tableBASE allocates space for the TSR in 4K chunks and will only allocate space as needed as tables are opened or defined in the TSR. The minimum amount of space that can be allocated for a TSR is 28K and the maximum is 2G.
tableBASE initializes the first portion of the TSR to contain control information. For smaller TSR sizes of about 1M to 3M, about 20K of the space is used for control information. For larger TSR sizes, between 1 to 2 percent of the TSR space is used for control information.
When tableBASE initializes, it does a DSPSERV request for a private dataspace of the TSR size requested. For non-VTS regions, the dataspace is allocated as SCOPE=SINGLE. For VTS regions, the dataspace is allocated as SCOPE=ALL. The MVS IEFUSI exit at your site may limit the number and/or sizes of dataspaces allocated by a single job step.
If your region defines the TSR size as 1M, this results in the building of the MVS system control blocks to support a virtual storage of 1M. However, if you only open tables to fill up 500K of the TSR, tableBASE will only allocate about 520K of space for the TSR, 20K being the overhead for the control information.
If your region defines the TSR size as 100M, this results in the building of MVS system control blocks to support a virtual storage of 100M. However, if you only open or define tables that take up 20M of space, tableBASE will only allocate about 22M of space for the TSR, 2M being the overhead for the control information.
Taking into account the small overhead for the space required to hold control information on the TSR, if you anticipate a large variance in the amount of space that you will require, we recommend that you define your TSR size to be the upper limit of all space that you expect to use during the life of your region.