Re: Exposing the Xact commit order to the user

Robert Haas  wrote:
> I think you're confusing two subtly different things.
The only thing I'm confused about is what benefit anyone expects to
get from looking at data between commits in some way other than our
current snapshot mechanism.  Can someone explain a use case where
what Jan is proposing is better than snapshot isolation?  It doesn't
provide any additional integrity guarantees that I can see.
> But the commit order is still the order the effects of those
> transactions have become visible - if we inserted a new read-only
> transaction into the stream at some arbitrary point in time, it
> would see all the transactions which committed before it and none
> of those that committed afterward.
Isn't that what a snapshot does already?
> your proposed fix sounds like it would be prohibitively expensive
> for many users. But can this actually happen?
How so?  The transaction start/end logging, or looking at that data
when building a snapshot?
-Kevin