Checkpoints

Checkpoints write dirty pages (pages that have been modified in memory, but not written to disk) to the database device. The Adaptive Server automatic (normal) checkpoint mechanism works to maintain a minimum recovery interval. By tracking the number of log records in the transaction log since the last checkpoint was performed, the mechanism estimates whether the time required to recover the transactions exceeds the recovery interval. If so, the checkpoint process scans all data caches and writes out all changed data pages.

When Adaptive Server has no user tasks to process, the housekeeper wash task begins writing dirty buffers to disk. These writes are done during the server’s idle cycles, so they are known as “free writes.” They result in improved CPU usage and a decreased need for buffer washing during transaction processing.