From a1713453b5bb0960271d8af11aa92cfaadb8aded Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Franz=20P=C3=B6schel?= <franz.poeschel@gmail.com>
Date: Fri, 28 Mar 2025 11:37:58 +0100
Subject: [PATCH 1/4] Emplace scalar tuple only when needed

---
 include/openPMD/backend/BaseRecord.hpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/openPMD/backend/BaseRecord.hpp b/include/openPMD/backend/BaseRecord.hpp
index 87364b46f4..cdddf422ad 100644
--- a/include/openPMD/backend/BaseRecord.hpp
+++ b/include/openPMD/backend/BaseRecord.hpp
@@ -28,6 +28,7 @@
 #include "openPMD/backend/Container.hpp"
 
 #include <array>
+#include <optional>
 #include <stdexcept>
 #include <string>
 #include <type_traits> // std::remove_reference_t
@@ -113,8 +114,7 @@ namespace internal
         {}
         ScalarIterator(T_BaseRecord *baseRecord, Left iterator)
             : m_baseRecordData(&baseRecord->get())
-            , m_scalarTuple(std::make_pair(
-                  RecordComponent::SCALAR, T_RecordComponent(*baseRecord)))
+            , m_scalarTuple(std::nullopt)
             , m_iterator(std::move(iterator))
         {}
 

From 0ab5c5f7690e4e999327ed0652fe97030eccdf14 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Franz=20P=C3=B6schel?= <franz.poeschel@gmail.com>
Date: Fri, 28 Mar 2025 12:17:42 +0100
Subject: [PATCH 2/4] Flush only dirty meshes/species

TODO: Maybe do this in more places, and also when reading
---
 src/Iteration.cpp | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/Iteration.cpp b/src/Iteration.cpp
index c991c2b79b..2a01aaede1 100644
--- a/src/Iteration.cpp
+++ b/src/Iteration.cpp
@@ -363,7 +363,12 @@ void Iteration::flush(internal::FlushParams const &flushParams)
             }
             meshes.flush(s.meshesPath(), flushParams);
             for (auto &m : meshes)
-                m.second.flush(m.first, flushParams);
+            {
+                if (m.second.dirtyRecursive())
+                {
+                    m.second.flush(m.first, flushParams);
+                }
+            }
         }
         else
         {
@@ -379,7 +384,12 @@ void Iteration::flush(internal::FlushParams const &flushParams)
             }
             particles.flush(s.particlesPath(), flushParams);
             for (auto &species : particles)
-                species.second.flush(species.first, flushParams);
+            {
+                if (species.second.dirtyRecursive())
+                {
+                    species.second.flush(species.first, flushParams);
+                }
+            }
         }
         else
         {

From b0dfe64bac66eccd22d74cce8a479bdd53508df8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Franz=20P=C3=B6schel?= <franz.poeschel@gmail.com>
Date: Fri, 28 Mar 2025 12:28:02 +0100
Subject: [PATCH 3/4] Improved specification of standards

---
 src/ParticleSpecies.cpp | 15 +++++++++------
 src/Record.cpp          |  4 ++--
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/src/ParticleSpecies.cpp b/src/ParticleSpecies.cpp
index 4006cc82ba..0c0be3ef4b 100644
--- a/src/ParticleSpecies.cpp
+++ b/src/ParticleSpecies.cpp
@@ -168,12 +168,15 @@ void ParticleSpecies::flush(
     }
     else
     {
-        auto it = find("position");
-        if (it != end())
-            it->second.setUnitDimension({{UnitDimension::L, 1}});
-        it = find("positionOffset");
-        if (it != end())
-            it->second.setUnitDimension({{UnitDimension::L, 1}});
+        if (flushParams.flushLevel != FlushLevel::SkeletonOnly)
+        {
+            auto it = find("position");
+            if (it != end())
+                it->second.setUnitDimension({{UnitDimension::L, 1}});
+            it = find("positionOffset");
+            if (it != end())
+                it->second.setUnitDimension({{UnitDimension::L, 1}});
+        }
 
         Container<Record>::flush(path, flushParams);
 
diff --git a/src/Record.cpp b/src/Record.cpp
index 7d41fce5c2..5be926d0e0 100644
--- a/src/Record.cpp
+++ b/src/Record.cpp
@@ -45,8 +45,8 @@ Record &Record::setUnitDimension(unit_representations::AsMap const &udim)
 }
 Record &Record::setUnitDimension(unit_representations::AsArray const &udim)
 {
-    return setUnitDimension(
-        unit_representations::asMap(udim, /* skip_zeros = */ false));
+    setAttribute("unitDimension", udim);
+    return *this;
 }
 
 void Record::flush_impl(

From a4df35d1b62bea80731d101c397f0243c3f567f8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Franz=20P=C3=B6schel?= <franz.poeschel@gmail.com>
Date: Mon, 31 Mar 2025 18:42:20 +0200
Subject: [PATCH 4/4] Don't forward empty Span operations to backend

---
 include/openPMD/RecordComponent.tpp | 9 +++++++++
 include/openPMD/Span.hpp            | 5 ++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/openPMD/RecordComponent.tpp b/include/openPMD/RecordComponent.tpp
index 7beaae8b9d..0ae1508bd1 100644
--- a/include/openPMD/RecordComponent.tpp
+++ b/include/openPMD/RecordComponent.tpp
@@ -370,6 +370,15 @@ RecordComponent::storeChunk(Offset o, Extent e, F &&createBuffer)
         dCreate.options = rc.m_dataset.value().options;
         IOHandler()->enqueue(IOTask(this, dCreate));
     }
+
+    if (size == 0)
+    {
+        // Don't forward this operation to the backend as it might create ugly
+        // zero-blocks in ADIOS2
+        setDirtyRecursive(true);
+        return DynamicMemoryView<T>();
+    }
+
     Parameter<Operation::GET_BUFFER_VIEW> getBufferView;
     getBufferView.offset = o;
     getBufferView.extent = e;
diff --git a/include/openPMD/Span.hpp b/include/openPMD/Span.hpp
index 93bc0d24f7..85570fd148 100644
--- a/include/openPMD/Span.hpp
+++ b/include/openPMD/Span.hpp
@@ -113,7 +113,10 @@ class DynamicMemoryView
     }
 
 public:
-    explicit DynamicMemoryView() = default;
+    explicit DynamicMemoryView()
+    {
+        m_param.out->backendManagedBuffer = false;
+    }
 
     /**
      * @brief Acquire the underlying buffer at its current position in memory.