Apache stop serving after reach the MaxClients setting

I have my apache server configured with worker MPM as following:

<IfModule mpm_worker_module>
    ServerLimit         20
    ThreadLimit         50
    StartServers        3
    MaxClients          1000
    MinSpareThreads     50
    MaxSpareThreads     200
    ThreadsPerChild     50
    MaxRequestsPerChild 10000
</IfModule>

The server takes about 2 millions requests everyday. When the requests coming up, the apache server will stop accepting new connection(browser can't connect). And the process will remain in the process list. The memory usage is about 10% and CPU is 0%. It seems the apache server didn't able to recycle the processes when it should.

I've found something related with the crash in error logs:

[Mon Aug 15 12:36:24 2011] [error] child process 11444 still did not exit, sending a SIGKILL
[Mon Aug 15 12:36:24 2011] [error] child process 12090 still did not exit, sending a SIGKILL
[Mon Aug 15 12:36:24 2011] [error] child process 10698 still did not exit, sending a SIGKILL
[Mon Aug 15 12:36:24 2011] [error] child process 12144 still did not exit, sending a SIGKILL
[Mon Aug 15 12:36:24 2011] [error] child process 12032 still did not exit, sending a SIGKILL
[Mon Aug 15 12:36:24 2011] [error] child process 10699 still did not exit, sending a SIGKILL
[Mon Aug 15 12:36:25 2011] [notice] caught SIGTERM, shutting down
[Mon Aug 15 12:37:31 2011] [notice] mod_python: Creating 8 session mutexes based on 20 max processes and 50 max threads.
[Mon Aug 15 12:37:31 2011] [notice] mod_python: using mutex_directory /tmp 
[Mon Aug 15 12:37:31 2011] [notice] Apache/2.2.17 (Ubuntu) mod_python/3.3.1 Python/2.7.1+ mod_ssl/2.2.17 OpenSSL/0.9.8o configured -- resuming normal operations
[Mon Aug 15 15:36:46 2011] [error] server is within MinSpareThreads of MaxClients, consider raising the MaxClients setting
[Mon Aug 15 15:38:48 2011] [error] server reached MaxClients setting, consider raising the MaxClients setting
[Mon Aug 15 16:17:31 2011] [warn] child process 766 still did not exit, sending a SIGTERM
[Mon Aug 15 16:17:31 2011] [warn] child process 767 still did not exit, sending a SIGTERM

Any Ideas? Thanks!

You might want to check your server status using mod_status. You may have connections that are not disconnecting and are stuck in a "sending reply" state (W). Check out this article on how to diagnosi this Solving httpd maxclients and modstatus report

Apache stop serving after reach the MaxClients setting

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