Metadata optimization: Only write ADIOS2 attributes from rank 0 in openPMD-api >= 0.16

include/picongpu/plugins/openPMD/Json.cpp

@@ -339,6 +339,37 @@ The key 'select' must point to either a single string or an array of strings.)EN
          * careful memory configuration is necessary anyway, so the
          * defaults don't matter.
          */
+#    if OPENPMDAPI_VERSION_GE(0, 16, 0)
+        /*
+         * In openPMD >= 0.16, additionally ignore all attribute metadata
+         * that comes from a rank other than rank 0.
+         * The openPMD plugin of PIConGPU writes attributes synchronously
+         * (since this is required in common configurations of HDF5).
+         * For ADIOS2 however, it's better to write attributes from single
+         * ranks only and avoid metadata duplication across ranks.
+         * This option tells the ADIOS2 backend of openPMD that it can
+         * safely ignore any attribute write if the current MPI rank is
+         * not 0.
+         */
+        std::string const& defaultValues = R"(
+{
+  "hdf5": {
+    "dataset": {
+      "chunks": "none"
+    }
+  },
+  "adios2": {
+    "attribute_writing_ranks": 0,
+    "engine": {
+      "preferred_flush_target": "buffer",
+      "parameters": {
+        "BufferChunkSize": 2147381248
+      }
+    }
+  }
+}
+        )";
+#    else
         std::string const& defaultValues = R"(
 {
   "hdf5": {
@@ -356,6 +387,7 @@ The key 'select' must point to either a single string or an array of strings.)EN
   }
 }
         )";
+#    endif
         std::stringstream json_to_string;
         json_to_string << config;
         auto merged = openPMD::json::merge(defaultValues, json_to_string.str());