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With Overlapped Operations z/OS DFSMS Using Data Sets SC23-6855-00 |
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To overlap I/O and processor activity, you can start several read or write operations before checking the first for completion. You cannot overlap read and write operations. However, as operations of one type must be checked for completion before operations of the other type are started or resumed. Note that each outstanding read or write operation requires a separate DECB. If a single DECB were used for successive read operations, only the last record read could be updated. In Figure 1, overlap is achieved by having a read or write request outstanding while each record is being processed. Figure 1. Updating a Member of a PDS
(If update is required, branch to R2UPDATE)
In the following statements, 'R2' and 'R3' refer
to the records that were read using the DECBs whose addresses are
in registers 2 and 3, respectively. Either register can point to either
DECBA or DECBB.
(If R3 requires an update, branch to R3UPDATE)
(If R2 was not updated, branch to CLOSEIT)
Note the use of the execute and list forms of the READ and WRITE macros, identified by the parameters MF=E and MF=L. |
Copyright IBM Corporation 1990, 2014
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