Tuning Apache and Tomcat

Altering Apache and Tomcat Parameters

Apache and Tomcat Parameters should only be modified with support or consulting as these parameters can have severe and catastrophic performance impacts on your server when improperly adjusted. SUSE will not be able to provide support for catastrophic failure when these advanced parameters are modified without consultation. Tuning values for Apache httpd and Tomcat requires that you align these parameters with your server hardware. Furthermore testing of these altered values should be performed within a test environment.

Apache’s httpd MaxClients Parameter

The MaxClients setting determines the number of Apache httpd processes, and thus limits the number of client connections that can be made at the same time (SUSE Manager uses the pre-fork MultiProcessing Modules). The default value for MaxClients in SUSE Manager is 150. If you need to set the MaxClients value greater than 150, Apache httpd’s ServerLimit setting and Tomcat’s maxThreads must also be increased accordingly (see below).

The Apache httpd MaxClients parameter must always be less or equal than Tomcat’s maxThreads parameter!

If the MaxClients value is reached while the software is running, new client connections will be queued and forced to wait, this may result in timeouts. You can check the Apache httpd’s error.log for details:

[error] Server reached MaxClients setting, consider increasing the MaxClients setting

The default MaxClients parameter can be overridden on SUSE Manager by editing the server-tuning.conf file located at /etc/apache2/. For example server-tuning.conf file:

# prefork MPM
   <IfModule prefork.c>
           # number of server processes to start
           # http://httpd.apache.org/docs/2.2/mod/mpm_common.html#startservers
           StartServers         5
           # minimum number of server processes which are kept spare
           # http://httpd.apache.org/docs/2.2/mod/prefork.html#minspareservers
           MinSpareServers      5
           # maximum number of server processes which are kept spare
           # http://httpd.apache.org/docs/2.2/mod/prefork.html#maxspareservers
           MaxSpareServers     10
           # highest possible MaxClients setting for the lifetime of the Apache process.
           # http://httpd.apache.org/docs/2.2/mod/mpm_common.html#serverlimit
           ServerLimit        150
           # maximum number of server processes allowed to start
           # http://httpd.apache.org/docs/2.2/mod/mpm_common.html#maxclients
           MaxClients         150
           # maximum number of requests a server process serves
           # http://httpd.apache.org/docs/2.2/mod/mpm_common.html#maxrequestsperchild
           MaxRequestsPerChild  10000
   </IfModule>

Whenever the Apache httpd MaxClients parameter is changed, the ServerLimit must also be updated to the same value, or the change will have no effect.

Tomcat’s maxThreads Parameter

Tomcat’s maxThreads represents the maximum number of request processing threads that it will create. This value determines the maximum number of simultaneous requests that it is able to handle. All HTTP requests to the SUSE Manager server (from clients, browsers, XMLRPC API scripts, etc.) are handled by Apache httpd, and some of them are routed to Tomcat for further processing. It is thus important that Tomcat is able to serve the same amount of simultaneous requests that Apache httpd is able to serve in the worst case. The default value for SUSE Manager is 200 and should always be equal or greater than Apache httpd’s MaxClients. The maxThreads value is located within the server.xml file located at /etc/tomcat/.

Example relevant lines in server.xml:

<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" URIEncoding="UTF-8" address="127.0.0.1" maxThreads="200" connectionTimeout="20000"/>
<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" URIEncoding="UTF-8" address="::1" maxThreads="200" connectionTimeout="20000"/>
Tuning Notes

When configuring Apache httpd’s MaxClients and Tomcat’s maxThreads parameters you should also take into consideration that each HTTP connection will need one or more database connections. If the RDBMS is not able to serve an adequate amount of connections, issues will arise. See the following equation for a rough calculation of the needed amount of database connections:

((3 * java_max) +  apache_max + 60)

Where:

  • 3 is the number of Java processes the server runs with pooled connections (Tomcat, Taskomatic and Search)

  • java_max is the maximum number of connections per Java pool (20 by default, changeable in /etc/rhn/rhn.conf via the hibernate.c3p0.max_size parameter)

  • apache_max is Apache httpd’s MaxClients

  • 60 is the maximum expected number of extra connections for local processes and other uses