Re: [HACKERS] Big IN() clauses etc : feature proposal

On Thu, 2006-05-11 at 12:18, Jim C. Nasby wrote:
> On Wed, May 10, 2006 at 08:31:54PM -0400, Tom Lane wrote:
> > "Jim C. Nasby" <jnasby(at)pervasive(dot)com> writes:
> > > On Tue, May 09, 2006 at 03:13:01PM -0400, Tom Lane wrote:
> > >> PFC <lists(at)peufeu(dot)com> writes:
> > >>> Fun thing is, the rowcount from a temp table (which is the problem here)
> > >>> should be available without ANALYZE ; as the temp table is not concurrent,
> > >>> it would be simple to inc/decrement a counter on INSERT/DELETE...
> > >>
> > >> No, because MVCC rules still apply.
> >
> > > But can anything ever see more than one version of what's in the table?
> >
> > Yes, because there can be more than one active snapshot within a single
> > transaction (think about volatile functions in particular).
>
> Any documentation on how snapshot's work? They're a big mystery to me.
> :(

http://www.postgresql.org/docs/8.1/interactive/mvcc.html

Does the concurrency doc not cover this subject well enough (I'm not
being sarcastic, it's a real question)