History files are internal database files containing references to the undo log files of completed transactions. The history files tell you which undo log file belongs to which completed transaction.
History files are used only by liveCache database instances.
The initial history files are generated in the data area when the database instance is created. At each savepoint, the updated history files are stored in the data area.
For performance reasons, there are always several history files open in parallel. The database system uses the MAXUSERTASKS general database parameter to calculate the number of history files.