The performance and behaviour of the Realm Server is inseparably linked to the amount of maximum heap memory allocated to the Java VM hosting it. The Realm Server is capable of scaling depending on the hardware platform it is hosted on, and that is determined by the memory available to the Java VM. The Realm detects this and switches its mode of operation to Small Memory Mode, Medium Memory Mode or Large Memory Mode.

Allocating 16MB or less of heap memory to the Java VM hosting the Universal Messaging Realm will make it operate in small memory mode. This is confirmed at start-up by a log entry like the following:

The Universal Messaging Realm small memory mode should be used when running a Realm on mobile or embedded devices, or other machines with very limited memory resources available. Apart from limited memory available to store events in reliable channels, all thread pooled sub systems are changed to have only one thread. It is therefore recommended that persistent channels should always be used on such Realms. The performance will also be reduced by the fact that all caching is disabled in this mode.

All of the functionality provided by the innovative Universal Messaging server side Realms are available in the small memory mode and hence on handheld devices etc.

Allocating 16MB or more of heap memory to the Java VM hosting the Universal Messaging Realm will make it operate in medium memory mode. This is confirmed at start-up by a log entry like the following:

The Universal Messaging Realm medium memory mode should be used when running Realms on development or where memory is at a premium. All thread pooled sub systems will start up with our recommended default values for this mode. Tuning the Realm to higher values for those sub systems will increase the Realm's memory requirements and increase caching age values.

Allocating 70MB or more of heap memory to the Java VM hosting the Universal Messaging Realm will make it operate in large memory mode. This is confirmed at start-up by a log entry like the following:

The Universal Messaging Realm large memory mode should be used when running Realms on development, staging or production environments, or when using reliable channels. All thread pooled sub systems will start up with our recommended default values for this mode.. Tuning the Realm to higher values for those sub systems will increase the Realm's memory requirements and increase caching age values.