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"Muqun (Kent) Yang" <ymuqun@xxxxxxxxxxxxx> writes: > Ed: > On Wed, 29 Jun 2005, Ed Hartnett wrote: > >> Howdy all! >> >> I have a question about parallel programming with HDF5. Do parallel >> programmers just not use unlimited dimensions? >> > You can use unlimited dimensions for parallel programming. >> I noticed that H5Dextend is a collective operation. This would make it >> difficult for programs to add a record at a time. >> > > I don't think it is difficult as long as all processors participate. But doesn't that waste a lot of cycles, wait to sync up every time a new record is written? As I understand it, using fixed-length data, my different processes could write their data and go on their merry way, without waiting for anything. Maybe this just doesn't matter much because it's not the bottleneck. > > I may miss something. Parallel NetCDF tests I wrote include unlimited > dimension dataset tests for both collective and independent modes. Tests > passed. > > Although H5Dextend is collective, I remember that I noticed that doesn't > matter for netCDF4 users. I may be wrong. Maybe other people can give > some insights. > As currently implemented, H5Dextend is called when needed as you write the data in netcdf. That is, if you are writing a record at a time, H5Dextend is called for each record. Thanks, Ed -- Ed Hartnett -- ed@xxxxxxxxxxxxxxxx