(integer, seconds > 0) Lifetime in seconds of a historical record. Records older than this lifetime will be purged from memory; history files older than this lifetime will be deleted from disk. By default, a value of 259,200 seconds (3 days) is used. Records stored in memory are purged in sweeps by a thread dedicated to managing the in-memory data. These sweeps occur every HASH_FILE_ROLLOVER_PERIOD seconds. Files on disk are purged when it becomes necessary to open a new history file.