deletions of namespaces and projects tables. They will be used for syncing those tables to their ci-mirrors.

This MR did not include specs and foreign key definitions because those ci-mirror tables are not available yet. (will be added in: !75621 (merged))

DB

UP

== 20211130201100 TrackDeletionsInNamespaces: migrating =======================
-- execute("CREATE TRIGGER namespaces_loose_fk_trigger\nAFTER DELETE ON namespaces REFERENCING OLD TABLE AS old_table\nFOR EACH STATEMENT\nEXECUTE FUNCTION insert_into_loose_foreign_keys_deleted_records();\n")
   -> 0.0023s
== 20211130201100 TrackDeletionsInNamespaces: migrated (0.0023s) ==============

== 20211130201101 TrackDeletionsInProjects: migrating =========================
-- execute("CREATE TRIGGER projects_loose_fk_trigger\nAFTER DELETE ON projects REFERENCING OLD TABLE AS old_table\nFOR EACH STATEMENT\nEXECUTE FUNCTION insert_into_loose_foreign_keys_deleted_records();\n")
   -> 0.0014s
== 20211130201101 TrackDeletionsInProjects: migrated (0.0014s) ================

DOWN

== 20211130201101 TrackDeletionsInProjects: reverting =========================
-- execute("DROP TRIGGER IF EXISTS projects_loose_fk_trigger ON projects")
   -> 0.0011s
== 20211130201101 TrackDeletionsInProjects: reverted (0.0012s) ================

== 20211130201100 TrackDeletionsInNamespaces: reverting =======================
-- execute("DROP TRIGGER IF EXISTS namespaces_loose_fk_trigger ON namespaces")
   -> 0.0011s
== 20211130201100 TrackDeletionsInNamespaces: reverted (0.0011s) ==============

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.