IBM OS/390 User Manual
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Planning for Installation
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DFSMSdfp Storage Administration Reference
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Using Data Sets
SHAREOPTIONS (X 4)
Cross-system SHR(x 4) provides the same limited protection across systems as
cross-region SHR(4). Extensions of the data set
cross-region SHR(4). Extensions of the data set
′
s high-used RBA are prohibited.
To provide complete integrity protection it is the user
′
s responsibility to write
Assembler routines using the RESERVE/RELEASE macros in addition to the
ENQ/DEQ macros required for cross-region. This is a complex undertaking. If it
was simple and/or if performance was acceptable, OS/390 VSAM would have
implemented it. Alternatives to complete DASD sharing of VSAM data sets
should be considered first. See
ENQ/DEQ macros required for cross-region. This is a complex undertaking. If it
was simple and/or if performance was acceptable, OS/390 VSAM would have
implemented it. Alternatives to complete DASD sharing of VSAM data sets
should be considered first. See
DFSMS/MVS Using Data Sets, SC26-4922, for
greater detail on coding RESERVE/RELEASE routines and the alternatives.
SHAREOPTIONS (X 3)
If SHR(x 3) is used, all data set opens are allowed across systems. OS/390
VSAM provides no protection for the data set.
VSAM provides no protection for the data set.
5.6.6.4 DASD Sharing Considerations
A second system opening a data set that is open for output on another system
will receive the OPEN return code 116 (X
will receive the OPEN return code 116 (X
′74′)
which indicates the data set was
not properly closed. VSAM will automatically issue the VERIFY macro for the
program.
program.
Once the data set is open, a cross-system program must contend with the
possibility that the data, indexes, extents, the RBA of records, and the
High-Used-RBA of the data set may be changing due to updates in another
system. This may cause VSAM error codes and/or abends of the programs using
the data set.
possibility that the data, indexes, extents, the RBA of records, and the
High-Used-RBA of the data set may be changing due to updates in another
system. This may cause VSAM error codes and/or abends of the programs using
the data set.
Alternatives to VSAM Data Set Sharing
Probably the simplest way to avoid the problems of cross-system and
cross-region sharing is to schedule all data set access through a single system
and address space. This generally means that batch updates must be performed
while the files are unavailable to CICS systems.
cross-region sharing is to schedule all data set access through a single system
and address space. This generally means that batch updates must be performed
while the files are unavailable to CICS systems.
CICS VSAM data sets can be accessed from multiple CICS address spaces via
the CICS Multiple Region Option (MRO) or across systems with Inter-Systems
Communication (ISC). However, there is no CICS support for cross-region or
cross-system sharing of VSAM data sets with batch jobs.
the CICS Multiple Region Option (MRO) or across systems with Inter-Systems
Communication (ISC). However, there is no CICS support for cross-region or
cross-system sharing of VSAM data sets with batch jobs.
IMS/VS DC and DB offer methods of cross-system and cross-region sharing of
DL/I (IMS) data bases via the IMS Resource Lock Manager (IRLM) and Data
Base Resource Control (DBRC). See the appropriate IMS/VS manuals for details.
DL/I (IMS) data bases via the IMS Resource Lock Manager (IRLM) and Data
Base Resource Control (DBRC). See the appropriate IMS/VS manuals for details.
CICS/OS provides for cross address space sharing of IMS/VS data bases via the
CICS Shared Data Base facility.
CICS Shared Data Base facility.
The DB2 Transparency Feature allows some VSAM files to be loaded into DB2
table spaces and accessed with existing batch or CICS/OS VSAM applications.
table spaces and accessed with existing batch or CICS/OS VSAM applications.
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VSE to OS/390 Migration Workbook