Abort, cont.
 | To perform UNDO, must have a lock on data!
 | No problem!
| |
| Before restoring old value of a page, write a CLR:
| You continue logging while you UNDO!!
| CLR has one extra field: undonextLSN
 | Points to the next LSN to undo (i.e. the prevLSN of the record we’re currently undoing).
| | CLRs never Undone (but they might be Redone when repeating history: guarantees Atomicity!)
| | | |
| At end of UNDO, write an “end” log record.
|
|
