Memory settings
The following sample sets

PermGen space is set to 256 MB
Minimum application memory is 512 MB
Maximum application memory is 1 GB

Max total memory in this setup is 1280 MB which will work just fine in most cases
-Xmx512m -Xms1024m -XX:MaxPermSize=256m
In very memory constrained environments (server <= 1GB) use the following settings, with a max use of 512 mB
-Xmx384m -Xms384m -XX:PermSize=128m -XX:MaxPermSize=128m

Tomcat6
Windows 

 The service can be changed by 

 

 Open prompt as  Administrator 

 Run the following commands 

 

 cd "C:\Program Files\Apache Software Foundation\Tomcat 6.0\bin

Tomcat6w.exe //ES//tomcat6 

 

 Klik "Java" page 

 Set the values

 

 Initial memory pool (aka "Xms"): 512m 

 Maximum memory pool (aka "Xmx"): 1024m 

 Add an extra line to Java Options 

 

 

 

 -XX:MaxPermSize=256m 

 

 Klik OK 

 

 Linux 

 Find  catalina.sh  in something like:  /usr/share/tomcat6/bin 

 Assign following line to JAVA_OPTS variable and add it into catalina.sh file. 

 JAVA_OPTS="-Djava.awt.headless=true -server -Xmx512m -Xms1024m -XX:MaxPermSize=256m"

Tomcat7
Windows 

 As Tomcat 6 except for step 2 

 cd "C:\Program Files\Apache Software Foundation\Tomcat 7.0\bin

Tomcat7w.exe //ES//tomcat7 

 See the visual guide here 

 http://plavc.wordpress.com/2012/02/08/tomcat-service-on-windows/ 

 Linux 

 sudo nano /etc/tomcat7/tomcat7.conf

Tomcat8
Windows 

 As Tomcat 7 except for step 2 

 cd "C:\Program Files\Apache Software Foundation\Tomcat 8.5\bin

Tomcat8w.exe //ES//tomcat8

JBoss 7.x
Windows 

 

 Edit [JBoss home]\bin\standalone.conf.bat 

 Ensure the following value is present 

 

 set "JAVA_OPTS= -Xmx512m -Xms1024m -XX:MaxPermSize=256m"