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From: Bruce Ferrell (bferrellbaywinds.org)
Date: Thu May 09 2013 - 20:04:58 CDT
On 05/09/2013 03:25 PM, Robinson, Eric wrote:
>>> -----Original Message-----
>>> From: Robinson, Eric [mailto:eric.robinsonpsmnv.com]
>>> Sent: Thursday, May 09, 2013 1:58 PM
>>> To: mysqllists.mysql.com
>>> Subject: Slow Response -- What Does This Sound Like to You?
>>> We have a situation where users complain that the system
>>> 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
>> MyISAM? Or InnoDBm to have been finished
>> Lock_time perhaps applies only to table locks on MyISAM.
>> SHOW ENGINE InnoDB STATUS;
>> You may find some deadlocks.
>> Is Replication involved?
>> Anyone doing an ALTER?
> MyISAM, no replication involved, and nobody is altering the database. This happens whenever people run certain reports.
One thing I'd look at to start is the error log, if enabled. After that, I'd look at running mysqltuner to get a look at statistics before and after one of these events. I know
there are those who prefer the Percona toolkit, but those pull lots raw stats and offers little in terms of suggestions... Unless you wish to engage Percona.
Be aware, there are two versions of mysqltuner. The one I use is found at http://mysqltuner.pl. I know, it's old, but it at least runs. The newer one doesn't seem to have been
brought to completion.
You might want to enable the slow query option that logs queries that execute without indexes. They can be real killers. Reports that use views often cause this as views become
complex joins under the hood that can easily miss your indexes resulting in full table scans.
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