When Adaptive Server has no user tasks to process, a housekeeper wash task automatically begins writing dirty buffers to disk. If the housekeeper task can flush all active buffer pools in all configured caches, it wakes up the checkpoint task. The checkpoint task determines whether it must perform a checkpoint on the database.
Checkpoints that occur as a result of the housekeeper wash task are known as free checkpoints. They do not involve writing many dirty pages to the database device, since the housekeeper wash task has already done this work. They may result in a shorter recovery time for the database.
See Chapter 3, “Using Engines and CPUs,” in the Performance and Tuning Series: Basics.
