Apache problems (response + memory usage)

Monday 06 August 2007 7:25:55 am

Hi everbody,

just wondering if anyone has encountered similar problems, and/or has an idea what might be wrong with a server showing very poor performance.

Symptoms are:
Top shows a lot more Virtual memory than on some other installations (roughly twice as much) and with very little shared memory, causing the server to be able to handle to few processes before it starts swapping.

When MaxClients are reached, the server uses a very long time to handle connection timeouts. This also happens when MaxClients are set low enough to avoid swapping.

Do anyone recognise these symptoms, or have suggestions to tests worth running?

The installation is a Xen virtual server running Debian Etch on dual AMD64.
Apache 1.3.34-4.1
Version: 6:4.4.7-0.dotdeb.1
MySQL 5.0.32-7etch1

Tuesday 07 August 2007 7:21:33 am

Earlier, tests showed that using a php accelerator only gave a very slight performance boost. So we had no accelerator running. But we wanted to test with an accelerator, and this actually helped a great deal. The server became much more responsive and can now handle much more load than earlier.

The strange thing though, is that each process now uses even more virtual memory. Around 200 MB per process. And shared memory is only around 35MB per process. To me these numbers make no sense any more. It seems that memory allocated for each process is much higher than is actually used. (70 clients on 2GB and still free mem)

The PHP accelerator helped a great bit. But I still don't understand what's going on.

Tuesday 07 August 2007 1:30:30 pm

Hi Atle,

It's a lots of things that can cause the problem you are experiences. You should go through your configuration for Apache/PHP, and make sure your not giving away more memory then you got. You can use pmap to see what Apache use all the memory to.

You should also monitor system resources over time by some tools like Munin. I will make it much easier to see the consequence's when doing small changes on your server, and easier to see whats causing the problem.

Also make sure your running your vm with paravirtualization, and not full virtualization.

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