On 5/24/2010 12:51 PM, Kevin Grittner wrote:
> 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?
It does and the proposed is a mere alternative serving the same purpose.
Have you ever looked at one of those queries, that Londiste or Slony
issue against the provider DB in order to get all the log data that has
been committed between two snapshots? Is that really the best you can
think of?
Jan
--
Anyone who trades liberty for security deserves neither
liberty nor security. -- Benjamin Franklin