Comment 9 for bug 955776

Hi Anton,

my educated guess is that MariaDB-5.3 introduces some optimizer feature that adds a penalty for at least some queries that you (or your customers) are running.

By looking at the optimizer_switch, it seems the only change between your "good" settings and the MariaDB 5.3 defaults is engine_condition_pushdown. Default is "on", you set it to "off".

While we know of some workload where ICP leads to performance loss, it has always been in the range of few percent, never as much as your cpu graph suggests.

The only other optimizer features that you have turned on are for the index merge algorithms. Those are quite mature and as far as I know there was no changes to those between MariaDB 5.2 and 5.3.

Since you mention the slow log - do you happen to have examples of slow queries? What we would need are example queries and table structure/data where turning ICP on shows a significant performance loss.

You also mention that the new optimizer flags don't always work. So you might have queries in the slow log with 5.3 that were never slow with 5.2? Such examples would be very helpful too.