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Slow Response -- What Does This Sound Like to You?

From: Robinson, Eric (eric.robinsonpsmnv.com)
Date: Thu May 09 2013 - 15:58:25 CDT

We have a situation where users complain that the system periodically freezes for 30-90 seconds. We check the slow query logs and find that one user issued a complex query that did indeed take 30-90 seconds to complete. However, NO slow queries are recorded for the other 50 users, before, during, or after the freeze. Note that the complex query in question always shows: "Lock_time: 0".

Q: What conditions could cause single query to lock up a database for a while for all users (even though it shows "lock time: 0") but no other slow queries would show in the logs for any other users who are hitting the database at the same time?

OS: RHEL3 x64
CPU: 8 x 2.9GHz Xeon
RAM: 32GB
Disk: RAID 5 (6 x 512GB SSD)
MySQL: 5.0.95 x64
Engine: MyISAM

--
Eric Robinson

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