Major Description
There is a flag called reduceMemoryFootprint which will clear out the unmarshalled state of a message after it is added to a queue/topic because that state isn't counted towards the size and can lead to OOM errors.
However, even setting this flag, I am still seeing some brokers run out of memory. After analyzing the heap dumps I have found 2 reasons for this:
1) Non-persistent messages do not have their unmarshalled state cleared. This was done because when a message is persisted it is guaranteed to have the marshalled state. However we can still clear the memory for non-persistent messages as long as we check to make sure the marshalled state exists first, which it will for transports like TCP but won't exist for the VM transport.
2) When a message is added to a subscription the properties are needed to check which subscription messages can be dispatched to. This causes the memory to be unmarshalled again.
In the topic case, we should probably defer the clearing of the state until after the message is added to a subscription because messages are immediately dispatched to topic subs so we don't unnecessarily have to convert the data twice. In the queue case it probably makes sense to clear memory on add to the queue and on add to the subscription.