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Displaying posts with tag: bugfixes (reset)

A proposal for method of delivering optimizer bug fixes
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Working on query optimizer bugs can be a rather frustrating experience. First, as soon as some query doesn't run as fast it theoretically could people will consider it a bug. On one hand that's great, you get a constant stream of user input, but on the other hand you end up with a whole pile of "bugs" which you can't hope to finish.

What's more frustrating is that even if you manage to create a fix for an optimizer bug, there are chances it won't be allowed into next GA (currently 5.0.70) or approaching-GA (currently 5.1.30) release (GA is our term for "stable" or "release").

The reason behind this is that most optimizer bugfixes cause the optimizer to pick different query …

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Bugfix: DATE vs DATETIME comparisons are now sargable again
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We (me coding, Igor and Evgen reviewing) have fixed BUG#32198. According to Support/Bugs team, the bug was causing pain to a number of people, so I thought it deserved a post. The problem was as follows:

  • Before MySQL 5.0.42, comparisons in form
      date_column CMP datetime_const
    

    were interpreted as comparisons of DATEs (CMP is one of =, <, > , <=, or >=). The time part of datetime_const was ignored.

  • In 5.0.42 we've fixed it to perform in a way that is closer to the SQL standard: the comparisons are now resolved by comparing values as DATETIMEs. Our …
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