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Backout logging events z/OS DFSMStvs Planning and Operating Guide SC23-6877-00 |
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Logging begins when a request is made to add, delete,
or update a record. An application might issue a pure read request
and then later issue a get-for-update request (the first read did
not initiate logging). Two VSAM requests, put (either
update or add) and erase, can modify a record. The
purpose of the undo log is to contain a copy of the data prior to
any changes being made, so backout logging is always done when any
indication is given of intent to update the data. Backout logging
is done at the following times:
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