Re: MERGE Specification

On 4/25/08, Robert Treat <xzilla(at)users(dot)sourceforge(dot)net> wrote:
> On Thursday 24 April 2008 23:40, Tom Lane wrote:
> > Robert Treat <xzilla(at)users(dot)sourceforge(dot)net> writes:
> > > Perhaps a better option would be to implement Merge per spec, and then
> > > implement a "replace into" command for the oltp scenario. This way you
> > > keep the spec behavior for the spec syntax, and have a clearly non-spec
> > > command for non-spec behavior.
> >
> > In that case, it's a fair question to ask just who will use the "spec"
> > syntax. As far as I can tell from years of watching the mailing lists,
> > there is plenty of demand for a concurrent-safe insert-or-update
> > behavior, and *exactly zero* demand for the other. I challenge you to
> > find even one request for the "spec" behavior in the mailing list
> > archives. (Simon doesn't count.)
> >
>
>
> AIUI the current implementation is designed to avoid race conditions partially
> at the cost of being insert friendly and somewhat update unfriendly. My guess
> is that most of the people wanting this for OLTP use want an update friendly
> implementation (that's certainly been the majority of cases I've needed
> myself, and that I have seen others use).

This seems to hint that there should be 2 variants of merge/upsert
- insert-friendly and update-friendly... It seems unlikely one implementation
can be both. And especially bad would be implementation that is neither.

--
marko