File Management

Prevayler writes two different kinds of files to disk: Transaction Journals and Snapshots. They require no special manual care (except for regular backups), but there are some caveats to be aware of.

Transaction Journals

Transaction journals in Prevayler are handled by a Journal object registered via PrevaylerFactory. The Journal interface is defined as this:

The default Journal implementation used is PersistentJournal, which writes transaction journals sequentially, creating one file per Transaction executed. All PersistentJournal-generated file names are exactly 27 characters long, and are numbered sequentially (e.g., 0000000000000000089.journal), and contain a serialized version of that transaction.

Snapshots

Snapshots are serialized versions of your whole object graph. The default implementation of Prevayler writes them using Java serialization, but you can create them using different serialization methods (e.g., writing to an XML file). This can be accomplished by using different SnapshotManagers, and handing them to your PrevaylerFactory.

The default SnapshotManager uses the same file name conventions as the PersistentJournal, which writes Transaction Journals. That is, file names are always exactly 28 characters long, are numbered sequentially (e.g., 0000000000000000183.snapshot), and contain a serialized version of your prevalent system.