Transactions - Rollback Journal

1 - About

A rollback journal creates and manages information that is used to primarily roll back (undo) changes from a transaction to the database but has also other functionalities, see features

A rollback journal consists of records of the actions of transactions, primarily before they are committed.

There is two well known implementations:

3 - Features

A Rollback journal of records is used to:

  • Roll back transactions when a ROLLBACK statement is issued. When a ROLLBACK statement is issued, rollback records are used to undo changes that were made to the database by the uncommitted transaction.
  • fault tolerance If a failure prevents modified data from being permanently written to the original data files, then the changes can be obtained from the rollback journal (not from the transaction log ?), so work is never lost.
  • recover the database. During database recovery, rollback records are used to undo any uncommitted changes applied from the transactions log to the original data files.
  • Provide read consistency through multiple sessions. To manage the multiversion read consistency, the database must create a read-consistent set of data when a table is simultaneously queried and updated.
  • Analyze data as of an earlier point in time. See Oracle Flashback Query
  • Recover from logical corruptions

4 - Management

4.1 - Reduce

You can reduce the undo generation by introducing multiple commits in a loop while loading data, but the overall elapsed time will increase.

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