GSAM databases

GSAM databases are sequentially organized databases that are designed to be compatible with z/OS® data sets.

Start of change GSAM databases have no hierarchy, database records, physical segments, or keys. GSAM databases can be in a data set previously created or in one later accessed by the z/OS access methods VSAM or QSAM/BSAM. GSAM data sets can use fixed-length or variable-length records when VSAM is used, or fixed-length, variable-length, or undefined-length records when QSAM/BSAM is used. End of change

Start of change Optionally, you can define a single virtual segment with multiple non-searchable fields in a GSAM DBD to add field metadata from COBOL copybooks to the GSAM DBD record in the IMS catalog. IMS ignores the virtual segment and the non-searchable fields, but application programs and products, such as IMS Enterprise Suite Explorer for Development, can retrieve the metadata from the IMS catalog when they access the GSAM database through the IMS Universal drivers. End of change

If VSAM is used to process a GSAM database, the VSAM data set must be entry sequenced and on a DASD. If QSAM/BSAM is used, the physical sequential (DSORG=PS) data set can be placed on a DASD or tape unit. If BSAM is used, the GSAM data sets can be defined as z/OS large format data sets by specifying DSNTYPE=LARGE on the DD statements.

GSAM supports DFSMS striped extended-format data sets for both VSAM and BSAM.

GSAM database data sets can be allocated in the extended addressing space (EAS) of an extended address volume (EAV).

Restriction: GSAM databases cannot be used with CICS® applications.

Because GSAM databases are supported in a DCCTL environment, you can use them when you need to process sequential non-IMS data sets using a BMP program.

GSAM databases are loaded in the order in which you present records to the load program. You cannot issue DLET and REPL calls against GSAM databases; however, you can issue ISRT calls after the database is loaded but only to add records to the end of the data set. Records are not randomly added to a GSAM data set.

Although random processing of GSAM and SHSAM databases is possible, random processing of a GSAM database is done using a GU call qualified with a record search argument (RSA). This processing is primarily useful for establishing position in the database before issuing a series of GN calls.

Although SHSAM and SHISAM databases can be processed in any processing region, GSAM databases can only be processed in a batch or batch message processing region.

The following IMS options do not apply to GSAM databases:

Logical relationships
Secondary indexing
Segment edit/compression exit routine
Field-level sensitivity
Data Capture exit routines
Logging or reorganization
Multiple data set groups

For more information about GSAM data sets and access methods, including information about the GSAM use of striped extended-format data sets, see Processing GSAM databases in IMS Version 14 Application Programming.

For more information about z/OS data sets, see z/OS DFSMS: Using Data Sets, as well as the z/OS DFSMShsm, DFSMSdss, and DFSMSdfp storage administration guides and references.