On 7/21/2011 10:22 AM, Grant wrote:
I ran into an out of memory problem. The first mention of it in the
kernel log is "mysqld invoked oom-killer". I haven't run into this
before. I do have a swap partition but I don't activate it based on
something I read previously that I later found out was wrong so I
suppose I should activate it. Is fstab the way to do that? I have a
commented line in there for swap.
...
If you're running any other servers that utilize MySQL like Apache or
something, check its access logs to see if you had an abnormal number
of connections. Bruteforce hacking or some kind of flooding/DOS attack
might cause it to use more memory than it ordinarily would.
I don't know why I didn't check the apache2 error log before, but I
got the following entry 2 seconds before the server became
unresponsive:
[error] server reached MaxClients setting, consider raising the
MaxClients setting
I use the default 256 for MaxClients. This confirms the server was
brought down by too many child processes consuming too much memory.
Looking back at the access_log, it's clear this condition was caused
by the single IP which requested one of my pages about 300 times over
the course of 1 minute. This caused my entire server to lock up for
hours until I rebooted it.
I hesitate to reduce MaxClients from 256. I think my server should be
able to handle it since it's the default. So I need to prevent my
apache2 child processes from consuming so much memory? apache2 was
restarted about an hour before the lockup so it had a pretty fresh
start. I do use mod_perl which is a memory hog from what I
understand. Do I just need more RAM?
Most people do not think about this correctly. Can your server run
10000 Apache processes? No, not enough resources. 1000? No, same
problem. 256? I'd say no based on this thread. If you're not going to
set it at 10000 why try to keep it at 256?
Next image a grocery store with 256 checkout lanes, but only four
cashiers. Four cashiers trying to run that many lanes is actually slower
than having only four lanes. However 32 lanes could faster than 4.
People can have their groceries setup, baggers aren't getting in the
way, etc. The analogy breaks down a bit, but you get the point.
There is no performance gain in configuring for concurrency your
hardware and software can not support.
kashani
