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@askmonty.org-20111126082752-u8s9tv928lc67c8o) This change has grown to be more than just refactoring: - EXPLAIN now shows "Start temporary" at different position (documentation pending) - 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 @@optimizer_prune_level=0 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... BR Sergei -- Sergei Petrunia, Software Developer Monty Program AB, http://askmonty.org Blog: http://s.petrunia.net/blog