Explain why serial equivalence requires that once a transaction has released a lock on an object, it is not allowed to obtain any more locks.

A server manages the objects . The server provides two operations for its clients:


read (i) returns the value of


write(i, Value) assigns Value to


The transactions T and U are defined as follows:





T: x= read (i); write(j, 44); U: write(i, 55);write(j, 66);





U: write(i, 55);write(j, 66);





Describe an interleaving of the transactions T and U in which locks are released early with the effect that the interleaving is not serially equivalent.


Because the ordering of different pairs of conflicting operations of two transactions must be the same. For an example where locks are released early:

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