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Unformatted text preview: to 2. 3. (a) Undo operation is no longer needed because the database (disk) does not reflect updates due to any uncommitted transaction. In other words, if a transaction was active when the system crashed, the values in the disk have not been modified by the transaction. (b) There is the potential for running out of buffer space because updates must be held in the buffers until the transaction commits. 4. (a) Redo operation is no longer needed because if a log record < T commit> is found in the log during recovery, all changes made by T were previously written to disk. Thus, T by itself could not have left the database in an inconsistent state when the failure occurred. (b) o The commit of transactions might be slowed down as it forces all modified blocks to be flushed to disk before commit. o It may incur more output operations because frequently updated blocks are output multiple times, once for each transaction....
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This note was uploaded on 01/11/2012 for the course CS CS4482 taught by Professor Drlee during the Winter '11 term at City University of Hong Kong.
- Winter '11