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

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Logging

When changes are made to the data in tables, which subsequently changes the table space and index spaces, DB2 writes one or more records to its log so that a back out of the changes can be performed if the unit of work fails. DB2 can also use this information to “re-apply” changes that may have been lost when recovering to a previous point in time. The primary purpose of the active log is to record all changes (inserts, updates, and deletes) made to DB2 objects. The DML (Data Manipulation) statements are recorded in the log as follows:

  • Insert: entire after image of the record is logged called a redo record.

  • Delete: the before image is recorded called an undo record.

  • Update: both the before and after images (undo and redo record) are ...

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