How Strict 2PL avoids unrepeatable read problem?

Question

Please explain. Use the below transaction.

Comments

@Shaik Masthan Can you answer this?

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i am thinking is this transaction runs without deadlock under strict 2PL ?

If there is no deadlock ==> it avoid unrepeatable problem.

if deadlock is present ? then what to say ?

Answer 1

Any 2 PL if does not cause deadlock will ensure conflict serializability.

Now every conflict serializable schedule is free from unrepeatable read problem.

So every strict schedule is free from unrepeatable read problem.

Comments

@OneZero thats alright. but see the schedule even after applying strict 2pl T1 is reading two different A values.

 

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@susgir2

Is it possible to write the above code in 2PL form?

It will cause a deadlock while attempting to perform 2PL.

Once deadlock occurs, we can use deadlock handling methods to terminate a transaction 

When the transaction restarts we will have have a deadlock set of transactions on which we can apply strict 2 PL.

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How can you conclude every conflict serailizable schedule is free from unrepeatable read problem?