Httpd worker MPM Configuration
Internal
Overview
Diagram
The configuration elements described below are represented on the mod_jk Concepts Diagram.
Enabling woker MPM Mode
If you configure httpd yourself, make sure you compiled it with worker MPM support.
If you use Red Hat EWS, worker support comes pre-compiled into $APACHE_HOME/sbin/httpd.worker, make sure the start script is using that.
For more details about compiling httpd with the right MPM mode, see:
MaxClients, MaxRequestWorkers
- http://httpd.apache.org/docs/2.2/mod/mpm_common.html#maxclients
- http://httpd.apache.org/docs/current/mod/mpm_common.html#maxrequestworkers
"MaxClients" and "MaxRequestWorkers" are equivalent, since 2.3.13 "MaxClients" was renamed "MaxRequestWorkers", but for the time being, both names are valid and supported.
MaxClients represents the maximum number of connections that will be processed simultaneously by the entire server, seen as the sum of all active children processes. The default value is 400 = 16 (ServerLimit) * 25 (ThreadsPerChild). The directive restricts the total number of threads that will be available to serve clients.
Any connection attempts over the MaxClients limit will normally be queued, up to a number based on the ListenBacklog directive. Once a child process becomes available after handling at least one of its current requests, the connection will then be serviced.
Even if ServerLimit is set to a high value (ThreadsPerChild left to default), the number of concurrent connection is limited by MaxClients. This was tested and proven.
MaxClients Idiosyncrasies
- MaxClients must be at least equals with ThreadsPerChild. If not, httpd will warn at startup and automatically adjust the value to be equals with ThreadsPerChild.
- MaxClients must be an integer multiple of ThreadsPerChild. If it's not, it will be adjusted automatically, and the server will issue an error message similar to the one presented below:
MaxClients (12) is not an integer multiple of ThreadsPerChild (10), lowering MaxClients to 10