5.3 What is ‘HWMPUT’?

HWMPUT stands for "high-watermark put (first)." The rationale behind HWMPUT is that with this flag set, all new records (new DBPUTs) would start at the "high-watermark" and move forward, into previously unused space in IMAGE datasets.

The advantage of doing this is that all of these chronologically entered records will have very good "locality" (i.e., they would be physically next to each other on the discs). This means they can be read and retrieved much faster than if they were simply filling up all of the empty spaces in the dataset first, the TurboIMAGE default. In the default case, records can wind up being scattered all over a disc, in a much more fragmented fashion.