Hibernate Search uses various back ends to process batches of work. The back end is not limited to the configuration option default.worker.backend. This property specifies a implementation of the BackendQueueProcessor interface which is a part of a back end configuration. Additional settings are required to set up a back end, for example the JMS back end.

In the Lucene mode, all index updates for a node (JVM) are executed by the same node to the Lucene directories using the directory providers. Use this mode in a non-clustered environment or in clustered environments with a shared directory store.

Lucene mode targets non-clustered or clustered applications where the Directory manages the locking strategy. The primary advantage of Lucene mode is simplicity and immediate visibility of changes in Lucene queries. The Near Real Time (NRT) back end is an alternate back end for non-clustered and non-shared index configurations.

Index updates for a node are sent to the JMS queue. A unique reader processes the queue and updates the master index. The master index is subsequently replicated regularly to slave copies to establish the master/slave pattern. The master is responsible for Lucene index updates. The slaves accept read and write operations but process read operations on local index copies. The master is the sole responsible for updating the Lucene index. Only the master applies the local changes in an update operation.

This mode targets clustered environments where throughput is critical and index update delays are affordable. The JMS provider ensures reliability and uses the slaves to change the local index copies.