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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
Date: 2011-01-03 17:48:57
Message-ID: 1294076937.19612.1812.camel@ebony (view raw or flat)
Thread:
Lists: pgsql-hackers
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
 


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