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From "N.Z. Bear" <>
Subject [users@httpd] Child process sudden memory explosion
Date Sun, 16 Jan 2005 02:46:01 GMT

I am experiencing a problem with httpd child processes suddenly
exploding in memory size and consuming all available memory. The
behavior is sudden, not gradual: within a few seconds or a minute the
process swells to several orders of magnitude larger than its usual

Listed below is a ps aux; the first httpd is a 'normal' one, the second
is the problem child:

nobody   23166  0.0  0.1 17572 2148 ?        S    16:06   0:00
nobody   23167  1.4 63.7 2245624 1315584 ?   D    16:06   1:00

Generally only a small number of child processes display this behavior:
often just one at a time.

The system setup is Linux with Apache 1.3.33, PHP 4.3.10 and MySQL
4.0.22-standard. I am not running mod_perl. 

The vast majority of traffic on the site is PHP scripts, some of which
access the MySQL backend. I strongly suspect a problem in one of the
scripts, but have not been able to identify specifically which one. I
added the '%P' variable to my Apache log file and am now able to
identify the specific requests that the Apache child process which
explodes was handling prior to the error, but thus far no pattern has
emerged (different scripts appear last each time). I suspect that the
last entry I see in the log is the last successful request, not the one
that causes the problem. (I am aware of log_forensic, which I learned
would provide log output of a request *before* processing, but my skills
are not sufficient to make me feel comfortable rebuilding my Apache
server to include it at this time). 

I am working around the issue with a cron script that checks if a child
process has exploded and then restarts Apache if needed; this helps to
mask the issue but is obviously not a fix. I have considered setting
max_requests_per_child to a non-zero value but based on my understanding
I doubt it would help (given that this is not a gradual leak but a case
where the process goes wild in the middle of a request). 

I recognize that it is unlikely that this problem can be
diagnosed-at-a-distance, but would welcome suggestions on debugging
tools and techniques which might help me narrow down the problem area.
In particular: other than log_forensic, is there a way to truly see what
that child process was doing when it went rogue? 

Any and all suggestions are appreciated; thanks...

N.Z. Bear
The Truth Laid Bear

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