Re: performance degrades with filesize

• To: Steve Emmerson <steve@xxxxxxxxxxxxxxxx>
• Subject: Re: performance degrades with filesize
• From: John Galbraith <john@xxxxxxxxxxxxxxx>
• Date: Mon, 10 Sep 2001 13:26:23 -0600

>>>>> "Steve" == Steve Emmerson <steve@xxxxxxxxxxxxxxxx> writes:

    >> ... I can't be certain but it seems like the entire file is
    >> rewritten when the unlimited dimension increases.

    Steve> The C implementation from the Unidata Program Center of the
    Steve> netCDF API *does not* rewrite the entire netCDF file when the
    Steve> unlimited dimension is increased -- effectively, the file is
    Steve> simply appended to.

That is why I say "seems", because the write time "seems" to be
proportional to the size of the file.  I have no evidence that the file is
actually being copied.  In fact, I would be surprised if it was and would
suspect that I am calling the netcdf library incorrectly.  I probably am
calling it incorrectly, based on this trouble I am having, but I don't know
what my problem is yet.

    Steve> I don't know about the Python interface.

The Python interface basically just converts the python array slices to
netcdf arguments and calls ncvarputg().  (Python arrays are contiguous
values).  The Python module never actually touches the netcdf file except
through that call to ncvarputg().  Even if the python wrapper was deathly
slow, it would be the same deathly slow interval every write and it
wouldn't be dependent on the file size.

Maybe there is some issue with calling the old netcdf API?

Thanks,
        John


-- 
John Galbraith                    email: john@xxxxxxxxxxxxxxx
Los Alamos National Laboratory,   home phone: (505) 662-3849
                                  work phone: (505) 665-6301

• References:
  • Re: performance degrades with filesize
    • From: Ethan Alpert
  • Re: performance degrades with filesize
    • From: Steve Emmerson