Comments - Query optimization
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I spent a lot of time to 11.0 to fix all known optimizer things. I have verified that the new optimizer with all changed plans in the mtr test suite and also with several customer queries that caused problems in earlier MariaDB versions and in almost all cases 11.0 did give a better plan.
That said, i do not think that 11.0 is perfect yet. It just a better base for the optimizer than any earlier MariaDB versions. Thanks to the changes and cleanups, it is much easier to extend and improve things in the optimizer in 11.0.
The main problem is 11.0 has had very little testing from high level users and because of that I have not got any feedback about the 11.0 optimizer performance.
We are working on extending maxscale to be able to simultaneous replicate to multiple servers, like 10.11 and 11.0 and compare result and timings. This is done partly to allow high level users to test 11.0 and provide feedback from running 11.0 in production. This will help us to find and fix any issues in 11.0.
If you, or anyone else are experiencing problems with the optimizer in 11.0 or above, please provide a test case in a Jira task and we will do our best to fix the issue ASAP.