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Process documentation Undo Log Management Locate the document in the library structure

Purpose

To execute a ROLLBACK of a transaction, for each transaction the database system saves the original values of the database objects – that is, the values before the start of the transaction – that are to be changed by the transaction. This information is known as the undo log entries or before images.

liveCache database instances use undo log entries for consistent views as well.

Process Flow

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       1.      A database user opens a transaction that will change data.

       2.      Undo log management writes undo log entries for all database objects that will be changed by the transaction to an undo log file in the data area.

Caution

In extreme cases, the data area may be full. In this case, expand the data area by adding volumes with the Database Manager.

       3.      The following cases can occur:

¡        The transaction is canceled (ROLLBACK).

The database system uses the undo log files to roll back all changes.

¡        The transaction is closed with a COMMIT.

Undo log management transfers the undo log file to the history management. Later, a garbage collector deletes the undo log file.

See also:

Redo Log Management

Using Log Entries for a Restart or Restore

Logging Transactions

 

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