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DB2® Universal Database for OS/390® Version 7.1 Certification Guide by Susan Lawson, Richard Yevich

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Locking Data

DB2 uses transaction locking (using the IRLM), latches, and other non-IRLM mechanisms to control the concurrency and access of SQL statements and utilities. These mechanisms are there to associate a resource with a process so that other processes cannot access the same resource when it would cause lost updates and access to uncommitted data. Generally, a process will hold a lock on manipulated data until it has completed its work. This way it ensures that other processes do not get hold of data that has been changed and not committed. Another use is for repeatable read, when an application has the need to reread data that must still be in the same state as it was when it was initially read.

There are also user options to avoid locking ...

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