|
|
|
By reducing the need to sync the transaction log to disk, this new transaction processing mode can improve performance substantially. The tradeoff is that automatic recovery is not guaranteed to make good on all the committed transactions. To make recovery predictable and usable, we introduce the concept of a Restore Point (RP). A Restore Point is a place in a transaction log that has no active transactions. Two types of Restore Points are available:
Every N minutes (where N is a small number), the application will issue a lightweight checkpoint, and before restarting transactions, start an external activity log. If a crash occurs, it is possible to recover to the last Restore Point, and redo the activities in the external log.
A Checkpoint Restore Point provides a clean place in the log where roll forwards from a Dynamic Dump can stop and restart. Imagine that a system in operation runs a complete dynamic dump, and then periodically (each hour, each day, etc.) issues a Checkpoint Restore Point. A backup system can be maintained in fairly up-to-date fashion by using the Checkpoint Restore Points as convenient milestones to roll forward from and roll forward to.
