CA IDMS Tech Tip by Edward Gorga, Senior Principal Support Engineer for November 13, 2015
EXPAND PAGE is the quickest way to get more space in an area and can be done multiple times. However, If your current page size is getting close to the 32K maximum you will eventually need to unload/reload. The use of EXPAND PAGE was always designed to be used as an emergency only until you could schedule the time to do an unload/reload.
The preferred method of expansion is to use unload/reload, it is the only way fix overflows & store as much data as possible onto their target pages. If you are having performance problems then an unload/reload is the best option. It will it reorganize indexes and improve the placement of existing data which may have overflowed due to lack of space on a page.
If the database is very large you can use the REORG utility statement instead. The REORG utility unloads and reloads the database using parallel processing to reduce the amount of time it takes to reorganize the data. For more information on REORG see the Utilities Guide.
There is one other option to increase space, extend the number of pages in the area by using the EXTEND SPACE clause of the AREA statement and adding a new file for the increased page range. It adds free space only at the end of the area. However, CALC records will continue to only target to pages in the original page range. If no space is available to hold the new occurrences, they will overflow into the extended page range.