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Recoverable schedule is: A schedule where, for each pair of transactions Ti and Tj, if Tj reads a data item previously written by Ti, then the commit operation of Ti precedes the commit operation of Tj.

T1        T2      T3
w(x) 
                 w(x)
         r(x)   commit
        commit
commit

In this case, T2 commits before T1, so is it non-recoverable?

I understand T3 have to commit before T2 to make it recoverable.

However, T3 has override T1's written value, does T1 have to commit before T2 to achieve a recoverable schedule?

Please help me! Thank you so much!

Bailey Lee
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  • See http://stackoverflow.com/questions/1306869/are-nested-transactions-allowed-in-mysql for more info. Use save points if you need to rollback to a certain point. – Sloan Thrasher Apr 10 '17 at 13:31
  • @Sloan thanks you for your answer. But my question is, whether the example is a recoverable schedule? – Bailey Lee Apr 10 '17 at 13:49
  • See this about recoverable schedules: https://sites.google.com/site/projectcodebank/computer-engineering-notes/recoverable-and-cascadeless – Sloan Thrasher Apr 10 '17 at 13:53
  • @SloanThrasher Because T3 has override x that written by T1, I don't understand does T1 also have to commit before T2, to make it recoverable. – Bailey Lee Apr 10 '17 at 13:59

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