UPDATE merge_requests SET updated_at WHERE merge_requests.id = ?
The query in the title is being run very frequently but seems a bit odd- only the "updated_at" field is being updated in that query- no actual data is being updated. If this is part of a transaction where another field of merge_requests is being changed then it would really be best to arrange for both fields to be updated at once instead of updating them independently.
Alternatively, perhaps this query can be eliminated entirely since no data on the row is actually being changed.
This query runs 0.7 times per second, or about 60 000 times a day, making it a pretty frequent query.