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Re: 20030618: NetCDF performance problems

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  • Subject: Re: 20030618: NetCDF performance problems
  • Date: Wed, 18 Jun 2003 10:03:06 -0600
>To: address@hidden
>From: Gottfried Necker <address@hidden>
>Subject: NetCDF performance problems.
>Organization: ?
>Keywords: 200306180911.h5I9BvLd025090 netCDF 3.5.1-beta10 Fujitsu VPP

Hi Gottfried,

> > 
> > Another possibility would be providing you with some versions between
> > beta3 and beta10 that would help isolate which changes caused the
> > problem.
> I tried with netcdf-3.5.1-beta5 and there's no problem. I went back to
> beta10 and got the problem again. I diffed the libsrc directory and
> the only substantial difference between these versions is in
> posixio.c, where the call to ftruncate is replaced by calls to seek. I
> will try to put the code with ftruncate into beta10 to see what
> happens. But I don't have the time to do it now. I will try this on
> friday.

Thanks, just this information is a big help.  I'm also anxious to hear
what you find out when substituting ftruncate for the call to lseek.
The revision notice we have on that change was:

  ... eliminated unnecessary use of ftruncate(), because it fails on
  FAT32 file systems under Linux.

If this causes a performance problem on other systems, maybe we can
find a better fix for the Linux problem.

--Russ

_____________________________________________________________________

Russ Rew                                         UCAR Unidata Program
address@hidden                      http://my.unidata.ucar.edu