use of MPI derived types in Flexible API

[Wei-keng Liao]

Hi, Jim

Do you mean the local I/O buffer contains a list of non-contiguous data in memory?
Or do you mean "distributed" as data is partitioned across multiple MPI processes?

The varm APIs and the "flexible" APIs that take an MPI derived datatype argument
are for users to describe non-contiguous data in the local I/O buffer. The imap
and MPI datatype argument has no effect to the data access in files. So, I need
to know which case you are referring to first.

Thanks for pointing out the error in the user guide. It is fixed. 

Wei-keng

On Sep 24, 2014, at 2:30 PM, Jim Edwards wrote:

> I want to write a distributed variable to a file and the way the 
> data is distributed is fairly random with respect to the ordering on the file.   
> 
> It seems like I can do several things from each task in order to write the data -
> 
> 	• I can specify several blocks of code using start and count and make mulitple calls on each task to ncmpi_bput_vara_all
> 	• I can define an MPI derived type and make a single call to ncmpi_bput_var_all on each task
> 	• I (think I) can use ncmpi_bput_varm_all and specify an imap  (btw: the pnetcdf users guide has this interface wrong)
> Are any of these better from a performance standpoint?
> 
> Thanks,
> 
> 
> 
> 
> -- 
> Jim Edwards
> 
> CESM Software Engineer
> National Center for Atmospheric Research
> Boulder, CO