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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 13:50:39 GMT
I can think about it during weekend (at last) :) first  - two general questions:
1) this sizeof method would return size of object and all objects that are referenced by it;
so invoking it in the loop for array and adding the result is not good because some objects
can be referenced many times
2)there is no problem with primitives and strings :) but what we do with all other classes;
it it enough to check all attributes by reflection (probably invoking setAccessible) until
we have only primitives and arrays of primitives?

As I read this article in the JavaWorld (I have never time for that :() this sizeof is very
tricky :( So some simplyfying assumptions must be made

More ideas after weekend
Michal Malecki
  ----- Original Message ----- 
  From: Clinton Begin 
  To: user-java@ibatis.apache.org 
  Sent: Friday, July 22, 2005 3:26 PM
  Subject: Re: Estimating amount of memory need for cache



  Good idea Michal,

  Sounds like something useful that could be added to Commons Lang.  Would you have an interest
in contributing it, or are you going to make me write it?  ;-)

  Cheers,
  Clinton


  On 7/22/05, Michal Malecki <misiek_x@poczta.onet.pl> wrote:
    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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