diff --git a/thorlcr/activities/hashdistrib/thhashdistribslave.cpp b/thorlcr/activities/hashdistrib/thhashdistribslave.cpp
index f34d124b803..e3dc4d344b0 100644
--- a/thorlcr/activities/hashdistrib/thhashdistribslave.cpp
+++ b/thorlcr/activities/hashdistrib/thhashdistribslave.cpp
@@ -95,6 +95,7 @@ class CDistributorBase : implements IHashDistributor, implements IExceptionHandl
     size32_t fixedEstSize;
     Owned<IRowWriter> pipewr;
     Owned<ISmartRowBuffer> piperd;
+    mutable CriticalSection critPiperd;
 
 protected:
     /*
@@ -1189,21 +1190,24 @@ class CDistributorBase : implements IHashDistributor, implements IExceptionHandl
         ihash = _ihash;
         iCompare = _iCompare;
         keepBestCompare = _keepBestCompare;
-        if (allowSpill)
         {
-            StringBuffer temp;
-            GetTempFilePath(temp,"hddrecvbuff");
-            if (newLookAhead)
+            CriticalBlock block(critPiperd);
+            if (allowSpill)
             {
-                options.totalCompressionBufferSize = pullBufferSize; // hd option overrides defaults
-                ICompressHandler *compressHandler = pullBufferSize ? queryDefaultCompressHandler() : nullptr;
-                piperd.setown(createCompressedSpillingRowStream(activity, temp.str(), false, rowIf, options, compressHandler));
+                StringBuffer temp;
+                GetTempFilePath(temp,"hddrecvbuff");
+                if (newLookAhead)
+                {
+                    options.totalCompressionBufferSize = pullBufferSize; // hd option overrides defaults
+                    ICompressHandler *compressHandler = pullBufferSize ? queryDefaultCompressHandler() : nullptr;
+                    piperd.setown(createCompressedSpillingRowStream(activity, temp.str(), false, rowIf, options, compressHandler));
+                }
+                else
+                    piperd.setown(createSmartBuffer(activity, temp.str(), pullBufferSize, rowIf));
             }
             else
-                piperd.setown(createSmartBuffer(activity, temp.str(), pullBufferSize, rowIf));
+                piperd.setown(createSmartInMemoryBuffer(activity, rowIf, pullBufferSize));
         }
-        else
-            piperd.setown(createSmartInMemoryBuffer(activity, rowIf, pullBufferSize));
 
         pipewr.set(piperd->queryWriter());
         connected = true;
@@ -1245,7 +1249,10 @@ class CDistributorBase : implements IHashDistributor, implements IExceptionHandl
         deserializer = NULL;
         fixedEstSize = 0;
         input.clear();
-        piperd.clear();
+        {
+            CriticalBlock block(critPiperd);
+            piperd.clear();
+        }
         pipewr.clear();
         ihash = NULL;
         iCompare = NULL;
@@ -1447,6 +1454,9 @@ class CDistributorBase : implements IHashDistributor, implements IExceptionHandl
     virtual void mergeStats(CRuntimeStatisticCollection &stats) const
     {
         sender.mergeStats(stats);
+        CriticalBlock block(critPiperd);
+        if (piperd)
+            mergeRemappedStats(stats, piperd, diskToTempStatsMap);
     }
     // IExceptionHandler impl.
     virtual bool fireException(IException *e)
diff --git a/thorlcr/thorutil/thbuf.cpp b/thorlcr/thorutil/thbuf.cpp
index 96915818937..ac77b2e9899 100644
--- a/thorlcr/thorutil/thbuf.cpp
+++ b/thorlcr/thorutil/thbuf.cpp
@@ -76,6 +76,7 @@ class CSmartRowBuffer: public CSimpleInterface, implements ISmartRowBuffer, impl
     ThorRowQueue *out;
     CFileOwner tmpFileOwner;
     Owned<IFileIO> tempFileIO;
+    mutable CriticalSection critTmpFileIO;
     SpinLock lock;
     bool waiting;
     Semaphore waitsem;
@@ -146,6 +147,7 @@ class CSmartRowBuffer: public CSimpleInterface, implements ISmartRowBuffer, impl
         }
         if (!tempFileIO) {
             SpinUnblock unblock(lock);
+            CriticalBlock block(critTmpFileIO);
             tempFileIO.setown(tmpFileOwner.queryIFile().open(IFOcreaterw));
             if (!tempFileIO)
             {
@@ -424,6 +426,14 @@ class CSmartRowBuffer: public CSimpleInterface, implements ISmartRowBuffer, impl
     {
         return this;
     }
+    virtual unsigned __int64 getStatistic(StatisticKind kind) const override
+    {
+        CriticalBlock block(critTmpFileIO);
+        if (tempFileIO)
+            return tempFileIO->getStatistic(kind);
+        else
+            return 0;
+    }
 };
 
 
@@ -607,6 +617,10 @@ class CSmartRowInMemoryBuffer: public CSimpleInterface, implements ISmartRowBuff
     {
         return this;
     }
+    virtual unsigned __int64 getStatistic(StatisticKind kind) const override
+    {
+        return 0;
+    }
 };
 
 
@@ -708,6 +722,7 @@ class CCompressedSpillingRowStream: public CSimpleInterfaceOf<ISmartRowBuffer>,
     memsize_t pendingFlushToDiskSz = 0;
     CFileOwner *currentOwnedOutputFile = nullptr;
     Owned<IFileIO> currentOutputIFileIO; // keep for stats
+    mutable CriticalSection critCurrentOutputIFileIO;
     CriticalSection outputFilesQCS;
     std::queue<CFileOwner *> outputFiles;
     unsigned writeTempFileNum = 0;
@@ -733,6 +748,7 @@ class CCompressedSpillingRowStream: public CSimpleInterfaceOf<ISmartRowBuffer>,
     RowEntry readFromStreamMarker = { nullptr, 0, 0 };
 
     // misc
+    CRuntimeStatisticCollection inactiveStats;
     bool grouped = false; // ctor input parameter
     CriticalSection readerWriterCS;
 #ifdef STRESSTEST_SPILLING_ROWSTREAM
@@ -766,7 +782,12 @@ class CCompressedSpillingRowStream: public CSimpleInterfaceOf<ISmartRowBuffer>,
 
         auto res = createSerialOutputStream(iFile, compressHandler, options, 2); // (2) input & output sharing totalCompressionBufferSize
         outputStream.setown(std::get<0>(res));
-        currentOutputIFileIO.setown(std::get<1>(res));
+        {
+            CriticalBlock b(critCurrentOutputIFileIO);
+            if (currentOutputIFileIO)
+                mergeStats(inactiveStats, currentOutputIFileIO);
+            currentOutputIFileIO.setown(std::get<1>(res));
+        }
         outputStreamSerializer = std::make_unique<COutputStreamSerializer>(outputStream);
     }
     void createNextInputStream()
@@ -1005,7 +1026,8 @@ class CCompressedSpillingRowStream: public CSimpleInterfaceOf<ISmartRowBuffer>,
 
     explicit CCompressedSpillingRowStream(CActivityBase *_activity, const char *_baseTmpFilename, bool _grouped, IThorRowInterfaces *rowIf, const LookAheadOptions &_options, ICompressHandler *_compressHandler)
         : activity(*_activity), baseTmpFilename(_baseTmpFilename), grouped(_grouped), options(_options), compressHandler(_compressHandler),
-          meta(rowIf->queryRowMetaData()), serializer(rowIf->queryRowSerializer()), allocator(rowIf->queryRowAllocator()), deserializer(rowIf->queryRowDeserializer())
+          meta(rowIf->queryRowMetaData()), serializer(rowIf->queryRowSerializer()), allocator(rowIf->queryRowAllocator()), deserializer(rowIf->queryRowDeserializer()),
+          inactiveStats(tempFileStatistics)
     {
         size32_t minSize = meta->getMinRecordSize();
 
@@ -1053,6 +1075,14 @@ class CCompressedSpillingRowStream: public CSimpleInterfaceOf<ISmartRowBuffer>,
     {
         return this;
     }
+    virtual unsigned __int64 getStatistic(StatisticKind kind) const
+    {
+        unsigned __int64 v = inactiveStats.queryStatistic(kind).get();
+        CriticalBlock b(critCurrentOutputIFileIO);
+        if (currentOutputIFileIO)
+            v += currentOutputIFileIO->getStatistic(kind);
+        return v;
+    }
 // IRowStream
     virtual const void *nextRow() override
     {
diff --git a/thorlcr/thorutil/thbuf.hpp b/thorlcr/thorutil/thbuf.hpp
index 69a28f04824..76dfa3cbcfd 100644
--- a/thorlcr/thorutil/thbuf.hpp
+++ b/thorlcr/thorutil/thbuf.hpp
@@ -61,6 +61,7 @@ struct LookAheadOptions : CommonBufferRowRWStreamOptions
 interface ISmartRowBuffer: extends IRowStream
 {
     virtual IRowWriter *queryWriter() = 0;
+    virtual unsigned __int64 getStatistic(StatisticKind kind) const = 0;
 };
 
 class CActivityBase;