Checkpoints, Savepoints, and Transaction Rollback

Besides permitting concurrency, transaction processing plays an important role in data recovery. Database recovery always recovers every committed transaction. Transactions that have not committed at the time of a database failure are not recovered.

Sybase IQ relies on three transaction-related commands that help you recover a stable set of data in the event of system or media failure. These commands set checkpoints, set and release savepoints, and roll back transactions.

• Checkpoints
  A checkpoint marks a significant point in a transaction, when Sybase IQ writes to disk certain information it tracks internally. IQ uses this information in the event you need to recover your database.
• Savepoints Within Transactions
  Sybase IQ supports savepoints within a transaction.
• Transaction Rollback
  When you roll back a transaction, you undo all of the operations in that transaction.
• System Recovery
  In the event of a system failure or power outage, or when you restart the database server after it has been stopped, Sybase IQ attempts to recover automatically.
• How Transaction Information Aids Recovery
  The Sybase IQ recovery mechanism is designed for the data warehouse. Typically in this environment, few transactions occur, but each transaction can be quite time consuming.