Re: larger data set size

• To: John J Brecht <john.brecht@xxxxxxx>
• Subject: Re: larger data set size
• From: Robert S Laramee <rlaramee@xxxxxxxxxxxxxxx>
• Date: Fri, 31 Mar 2000 20:50:22 -0500 (EST)

Hi John,

> Something I've noticed, with regard to Java3D, that's particularly
> vexing is that it doesn't seem to to garbage disposal very effectively,
> if at all.  If I take one data set, and then start to visualize in
> different ways, more and more memory is steadily consumed, never to be
> made available again.  Is this just a WinNT issue, or is it the case on
> other platforms as well?  IS this something the new Java3D is supposed
> to fix?
> 
> along these same lines, i have a little app i wrote that reads ASCII
> data files, builds a VisAD data structure with the data and writes out
> netCDF files (for use with the SpreadSheet).  these netCDF files are
> signifigantly larger than the ASCII!  2.6 Mb of ASCII data becomes a 4.6
> Mb netCDF file.  is this expected, or is it likely i'm doing something
> wrong?

Are you using Java's Output Object Serialization to do this?  I ran into a
very similar problem with Java's ObjectOutputStream. If you are invoking:

ObjectOutputStream.writeObject() 

for each one of your objects (which I was doing for all 128^3 (or 64^3) of
our cube objects) then something that looks like a memory leak will
appear.  Each call to writeObject() will actually save a reference to that
object.  This is for case you are writing something that looks like a
graph, the serialization object may then save the entire graph with
dependencies.  If you're not writing a graph (no dependencies or pointers
necessary) than you can invoke:

ObjectOutputStream.reset()

and that will free up all those pointers taking up all that memory.
This is all documented in a bug report at www.javasoft.com but I
can't seem to bring up the URL again at this moment.

However, there's a catch, at least there was with my program on Linux. I
was finding that the size of the output file actually changed depending on
how many times I invoked the reset() method.  The more often it was
called, the bigger my file size got, in some cases 3 times larger.  So I
just call the reset() method as seldom as I can.

-cheers, bob

Robert S Laramee        tel:    (603) 868-1361
9 Woodman Ave, #316     office: (603) 862-0350
Durham, NH 03828        URL:   http://www.cs.unh.edu/~rlaramee

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