Performance Issue due to server reached MaxRequestWorkers on Apache httpd

Environment

• Red Hat Enterprise Linux (RHEL)
• Red Hat JBoss Enterprise Application Platform (EAP)
• Red Hat JBoss Web Server (JWS)
• Red Hat JBoss Core Services (JBCS)
• Apache Web Server (httpd)

Issue

• The Apache httpd hangs after reaching 256 connections. We see below error message in error_log.

     AH00161: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting
  

• The Apache httpd server is running out of MaxRequestWorkers very quickly. How to increase MaxRequestWorkers?

• Httpd only allowing 256 connections in Prefork mpm

Resolution

• Tune up the MPM settings by increasing MaxRequestWorkers and related directives using our This content is not included.Load Balancer Configuration Tool.
• For more information about MPM tuning, refer to Tuning Apache HTTPD MPM Worker and Event
• This message can also happen after upgrading to JBCS httpd 2.4.51+ as noted in httpd exhausted with smaller pool size after upgrading to JBCS httpd 2.4.51
• For understanding what MaxClients / MaxRequestWorkers is capable to handle, refer to Understanding the MaxClients/MaxRequestWorkers Apache is capable of handling

Root Cause

• The amount of traffic was greater than the request worker limit specified in directive MaxRequestWorkers, exhausting httpd's thread pool.
• The Prefork MPM ServerLimit defaults to 256, so if the MaxRequestWorkers is increased beyond that number, Apache httpd will throw a warning message and truncate the MaxRequestWorkers down to 250.

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