The maximum amount of memory in megabytes that the JVM will be allowed to use.
The default value is "0" (zero), which will cause the JVM's default value to be used.
For most JVMs, the default value is "64MB".
If a non-zero value is specified for this property, then an appropriate
-Xmx parameter will be added to the Java command generated by the Wrapper.
If specified, the maximum memory must be greater than or equal to the value set for the
The exact upper limit depends on the JVM,
but for 32-bit JVMs, it tends to be a less that 2048Mb, closer to 1800Mb in most cases.
64-bit JVMs allow much higher settings, which is one of the main reasons for using a 64-bit JVM.
If this property is set to "0" (zero), then it is also possible to specify
the -Xmx parameter manually using the
This property is provided as a convenience for most users, and also makes it possible to set relative memory sizes as described below.
If you require more complicated memory configurations, this can be done using the wrapper.java.additional.<n> properties as follows:
Equivalent Example: (3MB)
If an application is experiencing
then this often indicates that the maximum amount of memory available to the application
needs to be increased.
Be aware that setting the maximum memory to a value
which is greater than the amount of actual memory on the machine
will result in memory swapping.
Memory swapping is a function of the OS (operating system),
and thus its performance is highly OS specific.
However from experience, this tends to result in a large decrease in application performance.
In most cases, it is better to set the maximum memory to a value
which fits within available memory and then rely on Java's garbage collection.
Unless you really do know everything there is to know about memory
and Garbage Collection in Java,
I would recommend reading through the following document.
It describes in detail how the initial and maximum memory values
affect Java performance and also goes into detail about
what can be done to improve that performance for a given application.
At times, it is necessary to set the memory thresholds relative to
the amount of physical memory available on the system.
This property accepts a percentage value between 1 and 100 which will translate into a size in MBs.
For 32-bit versions of the Wrapper,
the value will be calculated relative to lower of physical memory and 2048MB.
In the above example (60%), if 1GB (1024MB) of memory is installed on the system,
the maximum memory will be set to 614MB (=1024 x 60%).
Java behaves very poorly if the JVM has any of its memory swapped
so it is important to take the OS requirements
and any other applications into account when deciding on a safe memory level.
This feature is currently not working correctly on AIX versions.
The problem is being looked into,
but did not want to hold up the release of Wrapper due to only this reason.