Moodle in English: mysql high CPU

mysql high CPU

by Alan Dawson - Tuesday, September 27, 2011, 11:22 PM

Hi. I have 2 moodle instances, a live on and a test one.

Live instance

Running Moodle 1.9.13+ on Debian Lenny

VMware ESX virtualised machine

MySQL 5.0.51a

PHP 5.2.6-1+lenny13

4GB RAM

4x 2Ghz CPU

Test instance

Running Moodle 1.9.13+ on Debian Lenny

MySQL 5.0.51a

PHP 5.2.6-1+lenny13

1GB RAM

1x 2Ghz CPU

Performance is acceptable for most usage, but creation and modification of courses is slow. This takes about 1min with the users browser hanging until it completes.

mysqld pegs a processor at 100% utilisation whilst this is happening.

The problem is not related to usage of the host, as both live and test ( which has practically zero utilisation ) show this behaviour.

Our mysql database is around 1.3Gbytes in size

Any hints on improving this appreciated.

Re: mysql high CPU

by andy emerine - Wednesday, October 19, 2011, 9:01 PM

Did you figure this out? We have a very similar problem. Randomly when we have over 10 concurrent users the CPU spikes. It seems the more users the higher the chance for the site to lock up. The site times out and/or brings users to a database overload page. I had 60 users try to upload an assignment this morning. It brought the server to a hault. I've had this happen even when users are logging in.

This doesn't appear to be memory related, as the memory usage on the box was fairly low. The CPU however, was pegged. I'm not sure what would be causing the CPU to have such high usage. Maybe this is LDAP related. I wish there was a way to figure out what's causing this CPU spike.

The server is a VM that has 2 vCPU's at 2.6Ghz, and 1.5GB RAM. It's a dedicated VM with only one website running on it.

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Re: mysql high CPU

by Alan Dawson - Tuesday, November 1, 2011, 7:08 PM

we fixed this for us.

Our moodle database has been around for some years, and the tables were MyISAM

We converted to Innodb and then made some further optimisations based on recommendations from the MySQLtuner scripts https://github.com/rackerhacker/MySQLTuner-perl

This time to add a course from ~ 70s to 20s

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Re: mysql high CPU

by Alejandro Lengua - Friday, May 18, 2012, 8:24 PM

Hello Alan,

Nice suggestion. I wonder if changing tables from MyISAM to InnoDB is a safe process. Are there any tables that should be changed first?

BTW, Is this only command needed to run?
ALTER TABLE t1 ENGINE=InnoDB;

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Hardware and performance

mysql high CPU