Apache/PHP hangs on POST/submit form

selig

I have been having this problem for months. I have a webhosting server and from time to time, every submit of any PHP form hangs. There are no errors in the log and I have updated all packages over the previous months. I even created a brand new chroot with all packages compiled from scratch and installed a new kernel but nothing helps. It seems random, sometimes the server can last for a couple of weeks without any problem but then there are days when it happens several times. It used to be worse when I had the worker MPM, I have switched to prefork in the meantime. That helped a bit but did not solve the problem. I have also tried decreasing the max requests per child directive, in hopes that if PHP leaks or hangs, the process will get restarted more frequently, solving the problem. But it did not really help either.

Now I do not know what else to try or where to look. Any ideas would be appreciated.

audiodef · Posted: Fri Dec 21, 2012 2:25 pm Post subject:

What kind of webhosting server? Shared, virtual private or rented hardware? I assume the server OS is Gentoo, since you're posting here.
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selig · Posted: Sat Dec 22, 2012 8:55 pm Post subject:

It is my own hardware, nothing virtual.

audiodef · Posted: Sat Dec 22, 2012 9:15 pm Post subject:

Can you post:

emerge --info

emerge -pv apache

emerge -pv php

?
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selig · Posted: Sat Dec 29, 2012 10:47 am Post subject:

emerge --info:

lxg · Posted: Sat Dec 29, 2012 12:19 pm Post subject:

Is it possible that the bottleneck is your MySQL server? For example it might be that slow queries on a large data basis cause MySQL to have too many open connections, and (depending on its configuration) it waits until a new slot is available.

What types of PHP applications do you have installed? In your WordPress installation(s), what plugins do you use? Did you try deactivating them? Sometimes they are horribly coded and cause the weirdest problems.
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selig · Posted: Sun Dec 30, 2012 3:38 pm Post subject:

MySQL is not the bottleneck, it is not doing anything when this problem occurs. Also, there are not many open connections to the database.

The biggest problem is that it is a webhosting server and I have no control over what my customers are using. I cannot just go and disable some wordpress plugins in their installation. Unfortunately, this makes it really difficult to trace the root of the problem. I am quite sure that something must trigger it, some weird PHP script one of my customers is using, a wordpress plugin, something like that. On the other hand, since I am using apache/prefork, the processes should be isolated and even if one of them slows down, the rest should work normally.

lxg · Posted: Sun Dec 30, 2012 4:01 pm Post subject:

selig · Posted: Thu Jan 03, 2013 12:56 pm Post subject:

Thanks for the tip, I will try Munin and see what it can tell me.