On 8/20/2007 9:50 AM, Lindy Mayfield wrote:
Thanks all for the clarification. This is a synopsis up what I learned,
which was sort of what I thought:
...snipped...
- Still, though, when you get down to it, it is still QSAM and
multi-user access (without some sort of higher level manager) would
solely depend on ENQ, which, if I'm not wrong, would be pretty lame.
I'm not sure what you mean by "lame".
Properly used, ENQ will provide all that you need for data integrity.
In order for two users (jobs) to have the data set allocated
concurrently, they would have to specify DISP=SHR. Anyone doing an
update -should- instead specify DISP=OLD, which would prevent any problems.
If a single updater does specify DISP=SHR (perhaps to allow simultaneous
reading) then it's not clear whether any readers would see the old or
the new data. On the other hand one usually can not predict whether the
updater will update before or after someone reads the record, so I don't
think that matters.
If two updaters try to run, specifying DISP=SHR, I believe that the
second one to try the OPEN will get some flavor of S213 ABEND on any
supported z/OS release.
--
Walt Farrell, CISSP
IBM STSM, z/OS Security Design
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