Bug #33486 Optimizer trace tool needed
Submitted: 22 Dec 2007 21:04 Modified: 8 Dec 2011 3:35
Reporter: Mark Callaghan Email Updates:
Status: Closed Impact on me:
Category:MySQL Server: Optimizer Severity:S4 (Feature request)
Version:5.0 OS:Any
Assigned to: Guilhem Bichot CPU Architecture:Any
Tags: debug, Optimizer, trace

[22 Dec 2007 21:04] Mark Callaghan
Sergey Petrunia has written about this -- http://s.petrunia.net/blog/?p=23

A mechanism to trace the work of the optimizer is needed. When debugging a bad plan, there is not much that can be done besides looking at explain plan, SHOW INDEXES and actual selectivities. All the choices made by the optimizer are secret, except for the final choices. This will become more serious with each release as more features are added to the optimizer because more features means more decisions and more decisions means more incorrect decisions in the optimizer.

How to repeat:

Suggested fix:
[24 Dec 2007 14:59] Valeriy Kravchuk
Thank you for a reasonable feature request.
[21 Nov 2011 15:30] Guilhem Bichot
This has been implemented in 5.6.3. Not all decisions are traced yet, but quite a few are.
and also
[8 Dec 2011 3:35] Mark Callaghan
Wow, nice work