improve waitForSync performance for mmfiles

arangod/MMFiles/MMFilesCollection.cpp

@@ -2778,8 +2778,6 @@ int MMFilesCollection::insert(transaction::Methods* trx, VPackSlice const slice,
     bool const useDeadlockDetector =
       (lock && !trx->isSingleOperationTransaction() && !trx->state()->hasHint(transaction::Hints::Hint::NO_DLD));
     try {
-      // TODO Do we use the CollectionLocker on LogicalCollections
-      // or do we use it on the SE specific one?
       arangodb::MMFilesCollectionWriteLocker collectionLocker(
           this, useDeadlockDetector, lock);
 

arangod/MMFiles/MMFilesTransactionState.cpp

@@ -282,7 +282,9 @@ int MMFilesTransactionState::addOperation(TRI_voc_rid_t revisionId,
     }
     if (localWaitForSync) {
       // also sync RocksDB WAL
-      MMFilesPersistentIndexFeature::syncWal();
+      if (collection->getPhysical()->hasIndexOfType(arangodb::Index::TRI_IDX_TYPE_PERSISTENT_INDEX)) {
+        MMFilesPersistentIndexFeature::syncWal();
+      }
     }
     operation.setTick(slotInfo.tick);
     fid = slotInfo.logfileId;

arangod/StorageEngine/PhysicalCollection.cpp

@@ -66,6 +66,16 @@ void PhysicalCollection::drop() {
   }
 }
 
+bool PhysicalCollection::hasIndexOfType(arangodb::Index::IndexType type) const {
+  READ_LOCKER(guard, _indexesLock);
+  for (auto const& idx : _indexes) {
+    if (idx->type() == type) {
+      return true;
+    }
+  }
+  return false;
+}
+
 std::shared_ptr<Index> PhysicalCollection::lookupIndex(
     TRI_idx_iid_t idxId) const {
   READ_LOCKER(guard, _indexesLock);

arangod/StorageEngine/PhysicalCollection.h

@@ -26,6 +26,7 @@
 
 #include "Basics/Common.h"
 #include "Basics/ReadWriteLock.h"
+#include "Indexes/Index.h"
 #include "VocBase/voc-types.h"
 
 #include <velocypack/Builder.h>
@@ -94,6 +95,8 @@ class PhysicalCollection {
   ///////////////////////////////////
 
   virtual void prepareIndexes(arangodb::velocypack::Slice indexesSlice) = 0;
+  
+  bool hasIndexOfType(arangodb::Index::IndexType type) const;
 
   /// @brief Find index by definition
   virtual std::shared_ptr<Index> lookupIndex(