Last Friday (10/7/2011) we started having httpd.worker processes grow from the typical 10-15M memory reserved to 10G+ (gigabytes) in a matter of 1-2 minutes. This obviously brings the server to a halt as it starts swapping etc. We have to reboot the server in order to get it running again. If we catch it in time we can kill the offending httpd.worker and all is well for the time being.


  • RHEL 5.5
  • Apache httpd-2.2.3-45.el5_6.2.x86_64.rpm (Patched to prevent the recent byte range filter vulnerability)
  • Using Apache MPM worker (not prefork)
  • mod_jk 1.2.28
  • mod_rewrite
  • OpenSSL (latest red hat version)
  • Tomcat / JBoss Web 2.1 (JBoss 5.1.0)
  • dedicated servers (unshared), 12 gigs of RAM on each


  • Under normal load all of a sudden one httpd.worker process will grow from 10M to several Gigs in reserved memory. Have to kill -9 the process or else server grinds to a halt
  • Will occasionally happen to multiple httpd.worker processes around the same time
  • Once the offending process(es) has been killed, all is normal again (matter of minutes).
  • Has been happening approx. every 8 - 12 hours since last Friday, no clear pattern.
  • No spikes in request traffic leading up to it
  • No odd traffic / errors in access_log and error_log

Additional notes

  • Our normal load is ~5-10 requests / sec on each of server, not crazy.
  • We set (after this started) MaxRequestsPerChild to 250 and workers are being properly cycled. Implies that the issue is from a single or small set of requests
  • We've made no application / system configuration changes in the last 2 weeks.
  • As it's not a sustained issue (goes away in a matter of minutes) it doesn't feel like a
  • It sounds exactly like the byte range filter vulnerability, but we've patched and tested for that (https://issues.apache.org/bugzilla/show_bug.cgi?id=51714)
    • I've read several posts on server fault (and elsewhere) but haven't found any that describe a single work process going out of control with memory


  • What can cause an individual httpd.worker processes' memory to grow out of control like this? Or even anything beyond the typical amount (10m-15m for our config)?
  • Any suggestions for troubleshooting this? We're watching top, server-status, jkstatus, monitoring with cacti, have monit installed and are getting mod_jk logging going.

Apache / mod_jk / Tomcat (JbossWeb) Configuration

From httpd.conf...

<IfModule worker.c> 
StartServers         2 
MaxClients         500 
MinSpareThreads     25 
MaxSpareThreads    150
ThreadsPerChild     50 
MaxRequestsPerChild  250 

From mod_jk's worker.properties...

# Define Node1 worker.node1.port=8009
worker.node1.host= worker.node1.type=ajp13
worker.node1.lbfactor=1 worker.node1.connection_pool_timeout=60
worker.node1.connection_pool_size=35 worker.node1.connect_timeout=5000

From tomcat's server.xml...

<Connector protocol="AJP/1.3" port="8009"
address="${jboss.bind.address}" redirectPort="8443" maxThreads="350"
connectionTimeout="60000" enableLookups="false"/>

Would appreciate any input!

  • Ok we have actually figured out how to reproduce this issue. It happens with a particularly formatted URL. As soon as we figure out whether it's our configuration vs an apache bug I will report back here for others than run into it. – Rich Taylor Oct 10 '11 at 23:31

We have official found and fixed the issue, it was simply a loop in our mod_rewrite rules. It had been in place for months but nobody had hit the particular URL that caused the issue. So that is at least one example of some that can cause a single httpd.worker process to spiral out of control with memory consumption.

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