Mysql running out of memory

memorymemory usageMySQL

I am having a lot of trouble with mysql eating too much ram on a small machine and am looking for some help in figuring out why it is eating so much.

I have a small virtual machine with 256MB of RAM running Debian Wheezy. On this server I have apache2 and mysql installed. I don't do very much on this server, only a few lightly used websites and a mail server.

For some reason, several times a day, my mysql server crashes. When I check my syslog I find the following error:

kernel: [3323593.630722] Out of memory in UB: OOM killed process 9471
(mysqld) score 0 vm:327824kB, rss:37080kB, swap:0kB

So as far as I can tell, mysql starts to eat up too much memory and is killed by the system. I log slow queries and keep a tab on my mysql.err log but I dont see anything of much value in those that would show me why mysql starts to eat so much memory.

My my.cnf file has these options set:

key_buffer              = 8M
max_allowed_packet      = 16M
thread_stack            = 128K
thread_cache_size       = 8

query_cache_limit       = 512K
query_cache_size        = 8M

The other thing is that when I check the amount of memory being used when I start mysql and even during the day while it is running, I usually have about 128MB free. I don't see how mysql would end up eating that amount ever.

What can I do to track this problem down?

Best Answer

256 MB for both Apache and MySQL is extremely low. I always recommend atleast 512MB for that combination (and thats the bare minimum). What your saying however is not necessarily MySQL causing the problem, its just the OOM killer killing MySQL because the VM ran out of memory. Besides that MySQL has alot of defaults, so even if you did not set them in the my.cnf, innodb_buffer_pool_size will claim 8MB and so on.

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