Re: Unrepeatable Read: why a problem

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 27 Apr 2007 18:04:30 GMT
Message-ID: <OWqYh.28524$PV3.301979@ursa-nb00s0.nbnet.nb.ca>

Ravi wrote:

> 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).

Why indeed! Hence the ability to choose among different isolation levels in various products.

> 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.

That depends. How many petabytes is your buffer? Received on Fri Apr 27 2007 - 13:04:30 CDT