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From "Joshua Slive" <jos...@slive.ca>
Subject Re: [users@httpd] Segfault & MaxClients problems [long]
Date Mon, 07 Aug 2006 16:05:43 GMT
On 8/7/06, Daniel A. Ramaley <daniel.ramaley@drake.edu> wrote:

> Symptom 1:
>
> After starting Apache during periods of high load the server appears to
> run fine for awhile ("awhile" is highly variable but on the order of 90
> minutes) then starts returning empty pages. When the empty pages start,
> Apache's error_log gets filled with lines like this:
>
> [Fri Aug 04 14:18:29 2006] [notice] child pid 16021 exit signal
> Segmentation fault (11), possible coredump in /etc/httpd/core
>
> These errors are very intermittent (occurring every few hours to every
> few weeks) during periods of light load. I have had CoreDumpDirectory
> defined for awhile and have amassed quite a collection of core files.
> This is the first few lines of what gdb reports for one of the dumps:
>
> (gdb) bt
> #0  0x0000002a99ff2492 in preg_replace_impl (ht=Variable "ht" is not
> available.)
>     at /usr/src/redhat/BUILD/php-4.3.9/ext/pcre/php_pcre.c:1154
> #1  0x0000002a9a0ac255 in execute (op_array=0x552afe2798)
>     at /usr/src/redhat/BUILD/php-4.3.9/Zend/zend_execute.c:1640
> #2  0x0000002a9a0a9386 in execute (op_array=0x552aff7fb8)
>     at /usr/src/redhat/BUILD/php-4.3.9/Zend/zend_execute.c:1684
> #3  0x0000002a9a0a9386 in execute (op_array=0x552b0e26c8)
>     at /usr/src/redhat/BUILD/php-4.3.9/Zend/zend_execute.c:1684
> #4  0x0000002a9a0a9386 in execute (op_array=0x552af80db8)
>     at /usr/src/redhat/BUILD/php-4.3.9/Zend/zend_execute.c:1684

That is clearly a programming error either in php or pcre.  You might
want to try php forums or the php bug database to see if you can find
the solution.


>
> Symptom 2:
>
> At other times messages about MaxClients show up. I don't believe the
> server is actually running out of processes to serve requests since
> even during the academic year when it is very busy requests are handled
> quickly enough that there are seldom more than a dozen or two in
> progress at any moment.
>
> [Fri Aug 04 02:30:02 2006] [error] server reached MaxClients setting,
> consider raising the MaxClients setting

>     119 processes closing connections
>       2 processes reading requests
>       4 processes sending replies
>       3 processes waiting for connections

This problem seems unrelated to the first.  It does seem unusual to
have all those processes in the closing phase.  When you look at the
full server-status output, do many of the lines comes from the same
IP?  This would be an indication of a (deliberate or accidental)
denial of service attack.  Otherwise, you could look at commonality
between the types of requests they are processing.

Joshua.

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