Thomas Write Rule

Question

Answer 1

Ans: A

http://en.wikipedia.org/wiki/Thomas_write_rule

Comments

Isn't c also allowed?

Older transaction T2 performs a write on A...then younger transaction T1 performs a read on A( no voilation) as Thomas rule is defined only for Write request

T1 performs write on B and then T2 performs read on B (no voilation)..

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Thomas write rule is only for writes and can be summarized as ignore outdated writes.

It states that, if a more recent transaction has already written the value of an object, then a less recent transaction does not need perform its own write since it will eventually be overwritten by the more recent one.

In option c....there is no such situation of two consecutive writes on same data item.

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won't both a and c would be true..?can you please explain why c is not true..?

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In a ---> there are consecutive writes by T2 and T1 on the same item, i.e. B

In c --->there are consecutive writes by T2 on A and T1 on B. Here though there are consecutive writes but on different data items. Now read my above comment of Thomas rule statement.