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There is a problem with accessing fields, that I
think can be only solves with bytecode manipulation. More specifically - using
reflection we can check all public fields (getFields) and all fields in the
specific class (getDeclaredFields and then setAcesible for all
private/protected/package). There is no way to check private/protected/package
fields of the superclasses. Any ideas are welcomed, first prototype of the
utility - tomorrow
regards
Michal Malecki
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
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