Use H5Lexists to be more efficient in lookup

Author: franzpoeschel

src/IO/HDF5/HDF5IOHandler.cpp

@@ -442,39 +442,29 @@ void HDF5IOHandlerImpl::createDataset(
             // The dataset might already exist in the file from a previous run
             // We delete it, otherwise we could not create it again with
             // possibly different parameters.
-            // This is inefficient, as only the link to the dataset will be
-            // removed, but not the actual dataset
-            // But such is life if overwriting an iteration in Append mode
-            H5G_info_t group_info;
-            herr_t status = H5Gget_info(node_id, &group_info);
-            VERIFY(
-                status == 0,
-                "[HDF5] Internal error: Failed to get HDF5 group info for " +
-                    concrete_h5_file_position(writable) +
-                    " during dataset creation");
-            for (hsize_t i = 0; i < group_info.nlinks; ++i)
+            if (htri_t link_id = H5Lexists(node_id, name.c_str(), H5P_DEFAULT);
+                link_id > 0)
             {
-                if (H5G_DATASET != H5Gget_objtype_by_idx(node_id, i))
-                {
-                    continue;
-                }
-                ssize_t name_length =
-                    H5Gget_objname_by_idx(node_id, i, nullptr, 0);
-                std::vector<char> charbuffer(name_length + 1);
-                H5Gget_objname_by_idx(
-                    node_id, i, charbuffer.data(), name_length + 1);
-                if (std::strncmp(
-                        name.c_str(), charbuffer.data(), name_length + 1) != 0)
-                {
-                    continue;
-                }
-                status = H5Ldelete(node_id, name.c_str(), H5P_DEFAULT);
+                // This only unlinks, but does not delete the dataset
+                // Deleting the actual dataset physically is now up to HDF5:
+                // > when removing an object with H5Ldelete, the HDF5 library
+                // > should be able to detect and recycle the file space when no
+                // > other reference to the deleted object exists
+                // https://github.com/openPMD/openPMD-api/pull/1007#discussion_r867223316
+                herr_t status = H5Ldelete(node_id, name.c_str(), H5P_DEFAULT);
                 VERIFY(
                     status == 0,
                     "[HDF5] Internal error: Failed to delete old dataset '" +
                         name + "' from group for overwriting.");
-                break;
             }
+            else if (link_id < 0)
+            {
+                throw std::runtime_error(
+                    "[HDF5] Internal error: Failed to check for link existence "
+                    "of '" +
+                    name + "' inside group for overwriting.");
+            }
+            // else: link_id == 0: Link does not exist, nothing to do
         }
 
         Datatype d = parameters.dtype;