Question 3: Consider an ARIES style algorithm that uses pageLSN to track state of the pages, and CLRs are written to ens

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Question 3 Consider An Aries Style Algorithm That Uses Pagelsn To Track State Of The Pages And Clrs Are Written To Ens 1 (161.89 KiB) Viewed 65 times

Question 3: Consider an ARIES style algorithm that uses pageLSN to track state of the pages, and CLRs are written to ensure that the page state is tracked correctly irrespective of rollbacks in the middle of the execution. 1. Explain the importance of writing CLRs. One option in undoing log record with Isnl snl, 1' data instead of writing CLRs during transaction roll back, is to reset the pageLSN of the page to the LSN of the log record that modified the page before I (that is, the log record with a lower Isn value).Construct a counterexample that illustrates what can go wrong if this scheme is used for handling transaction rollbacks. 2. Assume that we were using page level locks to ensure strictness. Is writing CLRs still important? That is, can you design transaction roll back and restart algorithms that work correctly but do not require CLRs to be written under the assumption of page level locking. 3. In the restart algorithm, during the redo pass we repeat the entire history (that is, the effects of both committed as well as transactions that were active at the time of failure). One alternative is to instead perform redo selectively. That is, we only redo the effects of committed transactions and not of those transactions that were active at the time of failure. Illustrate through a counterexample what can go wrong with our algorithm if we were to perform selective redos.