Merge pull request #2640 in HDFFV/hdf5 from hdf5_1_12_opt_single_selection_io to hdf5_1_12

* commit 'df31370d45d53f2e8ba10e74791a91e7efdb818f':
  Add info to release notes about improvement for single element I/O.
  Eliminate allocating file & memory offset & length arrays when performing I/O on a single element.

2 files changed, 39 insertions, 28 deletions

diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt
index 61f8ba8..69a1ce7 100644
--- a/release_docs/RELEASE.txt
+++ b/release_docs/RELEASE.txt
@@ -109,8 +109,14 @@ Bug Fixes since HDF5-1.12.0 release
 ==================================
     Library
     -------
+    - Streamline I/O to a single element, improving performance for record
+        appends to chunked datasets.
+
+      (QAK - 2020/06/11)
+
     - Remove redundant tagging of metadata cache entries for some chunked
-        dataset operations.
+        dataset operations, slightly improving performance for chunked
+        datasets.
 
       (QAK - 2020/06/10)
 
diff --git a/src/H5Dselect.c b/src/H5Dselect.c
index a843d93..c5469c2 100644
--- a/src/H5Dselect.c
+++ b/src/H5Dselect.c
@@ -113,51 +113,38 @@ H5D__select_io(const H5D_io_info_t *io_info, size_t elmt_size,
     HDassert(io_info->store);
     HDassert(io_info->u.rbuf);
 
-    /* Get info from API context */
-    if(H5CX_get_vec_size(&dxpl_vec_size) < 0)
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't retrieve I/O vector size")
-
-    /* Allocate the vector I/O arrays */
-    if(dxpl_vec_size > H5D_IO_VECTOR_SIZE)
-        vec_size = dxpl_vec_size;
-    else
-        vec_size = H5D_IO_VECTOR_SIZE;
-    if(NULL == (mem_len = H5FL_SEQ_MALLOC(size_t, vec_size)))
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "can't allocate I/O length vector array")
-    if(NULL == (mem_off = H5FL_SEQ_MALLOC(hsize_t, vec_size)))
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "can't allocate I/O offset vector array")
-    if(NULL == (file_len = H5FL_SEQ_MALLOC(size_t, vec_size)))
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "can't allocate I/O length vector array")
-    if(NULL == (file_off = H5FL_SEQ_MALLOC(hsize_t, vec_size)))
-        HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "can't allocate I/O offset vector array")
-
     /* Check for only one element in selection */
     if(nelmts == 1) {
+        hsize_t single_mem_off;     /* Offset in memory */
+        hsize_t single_file_off;    /* Offset in the file */
+        size_t single_mem_len;      /* Length in memory */
+        size_t single_file_len;     /* Length in the file */
+
         /* Get offset of first element in selections */
-        if(H5S_SELECT_OFFSET(file_space, file_off) < 0)
+        if(H5S_SELECT_OFFSET(file_space, &single_file_off) < 0)
             HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "can't retrieve file selection offset")
-        if(H5S_SELECT_OFFSET(mem_space, mem_off) < 0)
+        if(H5S_SELECT_OFFSET(mem_space, &single_mem_off) < 0)
             HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "can't retrieve memory selection offset")
 
         /* Set up necessary information for I/O operation */
         file_nseq = mem_nseq = 1;
         curr_mem_seq = curr_file_seq = 0;
-        *file_off *= elmt_size;
-        *mem_off *= elmt_size;
-        *file_len = *mem_len = elmt_size;
+        single_file_off *= elmt_size;
+        single_mem_off *= elmt_size;
+        single_file_len = single_mem_len = elmt_size;
 
         /* Perform I/O on memory and file sequences */
         if(io_info->op_type == H5D_IO_OP_READ) {
             if((tmp_file_len = (*io_info->layout_ops.readvv)(io_info,
-                    file_nseq, &curr_file_seq, file_len, file_off,
-                    mem_nseq, &curr_mem_seq, mem_len, mem_off)) < 0)
+                    file_nseq, &curr_file_seq, &single_file_len, &single_file_off,
+                    mem_nseq, &curr_mem_seq, &single_mem_len, &single_mem_off)) < 0)
                 HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, FAIL, "read error")
         } /* end if */
         else {
             HDassert(io_info->op_type == H5D_IO_OP_WRITE);
             if((tmp_file_len = (*io_info->layout_ops.writevv)(io_info,
-                    file_nseq, &curr_file_seq, file_len, file_off,
-                    mem_nseq, &curr_mem_seq, mem_len, mem_off)) < 0)
+                    file_nseq, &curr_file_seq, &single_file_len, &single_file_off,
+                    mem_nseq, &curr_mem_seq, &single_mem_len, &single_mem_off)) < 0)
                 HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error")
         } /* end else */
 
@@ -168,6 +155,24 @@ H5D__select_io(const H5D_io_info_t *io_info, size_t elmt_size,
         size_t mem_nelem;           /* Number of elements used in memory sequences */
         size_t file_nelem;          /* Number of elements used in file sequences */
 
+        /* Get info from API context */
+        if(H5CX_get_vec_size(&dxpl_vec_size) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't retrieve I/O vector size")
+
+        /* Allocate the vector I/O arrays */
+        if(dxpl_vec_size > H5D_IO_VECTOR_SIZE)
+            vec_size = dxpl_vec_size;
+        else
+            vec_size = H5D_IO_VECTOR_SIZE;
+        if(NULL == (mem_len = H5FL_SEQ_MALLOC(size_t, vec_size)))
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "can't allocate I/O length vector array")
+        if(NULL == (mem_off = H5FL_SEQ_MALLOC(hsize_t, vec_size)))
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "can't allocate I/O offset vector array")
+        if(NULL == (file_len = H5FL_SEQ_MALLOC(size_t, vec_size)))
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "can't allocate I/O length vector array")
+        if(NULL == (file_off = H5FL_SEQ_MALLOC(hsize_t, vec_size)))
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "can't allocate I/O offset vector array")
+
         /* Allocate the iterators */
         if(NULL == (mem_iter = H5FL_MALLOC(H5S_sel_iter_t)))
             HGOTO_ERROR(H5E_DATASET, H5E_CANTALLOC, FAIL, "can't allocate memory iterator")