Transactions That Are Rolled Back

When a rollback occurs, the database server generates a compensation-log record (CLR) for each record in the logical log that is rolled back. The database server uses the CLRs if a system failure takes place during a rollback. The CLRs provide the database server with information on how far the rollback progressed before the failure occurred. In other words, the database server uses the CLRs to log the rollback.

If a CLR contains the phrase includes next record, the next log record that is printed is included within the CLR log record as the compensating operation. Otherwise, you must assume that the compensating operation is the logical undo of the log record to which the link field of the CLR points.


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