wrote:=20 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=20 to big servers here at Sun :) Nathan ------=_NextPart_000_0070_01C590F7.88EB48D0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

There is a problem with accessing = fields, that I=20 think can be only solves with bytecode manipulation. More specifically - = using=20 reflection we can check all public fields (getFields) and all fields in = the=20 specific class (getDeclaredFields and then setAcesible for all=20 private/protected/package). There is no way to check = private/protected/package=20 fields of the superclasses. Any ideas are welcomed, first prototype of = the=20 utility - tomorrow

regards

Michal Malecki

You=20 can keep a running set of instance references to ensure that you don't = count=20 the same object twice.

Cheers,
Clinton

On 7/22/05, Michal=20 Malecki <misiek_x@poczta.onet.pl>=20 wrote:

I can think about it during weekend = (at last)=20 :) first - two general questions:

1) this sizeof method would return = size of=20 object and all objects that are referenced by it; so invoking it in = the loop=20 for array and adding the result is not good because some objects can = be=20 referenced many times

2)there is no problem with = primitives and=20 strings :) but what we do with all other classes; it it enough to = check all=20 attributes by reflection (probably invoking setAccessible) until we = have=20 only primitives and arrays of primitives?

As I read this article in the = JavaWorld (I have=20 never time for that :() this sizeof is very tricky :( So some = simplyfying=20 assumptions must be made

More ideas after = weekend

Michal Malecki
-----=20 Original Message -----

From:=20 Clinton = Begin=20 To:=20 user-java@ibatis.apache.org

Sent:=20 Friday, July 22, 2005 3:26 PM

Subject:=20 Re: Estimating amount of memory need for cache

Good idea Michal,

Sounds like something = useful=20 that could be added to Commons Lang. Would you have an = interest in=20 contributing it, or are you going to make me write it? =20 ;-)

Cheers,
Clinton

On 7/22/05, Michal=20 Malecki <misiek_x@poczta.onet.pl> wrote:=20

I think that in many cases = estimating=20 memory taken maybe quite easy (when there are no circual=20 references). Then it's ease to write utility that would analyze = object=20 using reflection or to implement interface that has size() = method; If=20 you know structure of the bean and there are well known types = (strings,=20 primitives maybe dates/timestamps) estimating size is as = easy as=20 writing hashCode :)
Michal=20 Malecki

-----=20 Original Message -----
From:=20 Clinton Begin=20

To:=20 user-java@ibatis.apache.org Sent:=20 Friday, July 22, 2005 3:15 PM Subject:=20 Re: Estimating amount of memory need for cache

Thanks for the info Michal,

I = suppose=20 then you'd have to double expected size of each string in your = model=20 then, to make the estimate safer.

Too bad there isn't = something=20 along the lines of System.sizeOf (Object obj). =20

Cheers,
Clinton

On 7/22/05, Michal Malecki <misiek_x@poczta.onet.pl> wrote:=20

Hello,

I think it's not quite so = e.g. all=20 characters in the memory are 2 bytes and serialized there = are in=20 UTF-8

here is article about = it:

http://www.javaworld.com/javaworld/javaqa/2003-12/02-qa-1= 226-sizeof.html=20

Regards

Michal = Malecki

You=20 could serialize the results it to disk. That would = give you=20 a pessimistic estimation of the size it will be in = memory. =20 That is, the cost of serialization will be higher than the = amount=20 of RAM used, so you can feel relatively confident that it = will be=20 smaller in memory.

Cheers,
Clinton

On 7/21/05, Nathan Maves <Nathan.Maves@sun.com > = wrote:=20
What=20 is the best and most accurate way to calculate the space = needed
to cache a query.

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

The query=20 returns 5000 rows.

I know this seems high but = just humor=20 me and remember I have access
to big servers here at = Sun=20 = :)

Nathan

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