Re: anti-join chosen even when slower than old plan

От: Tom Lane
Тема: Re: anti-join chosen even when slower than old plan
Дата: ,
Msg-id: 18450.1289499783@sss.pgh.pa.us
(см: обсуждение, исходный текст)
Ответ на: Re: anti-join chosen even when slower than old plan  (Robert Haas)
Ответы: Re: anti-join chosen even when slower than old plan  (Tom Lane)
Re: anti-join chosen even when slower than old plan  (Robert Haas)
Список: pgsql-performance

Скрыть дерево обсуждения

anti-join chosen even when slower than old plan  ("Kevin Grittner", )
 Re: anti-join chosen even when slower than old plan  ("Kevin Grittner", )
  Re: anti-join chosen even when slower than old plan  (Tom Lane, )
   Re: anti-join chosen even when slower than old plan  ("Kevin Grittner", )
 Re: anti-join chosen even when slower than old plan  (Tom Lane, )
  Re: anti-join chosen even when slower than old plan  (Grzegorz Jaśkiewicz, )
  Re: anti-join chosen even when slower than old plan  ("Kevin Grittner", )
   Re: anti-join chosen even when slower than old plan  (Tom Lane, )
   Re: anti-join chosen even when slower than old plan  (Robert Haas, )
    Re: anti-join chosen even when slower than old plan  ("Kevin Grittner", )
     Re: anti-join chosen even when slower than old plan  (Tom Lane, )
      Re: anti-join chosen even when slower than old plan  (Robert Haas, )
       Re: anti-join chosen even when slower than old plan  (Kenneth Marshall, )
        Re: anti-join chosen even when slower than old plan  (Mladen Gogala, )
         Re: anti-join chosen even when slower than old plan  (Kenneth Marshall, )
         Re: anti-join chosen even when slower than old plan  (Bob Lunney, )
     Re: anti-join chosen even when slower than old plan  (Mladen Gogala, )
      Re: anti-join chosen even when slower than old plan  ("Kevin Grittner", )
       Re: anti-join chosen even when slower than old plan  (Mladen Gogala, )
        Re: anti-join chosen even when slower than old plan  (Tom Lane, )
         Re: anti-join chosen even when slower than old plan  (Mladen Gogala, )
         Re: anti-join chosen even when slower than old plan  (Bruce Momjian, )
        Re: anti-join chosen even when slower than old plan  (Craig James, )
       Re: anti-join chosen even when slower than old plan  (Robert Haas, )
        Re: anti-join chosen even when slower than old plan  (Tom Lane, )
         Re: anti-join chosen even when slower than old plan  (Tom Lane, )
          Re: anti-join chosen even when slower than old plan  (Robert Haas, )
           Re: anti-join chosen even when slower than old plan  (Tom Lane, )
            Re: anti-join chosen even when slower than old plan  ("Kevin Grittner", )
            Re: anti-join chosen even when slower than old plan  (Robert Haas, )
             Re: anti-join chosen even when slower than old plan  (<>, )
              Re: anti-join chosen even when slower than old plan  (Kenneth Marshall, )
             Re: anti-join chosen even when slower than old plan  (Cédric Villemain, )
              Re: anti-join chosen even when slower than old plan  (Robert Haas, )
               Re: anti-join chosen even when slower than old plan  (Tom Lane, )
                Re: anti-join chosen even when slower than old plan  (Robert Haas, )
                Re: anti-join chosen even when slower than old plan  (Cédric Villemain, )
                 Re: anti-join chosen even when slower than old plan  ("Marc Mamin", )
                  Re: anti-join chosen even when slower than old plan  (bricklen, )
                  Re: anti-join chosen even when slower than old plan  (Robert Haas, )
                Re: anti-join chosen even when slower than old plan  (Bruce Momjian, )
                 Re: anti-join chosen even when slower than old plan  (Cédric Villemain, )
                  Re: anti-join chosen even when slower than old plan  (Robert Haas, )
                   Re: anti-join chosen even when slower than old plan  (Cédric Villemain, )
                   Re: anti-join chosen even when slower than old plan  (Bruce Momjian, )
             Re: anti-join chosen even when slower than old plan  (Bruce Momjian, )
              Re: anti-join chosen even when slower than old plan  (Cédric Villemain, )
            Re: anti-join chosen even when slower than old plan  (Cédric Villemain, )
             Re: anti-join chosen even when slower than old plan  (Vitalii Tymchyshyn, )
              Re: anti-join chosen even when slower than old plan  (Cédric Villemain, )
               Re: anti-join chosen even when slower than old plan  (Vitalii Tymchyshyn, )
                Re: anti-join chosen even when slower than old plan  (Cédric Villemain, )
          Re: anti-join chosen even when slower than old plan  ("Kevin Grittner", )
           Re: anti-join chosen even when slower than old plan  ("Kevin Grittner", )
           Re: anti-join chosen even when slower than old plan  (Tom Lane, )
            Re: anti-join chosen even when slower than old plan  ("Kevin Grittner", )
            Re: anti-join chosen even when slower than old plan  (Jon Nelson, )
          Re: anti-join chosen even when slower than old plan  (Andres Freund, )
         Re: anti-join chosen even when slower than old plan  (Robert Haas, )
          Re: anti-join chosen even when slower than old plan  (Tom Lane, )
    Re: anti-join chosen even when slower than old plan  (Віталій Тимчишин, )
 Re: anti-join chosen even when slower than old plan  ("Kevin Grittner", )

Robert Haas <> writes:
> Let's back up a moment and talk about what the overall goal is, here.
> Ideally, we would like PostgreSQL to have excellent performance at all
> times, under all circumstances, with minimal tuning.  Therefore, we do
> NOT want to add variables that will, by design, need constant manual
> adjustment.  That is why I suggested that Tom's idea of an
> assume_cached GUC is probably not what we really want to do.   On the
> other hand, what I understand Mladen to be suggesting is something
> completely different.  He's basically saying that, of course, he wants
> it to work out of the box most of the time, but since there are
> guaranteed to be cases where it doesn't, how about providing some
> knobs that aren't intended to be routinely twaddled but which are
> available in case of emergency?  Bravo, I say!

Um ... those are exactly the same thing.  You're just making different
assumptions about how often you will need to twiddle the setting.
Neither assumption is based on any visible evidence, unfortunately.
I was thinking of assume_cached as something that could be
set-and-forget most of the time, and you're entirely right to criticize
it on the grounds that maybe it wouldn't.  But to support a proposal
that doesn't even exist yet on the grounds that it *would* be
set-and-forget seems a tad inconsistent.  We can't make that judgment
without a whole lot more details than have been provided yet for any
idea in this thread.

I do think that something based around a settable-per-table caching
percentage might be a reasonable way to proceed.  But the devil is in
the details, and we don't have those yet.

            regards, tom lane


В списке pgsql-performance по дате сообщения:

От: Ben
Дата:
Сообщение: Re: equivalent queries lead to different query plans for self-joins with group by?
От: Jon Nelson
Дата:
Сообщение: Re: postmaster consuming /lots/ of memory with hash aggregate. why?