Re: Unrepeatable Read: why a problem

Ravi <ra.ravi.rav_at_gmail.com> wrote in news:1177687111.583528.87470 _at_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/ Received on Fri Apr 27 2007 - 17:53:36 CEST