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Re: Server just hanging (Copying to tmp table)
Posted by: Jay Pipes
Date: August 30, 2005 11:33AM

Your query cache is doing OK, IMHO. It will fill to 100% usage eventually, but the hit rate is OK for now. I think the biggest problem is that you're queries aren't really optimized to use indexes. It's evident to me (from the ~30% of your SELECT statements that are performing table scans) that you're queries are either a) requesting too much information (like having no WHERE clause or really large ranges of values), or b) don't have appropriate indexes with decent selectivity on them.

Also, could you give some insight as to what kind of applications are running on the box? Are they OLAP or OLTP, or mixed? I see a very high number of UPDATE/REPLACE operations compared to INSERT, which would sometimes make me advise using InnoDB for certain application needs, particularly heavy OLTP apps with many single-key UPDATEs. Please provide more information on the applications and what they're used for.

In order to best explain what's going on, you will absolutely need to turn on the slow query log and profile the server for at least an hour or two. Then, could you use mysqldumpslow on your slow query log and post the top results? Then run an EXPLAIN on the top results and post the results here using the \G option in the mysql client. If you're not familiar with mysqldumpslow, Chapter 6 from my book goes over its usage. You can download the chapter for free on mysql's website:

http://dev.mysql.com/tech-resources/articles/pro-mysql-ch6.html

Cheers,

Jay Pipes
Community Relations Manager, North America, MySQL Inc.

Got Cluster? http://www.mysql.com/cluster
Personal: http://jpipes.com

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