Comment 1 for bug 806894

I too am seeing a lot of issues where semijoin is detrimental to use. For my application, subqueries are absolutely essential so I have been running maria 5.3 in production since at least september.

I occasionally run into areas where maria attempts to semijoin and it will cause the query to be 1 or more orders of magnitude slower. Unfortunately, about 1/10 as often I find that semijoin makes some painful queries wickedly fast, so I am forced to leave it on in some cases.

You have this marked as low priority but I would _really_ like to see this fixed for maria 5.3. I do consider this a major bug but semijoin is too optimistic about it's chances to handle some things and can wreak havoc on queries even mysql 5.5 can do faster.