The dynamic storage areas are used to supply CICS® tasks with the storage needed to execute your transactions. From the storage size that you specify on the DSALIM(dynamic storage area limit) and the EDSALIM (extended dynaimc storage area limit) parameters, CICS allocates the dynamic storage areas above and below the line respectively.
If the dynamic storage areas limits are too small, CICS performance is degraded. The system may periodically enter a short-on-storage condition, during which it curtails system activity until it can recover enough storage to resume normal operations. You can read online when GETMAIN you need to use in your CICS programs.
The dynamic storage areas limits should be as large as possible after due consideration of other areas, especially the MVS storage area above 16MB.
CICS GETMAIN requests for dynamic storage are satisfied from one of the following: the CDSA, UDSA, SDSA, ECDSA, , EUDSA, or the ESDSA during normal execution. The sizes of the dynamic storage areas are defined at CICS initialization, but the use of storage within them is very dynamic.