Creating / Accessing a Dataset with PHDF5

The programming model for accessing a dataset with Parallel HDF5 is:

1. Create or open a Parallel HDF5 file with a collective call to:
   C:        H5Dcreate,   H5Dopen
   F90:    h5dcreate_f,   h5dopen_f

2. Obtain a copy of the file transfer property list and set it to use collective or independent I/O.
   Do this by first passing a data transfer property list class type to:
   C:       H5Pcreate
   F90:   h5pcreate_f

   Then set the data transfer mode to either use independent I/O access or to use collective I/O, with a call to:

   C:       H5Pset_dxpl_mpio
   F90:   h5pset_dxpl_mpio_f

   Following are the parameters required by this call:

   C:
       herr_t H5Pset_dxpl_mpio (hid_t dxpl_id, H5FD_mpio_xfer_t xfer_mode )
            dxpl_id    IN: Data transfer property list identifier
            xfer_mode  IN: Transfer mode:
                           H5FD_MPIO_INDEPENDENT - use independent I/O access
                                                   (default)
                           H5FD_MPIO_COLLECTIVE  - use collective I/O access
   
   F90:
      h5pset_dxpl_mpi_f (prp_id, data_xfer_mode, hdferr)
            prp_id         IN: Property List Identifer (INTEGER (HID_T))
            data_xfer_mode IN: Data transfer mode  (INTEGER)
                                 H5FD_MPIO_INDEPENDENT_F (0)
                                 H5FD_MPIO_COLLECTIVE_F (1)
            hdferr         IN: Error code  (INTEGER)
   

3. Access the dataset with the defined transfer property list.
   • All processes that have opened a dataset may do collective I/O. Each process may do an independent and arbitrary number of data I/O access calls, using:
     C:        H5Dwrite,   H5Dread
     F90:    h5dwrite_f,   h5dread_f

   • If a dataset is unlimited, you can extend it with a collective call to:
     C:       H5Dextend
     F90:   h5dextend_f

The following code demonstrates a collective write using Parallel HDF5:

C:
    95      /*
    96       * Create property list for collective dataset write.
    97       */
    98      plist_id = H5Pcreate (H5P_DATASET_XFER);
    99      H5Pset_dxpl_mpio (plist_id, H5FD_MPIO_COLLECTIVE);
   100
   101      status = H5Dwrite (dset_id, H5T_NATIVE_INT, memspace, filespace,
   102                plist_id, data);

F90:
   108       ! Create property list for collective dataset write
   109       !
   110       CALL h5pcreate_f (H5P_DATASET_XFER_F, plist_id, error)
   111       CALL h5pset_dxpl_mpio_f (plist_id, H5FD_MPIO_COLLECTIVE_F, error)
   112
   113       !
   114       ! Write the dataset collectively.
   115       !
   116       CALL h5dwrite_f (dset_id, H5T_NATIVE_INTEGER, data, dimsfi, error, &
   117          file_space_id = filespace, mem_space_id = memspace, xfer_prp = plist_id)

[ C Example ] -- Dataset.c
[ FORTRAN90 Example ] -- dataset.f90

The HDF Group
Last Modified:   February 20, 2007