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

От: Andres Freund
Тема: Re: anti-join chosen even when slower than old plan
Дата: ,
Msg-id: 201011112111.05511.andres@anarazel.de
(см: обсуждение, исходный текст)
Ответ на: Re: anti-join chosen even when slower than old plan  (Tom Lane)
Список: pgsql-performance

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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", )

On Thursday 11 November 2010 19:58:49 Tom Lane wrote:
> I wrote:
> > I do think that something based around a settable-per-table caching
> > percentage might be a reasonable way to proceed.
>
> BTW ... on reflection it seems that this would *not* solve the use-case
> Kevin described at the start of this thread.  What he's got AIUI is some
> large tables whose recent entries are well-cached, and a lot of queries
> that tend to hit that well-cached portion, plus a few queries that hit
> the whole table and so see largely-not-cached behavior.  We can't
> represent that very well with a caching knob at the table level.  Either
> a high or a low setting will be wrong for one set of queries or the
> other.
>
> It might work all right if he were to partition the table and then have
> a different caching value attached to the currently-latest partition,
> but that doesn't sound exactly maintenance-free either.  Also, that only
> works with the current statically-planned approach to partitioned
> tables.  I think where we're trying to go with partitioning is that
> the planner doesn't consider the individual partitions, but the executor
> just hits the right one at runtime --- so cost modifiers attached to
> individual partitions aren't going to work in that environment.
>
> The most practical solution for his case still seems to be to twiddle
> some GUC or other locally in the maintenance scripts that do the
> full-table-scan queries.  Unfortunately we don't have an equivalent
> of per-session SET (much less SET LOCAL) for per-relation attributes.
> Not sure if we want to go there.
As dicussed in another thread some time ago another possibility is to probe
how well the data i cached using mincore() or similar...
While it presents problem with cache ramp-up it quite cool for other use-cases
(like this one).

Andre


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