Collective and Independent Operations with Parallel I/O in NetCDF-4

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35.6 Collective and Independent Operations with Parallel I/O in NetCDF-4

Some netCDF operations are collective (must be done by all processes at the same time), and others are independent (can be done by any process at any time.)

In MPI programs, I/O may be collective or independent.
All netCDF metadata writing operations are collective. That is, all creation of groups, types, variables, dimensions, or attributes.
Data reads and writes (ex. calls to nc_put_vara_int and nc_get_vara_int) may be independent (the default) or collective. To make writes to a variable collective, call the nc_var_par_access function.
```
/* Use these with nc_var_par_access(). */
#define NC_INDEPENDENT 0
#define NC_COLLECTIVE 1

EXTERNL int
nc_var_par_access(int ncid, int varid, int par_access);
```

2012 Unidata NetCDF Workshop > Parallel I/O with NetCDF