This is because if st goes wrong before the values

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Unformatted text preview: transac-on takes place, we keep logs Undo log remembers only the old values before a transac-on, and if something goes wrong we can go back to those old values Rule 1: Log of transac-on occurs before flush (output). This is because if s/t goes wrong before the values are wriIen on disk, we have values in memory to go back to Rule 2: Logging “commit” means that the transac-on was successful, so the record must have been flushed (output) to disk before we say it was successful and write “commit” to the log. Checkpoin-ng •  •  •  •  If system crashes, to recover you must go from latest to earliest, scanning for any uncommiIed transac-ons (this is expensive) With checkpoin-ng you can be sure every transac-on up to...
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This note was uploaded on 01/28/2014 for the course CS 411 taught by Professor Staff during the Fall '08 term at University of Illinois, Urbana Champaign.

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