Re: Unrepeatable Read: why a problem

Ravi <ra.ravi.rav@xxxxxxxxx> wrote in news:1177687111.583528.87470
@t39g2000prd.googlegroups.com:

Suppose I've got a part of schedule as:
...
T1 : Read(X)
T2 : Write(X)
T1 : Read(X)
...

We call this unrepeatable read problem as T1 does not get the same
value of X.
But I've got an objection. Why see it as a problem? Our operations may
want us to make T1 read the value of X overwritten by another
operation (ACID violation).

Then why would any transaction would read the data again, and moreover
would like to see the same data which was already with it in the
buffer.
Doesn't make sense.



A bank account:

T1:Read (X) = 100
T2:Write(X)= 10
T1:Write(X-80) --> Overdraft

Or:

T1:Read(X) = 100
T2:Delete(X)
T1:Write(X-80) --> Your account does not exist, have a nice day :)

Also:

http://research.microsoft.com/users/philbe/ccontrol/
.

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