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From: Craig Ringer <craig@2ndquadrant.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Simon Riggs <simon@2ndquadrant.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Michael Paquier <michael.paquier@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: MERGE SQL Statement for PG11
Date: Thu, 2 Nov 2017 10:58:33 +0800
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On 1 November 2017 at 01:55, Peter Geoghegan <pg@bowt.ie> wrote:

> The problem here is: Iff the first statement uses ON CONFLICT
> infrastructure, doesn't the absence of WHEN NOT MATCHED imply
> different semantics for the remaining updates and deletes in the
> second version of the query? You've removed what seems like a neat
> adjunct to the MERGE, but it actually changes everything else too when
> using READ COMMITTED.

Would these concerns be alleviated by adding some kind of Pg-specific
decoration that constrained concurrency-safe MERGEs?

So your first statement would be

 MERGE CONCURRENTLY ...

and when you removed the WHEN NOT MATCHED clause it'd ERROR because
that's no longer able to be done with the same concurrency-safe
semantics?

I don't know if this would be helpful TBH, or if it would negate
Simon's compatibility goals. Just another idea.

-- 
 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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  Cc: craig@2ndquadrant.com, pg@bowt.ie, simon@2ndquadrant.com, robertmhaas@gmail.com, michael.paquier@gmail.com
  Subject: Re: MERGE SQL Statement for PG11
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