Destage and Priority Switching
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
The record slots that contain modified data cannot be used for a new record that does not exist in the cache until the modified data in the existing slot is written to the disk device, commonly known as a DASD (Direct Access Storage Device). A performance problem will occur if modified data is allowed to become Least Recently Used (LRU) since the Least Recently Used entry is the entry that should be allocated when a new record slot is required. The solution is to scan the LRU list to search for modified data. However, this scan will hurt performance if no modified data is found. Modified data should be written to the DASD before the data reaches the LRU list bottom. To solve the above performance exposure, scanning for modified data is controlled by a dispatch counter.