CS4482tut8a - 3. a. A site can abort a transaction T under...

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CS4482/6492 Advanced Database Systems Tutorial 8 1. Recovery would happen as follows: Redo phase: a. Undo-List = T 0 , T 1 b. Start from the checkpoint entry and perform the redo operation. c. C = 600 d. T 1 is removed from the Undo-list. e. T 2 is added to the Undo list. f. A = 400 g. B = 2000 Undo phase: a. Undo-List = T 0 , T 2 b. Scan the log backwards from the end. c. A = 500; output the redo-only record < T 2 , A , 500 > d. output < T 2 abort > e. B = 2000; output the redo-only record < T 0 , B , 2000 > f. output < T 0 abort > At the end of the recovery process, the state of the system is as follows: A = 500 B = 2000 C = 600 The log records added during recovery are: < T 2 , A , 500 > < T 2 abort > < T 0 , B , 2000 > < T 0 abort > 2. The whole relation can be stored at site 1. EMPD_5 is a relation fragment at site 2 corresponding to department 5 and EMPD_4 is a relation fragment at site 3 corresponding to department 4.
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CS4482/6492 Advanced Database Systems Tutorial 8
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Unformatted text preview: 3. a. A site can abort a transaction T under the following circumstances: i. It has written the &lt;no T &gt; log record. ii. It has not yet written a &lt;ready T &gt; log-record. iii. It has written the &lt;ready T &gt; log record, but on inquiry it found out that some other site has an &lt;abort T &gt; log record. iv. It has written the &lt;abort T &gt; log record. v. It is itself the coordinator and has not yet written any decision log record. vi. It is itself the coordinator and has written the &lt;abort T &gt; log record. b. A site can commit a transaction T under the following circumstances: i. It has written the &lt;ready T &gt; log record, and on inquiry it found out that some other site has a &lt;commit T &gt; log record. ii. It has written the &lt;commit T &gt; log record. iii. It is itself the coordinator and has written the &lt;commit T &gt; log record. 4. a) (0,1,P), (0,2,P), (1,0,R), (2,0,A), (0,1,A), (0,2,A) b) 12 possible message sequences....
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CS4482tut8a - 3. a. A site can abort a transaction T under...

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