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How to improve sort speed for large single queries?
Posted by: Bob Bankay
Date: February 09, 2005 09:24PM

We have some very large statistics query that run against a mid sized table, about 10M rows and 10GB size.

The query is complex with many stepped phases that use 'ordered' and 'grouped'. The last time I ran the query it took about 2800 sec. The first 400 sec it did a lot of innodb IOs, and the rest of the time iostat showed lots of IO activity so I assumed that it was sorting. Here are some values that we have for per-thread buffers (I believe):

set-variable = sort_buffer=6M
set-variable = record_buffer=4M

This is fairly large compare to cnf examples that I have seen. Does it help large query performance? I there anything else that would?

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