Undo/Redo Logging
UNDO logging and REDO logging are incompatible in
- order of outputting
<COMMIT T> and changed data
- how data in buffers is handled during checkpoints
Undo/Redo logging combines aspects of both
- requires new kind of update log record
<T,X,v,v'> gives both old and new values for X
- removes incompatibilities between output orders
As for previous cases, requires write-ahead of log records.
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