History files are used during history management. A history file is an internal database file, which contains the access and statistical information about the undo log files of transactions that have ended.
When a database instance is created, the initial history files are stored in the data area. The number of history files is defined by the general database parameter MAXUSERTASKS. Once a transaction has ended, it writes an entry to its history file. This entry identifies the undo log file that is assigned to the transaction. With each savepoint, the history file is saved to the data area.
The history list is used to assign the history files to the garbage collectors.