1. in function _abortCacheGeneration a useless db transaction is used, since there is no rollback possible and only a single db update. Is this wanted?

2. in function _purgeByLike, the rollback on line 283 of mysql.php is a bug, as if there are nested transactions (which the driver supports), the code will rollback existing outer transactions. Using a commit is recommended here, to simply release the lock on the lines held with the FOR UPDATE select

3. in the same function, the select on line 297 risks to not see the same lines selected on line 271, if another process comes in with a commit in between and mysql transaction isolation level allows it. We should instead get a list of file names on 1st select, and use an IN() clause in the 2nd select using that list

4. function _fetch does not define $fname to pass on to _fetchmetadata

5. same for _rename

6. in function _report, static $numQueries should be replaced with self::$numQueries