The dynamic storage areas (DSAs) supply CICS® tasks with storage to run
transactions and are essential for CICS operation.
The DSAs in 24-bit storage are the CDSA, UDSA, SDSA, and RDSA. The
DSAs in 31-bit storage are the ECDSA, EUDSA, ESDSA, ERDSA, and ETDSA.
The DSAs in 64-bit storage are the GCDSA, GUDSA, and GSDSA.
The dynamic storage areas are made from virtual storage pages taken from MVS™ storage subpools. In the dynamic storage areas, CICS arranges the storage in CICS subpools. The subpools are dynamically acquired as needed, a page at a time, from within the dynamic storage area. The storage that individual subpools use is shown in the domain subpool statistics in the CICS storage manager statistics.
- 24-bit storage extents are usually allocated in multiples of 256 KB. However, when transaction isolation is in operation, the UDSA is allocated in 1 MB extents.
- 31-bit storage extents are allocated in multiples of 1 MB.
- 64-bit storage extents are allocated in multiples of
1 GB.
- The storage for the CDSA, ECDSA, ETDSA and GCDSA is always allocated from CICS-key storage.
- The STGPROT system initialization parameter
specifies whether you want storage protection to operate in the CICS region. When you specify STGPROT=YES and
the required hardware and software support for storage protection
is available, the storage for the CICS dynamic
storage areas for user applications is allocated from user-key storage.
These DSAs are the UDSA, SDSA, EUDSA, ESDSA, GUDSA, and GSDSA. If
you specify STGPROT=NO, the storage for these
DSAs is allocated from CICS-key storage.
If you specify STGPROT=YES but the hardware and software support for storage protection is not available, CICS issues an information message during initialization and operates without storage protection.
- The RENTPGM parameter specifies whether CICS allocates the read-only DSAs
from read-only key-0 protected storage.
When you specify RENTPGM=PROTECT, the read-only DSAs are allocated from read-only key-0 protected storage. These DSAs are the RDSA and the ERDSA. If you specify RENTPGM=NOPROTECT, the storage for these DSAs is allocated from CICS-key storage.
A dynamic storage area that is too small results in increased program compression or, more seriously, short-on-storage (SOS) conditions. You can examine the pressure on virtual storage by using the CICS storage manager statistics, which report the number of times that CICS went short on storage.
