This is a composite index on (target_project_id, merge_commit_sha, id)
that allows queries such as the following to use a full backwards index
scan:
SELECT "merge_requests".*
FROM "merge_requests"
WHERE "merge_requests"."deleted_at" IS NULL
AND "merge_requests"."target_project_id" = 13083
AND "merge_requests"."merge_commit_sha" = 'e80a893ff0ea8466099f6478183631af55933db2'
ORDER BY "merge_requests"."id" DESC
LIMIT 1;
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/38507
Yorick Peterse