Details
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Type:
Bug
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Status: Closed
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Priority:
Minor
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Resolution: Fixed
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Affects Version/s: None
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Fix Version/s: None
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Component/s: None
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Labels:
Description
As discussed previously, it is imperative for proper automatic testing that the new DSS-MRR-CPK optimizations announce themselves in EXPLAIN . The current "using join buffer" is too generic to be usful. Another string in the Extra column would be required, or , at the very least, some indication in EXPLAIN EXTENDED + SHOW WARNINGS. If the optimization is decided on runtime, some other method of knowing that it has triggered must be provided.
Also, modifying the optimizer variable @mrr_sort_keys does not cause any visible changes in the EXPLAIN. We have queries that are experiencing performance improvements and regressions due to the recent DS-MRR optimizations, but the EXPLAIN plan does not change even a single bit.
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Re: New DS-MRR optimizations must be visible in EXPLAIN
The EXPLAIN part have been addressed: EXPLAIN now shows whether key ordering, rowid ordering, or both of them were performed:
http://lists.askmonty.org/pipermail/commits/2011-April/001493.html
http://lists.askmonty.org/pipermail/commits/2011-April/001498.html
Re: New DS-MRR optimizations must be visible in EXPLAIN
SergeyP, unfortunately your solution has disconnected the EXPLAIN output from the optimizer switches that control it. In other words, a user would not know that if he gets a " Rowid-ordered scan" , he should use optimizer_use_mrr=disable to disable it. Previously, MRR was mentioned both in EXPLAIN and in the mysqld option.
Launchpad bug id: 631504
Re: New DS-MRR optimizations must be visible in EXPLAIN
Fix proposal and discussion here: https://lists.launchpad.net/maria-developers/msg03804.html