Universal Messaging servers provide 3 different memory modes. Typically, the Universal Messaging Realm server will be deployed using the large memory mode. When deploying a Universal Messaging server, one of the considerations for memory consumption concerns the volatility of your data, and specifically the types of channels and queues you are using.

The channels that consume the most memory are those channels that keep the events in memory and do not write events to persistent store. These channels are known as Simple and Reliable.

If you have a simple channel with a TTL of say 1 day (86400000 milliseconds), and you expect to publish a 1k event per second, this channel alone will consume approximately 86.4MB of memory. However if your data has a very short lifespan defined by setting a low TTL, then the memory consumption would be much less than it would be with a 1 day TTL.

This kind of calculation will indicate to you how much maximum memory the Realm Server JVM needs to be allocated to avoid running out of memory.

If you follow these simple guidelines, you should be able to estimate the memory required for your channels.