Re: determine snapshot after obtaining locks for first statement

On Thu, 2009-12-17 at 12:58 -0500, Robert Haas wrote:
> On Thu, Dec 17, 2009 at 12:51 PM, Kevin Grittner
> <Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
> > Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >
> >> I'm not very sure what a clearer explanation would look like
> >
> > As a stab at it, how about?:
> >
> > This behavior makes Read Committed mode unsuitable for many UPDATE
> > or DELETE commands with joins or subqueries
>
> I don't think that's any clearer, though it is more disparaging. :-)
>
> Note we also say: "The partial transaction isolation provided by Read
> Committed mode is adequate for many applications, and this mode is
> fast and simple to use; however, it is not sufficient for all cases.
> Applications that do complex queries and updates might require a more
> rigorously consistent view of the database than Read Committed mode
> provides."

What is needed here is a layman's context of what isolation modes are
good for what type of operation. Neither your explanation or Tom's is
particularly useful except to say, "Crap, I might be screwed but I don't
know if I am... how do I find out?"

Joshua D. Drake

>
> ...Robert
>

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