Overflow in Hazelcast Queue Store

One of the new features of Hazelcast 3 is the queue store.

Differently from map store; overflow is possible. If you set a memory Iimit; it starts persisting to disk and skipping the memory when queue reaches this limit.

Here the configuration:

<queue-store>
            <class-name>com.hazelcast.QueueStoreImpl</class-name>
            <properties>
                <property name="binary">false</property>
                <property name="memory-limit">1000</property>
                <property name="bulk-load">500</property>
            </properties>
</queue-store>

For above configuration:

• Items will be persisted in their Object form (deserialized one).
• If the size of the queue has reached 1000 (memory-limit), next element will be just persisted to disk it will not be stored in memory.
• Items will be loaded from store in bulks with size 500.

Some more notes:

• Use memory-limit when you avoid over-usage of RAM in case of high load.
• If you want all items in memory (and store) use Integer.MAX_VALUE, if you want all items just in store then use 0 as memory-limit.
• If you do not reach the store externally (just hazelcast uses the store) then make the binary configuration to true. That will increase the performance as a step for deserialization will be skipped.

Here you can see some examples of QueueStore implementation:

https://github.com/hazelcast/hazelcast/blob/master/hazelcast/src/test/java/com/hazelcast/collection/impl/queue/QueueStoreTest.java