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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
Hello everyone,My profiling results show that NetCDF Classic is very slow if the following output scheme is used:
// case 1 for var in variables define var write var endforor even if something like this is done (assuming that all the variables are defined already and they depend on an unlimited dimension):
// case 2 for var in variables append var endforIt seems to me that case 1 is slow because NetCDF (Classic) keeps the file header as small as possible (Section 4 of the NetCDF User's Guide is perfectly clear about this). Case 2, on the other hand, seems to be slow because (please correct me if I'm wrong) variables are stored contiguously. (In other words: if variables A and B are defined in this order, then appending X bytes to A requires moving B over by X bytes.)
My question is:How does NetCDF-4 compare to NetCDF Classic in this regard? Would switching to it improve write performance? (This is two questions, really: I'm interested in cases 1 and 2 separately.)
I would like to avoid re-factoring our code to do for var in variables define var endfor for var in variables write var endfor instead of what is described as "case 1" above. Thank you! -- Constantine Khroulev PISM (www.pism-docs.org) Developer/Maintainer University of Alaska Fairbanks
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