Re: Question about memory allocations

From: Steve
Subject: Re: Question about memory allocations
Date: ,
Msg-id: Pine.GSO.4.64.0704131229230.17955@kittyhawk.tanabi.org
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In response to: Re: Question about memory allocations  (Andrew McMillan)
Responses: Re: Question about memory allocations  (Ron)
Re: Question about memory allocations  (Carlos Moreno)
List: pgsql-performance

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how to efficiently update tuple in many-to-many relationship?  (Drew Wilson, )
 Re: how to efficiently update tuple in many-to-many relationship?  ("Merlin Moncure", )
 Re: how to efficiently update tuple in many-to-many relationship?  (Tom Lane, )
  Re: how to efficiently update tuple in many-to-many relationship?  (Drew Wilson, )
   Re: how to efficiently update tuple in many-to-many relationship?  (Tom Lane, )
    Re: how to efficiently update tuple in many-to-many relationship?  (Drew Wilson, )
     Re: how to efficiently update tuple in many-to-many relationship?  (Tom Lane, )
      Re: how to efficiently update tuple in many-to-many relationship?  (Drew Wilson, )
       Re: how to efficiently update tuple in many-to-many relationship?  (Tom Lane, )
        Question about memory allocations  (Steve, )
         Re: Question about memory allocations  (Tom Lane, )
          Re: Question about memory allocations  (Steve, )
         Re: Question about memory allocations  (Greg Smith, )
          Re: Question about memory allocations  (Steve, )
         Re: Question about memory allocations  (Andrew McMillan, )
          Re: Question about memory allocations  (Steve, )
           Re: Question about memory allocations  (Ron, )
            Re: Question about memory allocations  (Tom Lane, )
           Re: Question about memory allocations  (Carlos Moreno, )
            Re: Question about memory allocations  ("Jan de Visser", )

> Really?
>
> Wow!
>
> Common wisdom in the past has been that values above a couple of hundred
> MB will degrade performance.  Have you done any benchmarks on 8.2.x that
> show that you get an improvement from this, or did you just take the
> "too much of a good thing is wonderful" approach?
>

     Not to be rude, but there's more common wisdom on this particular
subject than anything else in postgres I'd say ;)  I think I recently read
someone else on this list who's laundry-listed the recommended memory
values that are out there these days and pretty much it ranges from
what you've just said to "half of system memory".

     I've tried many memory layouts, and in my own experience with
this huge DB, more -does- appear to be better but marginally so; more
memory alone won't fix a speed problem.  It may be a function of how much
reading/writing is done to the DB and if fsync is used or not if that
makes any sense :)  Seems there's no "silver bullet" to the shared_memory
question.  Or if there is, nobody can agree on it ;)


Anyway, talk to you later!


Steve


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