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5.3: optimizer status update and test requests


Hi Elena,

A quick update on what has been happening in 5.3 optimizer recently. The text
is FYI, requests for QA are marked with 'REQUEST':

== Semi-joins: no non-PS crashes, optimizations refactoring ==

When I was fixing BUG#887468, I have made some refactorings to 
semi-join optimization code and pushed them into 5.3-main 
(revno: 3316, revision-id: psergey@xxxxxxxxxxxx-20111126082752-u8s9tv928lc67c8o)

This change has grown to be more than just refactoring:
- EXPLAIN now shows "Start temporary" at different position (documentation
- The optimizer may pick certain plans that were not picked before.

REQUEST#1: please re-run semi-join optimization tests for the new server.

== Discovery of effects of @@optimizer_prune_level ==

I have (yesterday) found https://bugs.launchpad.net/maria/+bug/898747.
In a nutshell, default value of @@optimizer_prune_level=1 causes the optimizer
to prune away some semi-join query plans. There can be different views about
how serious BUG#898747 is, but its effect is that certain range of query plans
were not tested before.

REQUEST#2: re-run semi-join optimization tests with 


This can be joined with REQUEST#1 (however, if you find bugs, we're interested
to know whether they have been present before the revno:3316 patch).

To be continued...

Sergei Petrunia, Software Developer
Monty Program AB, http://askmonty.org
Blog: http://s.petrunia.net/blog

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