On 2014-09-30 14:51:57 -0700, Kevin Grittner wrote: > Josh Berkus <j...@agliodbs.com> wrote: > > On 09/30/2014 02:39 PM, Kevin Grittner wrote: > >> Josh Berkus <j...@agliodbs.com> wrote: > >>> On 09/30/2014 07:15 AM, Kevin Grittner wrote: > >>> > >>>> 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. > >> > >> I would not think that an approach which took a full table lock to > >> implement the more general case would be accepted. > > > > Why not? There are certainly cases ... like bulk loading ... where > > users would find it completely acceptable. Imagine that you're merging > > 3 files into a single unlogged table before processing them into > > finished data. > > So the expectation is that when we implement MERGE it will, by > default, take out an EXCLUSIVE lock for the entire target table for > the entire duration of the command? I would have expected a bit > more finesse.
I think it'd be acceptable. Alternatively we'll just accept that you can get uniqueness violations under concurrency. I many cases that'll be fine. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
