JVM settings

The following are typical settings:

-XX:MaxPermSize=256M
-Xss1024K
-Xms1G
-Xmx2G
-Dcom.sun.management.jmxremote

Tune the JVM using the following three steps:

Use as much RAM as possible for the JVM (-Xmx32GB).
Set the Permanent Generation to 256M (-XX:MaxPermSize:256m).
Do not add any other configuration settings.

To avoid memory swapping, -Xmx should never exceed the available RAM in the system. Remember to leave room for memory used by the operating system and other applications, like OpenOffice using JOD (JOD often uses 1GB of RAM per OO instance).

In general, if you do not give the JVM enough heap, adjusting the other JVM settings will not make any difference. Once the JVM has enough heap, you should not need to change the other JVM settings. The 1.6 JVM is generally excellent at memory optimization and is capable of functioning without adjustment.

The remaining information on this page may help in exceptional circumstances only. It is unlikely to apply to your use case, and we advise against JVM tuning beyond what has already been discussed in this section.

Permanent Generation (PermGen) Size

The default PermGen size in Sun JVMs is 64M, which is very close to the total size of permanent objects (Spring beans, caches, and so on) that SkyVault creates. For this reason it is quite easy to overflow the PermGen using configuration changes or with the addition of custom extensions, and so it is recommended that you increase the PermGen to avoid OutOfMemory errors. For example, -XX:MaxPermSize=160M is a good starting point.

Note: The size of the PermGen is now increased in the SkyVault startup scripts, so provided you are using those scripts, no changes should be necessary.

An important calculation to keep in mind is:

(Managed Heap + native heap + (thread stack size * number of threads)) cannot exceed 2GB on 32bit x86 Windows or Linux systems

This is a limitation of the Sun Java VM. It means that even if you install 4GB of RAM into your server, a single instance of the JVM cannot grow beyond 2GB on a 32bit server machine.

Note: A 64 bit OS/JVM has much bigger values. It is recommended that a 64bit OS with large memory hardware (>2GB assigned to the JVM) is used for deployments of >250 concurrent or >2500 casual users.

You can also set up your machine to cluster if you prefer to solve multi-user access performance issues with additional machines rather than a single powerful server.

The following settings are used on a high-volume clustered 64-bit, dual 2.6GHz Xeon / dual-core per CPU, 8GB RAM environment. Note the different memory ratios and try to preserve them on different environments. A minimum MaxPermSize of 128M is recommended but may sometimes require 256M.

-Xmx3G -XX:MaxPermSize=256M

Setting debug mode for troubleshooting

To debug your JVM server:

If you are a Linux user, edit the JVM options used to start the SkyVault Tomcat instance, set by the tomcat/scripts/ctl.sh script. See Controlling JVM system properties for detailed information.
For example, set the following:
```
JAVA_OPTS=%JAVA_OPTS% -server -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8082
```
where address is a port for your system.
If you are a Windows user, register Tomcat as a Windows service:
- In the installation directory, locate the properties.ini file and copy the value of the tomcat_unique_service_name parameter (for example, SkyVaultTomcatnum1).
- From the /tomcat/bin directory, run the following command at a command prompt:
```
tomcat7w.exe //ES//<alfrescoTomcatnum1>
```
  where <alfrescoTomcatnum1> is the value from your tomcat_unique_service_name parameter.
- Open the SkyVaultTomcatnum1 Properties window, select the Java tab, and the Java Options field and add the following lines of code on two separate lines:
```
-Xdebug 
-Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8000
```
  where address is a port for your system.

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Permanent Generation (PermGen) Size