On Tue, Oct 15, 2013 at 11:55 AM, Josh Berkus <j...@agliodbs.com> wrote:
> However, it does seem like the new syntax could be extended with and
> optional "USING unqiue_index_name" in the future (9.5), no?

There is no reason why we couldn't do that and just consider that one
unique index. Whether we should is another question - I certainly
think that mandating it would be very bad.

> I'm just checking that we're not painting ourselves into a corner with
> this particular implementation.  It's OK if it doesn't implement most
> things now; it's bad if it is impossible to build on and we have to
> support it forever.

I don't believe it does. In essence this just simply inserts a row,
and rather than throwing a unique constraint violation, locks the row
that prevented insertion from proceeding in respect of any tuple
proposed for insertion where it does not. That's all. You can build
lots of things with it that you can't today. Or you can not use it at
all. So that covers semantics, I'd say.

As for implementation: I believe that the implementation is by far the
most forward thinking (in terms of building infrastructure for a
proper MERGE) of any proposal to date.

Peter Geoghegan

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