Queue Capacity

For huge clusters or high data mutation rates, you might need to increase the replication queue size. The default queue size for replication queues is 10000. This means, if you have heavy put/update/remove rates, you might exceed the queue size so that the oldest, not yet replicated, updates might get lost. Note that a separate queue is used for each WAN Replication configured for IMap and ICache.

Queue capacity can be set for each target cluster by modifying related WanPublisherConfig.

You can change this property using the declarative configuration as shown below.

    <wan-replication name="my-wan-cluster">
        <wan-publisher group-name="london">

And, the following is the equivalent programmatic configuration:

WanReplicationConfig wanConfig = config.getWanReplicationConfig("my-wan-cluster");
WanPublisherConfig publisherConfig = new WanPublisherConfig();

Note that you can clear a member’s WAN replication event queue. It can be initiated through Management Center’s Clear Queues action or Hazelcast’s REST API. Below is the URL for its REST call:


This may be useful, for instance, to release the consumed heap if you know that the target cluster is being shut down, decommissioned, put out of use and it will never come back. Or, when a failure happens and queues are not replicated anymore, you could clear the queues using this clearing action.