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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
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