Re: INSERT ... ON CONFLICT {UPDATE | IGNORE}

On 09/30/2014 07:15 AM, Kevin Grittner wrote:
> There are certainly other ways to do it, although they require more
> work.  As far as UPSERT goes, I agree that we should require such
> an index, at least for the initial implementation and into the
> foreseeable future.  What I'm saying is that if we implement it
> using the standard MERGE syntax, then if the features of MERGE are
> extended it will continue to work even in the absence of such an
> index.  The index becomes a way of optimizing access rather than
> defining what access is allowed.
> 
> At the risk of pushing people away from this POV, I'll point out
> that this is somewhat similar to what we do for unlogged bulk loads
> -- if all the conditions for doing it the fast way are present, we
> do it the fast way; otherwise it still works, but slower.

Except that switching between fast/slow bulk loads affects *only* the
speed of loading, not the locking rules.  Having a statement silently
take a full table lock when we were expecting it to be concurrent
(because, for example, the index got rebuilt and someone forgot the
UNIQUE) violates POLA from my perspective.

-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com