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

7.27 Unit of work and unit of recovery
Start of program synchronized implicit
update 1
update 2
commit synchronized explicit
update 3
update 4
update 5 }
B
commit synchronized explicit
update 6 } C
End of program synchronized implicit
Figure 7-36 Unit of recovery example
Unit of work and unit of recovery
A unit of work (UOW) is the term used in CICS publications for a set of updates that are
treated as an atomic set of changes.
RRS uses unit of recovery (UR) to mean much the same thing. Thus, a unit of recovery is the
set of updates between synchronization points. There are implicit synchronization points at
the start and at the end of a transaction. Explicit synchronization points are requested by an
application within a transaction or batch job. It is preferable to use explicit synchronization for
greater control of the number of updates in a unit of recovery.
Changes to data are durable after a synchronization point. That means that the changes
survive any subsequent failure.
In Figure 7-36 there are three units of recovery, noted as A, B and C. The synchronization
points between the units of recovery are either:
► Implicit - At the start and end of the program
► Explicit - When requested by commit
426 ABCs of z/OS System Programming Volume 3
} A
= unit of recovery