Re: Estimating amount of memory need for cache

Fri, 22 Jul 2005 07:02:16 -0700


You can keep a running set of instance references to ensure that you don't count the same object twice.

Cheers,
Clinton

On 7/22/05, Michal Malecki <[EMAIL PROTECTED]> wrote:
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 -----
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 <[EMAIL PROTECTED]> 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 -----
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 <[EMAIL PROTECTED]> 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:
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 <[EMAIL PROTECTED] > 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




Reply via email to