My personal and professional life


New usages of TREE explain plan in MySQL

As I wrote back in June (see TREE explain format in MySQL 8.0.16) a new execution plan format was introduced - TREE. It was a representation of the operations taken by the optimizer to satisfy a query in a nested form like a tree. The new format was defined experimental, so I was waiting to see how it would evolve in next versions. Well, last Friday as I was browsing the manual I noticed it's already updated for two new features coming in MySQL 8.0.18:
  • HASH joins would be visible only in TREE format. I find this rather strange, because you would expect to see this operation no matter the format of the plan, so I hope it's extended in future.
  • EXPLAIN ANALYZE would actually run the query and provide timing information about it's execution. I would also include additional iterator-based information about how the optimizer estimations compares to the actual execution.
I'm already eager to try the new version, which I presume should be released somewhere mid-October. Stay tuned as I'll write about these new features when they arrive and I'm able to play with them.

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