Implementing Abort(T)
If P was not transferred to stable storage, then deallocate its cache slot
If it was transferred, then P’s before-image must be in stable storage (else you couldn’t undo after a system failure)
Undo Rule - Do not flush an uncommitted update of P until P’s before-image is stable. (Ensures undo is possible.)
- Write-Ahead Log Protocol - Do not … until P’s before-image is in the log