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SubjectRE: Kernel 2.2.9 fails to handle load.
On 03-Jun-99 Yann Doussot wrote:
>
> I tried the ab programm (benchmark tool shipped with Apache). I've
> runned it with 2000 requests. After the run, the system is in very bad
> state: more than 100 Apache zombie process that does not go away and if I
> try a ps -aux, sometimes I got:
>
> zsh: fork failed: resource temporarily unavailable

It sounds like your machine went into heavy swap, ran out memory, and then
weird things started happening. Could it be related to the other OOM thread
that was going on recently? One thing to check in your Apache setup to
prevent this from happenning. Make sure the total number of server that can be
spawned (the MaxClients directive) don't case the machine to be swapping.
Here's the snippit from their webpage
http://www.apache.org/docs/misc/perf-tuning.html

---
The single biggest hardware issue affecting webserver performance is RAM. A
webserver should never ever have to swap, swapping increases the latency of
each request beyond a point that users consider "fast enough". This causes users
to hit stop and reload, further increasing the load. You can, and should,
control the MaxClients setting so that your server does not spawn so many
children it starts swapping.
---

Especially with PHP compiled in, each instance of Apache takes a decent amount
of memory, and your config only has 256MB ram total. On my machine, each
Apache+PHP process takes about 5MB. If you reach the 200 MaxClients you
described in your setup, you'll need 1GB of RAM to keep Apache in memory.
If you want to keep the MaxClients high, make sure you have enough swap laying
around to avoid running OOM. Running vmstat while benchmarking should give you
a good idea of what's hurting the server.

-Dave

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