Configure Tomcat Java JVM Memory, The Debian way

Setting the JVM memory alocation for tomcat should be trivial in theory we only need to pass the : -Xmx1024m parameter to JAVA_OPTS during tomcat startup. However that not the case. I’ve been looking for month how to change this Tomcat JVM paramater. Finally i got the answer tonight and i want to share my experience 🙂

Note : This was intended to use with the tomcat that come with ubuntu bundle (apt-get install tomcat)

In Debian the JAVA_OPTS paramater we need to change is located in this file /etc/default/tomcatX.X.

Change the JAVA_OPTS with this parameter :

JAVA_OPTS=”-Djava.awt.headless=true -Xmx1024m -XX:MaxPermSize=256m”

-Xmx : Set the maximal heap memory alocated for a tomcat server, a low value of this parameter can lead to OutOfMemoryExceptions.

-XX:MaxPermSize : The PermGen space is used for things that do not change (or change often). e.g. Java classes

The thing that we must be aware of is that both -Xmx and -XX:MaxPermSize takes different memory alocation. So if in the example we put 1024 Mb on Heap space and 256 Mb on PermGen we allowed a total of 1024 + 256 to be alocated on a single tomcat Instance.

After change these setting we can restart tomcat.

If we want to make sure that the setting is taking effect , we can make a simple servlet which check the memory parameter using this code :

Runtime runtime = Runtime.getRuntime();

NumberFormat format = NumberFormat.getInstance();

long maxMemory = runtime.maxMemory();
long allocatedMemory = runtime.totalMemory();
long freeMemory = runtime.freeMemory();

Writer wr = resp.getWriter();
StringBuilder sb = new StringBuilder();
sb.append("&lt;h1&gt;Server Info &lt;/h1&gt;");
sb.append("&lt;br&gt;&lt;b&gt;Free memory: &lt;/b&gt;" + format.format(freeMemory / 1024) + " MB ");
sb.append("&lt;br&gt;&lt;b&gt;Allocated memory : &lt;/b&gt;" + format.format(allocatedMemory / 1024) + " MB ");
sb.append("&lt;br&gt;&lt;b&gt;Max memory : &lt;/b&gt;" + format.format(maxMemory / 1024) + "MB ");
sb.append("&lt;br&gt;&lt;b&gt;Total free memory : &lt;/b&gt; " + format.format((freeMemory + (maxMemory - allocatedMemory)) / 1024) + " MB ");

wr.write(sb.toString());

Runtime runtime = Runtime.getRuntime();

NumberFormat format = NumberFormat.getInstance();

long maxMemory = runtime.maxMemory();

long allocatedMemory = runtime.totalMemory();

long freeMemory = runtime.freeMemory();

Writer wr = resp.getWriter();

StringBuilder sb = new StringBuilder();

sb.append("<h1>Server Info </h1>");

sb.append(" Free memory: " + format.format(freeMemory / 1024) + " MB ");

sb.append(" Allocated memory : " + format.format(allocatedMemory / 1024) + " MB ");

sb.append(" Max memory : " + format.format(maxMemory / 1024) + "MB ");

sb.append(" Total free memory : " + format.format((freeMemory + (maxMemory - allocatedMemory)) / 1024) + " MB ");

wr.write(sb.toString());

Hope thats help !

Reference :

http://rimuhosting.com/knowledgebase/linux/java/-Xmx-settings

http://codintips.blogspot.com.au/2010/01/add-more-jvm-memory-in-tomcat-on-ubuntu.html

Todi !

Configure Tomcat Java JVM Memory, The Debian way

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