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FW: 19990724: netCDF performance in Java


-----Original Message-----
From: John Caron [mailto:address@hidden]
Sent: Monday, July 26, 1999 4:10 PM
To: Lyn Greenhill
Subject: RE: 19990724: netCDF performance in Java


Hi Lyn:

I have been given your question to try to answer. You may not know, but
Glenn died in an airplane crash several months ago. We have a memorial
to him at http://www.unidata.ucar.edu/Glenn_Davis/get/memorial.html

Just as in C or Fortran, typically one extracts the array (actually a
"MultiArray") that you want out of the netcdf file in a single call.
Reading one element at a time is probably the cause of the lousy
performance you see.

I'm not sure what might have been causing your programmer to be "unable
to get netCDF to work". The first thing that comes to mind is that s/he
tried to extract a bigger array than you have memory for.  S/he should
calculate how big the array is, and make sure the JVM has enough memory
(see the -XmxNN flag to the java program).

Let me know how that goes, or send me more details.

John Caron



> -----Original Message-----
> From: Unidata Support [mailto:address@hidden]
> Sent: Friday, July 23, 1999 10:49 PM
> To: address@hidden
> Subject: 19990724: netCDF performance in Java
>
>
>
> ------- Forwarded Message
>
> >To: "Glenn P. Davis" <address@hidden>
> >cc: <address@hidden>
> >From: Lyn Greenhill <address@hidden>
> >Subject: netCDF performance in Java
> >Organization: DynaTech Engineering, Inc.
> >Keywords: 199907240015.SAA09004 netCDF Java
>
> Glenn:
>
> We are developing an engineering application in Java, with the model
> definition and results stored in a platform independent file.  To get
> this independence, we are using netCDF.  However, the speed at which
> netCDF reads/writes the data is completely unacceptable.  It takes
> several minutes (that's right, minutes) to open small files
> of a couple
> hundred kilobytes.
>
> Our programmer has implemented the I/O for all arrays
> <italic>one element
> at a time</italic>!  He says that he was unable to get netCDF
> to work by
> writing a full array directly.  Quite frankly, I find it hard
> to believe
> that netCDF can't do this.
>
> Do you have any tips/pointers/tricks on doing this.  Basically, we are
> writing a large amount of integers and doubles, some strings, and some
> derived types (like Matrix class from Jama, Complex class from JNL).
> Most everything is arrays, although some of the data are scalars.
>
> I appreciate any help you might offer.
>
> -----------------------
>
> Lyn Greenhill, P. E.
> DynaTech Engineering, Inc.
> 916-721-3300 x11
> 916-721-3366 fax
> <<address@hidden>
> http://www.dynatechengr.com
> "I can be anything I want to be...except an engineer"-Brett Favre
>
>
> ------- End of Forwarded Message
>