Control of tracking updates to reduce coupling facility overhead

The TRACKMOD NO option of CREATE or ALTER TABLESPACE can reduce coupling facility overhead caused by constant updating of the space map pages of the page sets.

With TRACKMOD NO, Db2 does not keep track of changed pages in the space map page of the page set. By choosing TRACKMOD NO and not tracking updates, less coupling facility overhead exists, but the cost of incremental image copies is much higher because Db2 must use a table space scan to read all pages to determine if the page has been changed and thus needs to be copied.

If longer copy times means you must take fewer incremental copies, monitor your active log data sets to ensure that you do not have to go to a tape archive data set to do recovery. You might need to make the active log data sets larger, specify more active log data sets, or archive to disk to avoid this possibility.

Recommendation: If you rarely or never use incremental image copies, or if you always use DFSMS concurrent copy with Db2 LOGONLY recovery, use TRACKMOD NO.