Hello,
We seem to have a problem with the usage of GET_LOCK on our mysql
server. Is there anyone who has experienced similar behavior, or could
provide some insight into what is going on?
/Niklas
Symptoms:
* mysqld CPU-usage is 100%
* Queries of the type GET_LOCK('lock_name', 10); seems to abound in the
mysql process list. These remain in the list for far longer than the
expected 10 seconds. At one instance the number of queries exceeded 600,
all of which had been active between 400 and 600 seconds. As it happens
to be a GET_LOCK query is the first one executed by our web application
on each request. There were also some RELEASE_LOCK queries in the list.
* The number of queries hanging on the list happened to exactly match
the maximum number of concurrent requests from the web servers.
* The queries remain for a time in the process list even after the web
servers (apache/php) has been taken down.
* The database seems to exhibit a slow decline in performance between
the point in time of its latest restart and a full stop. This has not
been thoroughly investigated yet however.
* Accessing the server through the CLI still works and regular queries
return as expected.
Occurrence:
* Intermittent, sometimes weeks apart, sometimes once day for a few days
in a row.
* Without an apparent correlation with the load of the machine.
Remedy until now:
Restarting mysqld and after that the apache processes, which sometimes
start to die of segmentation faults if this is neglected.
Configuration:
Server:
2 dual-core process (i.e. theoretical maximum cpu usage of 400%)
Tested on Mysql 5.0.44 and 5.0.38
Both the MyISAM and the InnoDB engines are in use (mostly InnoDB).
InnoDB uses a raw partition residing on a software raid level 10
consisting of 10 disks.
Clients:
Apache 2.2.4 (mpm-prefork)
PDO 1.0.3
PDO-MYSQL 1.0.2
PHP 5.2.1
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