Chapter 13. Persistence

This chapter covers persistence and its configuration in HornetQ.

HornetQ handles its own persistence. It ships with a high-performance journal, which is optimized for messaging-specific use cases.

The HornetQ journal is append only with a configurable file size, which improves performance by enabling single write operations. It consists of a set of files on disk, which are initially pre-created to a fixed size and filled with padding. As server operations (add message, delete message, update message, etc.) are performed, records of the operations are appended to the journal until the journal file is full, at which point the next journal file is used.

A sophisticated garbage collection algorithm determines whether journal files can be reclaimed and re-used when all of their data has been deleted. A compaction algorithm removes dead space from journal files and compresses the data.

The journal also fully supports both local and XA transactions.

The majority of the journal is written in Java, but interaction with the file system has been abstracted to allow different pluggable implementations. The two implementations shipped with HornetQ are:

The standard HornetQ core server uses the following journal instances:

Large messages are persisted outside the message journal. For more information see Chapter 21, Large Messages.

In low memory situations, configure HornetQ to page messages to disk. See Chapter 22, Paging for more information.

If persistence is not required, HornetQ can be configured not to persist any data, as discussed in Section 13.4, “Configuring HornetQ for Zero Persistence”.