[svn-r7790] Purpose:

    Bug fix & code cleanups

Description:
    Change our use of MPI derived datatypes to not create datatypes with
"0-sized" lengths, which causes the LANL Q machine to hang.

    Also, get rid of "prefer MPI derived datatypes" environment variable since
it has no advantage.

Platforms tested:
    FreeBSD 4.9 (sleipnir) w & w/o parallel
    h5committest

6 files changed, 72 insertions, 221 deletions

diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt
index e108856..c4b3754 100644
--- a/release_docs/RELEASE.txt
+++ b/release_docs/RELEASE.txt
@@ -60,6 +60,10 @@ Bug Fixes since HDF5-1.6.1 release
 
     Library
     -------
+        - Fixed problems with MPI datatypes that caused ASCI Q machine to
+            hang.  QAK - 2003/10/28
+        - Removed HDF5_MPI_PREFER_DERIVED_TYPES environment variable support,
+            since it had no benefit.  QAK - 2003/10/28
         - Single hyperslab selections (which were set with only one call to
             H5Sselect_hyperslab) that had dimensions that could be "flattened"
             but were interspersed with dimensions that could not be flattened
diff --git a/src/H5FDmpio.c b/src/H5FDmpio.c
index 599fd62..dc98bc2 100644
--- a/src/H5FDmpio.c
+++ b/src/H5FDmpio.c
@@ -170,9 +170,6 @@ static int interface_initialize_g = 0;
 /* Definitions for file MPI type property */
 #define H5FD_MPIO_XFER_FILE_MPI_TYPE_NAME       "H5FD_mpio_file_mpi_type"
 #define H5FD_MPIO_XFER_FILE_MPI_TYPE_SIZE       sizeof(MPI_Datatype)
-/* Definitions for whether to use MPI types property */
-#define H5FD_MPIO_XFER_USE_VIEW_NAME            "H5FD_mpio_use_view"
-#define H5FD_MPIO_XFER_USE_VIEW_SIZE            sizeof(unsigned)
 
 
 /*-------------------------------------------------------------------------
@@ -637,7 +634,7 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5FD_mpio_setup(hid_t dxpl_id, MPI_Datatype btype, MPI_Datatype ftype, unsigned use_view)
+H5FD_mpio_setup(hid_t dxpl_id, MPI_Datatype btype, MPI_Datatype ftype)
 {
     H5P_genplist_t *plist;      /* Property list pointer */
     herr_t      ret_value=SUCCEED;       /* Return value */
@@ -656,10 +653,6 @@ H5FD_mpio_setup(hid_t dxpl_id, MPI_Datatype btype, MPI_Datatype ftype, unsigned
     if(H5P_insert(plist,H5FD_MPIO_XFER_FILE_MPI_TYPE_NAME,H5FD_MPIO_XFER_FILE_MPI_TYPE_SIZE,&ftype,NULL,NULL,NULL,NULL,NULL)<0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't insert MPI-I/O property");
 
-    /* Set 'use view' property */
-    if(H5P_insert(plist,H5FD_MPIO_XFER_USE_VIEW_NAME,H5FD_MPIO_XFER_USE_VIEW_SIZE,&use_view,NULL,NULL,NULL,NULL,NULL)<0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't insert MPI-I/O property");
-
 done:
     FUNC_LEAVE_NOAPI(ret_value);
 }
@@ -700,10 +693,6 @@ H5FD_mpio_teardown(hid_t dxpl_id)
     if(H5P_remove(dxpl_id,plist,H5FD_MPIO_XFER_FILE_MPI_TYPE_NAME)<0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTDELETE, FAIL, "can't remove MPI-I/O property");
 
-    /* Remove 'use view' property */
-    if(H5P_remove(dxpl_id,plist,H5FD_MPIO_XFER_USE_VIEW_NAME)<0)
-        HGOTO_ERROR(H5E_PLIST, H5E_CANTDELETE, FAIL, "can't remove MPI-I/O property");
-
 done:
     FUNC_LEAVE_NOAPI(ret_value);
 }
@@ -1474,10 +1463,6 @@ H5FD_mpio_read(H5FD_t *_file, H5FD_mem_t UNUSED type, hid_t dxpl_id, haddr_t add
     MPI_Datatype		buf_type=MPI_BYTE;      /* MPI description of the selection in memory */
     int         		size_i, bytes_read, n;
     unsigned			use_view_this_time=0;
-    H5P_genplist_t              *plist;      /* Property list pointer */
-#ifndef NDEBUG
-    H5FD_mpio_xfer_t            xfer_mode;   /* I/O tranfer mode */
-#endif /* NDEBUG */
     herr_t              	ret_value=SUCCEED;
 
     FUNC_ENTER_NOAPI(H5FD_mpio_read, FAIL);
@@ -1509,30 +1494,27 @@ H5FD_mpio_read(H5FD_t *_file, H5FD_mem_t UNUSED type, hid_t dxpl_id, haddr_t add
 		(long)mpi_off, size_i );
 #endif
 
-    /* Obtain the data transfer properties */
-    if(NULL == (plist = H5I_object(dxpl_id)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list");
-#ifndef NDEBUG
-    xfer_mode=(H5FD_mpio_xfer_t)H5P_peek_unsigned(plist, H5D_XFER_IO_XFER_MODE_NAME);
-#endif /* NDEBUG */
-    
     /* Only look for MPI views for raw data transfers */
     if(type==H5FD_MEM_DRAW) {
+        H5P_genplist_t              *plist;      /* Property list pointer */
+        H5FD_mpio_xfer_t            xfer_mode;   /* I/O tranfer mode */
+
+        /* Obtain the data transfer properties */
+        if(NULL == (plist = H5I_object(dxpl_id)))
+            HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list");
+        xfer_mode=(H5FD_mpio_xfer_t)H5P_peek_unsigned(plist, H5D_XFER_IO_XFER_MODE_NAME);
+    
         /*
          * Set up for a fancy xfer using complex types, or single byte block. We
          * wouldn't need to rely on the use_view field if MPI semantics allowed
          * us to test that btype=ftype=MPI_BYTE (or even MPI_TYPE_NULL, which
          * could mean "use MPI_BYTE" by convention).
          */
-        if(H5P_exist_plist(plist,H5FD_MPIO_XFER_USE_VIEW_NAME)>0)
-            if(H5P_get(plist,H5FD_MPIO_XFER_USE_VIEW_NAME,&use_view_this_time)<0)
-                HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get MPI-I/O type property");
-
-        if (use_view_this_time) {
+        if(xfer_mode==H5FD_MPIO_COLLECTIVE) {
             MPI_Datatype		file_type;
 
-            /* Sanity check that views will only be used by collective I/O */
-            assert(xfer_mode==H5FD_MPIO_COLLECTIVE);
+            /* Remember that views are used */
+            use_view_this_time=TRUE;
 
             /* prepare for a full-blown xfer using btype, ftype, and disp */
             if(H5P_get(plist,H5FD_MPIO_XFER_MEM_MPI_TYPE_NAME,&buf_type)<0)
@@ -1552,10 +1534,6 @@ H5FD_mpio_read(H5FD_t *_file, H5FD_mem_t UNUSED type, hid_t dxpl_id, haddr_t add
              */
             mpi_off=0;
         } /* end if */
-        else {
-            /* Sanity check that independent I/O must be occuring */
-            assert(xfer_mode==H5FD_MPIO_INDEPENDENT);
-        } /* end else */
     } /* end if */
 
     /* Read the data. */
@@ -1781,9 +1759,6 @@ H5FD_mpio_write(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr,
     int         		size_i, bytes_written;
     unsigned			use_view_this_time=0;
     H5P_genplist_t              *plist;                 /* Property list pointer */
-#ifndef NDEBUG
-    H5FD_mpio_xfer_t            xfer_mode;   /* I/O tranfer mode */
-#endif /* NDEBUG */
     herr_t              	ret_value=SUCCEED;
 
     FUNC_ENTER_NOAPI(H5FD_mpio_write, FAIL);
@@ -1818,26 +1793,24 @@ H5FD_mpio_write(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr,
     /* Obtain the data transfer properties */
     if(NULL == (plist = H5I_object(dxpl_id)))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list");
-#ifndef NDEBUG
-    xfer_mode = H5P_peek_unsigned(plist, H5D_XFER_IO_XFER_MODE_NAME);
-#endif /* NDEBUG */
     
     if(type==H5FD_MEM_DRAW) {
+        H5FD_mpio_xfer_t            xfer_mode;   /* I/O tranfer mode */
+
+        /* Obtain the data transfer properties */
+        xfer_mode = H5P_peek_unsigned(plist, H5D_XFER_IO_XFER_MODE_NAME);
+
         /*
          * Set up for a fancy xfer using complex types, or single byte block. We
          * wouldn't need to rely on the use_view field if MPI semantics allowed
          * us to test that btype=ftype=MPI_BYTE (or even MPI_TYPE_NULL, which
          * could mean "use MPI_BYTE" by convention).
          */
-        if(H5P_exist_plist(plist,H5FD_MPIO_XFER_USE_VIEW_NAME)>0)
-            if(H5P_get(plist,H5FD_MPIO_XFER_USE_VIEW_NAME,&use_view_this_time)<0)
-                HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get MPI-I/O type property");
-
-        if (use_view_this_time) {
+        if(xfer_mode==H5FD_MPIO_COLLECTIVE) {
             MPI_Datatype		file_type;
 
-            /* Sanity check that views will only be used by collective I/O */
-            assert(xfer_mode==H5FD_MPIO_COLLECTIVE);
+            /* Remember that views are used */
+            use_view_this_time=TRUE;
 
             /* prepare for a full-blown xfer using btype, ftype, and disp */
             if(H5P_get(plist,H5FD_MPIO_XFER_MEM_MPI_TYPE_NAME,&buf_type)<0)
@@ -1857,10 +1830,6 @@ H5FD_mpio_write(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr,
              */
             mpi_off=0;
         } /* end if */
-        else {
-            /* Sanity check that independent I/O must occur */
-            assert(xfer_mode==H5FD_MPIO_INDEPENDENT);
-        } /* end else */
     } /* end if */
     else {
         unsigned		        block_before_meta_write=0;      /* Whether to block before a metadata write */
diff --git a/src/H5FDmpio.h b/src/H5FDmpio.h
index ae4cf4b..7bd2545 100644
--- a/src/H5FDmpio.h
+++ b/src/H5FDmpio.h
@@ -61,7 +61,7 @@ H5_DLL herr_t H5Pset_dxpl_mpio(hid_t dxpl_id, H5FD_mpio_xfer_t xfer_mode);
 H5_DLL herr_t H5Pget_dxpl_mpio(hid_t dxpl_id, H5FD_mpio_xfer_t *xfer_mode/*out*/);
 H5_DLL MPI_Comm H5FD_mpio_communicator(H5FD_t *_file);
 H5_DLL herr_t H5FD_mpio_setup(hid_t dxpl_id, MPI_Datatype btype,
-    MPI_Datatype ftype, unsigned use_view);
+    MPI_Datatype ftype);
 H5_DLL herr_t H5FD_mpio_teardown(hid_t dxpl_id);
 H5_DLL herr_t H5FD_mpio_wait_for_left_neighbor(H5FD_t *file);
 H5_DLL herr_t H5FD_mpio_signal_right_neighbor(H5FD_t *file);
diff --git a/src/H5S.c b/src/H5S.c
index e1d0327..0f1e905 100644
--- a/src/H5S.c
+++ b/src/H5S.c
@@ -51,7 +51,6 @@ static size_t			H5S_nconv_g = 0;	/*entries used*/
 #ifdef H5_HAVE_PARALLEL
 /* Global vars whose value can be set from environment variable also */
 hbool_t H5S_mpi_opt_types_g = TRUE;
-hbool_t H5S_mpi_prefer_derived_types_g = TRUE;
 #endif /* H5_HAVE_PARALLEL */
 
 /* Declare a free list to manage the H5S_simple_t struct */
@@ -98,12 +97,6 @@ H5S_init_interface(void)
         if (s && HDisdigit(*s))
             H5S_mpi_opt_types_g = (int)HDstrtol (s, NULL, 0);
     }
-    {
-        /* Prefer MPI derived types for collective data transfers? */
-        const char *s = HDgetenv ("HDF5_MPI_PREFER_DERIVED_TYPES");
-        if (s && HDisdigit(*s))
-            H5S_mpi_prefer_derived_types_g = (int)HDstrtol (s, NULL, 0);
-    }
 #endif /* H5_HAVE_PARALLEL */
 
 done:
diff --git a/src/H5Smpio.c b/src/H5Smpio.c
index 224f15a..44d391a 100644
--- a/src/H5Smpio.c
+++ b/src/H5Smpio.c
@@ -51,44 +51,39 @@
 static int             interface_initialize_g = 0;
 
 static herr_t
-H5S_mpio_all_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derived_types,
+H5S_mpio_all_type( const H5S_t *space, size_t elmt_size,
 		     /* out: */
 		     MPI_Datatype *new_type,
 		     size_t *count,
 		     hsize_t *extra_offset,
-		     hbool_t *use_view,
 		     hbool_t *is_derived_type );
 static herr_t
-H5S_mpio_none_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derived_types,
+H5S_mpio_none_type( const H5S_t *space, size_t elmt_size,
 		     /* out: */
 		     MPI_Datatype *new_type,
 		     size_t *count,
 		     hsize_t *extra_offset,
-		     hbool_t *use_view,
 		     hbool_t *is_derived_type );
 static herr_t
-H5S_mpio_hyper_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derived_types,
+H5S_mpio_hyper_type( const H5S_t *space, size_t elmt_size,
 		     /* out: */
 		     MPI_Datatype *new_type,
 		     size_t *count,
 		     hsize_t *extra_offset,
-		     hbool_t *use_view,
 		     hbool_t *is_derived_type );
 static herr_t
-H5S_mpio_hyper_contig_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derived_types,
+H5S_mpio_hyper_contig_type( const H5S_t *space, size_t elmt_size,
 		     /* out: */
 		     MPI_Datatype *new_type,
 		     size_t *count,
 		     hsize_t *extra_offset,
-		     hbool_t *use_view,
 		     hbool_t *is_derived_type );
 static herr_t
-H5S_mpio_space_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derived_types,
+H5S_mpio_space_type( const H5S_t *space, size_t elmt_size,
 		     /* out: */
 		     MPI_Datatype *new_type,
 		     size_t *count,
 		     hsize_t *extra_offset,
-		     hbool_t *use_view,
 		     hbool_t *is_derived_type );
 static herr_t
 H5S_mpio_spaces_xfer(H5F_t *f, const H5O_layout_t *layout, size_t elmt_size,
@@ -107,7 +102,6 @@ H5S_mpio_spaces_xfer(H5F_t *f, const H5O_layout_t *layout, size_t elmt_size,
  *		*count		  how many objects of the new_type in selection
  *				  (useful if this is the buffer type for xfer)
  *		*extra_offset     Number of bytes of offset within dataset
- *		*use_view         0 if view not needed, 1 if needed
  *		*is_derived_type  0 if MPI primitive type, 1 if derived
  *
  * Programmer:	rky 980813
@@ -115,27 +109,20 @@ H5S_mpio_spaces_xfer(H5F_t *f, const H5O_layout_t *layout, size_t elmt_size,
  * Modifications:
  *
  *      Quincey Koziol, June 18, 2002
- *      Added 'extra_offset' and 'use_view' parameters
- *
- *      Quincey Koziol, June 19, 2002
- *      Added 'prefer_derived_types' flag to choose whether MPI derived types
- *      should be created or not.
+ *      Added 'extra_offset' parameter
  *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5S_mpio_all_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derived_types,
+H5S_mpio_all_type( const H5S_t *space, size_t elmt_size,
 		     /* out: */
 		     MPI_Datatype *new_type,
 		     size_t *count,
 		     hsize_t *extra_offset,
-		     hbool_t *use_view,
 		     hbool_t *is_derived_type )
 {
     hsize_t	total_bytes;
     unsigned		u;
-    int         mpi_code;               /* MPI return code */
-    herr_t      ret_value=SUCCEED;       /* Return value */
 
     FUNC_ENTER_NOINIT(H5S_mpio_all_type);
 
@@ -147,33 +134,13 @@ H5S_mpio_all_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derived_
     for (u=0; u<space->extent.u.simple.rank; ++u)
         total_bytes *= space->extent.u.simple.size[u];
 
-    /* Check if we should prefer creating a derived type */
-    if(prefer_derived_types) {
-        /* fill in the return values */
-        H5_CHECK_OVERFLOW(total_bytes, hsize_t, int);
-        if (MPI_SUCCESS != (mpi_code=MPI_Type_contiguous( (int)total_bytes, MPI_BYTE, new_type )))
-            HMPI_GOTO_ERROR(FAIL, "MPI_Type_contiguous failed", mpi_code);
-        if(MPI_SUCCESS != (mpi_code=MPI_Type_commit(new_type)))
-            HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code);
-        *count = 1;
-        *extra_offset = 0;
-        *use_view = 1;
-        *is_derived_type = 1;
-    } /* end if */
-    else {
-        /* fill in the return values */
-        *new_type = MPI_BYTE;
-        H5_ASSIGN_OVERFLOW(*count, total_bytes, hsize_t, size_t);
-        *extra_offset = 0;
-        *use_view = 0;
-        *is_derived_type = 0;
-    } /* end else */
+    /* fill in the return values */
+    *new_type = MPI_BYTE;
+    H5_ASSIGN_OVERFLOW(*count, total_bytes, hsize_t, size_t);
+    *extra_offset = 0;
+    *is_derived_type = 0;
 
-done:
-#ifdef H5Smpi_DEBUG
-    HDfprintf(stdout, "Leave %s total_bytes=%Hu\n", FUNC, total_bytes );
-#endif
-    FUNC_LEAVE_NOAPI(ret_value);
+    FUNC_LEAVE_NOAPI(SUCCEED);
 } /* H5S_mpio_all_type() */
 
 
@@ -188,7 +155,6 @@ done:
  *		*count		  how many objects of the new_type in selection
  *				  (useful if this is the buffer type for xfer)
  *		*extra_offset     Number of bytes of offset within dataset
- *		*use_view         0 if view not needed, 1 if needed
  *		*is_derived_type  0 if MPI primitive type, 1 if derived
  *
  * Programmer:	Quincey Koziol, October 29, 2002
@@ -198,45 +164,22 @@ done:
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5S_mpio_none_type( const H5S_t *space, size_t UNUSED elmt_size, hbool_t prefer_derived_types,
+H5S_mpio_none_type( const H5S_t UNUSED *space, size_t UNUSED elmt_size,
 		     /* out: */
 		     MPI_Datatype *new_type,
 		     size_t *count,
 		     hsize_t *extra_offset,
-		     hbool_t *use_view,
 		     hbool_t *is_derived_type )
 {
-    int         mpi_code;               /* MPI return code */
-    herr_t      ret_value=SUCCEED;      /* Return value */
-
     FUNC_ENTER_NOINIT(H5S_mpio_none_type);
 
-    /* Check args */
-    assert(space);
-
-    /* Check if we should prefer creating a derived type */
-    if(prefer_derived_types) {
-        /* fill in the return values */
-        if (MPI_SUCCESS != (mpi_code=MPI_Type_contiguous(0, MPI_BYTE, new_type )))
-            HMPI_GOTO_ERROR(FAIL, "MPI_Type_contiguous failed", mpi_code);
-        if(MPI_SUCCESS != (mpi_code=MPI_Type_commit(new_type)))
-            HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code);
-        *count = 1;
-        *extra_offset = 0;
-        *use_view = 1;
-        *is_derived_type = 1;
-    } /* end if */
-    else {
-        /* fill in the return values */
-        *new_type = MPI_BYTE;
-        *count = 0;
-        *extra_offset = 0;
-        *use_view = 0;
-        *is_derived_type = 0;
-    } /* end else */
+    /* fill in the return values */
+    *new_type = MPI_BYTE;
+    *count = 0;
+    *extra_offset = 0;
+    *is_derived_type = 0;
 
-done:
-    FUNC_LEAVE_NOAPI(ret_value);
+    FUNC_LEAVE_NOAPI(SUCCEED);
 } /* H5S_mpio_none_type() */
 
 
@@ -251,7 +194,6 @@ done:
  *		*count		  how many objects of the new_type in selection
  *				  (useful if this is the buffer type for xfer)
  *		*extra_offset     Number of bytes of offset within dataset
- *		*use_view         0 if view not needed, 1 if needed
  *		*is_derived_type  0 if MPI primitive type, 1 if derived
  *
  * Programmer:	rky 980813
@@ -264,22 +206,17 @@ done:
  *		    H5S_MAX_RANK.
  *
  *      Quincey Koziol, June 18, 2002
- *      Added 'extra_offset' and 'use_view' parameters.  Also accomodate
+ *      Added 'extra_offset' parameter.  Also accomodate
  *      selection offset in MPI type built.
  *
- *      Quincey Koziol, June 19, 2002
- *      Added 'prefer_derived_types' flag to choose whether MPI derived types
- *      should be created or not.  (Ignored for this routine)
- *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5S_mpio_hyper_type( const H5S_t *space, size_t elmt_size, hbool_t UNUSED prefer_derived_types,
+H5S_mpio_hyper_type( const H5S_t *space, size_t elmt_size,
 		     /* out: */
 		     MPI_Datatype *new_type,
 		     size_t *count,
 		     hsize_t *extra_offset,
-		     hbool_t *use_view,
 		     hbool_t *is_derived_type )
 {
     struct dim {	/* less hassle than malloc/free & ilk */
@@ -560,7 +497,6 @@ H5S_mpio_hyper_type( const H5S_t *space, size_t elmt_size, hbool_t UNUSED prefer
     /* fill in the remaining return values */
     *count = 1;			/* only have to move one of these suckers! */
     *extra_offset = 0;
-    *use_view = 1;
     *is_derived_type = 1;
     HGOTO_DONE(SUCCEED);
 
@@ -569,7 +505,6 @@ empty:
     *new_type = MPI_BYTE;
     *count = 0;
     *extra_offset = 0;
-    *use_view = 1;      /* Note that this 'use_view' could go either way, but go with '1' for now */
     *is_derived_type = 0;
 
 done:
@@ -592,26 +527,20 @@ done:
  *		*count		  how many objects of the new_type in selection
  *				  (useful if this is the buffer type for xfer)
  *		*extra_offset     Number of bytes of offset within dataset
- *		*use_view         0 if view not needed, 1 if needed
  *		*is_derived_type  0 if MPI primitive type, 1 if derived
  *
  * Programmer:	Quincey Koziol, 2002/06/17
  *
  * Modifications:
  *
- *      Quincey Koziol, June 19, 2002
- *      Added 'prefer_derived_types' flag to choose whether MPI derived types
- *      should be created or not.
- *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5S_mpio_hyper_contig_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derived_types,
+H5S_mpio_hyper_contig_type( const H5S_t *space, size_t elmt_size,
 		     /* out: */
 		     MPI_Datatype *new_type,
 		     size_t *count,
 		     hsize_t *extra_offset,
-		     hbool_t *use_view,
 		     hbool_t *is_derived_type )
 {
     hsize_t	total_bytes;    /* Number of bytes in selection */
@@ -622,8 +551,6 @@ H5S_mpio_hyper_contig_type( const H5S_t *space, size_t elmt_size, hbool_t prefer
     hssize_t    offset[H5O_LAYOUT_NDIMS];       /* Offset in selection */
     int   	ndims;          /* Number of dimensions of dataset */
     int         i;              /* Local index */
-    int         mpi_code;               /* MPI return code */
-    herr_t      ret_value=SUCCEED;       /* Return value */
 
     FUNC_ENTER_NOINIT(H5S_mpio_hyper_contig_type);
 
@@ -636,7 +563,7 @@ H5S_mpio_hyper_contig_type( const H5S_t *space, size_t elmt_size, hbool_t prefer
     /* Compute the number of bytes in selection */
     total_bytes = (hsize_t)elmt_size*nelem;
 
-    /* Set up convenient aliased */
+    /* Set up convenient alias */
     ndims=space->extent.u.simple.rank;
 
     /* Initialize row sizes for each dimension */
@@ -654,33 +581,13 @@ H5S_mpio_hyper_contig_type( const H5S_t *space, size_t elmt_size, hbool_t prefer
     for(i=0,byte_offset=0; i<ndims; i++)
         byte_offset+=offset[i]*slab[i];
 
-    /* Check if we should prefer creating a derived type */
-    if(prefer_derived_types) {
-        /* fill in the return values */
-        H5_CHECK_OVERFLOW(total_bytes, hsize_t, int);
-        if (MPI_SUCCESS != (mpi_code=MPI_Type_contiguous( (int)total_bytes, MPI_BYTE, new_type )))
-            HMPI_GOTO_ERROR(FAIL, "MPI_Type_contiguous failed", mpi_code);
-        if(MPI_SUCCESS != (mpi_code=MPI_Type_commit(new_type)))
-            HMPI_GOTO_ERROR(FAIL, "MPI_Type_commit failed", mpi_code);
-        *count = 1;
-        *extra_offset = byte_offset;
-        *use_view = 1;
-        *is_derived_type = 1;
-    } /* end if */
-    else {
-        /* fill in the return values */
-        *new_type = MPI_BYTE;
-        H5_ASSIGN_OVERFLOW(*count, total_bytes, hsize_t, size_t);
-        *extra_offset = byte_offset;
-        *use_view = 0;
-        *is_derived_type = 0;
-    } /* end else */
+    /* fill in the return values */
+    *new_type = MPI_BYTE;
+    H5_ASSIGN_OVERFLOW(*count, total_bytes, hsize_t, size_t);
+    *extra_offset = byte_offset;
+    *is_derived_type = 0;
 
-done:
-#ifdef H5Smpi_DEBUG
-    HDfprintf(stdout, "Leave %s total_bytes=%Hu\n", FUNC, total_bytes );
-#endif
-    FUNC_LEAVE_NOAPI(ret_value);
+    FUNC_LEAVE_NOAPI(SUCCEED);
 } /* end H5S_mpio_hyper_contig_type() */
 
 
@@ -696,7 +603,6 @@ done:
  *		*count		  how many objects of the new_type in selection
  *				  (useful if this is the buffer type for xfer)
  *		*extra_offset     Number of bytes of offset within dataset
- *		*use_view         0 if view not needed, 1 if needed
  *		*is_derived_type  0 if MPI primitive type, 1 if derived
  *
  * Programmer:	rky 980813
@@ -704,24 +610,18 @@ done:
  * Modifications:
  *
  *      Quincey Koziol, June 18, 2002
- *      Added 'extra_offset' and 'use_view' parameters
- *
- *      Quincey Koziol, June 19, 2002
- *      Added 'prefer_derived_types' flag to choose whether MPI derived types
- *      should be created or not.
+ *      Added 'extra_offset' parameter
  *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5S_mpio_space_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derived_types,
+H5S_mpio_space_type( const H5S_t *space, size_t elmt_size,
 		     /* out: */
 		     MPI_Datatype *new_type,
 		     size_t *count,
 		     hsize_t *extra_offset,
-		     hbool_t *use_view,
 		     hbool_t *is_derived_type )
 {
-    int		err;
     herr_t	ret_value = SUCCEED;
 
     FUNC_ENTER_NOINIT(H5S_mpio_space_type);
@@ -735,14 +635,14 @@ H5S_mpio_space_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derive
         case H5S_SIMPLE:
             switch(space->select.type) {
                 case H5S_SEL_NONE:
-                    if ( H5S_mpio_none_type( space, elmt_size, prefer_derived_types,
-                        /* out: */ new_type, count, extra_offset, use_view, is_derived_type ) <0)
+                    if ( H5S_mpio_none_type( space, elmt_size,
+                        /* out: */ new_type, count, extra_offset, is_derived_type ) <0)
                         HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't convert \"all\" selection to MPI type");
                     break;
 
                 case H5S_SEL_ALL:
-                    if ( H5S_mpio_all_type( space, elmt_size, prefer_derived_types,
-                        /* out: */ new_type, count, extra_offset, use_view, is_derived_type ) <0)
+                    if ( H5S_mpio_all_type( space, elmt_size,
+                        /* out: */ new_type, count, extra_offset, is_derived_type ) <0)
                         HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't convert \"all\" selection to MPI type");
                     break;
 
@@ -753,15 +653,15 @@ H5S_mpio_space_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derive
 
                 case H5S_SEL_HYPERSLABS:
                     if((*space->select.is_contiguous)(space)) {
-                        err = H5S_mpio_hyper_contig_type( space, elmt_size, prefer_derived_types,
-                            /* out: */ new_type, count, extra_offset, use_view, is_derived_type );
+                        if(H5S_mpio_hyper_contig_type( space, elmt_size,
+                                /* out: */ new_type, count, extra_offset, is_derived_type )<0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't convert \"all\" selection to MPI type");
                     } /* end if */
                     else {
-                        err = H5S_mpio_hyper_type( space, elmt_size, prefer_derived_types,
-                            /* out: */ new_type, count, extra_offset, use_view, is_derived_type );
+                        if(H5S_mpio_hyper_type( space, elmt_size,
+                                /* out: */ new_type, count, extra_offset, is_derived_type )<0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't convert \"all\" selection to MPI type");
                     } /* end else */
-                    if (err<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't convert \"all\" selection to MPI type");
                     break;
 
                 default:
@@ -772,7 +672,7 @@ H5S_mpio_space_type( const H5S_t *space, size_t elmt_size, hbool_t prefer_derive
 
         case H5S_COMPLEX:
             /* not yet implemented */
-            ret_value = FAIL;
+            HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "complex data spaces are not supported yet");
             break;
 
         default:
@@ -824,12 +724,7 @@ done:
  *
  *      QAK - 2002/06/18
  *      Removed 'dc_plist' parameter, since it was not used.  Also, switch to
- *      getting the 'use_view' and 'extra_offset' settings for each selection.
- *
- *      Quincey Koziol, June 19, 2002
- *      Use 'prefer_derived_types' flag (from HDF5_MPI_PREFER_DERIVED_TYPES
- *      environment variable) to choose whether MPI derived types should be
- *      preferred or not.
+ *      getting the 'extra_offset' setting for each selection.
  *
  *-------------------------------------------------------------------------
  */
@@ -843,12 +738,9 @@ H5S_mpio_spaces_xfer(H5F_t *f, const H5O_layout_t *layout, size_t elmt_size,
     size_t	 mpi_buf_count, mpi_file_count;       /* Number of "objects" to transfer */
     hsize_t	 mpi_buf_offset, mpi_file_offset;       /* Offset within dataset where selection (ie. MPI type) begins */
     MPI_Datatype mpi_buf_type, mpi_file_type;   /* MPI types for buffer (memory) and file */
-    hbool_t	 mbt_use_view=0,        /* Whether we need to use a view for the buffer (memory) type */
-		 mft_use_view=0;        /* Whether we need to use a view for the file type */
     hbool_t	 mbt_is_derived=0,      /* Whether the buffer (memory) type is derived and needs to be free'd */
 		 mft_is_derived=0;      /* Whether the file type is derived and needs to be free'd */
     hbool_t	 plist_is_setup=0;      /* Whether the dxpl has been customized */
-    hbool_t	 prefer_derived_types=0;/* Whether to prefer MPI derived types or not */
     uint8_t	*buf=(uint8_t *)_buf;   /* Alias for pointer arithmetic */
     int         mpi_code;               /* MPI return code */
     herr_t	 ret_value = SUCCEED;   /* Return value */
@@ -865,27 +757,21 @@ H5S_mpio_spaces_xfer(H5F_t *f, const H5O_layout_t *layout, size_t elmt_size,
     /* Make certain we have the correct type of property list */
     assert(TRUE==H5P_isa_class(dxpl_id,H5P_DATASET_XFER));
 
-    /* Get the preference for MPI derived types */
-    /* (Set via the "HDF5_MPI_PREFER_DERIVED_TYPES" environment variable for now) */
-    prefer_derived_types= H5S_mpi_prefer_derived_types_g;
-
     /* create the MPI buffer type */
-    if (H5S_mpio_space_type( mem_space, elmt_size, prefer_derived_types,
+    if (H5S_mpio_space_type( mem_space, elmt_size,
 			       /* out: */
 			       &mpi_buf_type,
 			       &mpi_buf_count,
 			       &mpi_buf_offset,
-			       &mbt_use_view,
 			       &mbt_is_derived )<0)
     	HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't create MPI buf type");
 
     /* create the MPI file type */
-    if ( H5S_mpio_space_type( file_space, elmt_size, prefer_derived_types,
+    if ( H5S_mpio_space_type( file_space, elmt_size,
 			       /* out: */
 			       &mpi_file_type,
 			       &mpi_file_count,
 			       &mpi_file_offset,
-			       &mft_use_view,
 			       &mft_is_derived )<0)
     	HGOTO_ERROR(H5E_DATASPACE, H5E_BADTYPE, FAIL,"couldn't create MPI file type");
 
@@ -902,7 +788,7 @@ H5S_mpio_spaces_xfer(H5F_t *f, const H5O_layout_t *layout, size_t elmt_size,
      * Pass buf type, file type to the file driver. Request an MPI type
      * transfer (instead of an elementary byteblock transfer).
      */
-    if(H5FD_mpio_setup(dxpl_id, mpi_buf_type, mpi_file_type, (unsigned)(mbt_use_view || mft_use_view))<0)
+    if(H5FD_mpio_setup(dxpl_id, mpi_buf_type, mpi_file_type)<0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set MPI-I/O properties");
     plist_is_setup=1;
 
diff --git a/src/H5Sprivate.h b/src/H5Sprivate.h
index b8400eb..1a924d3 100644
--- a/src/H5Sprivate.h
+++ b/src/H5Sprivate.h
@@ -255,7 +255,6 @@ H5_DLL herr_t H5S_select_iter_release(H5S_sel_iter_t *sel_iter);
 /* Global vars whose value comes from environment variable */
 /* (Defined in H5S.c) */
 H5_DLLVAR hbool_t		H5S_mpi_opt_types_g;
-H5_DLLVAR hbool_t		H5S_mpi_prefer_derived_types_g;
 #endif /* _H5S_IN_H5S_C */
 #endif /* H5_HAVE_PARALLEL */