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ABCs of z/OS System Programming Volume 3 - IBM Redbooks

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7.36 Summary<br />

Figure 7-48<br />

Summary<br />

Base VSAM<br />

Functions and limitations<br />

VSAM record-level sharing<br />

Functions and limitations<br />

DFSMStvs<br />

Functions<br />

Summary<br />

In this chapter we showed the limitations <strong>of</strong> base VSAM that made it necessary to develop<br />

VSAM RLS. Further, we exposed the limitations <strong>of</strong> VSAM RLS that were the reason to<br />

enhance VSAM RLS by the functions provided by DFSMStvs.<br />

► Base VSAM<br />

– VSAM does not provide read or read/write integrity for share options other than 1.<br />

– User needs to use enqueue/dequeue macros for serialization.<br />

– The granularity <strong>of</strong> sharing on a VSAM cluster is at the control interval level.<br />

– Buffers reside in the address space.<br />

– Base VSAM does not support CICS as a recoverable resource manager; a CICS file<br />

owning region is necessary to ensure recovery.<br />

► VSAM RLS<br />

– Enhancement <strong>of</strong> base VSAM.<br />

– User does not need to serialize; this is done by RLS locking.<br />

– Granularity <strong>of</strong> sharing is record level, not CI level.<br />

– Buffers reside in the data space and Coupling Facility.<br />

– Supports CICS as a recoverable resource manager (CICS logging for recoverable data<br />

sets); no CICS file owning region is necessary.<br />

442 <strong>ABCs</strong> <strong>of</strong> z/<strong>OS</strong> <strong>System</strong> <strong>Programming</strong> <strong>Volume</strong> 3

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