Separating from T187521#4133553
commonswiki errors due to deadlocks on INSERT IGNORE INTO wbc_entity_usage seem to be common (not too worrying, but on of the most comon database errors), could the code be optimized to avoid those? I am guessing that the same row is written many times (once per change on the same item), and maybe that could be simplified somehow. INSERT IGNORE is a bit of a bad trick here, and we may be writing multiple times the same data without need. Given the changes are done by the job queue and arrive in any order, maybe transaction serialization can be relaxed?