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From "Michal Malecki" <misie...@poczta.onet.pl>
Subject Re: Estimating amount of memory need for cache
Date Fri, 22 Jul 2005 13:25:29 GMT
I think that in many cases estimating memory taken maybe quite easy (when there are no circual
references). Then it's ease to write utility that would analyze object using reflection or
to implement interface that has size() method; If you know structure of the bean and there
are well known types (strings, primitives maybe dates/timestamps)  estimating size is as easy
as writing hashCode :)
Michal Malecki
  ----- Original Message ----- 
  From: Clinton Begin 
  To: user-java@ibatis.apache.org 
  Sent: Friday, July 22, 2005 3:15 PM
  Subject: Re: Estimating amount of memory need for cache


  Thanks for the info Michal,

  I suppose then you'd have to double expected size of each string in your model then, to
make the estimate safer.

  Too bad there isn't something along the lines of System.sizeOf (Object obj).  

  Cheers,
  Clinton


  On 7/22/05, Michal Malecki <misiek_x@poczta.onet.pl> wrote:
    Hello,
    I think it's not quite so e.g. all characters in the memory are 2 bytes and serialized
there are in UTF-8
    here is article about it:
    http://www.javaworld.com/javaworld/javaqa/2003-12/02-qa-1226-sizeof.html 
    Regards
    Michal Malecki


      You could serialize the results it to disk.  That would give you a pessimistic estimation
of the size it will be in memory.  That is, the cost of serialization will be higher than
the amount of RAM used, so you can feel relatively confident that it will be smaller in memory.

      Cheers,
      Clinton


      On 7/21/05, Nathan Maves <Nathan.Maves@sun.com> wrote: 
        What is the best and most accurate way to calculate the space needed
        to cache a query.

        Say I have a query that returns 5 strings on average of 20 chars each.

        The query returns 5000 rows.

        I know this seems high but just humor me and remember I have access 
        to big servers here at Sun :)

        Nathan





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