Re: The C in ACID

Paul Mansour wrote:
> ...
> "However, these techniques [Atomicity, Isolation, and Durable], which
> are commonly known in the database technical community, do not
> entirely cope with the problem of consistency (C), which is primarily
> the responsibility of a user transaction to preserve."
> ...

I think the reason they "don't entirely cope" is because they are really separate, maybe even orthogonal. I think there is a danger in seeing A, I and D as logical concepts in the same sense that consistency is a logical db concept. I would say they are in fact, artifacts of various physical dbms implementations.

I prefer to think that the logical db has no concept of A, I and D. One might ask "how then, without recognizing A, I and D, could a dbms achieve them?" and I would say by expecting the users to take turns. In practice, it seems reasonable for the dbms to inflict an order on the users, ie., there may be a logic to a certain concurrency theory, but it is not the same logic we mean when we talk about a logical dbms.

I hope this doesn't sound mystical, I see it as part of the 'narrow view'. Even if it's not always practical to implement the narrow view directly, I think it is useful for talking about such concepts with more certainty. Come to think of it, I think I've known people who thought correct, consistent and certain were synonyms.

p Received on Mon Aug 21 2006 - 21:19:53 CEST