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Re: Query not always using indexes
Posted by: Øystein Grøvlen
Date: January 09, 2017 02:30AM

Hi,

That the optimizer will pick block nested join (BNL) over indexed join for such large tables looks like a bug in the optimizer. I hope you can file a bug at bugs.mysql.com so that we can look into this. The best would be if you could attach a reproducible test case. If that is not possible, please, attach an optimizer trace for the query. (See http://oysteing.blogspot.co.uk/2016/01/how-to-get-optimizer-trace-for-query.html for details.)

As a work-around, you can try turning off BNL with the NO_BNL optimizer hint. (See https://dev.mysql.com/doc/refman/5.7/en/optimizer-hints.html#optimizer-hints-table-level for details.)

Øystein Grøvlen,
Senior Principal Software Engineer,
MySQL Group, Oracle,
Trondheim, Norway

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