Testing the page validity

Part of the process of controlling cache coherency is testing to see if a page that is referenced in the buffer pool must be refreshed from the group buffer pool or disk because it might no longer be the most current version of the data.

This process is known as testing the page validity. Because Db2 tracks the level of interest in a page set across the group, it is not always necessary to make this test. The following table indicates when this test is performed.

For duplexed group buffer pools, only the primary structure is used for cross-invalidations.