Re: Re: new patch of MERGE (merge_204) & a question
about duplicated ctid
From:
Simon Riggs <simon(at)2ndQuadrant(dot)com>
To:
Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc:
Robert Haas <robertmhaas(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>,
Greg Smith <greg(at)2ndquadrant(dot)com>,
Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>,
Boxuan Zhai <bxzhai2010(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject:
Re: Re: new patch of MERGE (merge_204) & a question
about duplicated ctid
On Mon, 2011-01-03 at 19:01 +0200, Heikki Linnakangas wrote:
> > If we do that, then we definitely need a catch-all WHEN statement, so
> > that we can say
> >
> > WHEN NOT MATCHED
> > INSERT
> > WHEN MATCHED
> > UPDATE
> > ELSE
> > { INSERT into another table so we can try again in a minute
> > or RAISE error }
> >
> > Otherwise we will silently drop rows. Throwing an error every time isn't
> > useful behaviour.
>
> An ELSE clause would be nice, but it's not related to the question at
> hand. Only some serialization anomalities result in a row that matches
> neither WHEN MATCHED nor WHEN NOT MATCHED.
Concurrent UPDATEs, DELETEs, MERGE
> Others result in a duplicate
> key exception, for example.
Concurrent INSERTs, MERGE
So an ELSE clause is very relevant to handling anomalies in a useful
way.
--
Simon Riggs http://www.2ndQuadrant.com/books/
PostgreSQL Development, 24x7 Support, Training and Services
