diff --git a/arangod/Aql/AqlItemBlock.cpp b/arangod/Aql/AqlItemBlock.cpp
index f975a58c81..56d15f7235 100644
--- a/arangod/Aql/AqlItemBlock.cpp
+++ b/arangod/Aql/AqlItemBlock.cpp
@@ -287,6 +287,28 @@ void AqlItemBlock::shrink(size_t nrItems) {
   }
 
   decreaseMemoryUsage(sizeof(AqlValue) * (_nrItems - nrItems) * _nrRegs);
+  
+  for (size_t i = _nrItems * _nrRegs; i < _data.size(); ++i) {
+    AqlValue& a = _data[i];
+    if (a.requiresDestruction()) {
+      auto it = _valueCount.find(a);
+
+      if (it != _valueCount.end()) {
+        TRI_ASSERT((*it).second > 0);
+
+        if (--((*it).second) == 0) {
+          decreaseMemoryUsage(a.memoryUsage());
+          a.destroy();
+          try {
+            _valueCount.erase(it);
+            continue;  // no need for an extra a.erase() here
+          } catch (...) {
+          }
+        }
+      }
+    }
+    a.erase();
+  }
 
   // adjust the size of the block
   _nrItems = nrItems;
@@ -308,7 +330,7 @@ void AqlItemBlock::rescale(size_t nrItems, RegisterId nrRegs) {
   // way; because currently, we are tracking the memory we need, instead of the
   // memory we have.
   if (targetSize > _data.size()) {
-     _data.resize(targetSize);
+    _data.resize(targetSize);
   }
 
   TRI_ASSERT(targetSize <= _data.size());
diff --git a/arangod/Aql/AqlItemBlock.h b/arangod/Aql/AqlItemBlock.h
index 294d17ad8d..87bb77dcf7 100644
--- a/arangod/Aql/AqlItemBlock.h
+++ b/arangod/Aql/AqlItemBlock.h
@@ -241,6 +241,7 @@ class AqlItemBlock {
         if (_data[fromRow * _nrRegs + i].requiresDestruction()) {
           ++_valueCount[_data[fromRow * _nrRegs + i]];
         }
+        TRI_ASSERT(_data[currentRow * _nrRegs + i].isEmpty());
         _data[currentRow * _nrRegs + i] = _data[fromRow * _nrRegs + i];
       }
     }
diff --git a/arangod/Aql/AqlItemBlockShell.h b/arangod/Aql/AqlItemBlockShell.h
index 37773346ea..1a5883b7c7 100644
--- a/arangod/Aql/AqlItemBlockShell.h
+++ b/arangod/Aql/AqlItemBlockShell.h
@@ -69,8 +69,8 @@ class AqlItemBlockShell {
  public:
   using SmartAqlItemBlockPtr = std::unique_ptr<AqlItemBlock, AqlItemBlockDeleter>;
 
-  AqlItemBlock const& block() const { return *_block; };
-  AqlItemBlock& block() { return *_block; };
+  inline AqlItemBlock const& block() const { return *_block; }
+  inline AqlItemBlock& block() { return *_block; }
 
   AqlItemBlockShell(AqlItemBlockManager& manager, std::unique_ptr<AqlItemBlock> block);
 
@@ -89,7 +89,6 @@ class AqlItemBlockShell {
   SmartAqlItemBlockPtr _block;
 };
 
-
 }  // namespace aql
 }  // namespace arangodb
 
diff --git a/arangod/Aql/BlockFetcher.cpp b/arangod/Aql/BlockFetcher.cpp
index 209b04d013..b5bc16f29b 100644
--- a/arangod/Aql/BlockFetcher.cpp
+++ b/arangod/Aql/BlockFetcher.cpp
@@ -30,9 +30,9 @@ ExecutionState BlockFetcher<passBlocksThrough>::prefetchBlock(size_t atMost) {
   ExecutionState state;
   std::unique_ptr<AqlItemBlock> block;
   std::tie(state, block) = upstreamBlock().getSome(atMost);
-    TRI_IF_FAILURE("ExecutionBlock::getBlock") {
-      THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
-    }
+  TRI_IF_FAILURE("ExecutionBlock::getBlock") {
+    THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
+  }
 
   if (state == ExecutionState::WAITING) {
     TRI_ASSERT(block == nullptr);
@@ -56,7 +56,7 @@ ExecutionState BlockFetcher<passBlocksThrough>::prefetchBlock(size_t atMost) {
     _blockShellPassThroughQueue.push({state, blockShell});
   }
 
-  _blockShellQueue.push({state, blockShell});
+  _blockShellQueue.push({state, std::move(blockShell)});
   return ExecutionState::HASMORE;
 }
 
@@ -73,6 +73,8 @@ BlockFetcher<passBlocksThrough>::fetchBlock(size_t atMost) {
     }
     TRI_ASSERT(state == ExecutionState::HASMORE);
   }
+  
+  TRI_ASSERT(!_blockShellQueue.empty());
 
   ExecutionState state;
   std::shared_ptr<AqlItemBlockShell> blockShell;
@@ -81,7 +83,7 @@ BlockFetcher<passBlocksThrough>::fetchBlock(size_t atMost) {
 
   //auto inputBlockShell =
   //    std::make_shared<InputAqlItemBlockShell>(blockShell, _inputRegisters);
-  return {state, blockShell};
+  return {state, std::move(blockShell)};
 }
 
 template <bool allowBlockPassthrough>
@@ -99,6 +101,8 @@ BlockFetcher<allowBlockPassthrough>::fetchBlockForPassthrough(size_t atMost) {
     TRI_ASSERT(state == ExecutionState::HASMORE);
   }
 
+  TRI_ASSERT(!_blockShellPassThroughQueue.empty());
+
   ExecutionState state;
   std::shared_ptr<AqlItemBlockShell> blockShell;
   std::tie(state, blockShell) = _blockShellPassThroughQueue.front();
diff --git a/arangod/Aql/DistinctCollectExecutor.cpp b/arangod/Aql/DistinctCollectExecutor.cpp
index e25f5e8723..3f9636f3cc 100644
--- a/arangod/Aql/DistinctCollectExecutor.cpp
+++ b/arangod/Aql/DistinctCollectExecutor.cpp
@@ -55,13 +55,20 @@ DistinctCollectExecutorInfos::DistinctCollectExecutorInfos(
 }
 
 DistinctCollectExecutor::DistinctCollectExecutor(Fetcher& fetcher, Infos& infos)
-    : _infos(infos), _fetcher(fetcher) {
-  _seen = std::make_unique<std::unordered_set<std::vector<AqlValue>, AqlValueGroupHash, AqlValueGroupEqual>>(
-      1024,
-      AqlValueGroupHash(_infos.getTransaction(), _infos.getGroupRegisters().size()),
-      AqlValueGroupEqual(_infos.getTransaction()));
-};
-DistinctCollectExecutor::~DistinctCollectExecutor() = default;
+    : _infos(infos), _fetcher(fetcher),
+       _seen(1024,
+             AqlValueGroupHash(_infos.getTransaction(), _infos.getGroupRegisters().size()),
+             AqlValueGroupEqual(_infos.getTransaction())) {
+}
+
+DistinctCollectExecutor::~DistinctCollectExecutor() {
+  // destroy all AqlValues captured
+  for (auto& it : _seen) {
+    for (auto& it2 : it) {
+      const_cast<AqlValue*>(&it2)->destroy();
+    }
+  }
+}
 
 std::pair<ExecutionState, NoStats> DistinctCollectExecutor::produceRow(OutputAqlItemRow& output) {
   TRI_IF_FAILURE("DistinctCollectExecutor::produceRow") {
@@ -95,9 +102,9 @@ std::pair<ExecutionState, NoStats> DistinctCollectExecutor::produceRow(OutputAql
     }
 
     // now check if we already know this group
-    auto foundIt = _seen->find(groupValues);
+    auto foundIt = _seen.find(groupValues);
 
-    bool newGroup = foundIt == _seen->end();
+    bool newGroup = foundIt == _seen.end();
     if (newGroup) {
       size_t i = 0;
 
@@ -112,7 +119,7 @@ std::pair<ExecutionState, NoStats> DistinctCollectExecutor::produceRow(OutputAql
       for (auto const& it : groupValues) {
         copy.emplace_back(it.clone());
       }
-      _seen->emplace(std::move(copy));
+      _seen.emplace(std::move(copy));
     }
 
     // Abort if upstream is done
diff --git a/arangod/Aql/DistinctCollectExecutor.h b/arangod/Aql/DistinctCollectExecutor.h
index 814e008f2b..0401b6ddd4 100644
--- a/arangod/Aql/DistinctCollectExecutor.h
+++ b/arangod/Aql/DistinctCollectExecutor.h
@@ -112,7 +112,7 @@ class DistinctCollectExecutor {
  private:
   Infos const& _infos;
   Fetcher& _fetcher;
-  std::unique_ptr<std::unordered_set<std::vector<AqlValue>, AqlValueGroupHash, AqlValueGroupEqual>> _seen;
+  std::unordered_set<std::vector<AqlValue>, AqlValueGroupHash, AqlValueGroupEqual> _seen;
 };
 
 }  // namespace aql
diff --git a/arangod/Aql/EnumerateCollectionExecutor.cpp b/arangod/Aql/EnumerateCollectionExecutor.cpp
index 59a91134c1..b0130d32bf 100644
--- a/arangod/Aql/EnumerateCollectionExecutor.cpp
+++ b/arangod/Aql/EnumerateCollectionExecutor.cpp
@@ -94,7 +94,7 @@ EnumerateCollectionExecutor::EnumerateCollectionExecutor(Fetcher& fetcher, Infos
         _infos.getProjections(), _infos.getTrxPtr(), _infos.getCoveringIndexAttributePositions(),
         _allowCoveringIndexOptimization, _infos.getUseRawDocumentPointers()));
 
-};
+}
 
 EnumerateCollectionExecutor::~EnumerateCollectionExecutor() = default;
 
diff --git a/arangod/Aql/ExecutionBlockImpl.cpp b/arangod/Aql/ExecutionBlockImpl.cpp
index 976315a686..81d53e1e09 100644
--- a/arangod/Aql/ExecutionBlockImpl.cpp
+++ b/arangod/Aql/ExecutionBlockImpl.cpp
@@ -65,18 +65,11 @@ ExecutionBlockImpl<Executor>::ExecutionBlockImpl(ExecutionEngine* engine,
       _rowFetcher(_blockFetcher),
       _infos(std::move(infos)),
       _executor(_rowFetcher, _infos),
-      _outputItemRow(nullptr),
+      _outputItemRow(),
       _query(*engine->getQuery()) {}
 
 template <class Executor>
-ExecutionBlockImpl<Executor>::~ExecutionBlockImpl() {
-  if (_outputItemRow) {
-    std::unique_ptr<AqlItemBlock> block = _outputItemRow->stealBlock();
-    if (block != nullptr) {
-      _engine->itemBlockManager().returnBlock(std::move(block));
-    }
-  }
-}
+ExecutionBlockImpl<Executor>::~ExecutionBlockImpl() {}
 
 template <class Executor>
 std::pair<ExecutionState, std::unique_ptr<AqlItemBlock>> ExecutionBlockImpl<Executor>::getSome(size_t atMost) {
@@ -136,7 +129,7 @@ ExecutionBlockImpl<Executor>::getSomeWithoutTrace(size_t atMost) {
     // Count global but executor-specific statistics, like number of filtered
     // rows.
     _engine->_stats += executorStats;
-    if (_outputItemRow && _outputItemRow->produced()) {
+    if (_outputItemRow->produced()) {
       _outputItemRow->advanceRow();
     }
 
@@ -152,7 +145,7 @@ ExecutionBlockImpl<Executor>::getSomeWithoutTrace(size_t atMost) {
       auto outputBlock = _outputItemRow->stealBlock();
       // This is not strictly necessary here, as we shouldn't be called again
       // after DONE.
-      _outputItemRow.reset(nullptr);
+      _outputItemRow.reset();
 
       return {state, std::move(outputBlock)};
     }
@@ -169,7 +162,7 @@ ExecutionBlockImpl<Executor>::getSomeWithoutTrace(size_t atMost) {
   // we guarantee that we do return a valid pointer in the HASMORE case.
   TRI_ASSERT(outputBlock != nullptr);
   // TODO OutputAqlItemRow could get "reset" and "isValid" methods and be reused
-  _outputItemRow.reset(nullptr);
+  _outputItemRow.reset();
 
   return {state, std::move(outputBlock)};
 }
diff --git a/arangod/Aql/ExecutorExpressionContext.h b/arangod/Aql/ExecutorExpressionContext.h
index 2d7aac17a8..16871dae97 100644
--- a/arangod/Aql/ExecutorExpressionContext.h
+++ b/arangod/Aql/ExecutorExpressionContext.h
@@ -34,7 +34,7 @@ class InputAqlItemRow;
 
 class ExecutorExpressionContext final : public QueryExpressionContext {
  public:
-  ExecutorExpressionContext(Query* query, InputAqlItemRow& inputRow,
+  ExecutorExpressionContext(Query* query, InputAqlItemRow const& inputRow,
                             std::vector<Variable const*> const& vars,
                             std::vector<RegisterId> const& regs)
       : QueryExpressionContext(query), _inputRow(inputRow), _vars(vars), _regs(regs) {}
@@ -52,7 +52,7 @@ class ExecutorExpressionContext final : public QueryExpressionContext {
 
  private:
   /// @brief temporary storage for expression data context
-  InputAqlItemRow& _inputRow;
+  InputAqlItemRow const& _inputRow;
   std::vector<Variable const*> const& _vars;
   std::vector<RegisterId> const& _regs;
 };
diff --git a/arangod/Aql/FilterExecutor.cpp b/arangod/Aql/FilterExecutor.cpp
index a11575ffe9..327f4673a2 100644
--- a/arangod/Aql/FilterExecutor.cpp
+++ b/arangod/Aql/FilterExecutor.cpp
@@ -49,10 +49,10 @@ FilterExecutorInfos::FilterExecutorInfos(RegisterId inputRegister, RegisterId nr
                     std::move(registersToClear), std::move(registersToKeep)),
       _inputRegister(inputRegister) {}
 
-FilterExecutor::FilterExecutor(Fetcher& fetcher, Infos& infos) : _infos(infos), _fetcher(fetcher){};
+FilterExecutor::FilterExecutor(Fetcher& fetcher, Infos& infos) : _infos(infos), _fetcher(fetcher) {}
 FilterExecutor::~FilterExecutor() = default;
 
-std::pair<ExecutionState, FilterStats> FilterExecutor::produceRow(OutputAqlItemRow &output) {
+std::pair<ExecutionState, FilterStats> FilterExecutor::produceRow(OutputAqlItemRow& output) {
   TRI_IF_FAILURE("FilterExecutor::produceRow") {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
   }
diff --git a/arangod/Aql/FilterExecutor.h b/arangod/Aql/FilterExecutor.h
index 955c650cee..7e65959cab 100644
--- a/arangod/Aql/FilterExecutor.h
+++ b/arangod/Aql/FilterExecutor.h
@@ -54,7 +54,7 @@ class FilterExecutorInfos : public ExecutorInfos {
   FilterExecutorInfos(FilterExecutorInfos const&) = delete;
   ~FilterExecutorInfos() = default;
 
-  RegisterId getInputRegister() const noexcept { return _inputRegister; };
+  RegisterId getInputRegister() const noexcept { return _inputRegister; }
 
  private:
   // This is exactly the value in the parent member ExecutorInfo::_inRegs,
diff --git a/arangod/Aql/InputAqlItemRow.h b/arangod/Aql/InputAqlItemRow.h
index 62efafd42a..7464b16939 100644
--- a/arangod/Aql/InputAqlItemRow.h
+++ b/arangod/Aql/InputAqlItemRow.h
@@ -88,12 +88,12 @@ class InputAqlItemRow {
   inline AqlValue stealValue(RegisterId registerId) {
     TRI_ASSERT(isInitialized());
     TRI_ASSERT(registerId < getNrRegisters());
-    AqlValue a = block().getValueReference(_baseIndex, registerId);
+    AqlValue const& a = block().getValueReference(_baseIndex, registerId);
     if (!a.isEmpty() && a.requiresDestruction()) {
       // Now no one is responsible for AqlValue a
       block().steal(a);
     }
-    // This cannot fail, caller needs to take immediate owner shops.
+    // This cannot fail, caller needs to take immediate ownership.
     return a;
   }
 
diff --git a/arangod/Aql/OutputAqlItemRow.cpp b/arangod/Aql/OutputAqlItemRow.cpp
index 6708e128ef..993b93afa2 100644
--- a/arangod/Aql/OutputAqlItemRow.cpp
+++ b/arangod/Aql/OutputAqlItemRow.cpp
@@ -58,9 +58,10 @@ OutputAqlItemRow::OutputAqlItemRow(
   TRI_ASSERT(_blockShell != nullptr);
 }
 
-void OutputAqlItemRow::doCopyRow(const InputAqlItemRow& sourceRow, bool ignoreMissing) {
+void OutputAqlItemRow::doCopyRow(InputAqlItemRow const& sourceRow, bool ignoreMissing) {
   // Note that _lastSourceRow is invalid right after construction. However, when
   // _baseIndex > 0, then we must have seen one row already.
+  TRI_ASSERT(!_doNotCopyInputRow);
   TRI_ASSERT(_baseIndex == 0 || _lastSourceRow.isInitialized());
   bool mustClone = _baseIndex == 0 || _lastSourceRow != sourceRow;
 
@@ -100,7 +101,7 @@ std::unique_ptr<AqlItemBlock> OutputAqlItemRow::stealBlock() {
   std::unique_ptr<AqlItemBlock> block = blockShell().stealBlockCompat();
   if (numRowsWritten() == 0) {
     // blocks may not be empty
-    block.reset(nullptr);
+    block.reset();
   } else {
     // numRowsWritten() returns the exact number of rows that were fully
     // written and takes into account whether the current row was written.
diff --git a/arangod/Aql/OutputAqlItemRow.h b/arangod/Aql/OutputAqlItemRow.h
index 655b0367b7..4a5f754361 100644
--- a/arangod/Aql/OutputAqlItemRow.h
+++ b/arangod/Aql/OutputAqlItemRow.h
@@ -52,6 +52,11 @@ class OutputAqlItemRow {
                             std::shared_ptr<std::unordered_set<RegisterId> const> registersToKeep,
                             std::shared_ptr<std::unordered_set<RegisterId> const> registersToClear,
                             CopyRowBehaviour = CopyRowBehaviour::CopyInputRows);
+  
+  OutputAqlItemRow(OutputAqlItemRow const&) = delete;
+  OutputAqlItemRow& operator=(OutputAqlItemRow const&) = delete;
+  OutputAqlItemRow(OutputAqlItemRow&&) = delete;
+  OutputAqlItemRow& operator=(OutputAqlItemRow&&) = delete;
 
   // Clones the given AqlValue
   void cloneValueInto(RegisterId registerId, InputAqlItemRow const& sourceRow,
@@ -116,6 +121,7 @@ class OutputAqlItemRow {
 #endif
       _inputRowCopied = true;
       _lastSourceRow = sourceRow;
+      _lastBaseIndex = _baseIndex;
       return;
     }
 
@@ -160,7 +166,7 @@ class OutputAqlItemRow {
    */
   std::unique_ptr<AqlItemBlock> stealBlock();
 
-  bool isFull() { return numRowsWritten() >= block().size(); }
+  bool isFull() const { return numRowsWritten() >= block().size(); }
 
   /**
    * @brief Returns the number of rows that were fully written.
@@ -206,20 +212,20 @@ class OutputAqlItemRow {
   }
 
  private:
-  AqlItemBlockShell& blockShell() { return *_blockShell; }
-  AqlItemBlockShell const& blockShell() const { return *_blockShell; }
+  inline AqlItemBlockShell& blockShell() { return *_blockShell; }
+  inline AqlItemBlockShell const& blockShell() const { return *_blockShell; }
 
   std::unordered_set<RegisterId> const& outputRegisters() const {
     return *_outputRegisters;
-  };
+  }
 
   std::unordered_set<RegisterId> const& registersToKeep() const {
     return *_registersToKeep;
-  };
+  }
 
   std::unordered_set<RegisterId> const& registersToClear() const {
     return *_registersToClear;
-  };
+  }
 
   bool isOutputRegister(RegisterId registerId) const {
     return outputRegisters().find(registerId) != outputRegisters().end();
@@ -275,10 +281,10 @@ class OutputAqlItemRow {
 
   bool allValuesWritten() const {
     return _numValuesWritten == numRegistersToWrite();
-  };
+  }
 
-  AqlItemBlock const& block() const { return blockShell().block(); }
-  AqlItemBlock& block() { return blockShell().block(); }
+  inline AqlItemBlock const& block() const { return blockShell().block(); }
+  inline AqlItemBlock& block() { return blockShell().block(); }
 
   void doCopyRow(InputAqlItemRow const& sourceRow, bool ignoreMissing);
 };
diff --git a/arangod/Aql/ShortestPathExecutor.cpp b/arangod/Aql/ShortestPathExecutor.cpp
index 15e3f74e23..a5484fbd3e 100644
--- a/arangod/Aql/ShortestPathExecutor.cpp
+++ b/arangod/Aql/ShortestPathExecutor.cpp
@@ -143,12 +143,16 @@ std::pair<ExecutionState, NoStats> ShortestPathExecutor::produceRow(OutputAqlIte
   while (true) {
     if (_posInPath < _path->length()) {
       if (_infos.usesOutputRegister(ShortestPathExecutorInfos::VERTEX)) {
-        output.cloneValueInto(_infos.getOutputRegister(ShortestPathExecutorInfos::VERTEX),
-                              _input, _path->vertexToAqlValue(_infos.cache(), _posInPath));
+        AqlValue vertex = _path->vertexToAqlValue(_infos.cache(), _posInPath);
+        AqlValueGuard guard{vertex, true};
+        output.moveValueInto(_infos.getOutputRegister(ShortestPathExecutorInfos::VERTEX),
+                             _input, guard);
       }
       if (_infos.usesOutputRegister(ShortestPathExecutorInfos::EDGE)) {
-        output.cloneValueInto(_infos.getOutputRegister(ShortestPathExecutorInfos::EDGE),
-                              _input, _path->edgeToAqlValue(_infos.cache(), _posInPath));
+        AqlValue edge = _path->edgeToAqlValue(_infos.cache(), _posInPath);
+        AqlValueGuard guard{edge, true};
+        output.moveValueInto(_infos.getOutputRegister(ShortestPathExecutorInfos::EDGE),
+                             _input, guard);
       }
       _posInPath++;
       return {computeState(), s};
diff --git a/arangod/Graph/Traverser.cpp b/arangod/Graph/Traverser.cpp
index ff11d62137..2a0402b532 100644
--- a/arangod/Graph/Traverser.cpp
+++ b/arangod/Graph/Traverser.cpp
@@ -174,11 +174,10 @@ bool arangodb::traverser::Traverser::vertexMatchesConditions(arangodb::velocypac
   if (_opts->vertexHasFilter(depth)) {
     // We always need to destroy this vertex
     aql::AqlValue vertex = fetchVertexData(v);
+    aql::AqlValueGuard guard{vertex, true};
     if (!_opts->evaluateVertexExpression(vertex.slice(), depth)) {
-      vertex.destroy();
       return false;
     }
-    vertex.destroy();
   }
   return true;
 }
diff --git a/arangod/Scheduler/SupervisedScheduler.cpp b/arangod/Scheduler/SupervisedScheduler.cpp
index c32067627b..e8ce330085 100644
--- a/arangod/Scheduler/SupervisedScheduler.cpp
+++ b/arangod/Scheduler/SupervisedScheduler.cpp
@@ -169,7 +169,7 @@ void SupervisedScheduler::shutdown() {
       break;
     }
 
-    LOG_TOPIC(ERR, Logger::THREADS)
+    LOG_TOPIC(WARN, Logger::THREADS)
         << "Scheduler received shutdown, but there are still tasks on the "
         << "queue: jobsSubmitted=" << jobsSubmitted << " jobsDone=" << jobsDone;
     std::this_thread::sleep_for(std::chrono::seconds(1));