Merge remote-tracking branch 'upstream/develop' into develop

16 files changed, 369 insertions, 226 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 40b64f5..ff7402b 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -943,6 +943,21 @@ if (BUILD_SHARED_LIBS)
   file (MAKE_DIRECTORY "${HDF5_BINARY_DIR}/shared")
 endif ()
 
+if (LOCAL_BATCH_TEST)
+  if (LOCAL_BATCH_SCRIPT_NAME)
+    configure_file (
+        ${HDF5_SOURCE_DIR}/bin/batch/${LOCAL_BATCH_SCRIPT_NAME}.in.cmake
+        ${HDF5_BINARY_DIR}/${LOCAL_BATCH_SCRIPT_NAME} ESCAPE_QUOTES @ONLY
+    )
+  endif ()
+  if (LOCAL_BATCH_SCRIPT_PARALLEL_NAME)
+    configure_file (
+        ${HDF5_SOURCE_DIR}/bin/batch/${LOCAL_BATCH_SCRIPT_PARALLEL_NAME}.in.cmake
+        ${HDF5_BINARY_DIR}/${LOCAL_BATCH_SCRIPT_PARALLEL_NAME} ESCAPE_QUOTES @ONLY
+    )
+  endif ()
+endif ()
+
 if (NOT EXISTS ${HDF5_GENERATED_SOURCE_DIR}/H5Tinit.c)
   add_executable (H5detect ${HDF5_SRC_DIR}/H5detect.c)
   target_include_directories(H5detect PRIVATE "${HDF5_SRC_DIR};${HDF5_BINARY_DIR};$<$<BOOL:${HDF5_ENABLE_PARALLEL}>:${MPI_C_INCLUDE_DIRS}>")
diff --git a/src/H5CX.c b/src/H5CX.c
index ec18e14..0d20132 100644
--- a/src/H5CX.c
+++ b/src/H5CX.c
@@ -198,7 +198,7 @@ typedef struct H5CX_t {
     MPI_Datatype btype;         /* MPI datatype for buffer, when using collective I/O */
     MPI_Datatype ftype;         /* MPI datatype for file, when using collective I/O */
     hbool_t mpi_file_flushing;  /* Whether an MPI-opened file is being flushed */
-    hbool_t mpio_Proc0_BCast;   /* Whether a dataset meets read-proc0-and-bcast requirements */
+    hbool_t rank0_bcast;        /* Whether a dataset meets read-with-rank0-and-bcast requirements */
 #endif /* H5_HAVE_PARALLEL */
 
     /* Cached DXPL properties */
@@ -262,6 +262,8 @@ typedef struct H5CX_t {
     hbool_t mpio_coll_chunk_multi_ratio_coll_set; /* Whether instrumented "collective chunk multi ratio coll" value is set */
     int mpio_coll_chunk_multi_ratio_ind;  /* Instrumented "collective chunk multi ratio ind" value (H5D_XFER_COLL_CHUNK_MULTI_RATIO_IND_NAME) */
     hbool_t mpio_coll_chunk_multi_ratio_ind_set; /* Whether instrumented "collective chunk multi ratio ind" value is set */
+    hbool_t mpio_coll_rank0_bcast;  /* Instrumented "collective chunk multi ratio ind" value (H5D_XFER_COLL_CHUNK_MULTI_RATIO_IND_NAME) */
+    hbool_t mpio_coll_rank0_bcast_set; /* Whether instrumented "collective chunk multi ratio ind" value is set */
 #endif /* H5_HAVE_INSTRUMENTED_LIBRARY */
 #endif /* H5_HAVE_PARALLEL */
 
@@ -1255,6 +1257,32 @@ H5CX_get_mpi_file_flushing(void)
 
     FUNC_LEAVE_NOAPI((*head)->ctx.mpi_file_flushing)
 } /* end H5CX_get_mpi_file_flushing() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5CX_get_mpio_rank0_bcast 
+ *
+ * Purpose:     Retrieves if the dataset meets read-with-rank0-and-bcast requirements for the current API call context.
+ *
+ * Return:      Non-negative on success / Negative on failure
+ *
+ * Programmer:  M. Breitenfeld
+ *              December 31, 2018
+ *
+ *-------------------------------------------------------------------------
+ */
+hbool_t
+H5CX_get_mpio_rank0_bcast(void)
+{
+    H5CX_node_t **head = H5CX_get_my_context();  /* Get the pointer to the head of the API context, for this thread */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOERR
+
+    /* Sanity check */
+    HDassert(head && *head);
+
+    FUNC_LEAVE_NOAPI((*head)->ctx.rank0_bcast)
+} /* end H5CX_get_mpio_rank0_bcast() */
 #endif /* H5_HAVE_PARALLEL */
 
 
@@ -1610,33 +1638,6 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function:    H5CX_get_mpio_Proc0_BCast 
- *
- * Purpose:     Retrieves if the dataset meets read-proc0-and-bcast requirements for the current API call context.
- *
- * Return:      Non-negative on success / Negative on failure
- *
- * Programmer:  M. Breitenfeld
- *              December 31, 2018
- *
- *-------------------------------------------------------------------------
- */
-hbool_t
-H5CX_get_mpio_Proc0_BCast(void)
-{
-    H5CX_node_t **head = H5CX_get_my_context();  /* Get the pointer to the head of the API context, for this thread */
-
-    FUNC_ENTER_NOAPI_NOINIT_NOERR
-
-    /* Sanity check */
-    HDassert(head && *head);
-
-    FUNC_LEAVE_NOAPI((*head)->ctx.mpio_Proc0_BCast)
-
-} /* end H5CX_get_mpio_Proc0_BCast() */
-
-
-/*-------------------------------------------------------------------------
  * Function:    H5CX_get_mpio_chunk_opt_mode
  *
  * Purpose:     Retrieves the collective chunk optimization mode for the current API call context.
@@ -2213,6 +2214,34 @@ H5CX_set_mpi_file_flushing(hbool_t flushing)
 
     FUNC_LEAVE_NOAPI_VOID
 } /* end H5CX_set_mpi_file_flushing() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5CX_set_mpio_rank0_bcast
+ *
+ * Purpose:     Sets the "dataset meets read-with-rank0-and-bcast requirements" flag for the current API call context.
+ *
+ * Return:      <none>
+ *
+ * Programmer:  M. Breitenfeld
+ *              December 31, 2018
+ *
+ *-------------------------------------------------------------------------
+ */
+void
+H5CX_set_mpio_rank0_bcast(hbool_t rank0_bcast)
+{
+    H5CX_node_t **head = H5CX_get_my_context();  /* Get the pointer to the head of the API context, for this thread */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOERR
+
+    /* Sanity checks */
+    HDassert(head && *head);
+
+    (*head)->ctx.rank0_bcast = rank0_bcast;
+
+    FUNC_LEAVE_NOAPI_VOID
+} /* end H5CX_set_mpio_rank0_bcast() */
 #endif /* H5_HAVE_PARALLEL */
 
 
@@ -2420,34 +2449,6 @@ H5CX_set_mpio_global_no_coll_cause(uint32_t mpio_global_no_coll_cause)
     FUNC_LEAVE_NOAPI_VOID
 } /* end H5CX_set_mpio_global_no_coll_cause() */
 
-
-/*-------------------------------------------------------------------------
- * Function:    H5CX_set_mpio_Proc0_BCast
- *
- * Purpose:     Sets if the dataset meets read-proc0-and-bcast requirements for the current API call context.
- *
- * Return:      <none>
- *
- * Programmer:  M. Breitenfeld
- *              December 31, 2018
- *
- *-------------------------------------------------------------------------
- */
-void
-H5CX_set_mpio_Proc0_BCast(hbool_t mpio_Proc0_BCast)
-{
-    H5CX_node_t **head = H5CX_get_my_context();  /* Get the pointer to the head of the API context, for this thread */
-
-    FUNC_ENTER_NOAPI_NOINIT_NOERR
-
-    /* Sanity checks */
-    HDassert(head && *head);
-
-    (*head)->ctx.mpio_Proc0_BCast = mpio_Proc0_BCast;
-
-    FUNC_LEAVE_NOAPI_VOID
-} /* end H5CX_set_mpio_Proc0_BCast */
-
 #ifdef H5_HAVE_INSTRUMENTED_LIBRARY
 
 /*-------------------------------------------------------------------------
@@ -2652,6 +2653,40 @@ H5CX_test_set_mpio_coll_chunk_multi_ratio_ind(int mpio_coll_chunk_multi_ratio_in
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5CX_test_set_mpio_coll_chunk_multi_ratio_ind() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5CX_test_set_mpio_coll_rank0_bcast
+ *
+ * Purpose:     Sets the instrumented "read-with-rank0-bcast" flag for the current API call context.
+ *
+ * Note:        Only sets value if property set in DXPL
+ *
+ * Return:      Non-negative on success / Negative on failure
+ *
+ * Programmer:  Quincey Koziol
+ *              January 2, 2019
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5CX_test_set_mpio_coll_rank0_bcast(hbool_t mpio_coll_rank0_bcast)
+{
+    H5CX_node_t **head = H5CX_get_my_context();  /* Get the pointer to the head of the API context, for this thread */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT
+
+    /* Sanity checks */
+    HDassert(head && *head);
+    HDassert(!((*head)->ctx.dxpl_id == H5P_DEFAULT || 
+            (*head)->ctx.dxpl_id == H5P_DATASET_XFER_DEFAULT));
+
+    H5CX_TEST_SET_PROP(H5D_XFER_COLL_RANK0_BCAST_NAME, mpio_coll_rank0_bcast)
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5CX_test_set_mpio_coll_rank0_bcast() */
 #endif /* H5_HAVE_INSTRUMENTED_LIBRARY */
 #endif /* H5_HAVE_PARALLEL */
 
@@ -2696,6 +2731,7 @@ H5CX__pop_common(void)
     H5CX_SET_PROP(H5D_XFER_COLL_CHUNK_LINK_NUM_FALSE_NAME, mpio_coll_chunk_link_num_false)
     H5CX_SET_PROP(H5D_XFER_COLL_CHUNK_MULTI_RATIO_COLL_NAME, mpio_coll_chunk_multi_ratio_coll)
     H5CX_SET_PROP(H5D_XFER_COLL_CHUNK_MULTI_RATIO_IND_NAME, mpio_coll_chunk_multi_ratio_ind)
+    H5CX_SET_PROP(H5D_XFER_COLL_RANK0_BCAST_NAME, mpio_coll_rank0_bcast)
 #endif /* H5_HAVE_INSTRUMENTED_LIBRARY */
 #endif /* H5_HAVE_PARALLEL */
 
diff --git a/src/H5CXprivate.h b/src/H5CXprivate.h
index 22c6ebe..46d25d0 100644
--- a/src/H5CXprivate.h
+++ b/src/H5CXprivate.h
@@ -77,7 +77,7 @@ H5_DLL H5AC_ring_t H5CX_get_ring(void);
 H5_DLL hbool_t H5CX_get_coll_metadata_read(void);
 H5_DLL herr_t H5CX_get_mpi_coll_datatypes(MPI_Datatype *btype, MPI_Datatype *ftype);
 H5_DLL hbool_t H5CX_get_mpi_file_flushing(void);
-H5_DLL hbool_t H5CX_get_mpio_Proc0_BCast(void);
+H5_DLL hbool_t H5CX_get_mpio_rank0_bcast(void);
 #endif /* H5_HAVE_PARALLEL */
 
 /* "Getter" routines for DXPL properties cached in API context */
@@ -113,6 +113,7 @@ H5_DLL void H5CX_set_coll_metadata_read(hbool_t cmdr);
 H5_DLL herr_t H5CX_set_mpi_coll_datatypes(MPI_Datatype btype, MPI_Datatype ftype);
 H5_DLL herr_t H5CX_set_mpio_coll_opt(H5FD_mpio_collective_opt_t mpio_coll_opt);
 H5_DLL void H5CX_set_mpi_file_flushing(hbool_t flushing);
+H5_DLL void H5CX_set_mpio_rank0_bcast(hbool_t rank0_bcast);
 #endif /* H5_HAVE_PARALLEL */
 
 /* "Setter" routines for DXPL properties cached in API context */
@@ -131,7 +132,6 @@ H5_DLL void H5CX_set_mpio_actual_chunk_opt(H5D_mpio_actual_chunk_opt_mode_t chun
 H5_DLL void H5CX_set_mpio_actual_io_mode(H5D_mpio_actual_io_mode_t actual_io_mode);
 H5_DLL void H5CX_set_mpio_local_no_coll_cause(uint32_t mpio_local_no_coll_cause);
 H5_DLL void H5CX_set_mpio_global_no_coll_cause(uint32_t mpio_global_no_coll_cause);
-H5_DLL void H5CX_set_mpio_Proc0_BCast(hbool_t mpio_Proc0_BCast);
 #ifdef H5_HAVE_INSTRUMENTED_LIBRARY
 H5_DLL herr_t H5CX_test_set_mpio_coll_chunk_link_hard(int mpio_coll_chunk_link_hard);
 H5_DLL herr_t H5CX_test_set_mpio_coll_chunk_multi_hard(int mpio_coll_chunk_multi_hard);
@@ -139,6 +139,7 @@ H5_DLL herr_t H5CX_test_set_mpio_coll_chunk_link_num_true(int mpio_coll_chunk_li
 H5_DLL herr_t H5CX_test_set_mpio_coll_chunk_link_num_false(int mpio_coll_chunk_link_num_false);
 H5_DLL herr_t H5CX_test_set_mpio_coll_chunk_multi_ratio_coll(int mpio_coll_chunk_multi_ratio_coll);
 H5_DLL herr_t H5CX_test_set_mpio_coll_chunk_multi_ratio_ind(int mpio_coll_chunk_multi_ratio_ind);
+H5_DLL herr_t H5CX_test_set_mpio_coll_rank0_bcast(hbool_t rank0_bcast);
 #endif /* H5_HAVE_INSTRUMENTED_LIBRARY */
 #endif /* H5_HAVE_PARALLEL */
 
diff --git a/src/H5Dio.c b/src/H5Dio.c
index fe85d23..6062dff 100644
--- a/src/H5Dio.c
+++ b/src/H5Dio.c
@@ -657,22 +657,12 @@ H5D__write(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
 
     /* Various MPI based checks */
 #ifdef H5_HAVE_PARALLEL
-    if H5F_HAS_FEATURE(dataset->oloc.file, H5FD_FEAT_HAS_MPI) {
-        /* If MPI based VFD is used, no VL datatype support yet. */
+    if(H5F_HAS_FEATURE(dataset->oloc.file, H5FD_FEAT_HAS_MPI)) {
+        /* If MPI based VFD is used, no VL or region reference datatype support yet. */
         /* This is because they use the global heap in the file and we don't */
         /* support parallel access of that yet */
-        if(H5T_detect_class(type_info.mem_type, H5T_VLEN, FALSE) > 0)
-            HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "Parallel IO does not support writing VL datatypes yet")
-
-        /* If MPI based VFD is used, no VL datatype support yet. */
-        /* This is because they use the global heap in the file and we don't */
-        /* support parallel access of that yet */
-        /* We should really use H5T_detect_class() here, but it will be difficult
-         * to detect the type of the reference if it is nested... -QAK
-         */
-        if(H5T_get_class(type_info.mem_type, TRUE) == H5T_REFERENCE &&
-                H5T_get_ref_type(type_info.mem_type) == H5R_DATASET_REGION)
-            HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "Parallel IO does not support writing region reference datatypes yet")
+        if(H5T_is_vl_storage(type_info.mem_type) > 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "Parallel IO does not support writing VL or region reference datatypes yet")
     } /* end if */
     else {
         H5FD_mpio_xfer_t io_xfer_mode;      /* MPI I/O transfer mode */
diff --git a/src/H5Dmpio.c b/src/H5Dmpio.c
index 8850c59..f5da33d 100644
--- a/src/H5Dmpio.c
+++ b/src/H5Dmpio.c
@@ -37,7 +37,6 @@
 #include "H5Eprivate.h"       /* Error handling    */
 #include "H5Fprivate.h"       /* File access       */
 #include "H5FDprivate.h"      /* File drivers      */
-#include "H5FDmpi.h"          /* MPI-based file drivers */
 #include "H5Iprivate.h"       /* IDs               */
 #include "H5MMprivate.h"      /* Memory management */
 #include "H5Oprivate.h"       /* Object headers    */
@@ -83,20 +82,26 @@
 /* Macros to represent the regularity of the selection for multiple chunk IO case. */
 #define H5D_CHUNK_SELECT_REG          1
 
-/* Macros for reasons to not enable read-proc-and-bcast. */
-#define H5D_MPIO_PROC0_BCAST 0x00
-#define H5D_MPIO_NOT_H5S_ALL 0x01
-#define H5D_MPIO_GREATER_THAN_2GB 0x02
 
 /******************/
 /* Local Typedefs */
 /******************/
 /* Combine chunk address and chunk info into a struct for better performance. */
 typedef struct H5D_chunk_addr_info_t {
-  haddr_t chunk_addr;
-  H5D_chunk_info_t chunk_info;
+    haddr_t chunk_addr;
+    H5D_chunk_info_t chunk_info;
 } H5D_chunk_addr_info_t;
 
+/* Rank 0 Bcast values */
+typedef enum H5D_mpio_no_rank0_bcast_cause_t {
+    H5D_MPIO_RANK0_BCAST = 0x00,
+    H5D_MPIO_RANK0_NOT_H5S_ALL = 0x01,
+    H5D_MPIO_RANK0_NOT_CONTIGUOUS = 0x02,
+    H5D_MPIO_RANK0_NOT_FIXED_SIZE = 0x04,
+    H5D_MPIO_RANK0_GREATER_THAN_2GB = 0x08
+} H5D_mpio_no_rank0_bcast_cause_t;
+
+
 /*
  * Information about a single chunk when performing collective filtered I/O. All
  * of the fields of one of these structs are initialized at the start of collective
@@ -285,11 +290,11 @@ H5D__mpio_opt_possible(const H5D_io_info_t *io_info, const H5S_t *file_space,
     const H5S_t *mem_space, const H5D_type_info_t *type_info)
 {
     H5FD_mpio_xfer_t io_xfer_mode;      /* MPI I/O transfer mode */
-    unsigned local_cause[2] = {0,H5D_MPIO_PROC0_BCAST};  /* [0] Local reason(s) for breaking collective mode */
-                                                         /* [1] Flag if dataset is both: H5S_ALL and small */
-    unsigned global_cause[2] = {0,H5D_MPIO_PROC0_BCAST}; /* Global reason(s) for breaking collective mode */
+    unsigned local_cause[2] = {0,0};    /* [0] Local reason(s) for breaking collective mode */
+                                        /* [1] Flag if dataset is both: H5S_ALL and small */
+    unsigned global_cause[2] = {0,0};   /* Global reason(s) for breaking collective mode */
+    htri_t is_vl_storage;               /* Whether the dataset's datatype is stored in a variable-length form */
     htri_t ret_value = SUCCEED;         /* Return value */
-    hbool_t H5FD_MPIO_Proc0_BCast;      /* Flag if dataset is both: H5S_ALL and < 2GB */
 
     FUNC_ENTER_PACKAGE
 
@@ -302,7 +307,8 @@ H5D__mpio_opt_possible(const H5D_io_info_t *io_info, const H5S_t *file_space,
 
     /* For independent I/O, get out quickly and don't try to form consensus */
     if(H5CX_get_io_xfer_mode(&io_xfer_mode) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't get MPI-I/O transfer mode")
+        /* Set error flag, but keep going */
+        local_cause[0] |= H5D_MPIO_ERROR_WHILE_CHECKING_COLLECTIVE_POSSIBLE;
     if(io_xfer_mode == H5FD_MPIO_INDEPENDENT)
         local_cause[0] |= H5D_MPIO_SET_INDEPENDENT;
 
@@ -346,34 +352,56 @@ H5D__mpio_opt_possible(const H5D_io_info_t *io_info, const H5S_t *file_space,
      * is less than 3. The functions needed (MPI_Mprobe and MPI_Imrecv) will
      * not be available.
      */
-    if (io_info->op_type == H5D_IO_OP_WRITE &&
-        io_info->dset->shared->layout.type == H5D_CHUNKED &&
-        io_info->dset->shared->dcpl_cache.pline.nused > 0)
+    if(io_info->op_type == H5D_IO_OP_WRITE &&
+            io_info->dset->shared->layout.type == H5D_CHUNKED &&
+            io_info->dset->shared->dcpl_cache.pline.nused > 0)
         local_cause[0] |= H5D_MPIO_PARALLEL_FILTERED_WRITES_DISABLED;
 #endif
 
-    H5FD_MPIO_Proc0_BCast = FALSE;
-    /* Check to see if all the processes are reading the same data */
-    if((H5S_GET_SELECT_TYPE(file_space) != H5S_SEL_ALL)) {
-      /* Flag to do a MPI_Bcast of the data from one proc instead of 
-       * having all the processes involved in the persistent I/O.
-       */
-      local_cause[1] |= H5D_MPIO_NOT_H5S_ALL; 
-    }
+    /* Check if we are able to do a MPI_Bcast of the data from one rank
+     * instead of having all the processes involved in the collective I/O call.
+     */
+
+    /* Check to see if the process is reading the entire dataset */
+    if(H5S_GET_SELECT_TYPE(file_space) != H5S_SEL_ALL)
+        local_cause[1] |= H5D_MPIO_RANK0_NOT_H5S_ALL; 
+    /* Only perform this optimization for contigous datasets, currently */
+    else if(H5D_CONTIGUOUS != io_info->dset->shared->layout.type)
+        /* Flag to do a MPI_Bcast of the data from one proc instead of 
+         * having all the processes involved in the collective I/O.
+         */
+        local_cause[1] |= H5D_MPIO_RANK0_NOT_CONTIGUOUS; 
+    else if((is_vl_storage = H5T_is_vl_storage(type_info->dset_type)) < 0)
+        local_cause[0] |= H5D_MPIO_ERROR_WHILE_CHECKING_COLLECTIVE_POSSIBLE;
+    else if(is_vl_storage)
+        local_cause[1] |= H5D_MPIO_RANK0_NOT_FIXED_SIZE;
     else {
+        size_t type_size;       /* Size of dataset's datatype */
 
-     /* If the size of the dataset is less than 2GB then do an MPI_Bcast
-      * of the data from one process instead of having all the processes 
-      * involved in the persistent I/O.
-      */
+        /* Retrieve the size of the dataset's datatype */
+        if(0 == (type_size = H5T_GET_SIZE(type_info->dset_type)))
+            local_cause[0] |= H5D_MPIO_ERROR_WHILE_CHECKING_COLLECTIVE_POSSIBLE;
+        else {
+            hssize_t snelmts;   /* [Signed] # of elements in dataset's dataspace */
+
+            /* Retrieve the size of the dataset's datatype */
+            if((snelmts = H5S_GET_EXTENT_NPOINTS(file_space)) < 0)
+                local_cause[0] |= H5D_MPIO_ERROR_WHILE_CHECKING_COLLECTIVE_POSSIBLE;
+            else {
+                hsize_t dset_size;
 
-      hsize_t dset_storage_size;
-      H5D__get_storage_size(io_info->dset, &dset_storage_size);
+                /* Determine dataset size */
+                dset_size = ((hsize_t)snelmts) * type_size;
 
-      if(dset_storage_size > ((hsize_t)(H5_2GB) - 1) ) {
-        local_cause[1] |= H5D_MPIO_GREATER_THAN_2GB;
-      }
-    }
+               /* If the size of the dataset is less than 2GB then do an MPI_Bcast
+                * of the data from one process instead of having all the processes 
+                * involved in the collective I/O.
+                */
+                if(dset_size > ((hsize_t)(2.0F * H5_GB) - 1))
+                    local_cause[1] |= H5D_MPIO_RANK0_GREATER_THAN_2GB;
+            } /* end else */
+        } /* end else */
+    } /* end else */
     
     /* Check for independent I/O */
     if(local_cause[0] & H5D_MPIO_SET_INDEPENDENT)
@@ -386,23 +414,23 @@ H5D__mpio_opt_possible(const H5D_io_info_t *io_info, const H5S_t *file_space,
          */
         if(MPI_SUCCESS != (mpi_code = MPI_Allreduce(&local_cause, &global_cause, 2, MPI_UNSIGNED, MPI_BOR, io_info->comm)))
             HMPI_GOTO_ERROR(FAIL, "MPI_Allreduce failed", mpi_code)
-
     } /* end else */
 
     /* Set the local & global values of no-collective-cause in the API context */
     H5CX_set_mpio_local_no_coll_cause(local_cause[0]);
     H5CX_set_mpio_global_no_coll_cause(global_cause[0]);
 
+    /* Set read-with-rank0-and-bcast flag if possible */
+    if(global_cause[0] == 0 && global_cause[1] == 0) {
+        H5CX_set_mpio_rank0_bcast(TRUE);
+#ifdef H5_HAVE_INSTRUMENTED_LIBRARY
+        H5CX_test_set_mpio_coll_rank0_bcast(TRUE);
+#endif /* H5_HAVE_INSTRUMENTED_LIBRARY */
+    } /* end if */
+
     /* Set the return value, based on the global cause */
     ret_value = global_cause[0] > 0 ? FALSE : TRUE;
 
-    /* read-proc0-and-bcast if collective and H5S_ALL */
-    if(global_cause[0] == 0 && global_cause[1] == H5D_MPIO_PROC0_BCAST)
-      H5FD_MPIO_Proc0_BCast = TRUE;
-
-    /* Set Flag if dataset is both: H5S_ALL and < 2GB in the API context */
-    H5CX_set_mpio_Proc0_BCast(H5FD_MPIO_Proc0_BCast);
-
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* H5D__mpio_opt_possible() */
diff --git a/src/H5Dprivate.h b/src/H5Dprivate.h
index aaa3db2..6fb7889 100644
--- a/src/H5Dprivate.h
+++ b/src/H5Dprivate.h
@@ -95,7 +95,13 @@
 /* Definitions for all collective chunk instrumentation properties */
 #define H5D_XFER_COLL_CHUNK_SIZE        sizeof(unsigned)
 #define H5D_XFER_COLL_CHUNK_DEF         1
-#define H5D_XFER_COLL_CHUNK_FIX         0
+
+/* General collective I/O instrumentation properties */
+#define H5D_XFER_COLL_RANK0_BCAST_NAME  "coll_rank0_bcast"
+
+/* Definitions for general collective I/O instrumentation properties */
+#define H5D_XFER_COLL_RANK0_BCAST_SIZE  sizeof(hbool_t)
+#define H5D_XFER_COLL_RANK0_BCAST_DEF   FALSE
 #endif /* H5_HAVE_INSTRUMENTED_LIBRARY */
 
 /* Default temporary buffer size */
diff --git a/src/H5FDmpio.c b/src/H5FDmpio.c
index 911a5b6..3ab90aa 100644
--- a/src/H5FDmpio.c
+++ b/src/H5FDmpio.c
@@ -1336,28 +1336,6 @@ static herr_t
 H5FD__mpio_read(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type,
     hid_t H5_ATTR_UNUSED dxpl_id, haddr_t addr, size_t size, void *buf/*out*/)
 {
-<<<<<<< HEAD
-    H5FD_mpio_t                 *file = (H5FD_mpio_t*)_file;
-    MPI_Offset                  mpi_off;
-    MPI_Status                  mpi_stat;       /* Status from I/O operation */
-    int                         mpi_code;       /* mpi return code */
-    MPI_Datatype                buf_type = MPI_BYTE;      /* MPI description of the selection in memory */
-    int                         size_i;         /* Integer copy of 'size' to read */
-#if MPI_VERSION >= 3
-    MPI_Count                   bytes_read = 0; /* Number of bytes read in */
-    MPI_Count                   type_size;      /* MPI datatype used for I/O's size */
-    MPI_Count                   io_size;        /* Actual number of bytes requested */
-    MPI_Count                   n;
-#else
-    int                         bytes_read = 0; /* Number of bytes read in */
-    int                         type_size;      /* MPI datatype used for I/O's size */
-    int                         io_size;        /* Actual number of bytes requested */
-    int                         n;
-#endif
-    hbool_t                     use_view_this_time = FALSE;
-    hbool_t                     Proc0_BCast_enabled = FALSE; /* If read-proc0-and-bcast option was used */
-    herr_t                      ret_value = SUCCEED;
-=======
     H5FD_mpio_t *file = (H5FD_mpio_t*)_file;
     MPI_Offset  mpi_off;
     MPI_Status  mpi_stat;       /* Status from I/O operation */
@@ -1376,19 +1354,14 @@ H5FD__mpio_read(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type,
     int         n;
 #endif
     hbool_t     use_view_this_time = FALSE;
+    hbool_t     rank0_bcast = FALSE; /* If read-with-rank0-and-bcast flag was used */
     herr_t      ret_value = SUCCEED;
->>>>>>> 7bf6d847ae36940f1b1147820356795c7764dbeb
 
     FUNC_ENTER_STATIC
 
 #ifdef H5FDmpio_DEBUG
-<<<<<<< HEAD
-    if (H5FD_mpio_Debug[(int)'t'])
-        fprintf(stdout, "Entering H5FD_mpio_read\n" );
-=======
     if(H5FD_mpio_Debug[(int)'t'])
         HDfprintf(stdout, "%s: Entering\n", FUNC);
->>>>>>> 7bf6d847ae36940f1b1147820356795c7764dbeb
 #endif
 
     /* Sanity checks */
@@ -1407,14 +1380,8 @@ H5FD__mpio_read(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type,
         HGOTO_ERROR(H5E_INTERNAL, H5E_BADRANGE, FAIL, "can't convert from size to size_i")
 
 #ifdef H5FDmpio_DEBUG
-<<<<<<< HEAD
-    if (H5FD_mpio_Debug[(int)'r'])
-        fprintf(stdout, "in H5FD_mpio_read  mpi_off=%ld  size_i=%d\n",
-                (long)mpi_off, size_i );
-=======
     if(H5FD_mpio_Debug[(int)'r'])
         HDfprintf(stdout, "%s: mpi_off = %ld  size_i = %d\n", FUNC, (long)mpi_off, size_i);
->>>>>>> 7bf6d847ae36940f1b1147820356795c7764dbeb
 #endif
 
     /* Only look for MPI views for raw data transfers */
@@ -1431,11 +1398,7 @@ H5FD__mpio_read(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type,
          * us to test that btype=ftype=MPI_BYTE (or even MPI_TYPE_NULL, which
          * could mean "use MPI_BYTE" by convention).
          */
-<<<<<<< HEAD
-        if(xfer_mode==H5FD_MPIO_COLLECTIVE) {
-=======
         if(xfer_mode == H5FD_MPIO_COLLECTIVE) {
->>>>>>> 7bf6d847ae36940f1b1147820356795c7764dbeb
             MPI_Datatype file_type;
 
             /* Remember that views are used */
@@ -1463,13 +1426,8 @@ H5FD__mpio_read(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type,
         H5FD_mpio_collective_opt_t coll_opt_mode;
 
 #ifdef H5FDmpio_DEBUG
-<<<<<<< HEAD
-        if (H5FD_mpio_Debug[(int)'t'])
-            fprintf(stdout, "H5FD_mpio_read: using MPIO collective mode\n");
-=======
         if(H5FD_mpio_Debug[(int)'r'])
             HDfprintf(stdout, "%s: using MPIO collective mode\n", FUNC);
->>>>>>> 7bf6d847ae36940f1b1147820356795c7764dbeb
 #endif
         /* Get the collective_opt property to check whether the application wants to do IO individually. */
         if(H5CX_get_mpio_coll_opt(&coll_opt_mode) < 0)
@@ -1480,23 +1438,25 @@ H5FD__mpio_read(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type,
             if(H5FD_mpio_Debug[(int)'r'])
                 HDfprintf(stdout, "%s: doing MPI collective IO\n", FUNC);
 #endif
-            if(H5CX_get_mpio_Proc0_BCast()) {
+            /* Check whether we should read from rank 0 and broadcast to other ranks */
+            if(H5CX_get_mpio_rank0_bcast()) {
 #ifdef H5FDmpio_DEBUG
-              if(H5FD_mpio_Debug[(int)'t'])
-                 fprintf(stdout, "H5FD_mpio_read: doing Proc0-read-and-MPI_Bcast\n");
+                if(H5FD_mpio_Debug[(int)'r'])
+                    HDfprintf(stdout, "%s: doing read-rank0-and-MPI_Bcast\n", FUNC);
 #endif
-              if(file->mpi_rank == 0) {
-                if(MPI_SUCCESS != (mpi_code = MPI_File_read_at(file->f, mpi_off, buf, size_i, buf_type, &mpi_stat)))
-                  HMPI_GOTO_ERROR(FAIL, "MPI_File_read_at failed", mpi_code)
-              }
-              if(MPI_SUCCESS != (mpi_code = MPI_Bcast(buf, size_i, buf_type, 0, file->comm)))
-                HMPI_GOTO_ERROR(FAIL, "MPI_Bcast failed", mpi_code)
-              Proc0_BCast_enabled = TRUE;
-            }
-            else {
-              if(MPI_SUCCESS != (mpi_code = MPI_File_read_at_all(file->f, mpi_off, buf, size_i, buf_type, &mpi_stat)))
-                HMPI_GOTO_ERROR(FAIL, "MPI_File_read_at_all failed", mpi_code)
-            }
+                /* Indicate path we've taken */
+                rank0_bcast = TRUE;
+
+                /* Read on rank 0 Bcast to other ranks */
+                if(file->mpi_rank == 0)
+                    if(MPI_SUCCESS != (mpi_code = MPI_File_read_at(file->f, mpi_off, buf, size_i, buf_type, &mpi_stat)))
+                        HMPI_GOTO_ERROR(FAIL, "MPI_File_read_at failed", mpi_code)
+                if(MPI_SUCCESS != (mpi_code = MPI_Bcast(buf, size_i, buf_type, 0, file->comm)))
+                    HMPI_GOTO_ERROR(FAIL, "MPI_Bcast failed", mpi_code)
+            } /* end if */
+            else
+                if(MPI_SUCCESS != (mpi_code = MPI_File_read_at_all(file->f, mpi_off, buf, size_i, buf_type, &mpi_stat)))
+                    HMPI_GOTO_ERROR(FAIL, "MPI_File_read_at_all failed", mpi_code)
         } /* end if */
         else {
 #ifdef H5FDmpio_DEBUG
@@ -1516,33 +1476,28 @@ H5FD__mpio_read(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type,
     } /* end if */
     else
         if(MPI_SUCCESS != (mpi_code = MPI_File_read_at(file->f, mpi_off, buf, size_i, buf_type, &mpi_stat)))
-<<<<<<< HEAD
-          HMPI_GOTO_ERROR(FAIL, "MPI_File_read_at failed", mpi_code)
-    }
-=======
             HMPI_GOTO_ERROR(FAIL, "MPI_File_read_at failed", mpi_code)
->>>>>>> 7bf6d847ae36940f1b1147820356795c7764dbeb
 
-    if( !Proc0_BCast_enabled || (Proc0_BCast_enabled && file->mpi_rank == 0) ) {
-      /* How many bytes were actually read? */
+    /* Only retrieve bytes read if this rank _actually_ participated in I/O */
+    if(!rank0_bcast || (rank0_bcast && file->mpi_rank == 0) ) {
+        /* How many bytes were actually read? */
 #if MPI_VERSION >= 3
-<<<<<<< HEAD
-      if(MPI_SUCCESS != (mpi_code = MPI_Get_elements_x(&mpi_stat, buf_type, &bytes_read)))
+        if(MPI_SUCCESS != (mpi_code = MPI_Get_elements_x(&mpi_stat, buf_type, &bytes_read)))
 #else
-      if(MPI_SUCCESS != (mpi_code = MPI_Get_elements(&mpi_stat, MPI_BYTE, &bytes_read)))
-=======
-    if(MPI_SUCCESS != (mpi_code = MPI_Get_elements_x(&mpi_stat, buf_type, &bytes_read)))
-#else
-    if(MPI_SUCCESS != (mpi_code = MPI_Get_elements(&mpi_stat, MPI_BYTE, &bytes_read)))
->>>>>>> 7bf6d847ae36940f1b1147820356795c7764dbeb
+        if(MPI_SUCCESS != (mpi_code = MPI_Get_elements(&mpi_stat, MPI_BYTE, &bytes_read)))
 #endif
-        HMPI_GOTO_ERROR(FAIL, "MPI_Get_elements failed", mpi_code)
-    }
+            HMPI_GOTO_ERROR(FAIL, "MPI_Get_elements failed", mpi_code)
+    } /* end if */
  
-    if(Proc0_BCast_enabled ) {
-      if(MPI_SUCCESS != MPI_Bcast(&bytes_read, 1, MPI_LONG_LONG, 0, file->comm))
-        HMPI_GOTO_ERROR(FAIL, "MPI_Bcast failed", 0)
-    }
+    /* If the rank0-bcast feature was used, broadcast the # of bytes read to
+     * other ranks, which didn't perform any I/O.
+     */
+    /* NOTE: This could be optimized further to be combined with the broadcast
+     *          of the data.  (QAK - 2019/1/2)
+     */
+    if(rank0_bcast)
+        if(MPI_SUCCESS != MPI_Bcast(&bytes_read, 1, MPI_LONG_LONG, 0, file->comm))
+            HMPI_GOTO_ERROR(FAIL, "MPI_Bcast failed", 0)
 
     /* Get the type's size */
 #if MPI_VERSION >= 3
@@ -1550,7 +1505,7 @@ H5FD__mpio_read(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type,
 #else
     if(MPI_SUCCESS != (mpi_code = MPI_Type_size(buf_type, &type_size)))
 #endif
-    HMPI_GOTO_ERROR(FAIL, "MPI_Type_size failed", mpi_code)
+        HMPI_GOTO_ERROR(FAIL, "MPI_Type_size failed", mpi_code)
 
     /* Compute the actual number of bytes requested */
     io_size = type_size * size_i;
@@ -1562,15 +1517,6 @@ H5FD__mpio_read(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type,
     /*
      * This gives us zeroes beyond end of physical MPI file.
      */
-<<<<<<< HEAD
-    if ((n=(io_size-bytes_read)) > 0)
-     HDmemset((char*)buf+bytes_read, 0, (size_t)n);
-
-done:
-#ifdef H5FDmpio_DEBUG
-    if (H5FD_mpio_Debug[(int)'t'])
-       fprintf(stdout, "Leaving H5FD_mpio_read\n" );
-=======
     if((n = (io_size - bytes_read)) > 0)
         HDmemset((char*)buf+bytes_read, 0, (size_t)n);
 
@@ -1578,7 +1524,6 @@ done:
 #ifdef H5FDmpio_DEBUG
     if(H5FD_mpio_Debug[(int)'t'])
        HDfprintf(stdout, "%s: Leaving\n", FUNC);
->>>>>>> 7bf6d847ae36940f1b1147820356795c7764dbeb
 #endif
 
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5Obogus.c b/src/H5Obogus.c
index fbf04f2..f3cca0f 100644
--- a/src/H5Obogus.c
+++ b/src/H5Obogus.c
@@ -49,7 +49,7 @@ const H5O_msg_class_t H5O_MSG_BOGUS_VALID[1] = {{
     H5O_BOGUS_VALID_ID,		/*message id number             */
     "bogus valid",             	/*message name for debugging    */
     0,     	                /*native message size           */
-    0,				/* messages are sharable?       */
+    H5O_SHARE_IS_SHARABLE,      /* messages are sharable?       */
     H5O__bogus_decode,        	/*decode message                */
     H5O_bogus_encode,        	/*encode message                */
     NULL,          	        /*copy the native value         */
@@ -73,7 +73,7 @@ const H5O_msg_class_t H5O_MSG_BOGUS_INVALID[1] = {{
     H5O_BOGUS_INVALID_ID, 	/*message id number             */
     "bogus invalid",          	/*message name for debugging    */
     0,                          /*native message size           */
-    0,                          /* messages are sharable?       */
+    H5O_SHARE_IS_SHARABLE,      /* messages are sharable?       */
     H5O__bogus_decode,          /*decode message                */
     H5O_bogus_encode,           /*encode message                */
     NULL,                       /*copy the native value         */
diff --git a/src/H5Ocache.c b/src/H5Ocache.c
index fba4f6e..23c38b9 100644
--- a/src/H5Ocache.c
+++ b/src/H5Ocache.c
@@ -1402,10 +1402,9 @@ H5O__chunk_deserialize(H5O_t *oh, haddr_t addr, size_t len, const uint8_t *image
             HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "bad flag combination for message")
         if((flags & H5O_MSG_FLAG_WAS_UNKNOWN) && !(flags & H5O_MSG_FLAG_MARK_IF_UNKNOWN))
             HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "bad flag combination for message")
-        if((flags & H5O_MSG_FLAG_SHAREABLE)
-                && H5O_msg_class_g[id]
-                && !(H5O_msg_class_g[id]->share_flags & H5O_SHARE_IS_SHARABLE))
-            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "message of unsharable class flagged as sharable")
+        /* Delay checking the "shareable" flag until we've made sure id
+         * references a valid message class that this version of the library
+         * knows about */
 
         /* Reserved bytes/creation index */
         if(oh->version == H5O_VERSION_1)
@@ -1517,9 +1516,17 @@ H5O__chunk_deserialize(H5O_t *oh, haddr_t addr, size_t len, const uint8_t *image
                     mesgs_modified = TRUE;
                 } /* end if */
             } /* end if */
-            else
+            else {
+                /* Check for message of unshareable class marked as "shareable"
+                 */
+                if((flags & H5O_MSG_FLAG_SHAREABLE)
+                        && H5O_msg_class_g[id]
+                        && !(H5O_msg_class_g[id]->share_flags & H5O_SHARE_IS_SHARABLE))
+                    HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "message of unshareable class flagged as shareable")
+
                 /* Set message class for "known" messages */
                 mesg->type = H5O_msg_class_g[id];
+            } /* end else */
 
             /* Do some inspection/interpretation of new messages from this chunk */
             /* (detect continuation messages, ref. count messages, etc.) */
diff --git a/src/H5Omessage.c b/src/H5Omessage.c
index d6e3dce..18f3706 100644
--- a/src/H5Omessage.c
+++ b/src/H5Omessage.c
@@ -1598,16 +1598,23 @@ H5O_msg_is_shared(unsigned type_id, const void *mesg)
     FUNC_ENTER_NOAPI_NOINIT_NOERR
 
     /* Check args */
-    HDassert(type_id < NELMTS(H5O_msg_class_g));
-    type = H5O_msg_class_g[type_id];    /* map the type ID to the actual type object */
-    HDassert(type);
-    HDassert(mesg);
-
-    /* If messages in a class aren't sharable, then obviously this message isn't shared! :-) */
-    if(type->share_flags & H5O_SHARE_IS_SHARABLE)
-        ret_value = H5O_IS_STORED_SHARED(((const H5O_shared_t *)mesg)->type);
-    else
+#ifdef H5O_ENABLE_BOGUS
+    if(type_id >= NELMTS(H5O_msg_class_g))
         ret_value = FALSE;
+    else
+#endif /* H5O_ENABLE_BOGUS */
+    {
+        HDassert(type_id < NELMTS(H5O_msg_class_g));
+        type = H5O_msg_class_g[type_id];    /* map the type ID to the actual type object */
+        HDassert(type);
+        HDassert(mesg);
+
+        /* If messages in a class aren't sharable, then obviously this message isn't shared! :-) */
+        if(type->share_flags & H5O_SHARE_IS_SHARABLE)
+            ret_value = H5O_IS_STORED_SHARED(((const H5O_shared_t *)mesg)->type);
+        else
+            ret_value = FALSE;
+    } /* end block/else */
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5O_msg_is_shared() */
diff --git a/src/H5Opkg.h b/src/H5Opkg.h
index dbc8089..668f4f0 100644
--- a/src/H5Opkg.h
+++ b/src/H5Opkg.h
@@ -29,7 +29,7 @@
 #define H5O_NMESGS	8 		/*initial number of messages	     */
 #define H5O_NCHUNKS	2		/*initial number of chunks	     */
 #define H5O_MIN_SIZE	22		/* Min. obj header data size (must be big enough for a message prefix and a continuation message) */
-#define H5O_MSG_TYPES   27              /* # of types of messages            */
+#define H5O_MSG_TYPES   26              /* # of types of messages            */
 #define H5O_MAX_CRT_ORDER_IDX 65535     /* Max. creation order index value   */
 
 /* Versions of object header structure */
diff --git a/src/H5Oprivate.h b/src/H5Oprivate.h
index e0926e2..5987ecf 100644
--- a/src/H5Oprivate.h
+++ b/src/H5Oprivate.h
@@ -227,11 +227,11 @@ typedef struct H5O_copy_t {
  * Note: Must increment H5O_MSG_TYPES in H5Opkg.h and update H5O_msg_class_g
  *      in H5O.c when creating a new message type.  Also bump the value of
  *      H5O_BOGUS_INVALID_ID, below, to be one greater than the value of
- *      H5O_UNKNOWN_ID.
+ *      H5O_UNKNOWN_ID, and re-run gen_bogus.c.
  *
  * (this should never exist in a file)
  */
-#define H5O_BOGUS_INVALID_ID	0x001A  /* "Bogus invalid" Message.  */
+#define H5O_BOGUS_INVALID_ID	0x001a  /* "Bogus invalid" Message.  */
 
 /* Shared object message types.
  * Shared objects can be committed, in which case the shared message contains
@@ -651,6 +651,7 @@ typedef struct H5O_layout_t {
  */
 #define H5O_BOGUS_VALUE         0xdeadbeef
 typedef struct H5O_bogus_t {
+    H5O_shared_t        sh_loc;         /* Shared message info (must be first) */
     unsigned u;                         /* Hold the bogus info */
 } H5O_bogus_t;
 #endif /* H5O_ENABLE_BOGUS */
diff --git a/src/H5Pdxpl.c b/src/H5Pdxpl.c
index bfc1d93..8338d84 100644
--- a/src/H5Pdxpl.c
+++ b/src/H5Pdxpl.c
@@ -2017,6 +2017,7 @@ done:
     FUNC_LEAVE_API(ret_value)
 } /* end H5Pget_mpio_actual_io_mode() */
 
+
 /*-------------------------------------------------------------------------
  * Function:	H5Pget_mpio_no_collective_cause
  *
@@ -2053,8 +2054,6 @@ H5Pget_mpio_no_collective_cause(hid_t plist_id, uint32_t *local_no_collective_ca
 done:
     FUNC_LEAVE_API(ret_value)
 } /* end H5Pget_mpio_no_collective_cause() */
-
-
 #endif /* H5_HAVE_PARALLEL */
 
 
diff --git a/src/H5Ppublic.h b/src/H5Ppublic.h
index 2f094ea..078fe74 100644
--- a/src/H5Ppublic.h
+++ b/src/H5Ppublic.h
@@ -167,7 +167,8 @@ typedef enum H5D_mpio_no_collective_cause_t {
     H5D_MPIO_NOT_SIMPLE_OR_SCALAR_DATASPACES = 0x10,
     H5D_MPIO_NOT_CONTIGUOUS_OR_CHUNKED_DATASET = 0x20,
     H5D_MPIO_PARALLEL_FILTERED_WRITES_DISABLED = 0x40,
-    H5D_MPIO_NO_COLLECTIVE_MAX_CAUSE = 0x80
+    H5D_MPIO_ERROR_WHILE_CHECKING_COLLECTIVE_POSSIBLE = 0x80,
+    H5D_MPIO_NO_COLLECTIVE_MAX_CAUSE = 0x100
 } H5D_mpio_no_collective_cause_t;
 
 /********************/
diff --git a/src/H5T.c b/src/H5T.c
index 01ace87..9544488 100644
--- a/src/H5T.c
+++ b/src/H5T.c
@@ -295,6 +295,7 @@ static htri_t H5T__compiler_conv(H5T_t *src, H5T_t *dst);
 static herr_t H5T__set_size(H5T_t *dt, size_t size);
 static herr_t H5T__close_cb(H5T_t *dt);
 static H5T_path_t *H5T__path_find_real(const H5T_t *src, const H5T_t *dst, const char *name, H5T_conv_func_t *conv);
+static hbool_t H5T__detect_reg_ref(const H5T_t *dt);
 
 
 /*****************************/
@@ -5506,6 +5507,111 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ * Function:   H5T_detect_reg_ref
+ *
+ * Purpose:    Check whether a datatype contains (or is) a region reference
+ *             datatype.
+ *
+ * Return:      TRUE (1) or FALSE (0) on success
+ *		(Can't fail)
+ *
+ * Programmer:  Quincey Koziol
+ *              Saturday, January 5, 2019
+ *
+ *-------------------------------------------------------------------------
+ */
+static hbool_t
+H5T__detect_reg_ref(const H5T_t *dt)
+{
+    unsigned    u;                      /* Local index variable */
+    hbool_t     ret_value = FALSE;      /* Return value */
+
+    FUNC_ENTER_STATIC_NOERR
+
+    /* Sanity checks */
+    HDassert(dt);
+
+    /* Check if this datatype is a region reference */
+    if(H5T_REFERENCE == dt->shared->type && H5R_DATASET_REGION == dt->shared->u.atomic.u.r.rtype)
+        HGOTO_DONE(TRUE);
+
+    /* Check for types that might have the correct type as a component */
+    switch(dt->shared->type) {
+        case H5T_COMPOUND:
+            /* Iterate over all the compound datatype's fields */
+            for(u = 0; u < dt->shared->u.compnd.nmembs; u++)
+                /* Recurse on field's datatype */
+                if(H5T__detect_reg_ref(dt->shared->u.compnd.memb[u].type))
+                    HGOTO_DONE(TRUE);
+            break;
+
+        case H5T_ARRAY:
+        case H5T_VLEN:
+        case H5T_ENUM:
+            HGOTO_DONE(H5T__detect_reg_ref(dt->shared->parent));
+            break;
+
+        case H5T_NO_CLASS:
+        case H5T_INTEGER:
+        case H5T_FLOAT:
+        case H5T_TIME:
+        case H5T_STRING:
+        case H5T_BITFIELD:
+        case H5T_OPAQUE:
+        case H5T_REFERENCE:
+        case H5T_NCLASSES:
+        default:
+            break;
+    } /* end if */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5T__detect_reg_ref() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5T_is_vl_storage
+ *
+ * Purpose:     Check if a datatype will be stored in a variable-length form.
+ *
+ * Notes:       Currently, only variable-length string & sequences and region
+ *              references are stored in a variable-length form.
+ *
+ * Return:
+ *  One of two values on success:
+ *      TRUE - If the datatype will be stored in a variable-length form
+ *      FALSE - If the datatype will NOT be stored in a variable-length form
+ *  <0 is returned on failure
+ *
+ * Programmer:  Quincey Koziol
+ *              Saturday, January 5, 2019
+ *
+ *-------------------------------------------------------------------------
+ */
+htri_t
+H5T_is_vl_storage(const H5T_t *dt)
+{
+    htri_t ret_value = FALSE;
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    /* Sanity check */
+    HDassert(dt);
+
+    /* VL and region reference datatypes are stored in variable-length form */
+    if(H5T_detect_class(dt, H5T_VLEN, FALSE))
+        ret_value = TRUE;
+    else if(H5T_detect_class(dt, H5T_REFERENCE, FALSE))
+        ret_value = H5T__detect_reg_ref(dt);
+    else
+        ret_value = FALSE;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5T_is_vl_storage() */
+
+
+/*-------------------------------------------------------------------------
  * Function:    H5T_upgrade_version_cb
  *
  * Purpose:     H5T__visit callback to Upgrade the version of a datatype
diff --git a/src/H5Tprivate.h b/src/H5Tprivate.h
index 6b6446f..3dcbb2c 100644
--- a/src/H5Tprivate.h
+++ b/src/H5Tprivate.h
@@ -145,6 +145,7 @@ H5_DLL H5T_t *H5T_get_actual_type(H5T_t *dt);
 H5_DLL herr_t H5T_save_refresh_state(hid_t tid, struct H5O_shared_t *cached_H5O_shared);
 H5_DLL herr_t H5T_restore_refresh_state(hid_t tid, struct H5O_shared_t *cached_H5O_shared);
 H5_DLL hbool_t H5T_already_vol_managed(const H5T_t *dt);
+H5_DLL htri_t H5T_is_vl_storage(const H5T_t *dt);
 
 /* Reference specific functions */
 H5_DLL H5R_type_t H5T_get_ref_type(const H5T_t *dt);