Storage Management

CICS manages its own storage in areas called Dynamic Storage Areas (DSAs). Understanding DSAs helps you fix storage shortages and storage violations.

Dynamic Storage Areas

• CICS storage is divided into DSAs above and below the 16 MB line, for CICS code and for user programs.
• Main DSAs: CDSA and ECDSA for CICS code, UDSA and EUDSA for user programs, SDSA and ESDSA for shared storage, RDSA and ERDSA for read-only storage.
• Storage above the 16 MB line (the E* DSAs) is used by default because it is much larger.
• The SIT parameters DSALIM and EDSALIM set the maximum size of storage below and above the line.

GETMAIN and FREEMAIN

• Programs get extra working storage with EXEC CICS GETMAIN and must return it with EXEC CICS FREEMAIN.
• Storage from GETMAIN is task-lifetime storage by default. It is freed automatically when the task ends.
• Always check the response code after GETMAIN. If CICS is short on storage, GETMAIN fails instead of abending.
• Shared storage lives beyond one task. Free it explicitly, or it stays allocated until CICS restarts.

Short on storage (SOS)

• SOS happens when a DSA fills up. CICS suspends new tasks until storage is freed.
• Find the cause with statistics: look for tasks holding large GETMAIN areas or a storage leak.
• A storage leak is a program that GETMAINs storage in a loop or never FREEMAINs shared storage.
• Storage protection (SIT STGPROT=YES) stops programs from accidentally overwriting CICS storage.

Example: GETMAIN and FREEMAIN

• Get a work area, use it, then free it. Always check the response after GETMAIN.
• WORKING-STORAGE SECTION. 01 WS-AREA-LENGTH PIC S9(8) COMP VALUE 500. 01 WS-WORK-PTR USAGE POINTER. 01 WS-RESPONSE PIC S9(8) COMP. PROCEDURE DIVISION. EXEC CICS GETMAIN SET(WS-WORK-PTR) FLENGTH(WS-AREA-LENGTH) INITIMG(LOW-VALUE) RESP(WS-RESPONSE) END-EXEC. IF WS-RESPONSE NOT = DFHRESP(NORMAL) EXEC CICS SEND TEXT FROM('NO STORAGE AVAILABLE') END-EXEC EXEC CICS RETURN END-EXEC END-IF. * --- use the storage through WS-WORK-PTR --- EXEC CICS FREEMAIN DATAPOINTER(WS-WORK-PTR) END-EXEC.
• SET gives you the address of the new storage. INITIMG sets every byte to a starting value.
• FREEMAIN with DATAPOINTER returns task-lifetime storage. Never use the pointer after freeing it.