At 07:07 -0500 on 06/17/2014, Mike Schwab wrote about Re: RENT, REFR
and key=0 storage - A correction:
This was a VSAM file with multiple record layouts. One record for
most screen information. One record per line of comment text, about 8
per screen. It would read the records and display the screen. When
the user said update, it would read the record, update the
information, and update, add, or delete the lines of text as needed.
No lock while displayed on screen.
If you want to insure that an update does not destroy data that is
being updated, you would need to have some way of verifying that the
data you are viewing before you make your revisions on the screen is
still in its original state when you are ready to actually commit the
updates. This would entail saving the original state, issuing a "I'm
Updating" lock when you are ready to commit, rereading the records
again to compare to the saved versions, doing the commits if the
compares succeed (and then releasing the lock) or doing some type of
recovery action informing the user that the data had been changed
while he was entering his updates.
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