Today is the first day at the conference (aside from the tutorials, which were yesterday). Here’s what I went to:
New Subquery Optimizations in 6.0
By Sergey Petrunia. This was a similar session to one I went to last year. MySQL has a few cases where subqueries are badly optimized, and this session went into the details of how this is being addressed in MySQL 6.0. There are several new optimization techniques for all types of subqueries, such as inside-out subqueries, materialization, and converting to joins. The optimizations apply to scalar subqueries and subqueries in the FROM clause. Performance results are very good, depending on which data you choose to illustrate. The overall point is that the worst-case subquery nastiness should be resolved. I’m speaking of WHERE NOT IN(SELECT…) and friends. It remains to be seen how this shakes out as 6.0 matures, and what edge cases will pop up.
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