When Adaptive Server has no user tasks to process, a housekeeper task automatically begins writing dirty buffers to disk and performing other maintenance tasks. Because these writes are done during the server’s idle cycles, they are known as free writes. They result in improved CPU utilization and a decreased need for buffer washing during transaction processing. They also reduce the number and duration of checkpoint spikes (times when the checkpoint process causes a short, sharp rise in disk writes).
The housekeeper is the garbage collector. It cleans up data that was logically deleted and resets the rows so the tables have space again.