Thursday, September 15, 2005

Page oriented redo/undo versus Logical Undo

ARIES uses the term page-oriented redo/undo to describe logging that is always applied to a specific page. This means that if some page P1 generated a undo/redo log record L1, then during redo, the redo portion of L1 will be applied to P1, and during undo, the undo portion of L1 will be applied to P1.

The term Logical Undo is used to describe logging where the undo action may not always be applied to the page that generated the log record. However, Logical Undos can still be page-oriented. The difference is that the undo action may be applied to a different page. It is also possible for a logical undo operation to modify more than one page, and generate additional log records.

Since a Logical Undo can be page-oriented, the term page-oriented undo is ambiguous.

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