Re: Commits 8de72b and 5457a1 (COPY FREEZE)

On Mon, Dec 10, 2012 at 08:04:55PM -0500, Robert Haas wrote:
> You know, I hadn't been taking that option terribly seriously, but
> maybe we ought to reconsider it. It would certainly be simpler, and
> as you point out, it's not really any worse from an MVCC point of view
> than anything else we do. Moreover, it would make this available to
> clients like pg_dump without further hackery.
>
> I think the current behavior, where we treat FREEZE as a hint, is just
> awful. Regardless of whether the behavior is automatic or manually
> requested, the idea that you might get the optimization or not
> depending on the timing of relcache flushes seems very much
> undesirable. I mean, if the optimization is actually important for
> performance, then you want to get it when you ask for it. If it
> isn't, then why bother having it at all? Let's say that COPY FREEZE
> normally doubles performance on a data load that therefore takes 8
> hours - somebody who suddenly loses that benefit because of a relcache
> flush that they can't prevent or control and ends up with a 16 hour
> data load is going to pop a gasket.

Why was this patch applied when there are obviously so many concerns
about its behavior? Was that not clear at commit time?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +