diff --git a/thorlcr/activities/nsplitter/thnsplitterslave.cpp b/thorlcr/activities/nsplitter/thnsplitterslave.cpp
index 56c5dbe0c91..7b47c37539b 100644
--- a/thorlcr/activities/nsplitter/thnsplitterslave.cpp
+++ b/thorlcr/activities/nsplitter/thnsplitterslave.cpp
@@ -148,7 +148,7 @@ class NSplitterSlaveActivity : public CSlaveActivity, implements ISharedSmartBuf
         }
     }
 public:
-    NSplitterSlaveActivity(CGraphElementBase *_container) : CSlaveActivity(_container), writer(*this)
+    NSplitterSlaveActivity(CGraphElementBase *_container) : CSlaveActivity(_container, nsplitterActivityStatistics), writer(*this)
     {
         numOutputs = container.getOutputs();
         connectedOutputSet.setown(createBitSet());
@@ -360,6 +360,12 @@ class NSplitterSlaveActivity : public CSlaveActivity, implements ISharedSmartBuf
         if (smartBuf)
             smartBuf->cancel();
     }
+    virtual void gatherActiveStats(CRuntimeStatisticCollection &activeStats) const
+    {
+        PARENT::gatherActiveStats(activeStats);
+        if (smartBuf)
+            mergeStats(activeStats, smartBuf);
+    }
 // ISharedSmartBufferCallback impl.
     virtual void paged() { pagedOut = true; }
     virtual void blocked()
diff --git a/thorlcr/master/thactivitymaster.cpp b/thorlcr/master/thactivitymaster.cpp
index 82ca2d647a9..f80ee0bd258 100644
--- a/thorlcr/master/thactivitymaster.cpp
+++ b/thorlcr/master/thactivitymaster.cpp
@@ -170,7 +170,6 @@ class CGenericMasterGraphElement : public CMasterGraphElement
             case TAKcase:
             case TAKchildcase:
             case TAKdegroup:
-            case TAKsplit:
             case TAKproject:
             case TAKprefetchproject:
             case TAKprefetchcountproject:
@@ -210,6 +209,9 @@ class CGenericMasterGraphElement : public CMasterGraphElement
             case TAKemptyaction:
                 ret = new CMasterActivity(this);
                 break;
+            case TAKsplit:
+                ret = new CMasterActivity(this, nsplitterActivityStatistics);
+                break;
             case TAKsoap_rowdataset:
             case TAKsoap_rowaction:
             case TAKsoap_datasetdataset:
diff --git a/thorlcr/thorutil/thbuf.cpp b/thorlcr/thorutil/thbuf.cpp
index d64d06da1a2..43798dd73bb 100644
--- a/thorlcr/thorutil/thbuf.cpp
+++ b/thorlcr/thorutil/thbuf.cpp
@@ -1175,6 +1175,10 @@ class CSharedWriteAheadBase : public CSimpleInterface, implements ISharedSmartBu
             queryCOutput(c).reset();
         inMemRows->reset(0);
     }
+    virtual unsigned __int64 getStatistic(StatisticKind kind) override
+    {
+        return 0;
+    }
 friend class COutput;
 friend class CRowSet;
 };
@@ -1197,7 +1201,7 @@ bool CRowSet::Release() const
 
 class CSharedWriteAheadDisk : public CSharedWriteAheadBase
 {
-    Owned<IFile> spillFile;
+    Owned<CFileOwner> spillFile;
     Owned<IFileIO> spillFileIO;
     CIArrayOf<Chunk> freeChunks;
     PointerArrayOf<Chunk> freeChunksSized;
@@ -1206,6 +1210,8 @@ class CSharedWriteAheadDisk : public CSharedWriteAheadBase
     Linked<IEngineRowAllocator> allocator;
     Linked<IOutputRowDeserializer> deserializer;
     IOutputMetaData *serializeMeta;
+    size_t sizeSpilled = 0;
+    stat_type spillElapsedCycles = 0;
 
     struct AddRemoveFreeChunk
     {
@@ -1484,7 +1490,11 @@ class CSharedWriteAheadDisk : public CSharedWriteAheadBase
             mb.append((byte)0);
             size32_t len = mb.length();
             chunk.setown(getOutOffset(len)); // will find space for 'len', might be bigger if from free list
+            CCycleTimer startCycles;
             spillFileIO->write(chunk->offset, len, mb.toByteArray());
+            spillElapsedCycles += startCycles.elapsedCycles();
+            sizeSpilled += len;
+            spillFile->noteSize(highOffset);
 #ifdef TRACE_WRITEAHEAD
             ActPrintLogEx(&activity->queryContainer(), thorlog_all, MCdebugProgress, "Flushed chunk = %d (savedChunks pos=%d), writeOffset = %" I64F "d, writeSize = %d", inMemRows->queryChunk(), savedChunks.ordinality(), chunk->offset, len);
 #endif
@@ -1507,16 +1517,15 @@ class CSharedWriteAheadDisk : public CSharedWriteAheadBase
         allocator(rowIf->queryRowAllocator()), deserializer(rowIf->queryRowDeserializer()), serializeMeta(meta->querySerializedDiskMeta())
     {
         assertex(spillName);
-        spillFile.setown(createIFile(spillName));
-        spillFile->setShareMode(IFSHnone);
-        spillFileIO.setown(spillFile->open(IFOcreaterw));
+        Owned<IFile> tempFile  = createIFile(spillName);
+        tempFile->setShareMode(IFSHnone);
+        spillFile.setown(new CFileOwner(tempFile, activity->queryTempFileSizeTracker()));
+        spillFileIO.setown(spillFile->queryIFile().open(IFOcreaterw));
         highOffset = 0;
     }
     ~CSharedWriteAheadDisk()
     {
         spillFileIO.clear();
-        if (spillFile)
-            spillFile->remove();
 
         for (;;)
         {
@@ -1538,6 +1547,20 @@ class CSharedWriteAheadDisk : public CSharedWriteAheadBase
         highOffset = 0;
         spillFileIO->setSize(0);
     }
+    virtual unsigned __int64 getStatistic(StatisticKind kind) override
+    {
+        switch(kind)
+        {
+            case StSizeSpillFile:
+                return sizeSpilled;
+            case StTimeSpillElapsed:
+                return cycle_to_nanosec(spillElapsedCycles);
+            case StNumSpills:
+                return 1;
+            default:
+                return 0;
+        }
+    }
 };
 
 ISharedSmartBuffer *createSharedSmartDiskBuffer(CActivityBase *activity, const char *spillname, unsigned outputs, IThorRowInterfaces *rowIf)
diff --git a/thorlcr/thorutil/thbuf.hpp b/thorlcr/thorutil/thbuf.hpp
index f75b353951f..15a6813828e 100644
--- a/thorlcr/thorutil/thbuf.hpp
+++ b/thorlcr/thorutil/thbuf.hpp
@@ -69,6 +69,7 @@ interface ISharedSmartBuffer : extends IRowWriter
     virtual IRowStream *queryOutput(unsigned output) = 0;
     virtual void cancel()=0;
     virtual void reset() = 0;
+    virtual unsigned __int64 getStatistic(StatisticKind kind) = 0;
 };
 
 extern graph_decl ISharedSmartBuffer *createSharedSmartMemBuffer(CActivityBase *activity, unsigned outputs, IThorRowInterfaces *rowif, unsigned buffSize=((unsigned)-1));
diff --git a/thorlcr/thorutil/thormisc.cpp b/thorlcr/thorutil/thormisc.cpp
index a97fc94c5f8..1ec2f83d2c6 100644
--- a/thorlcr/thorutil/thormisc.cpp
+++ b/thorlcr/thorutil/thormisc.cpp
@@ -73,7 +73,7 @@ Owned<IPropertyTree> globals;
 static Owned<IMPtagAllocator> ClusterMPAllocator;
 
 // stat. mappings shared between master and slave activities
-const StatisticsMapping spillStatistics({StTimeSpillElapsed, StTimeSortElapsed, StNumSpills, StSizeSpillFile});
+const StatisticsMapping spillStatistics({StTimeSpillElapsed, StTimeSortElapsed, StNumSpills, StSizeSpillFile, StSizePeakTempDisk});
 const StatisticsMapping soapcallStatistics({StTimeSoapcall});
 const StatisticsMapping basicActivityStatistics({StTimeTotalExecute, StTimeLocalExecute, StTimeBlocked});
 const StatisticsMapping groupActivityStatistics({StNumGroups, StNumGroupMax}, basicActivityStatistics);
@@ -92,8 +92,9 @@ const StatisticsMapping graphStatistics({StNumExecutions, StSizeSpillFile, StSiz
 const StatisticsMapping diskReadPartStatistics({StNumDiskRowsRead}, diskReadRemoteStatistics);
 const StatisticsMapping indexDistribActivityStatistics({}, basicActivityStatistics, jhtreeCacheStatistics);
 const StatisticsMapping soapcallActivityStatistics({}, basicActivityStatistics, soapcallStatistics);
-const StatisticsMapping hashDedupActivityStatistics({StNumSpills, StSizeSpillFile, StTimeSortElapsed, StSizePeakTempDisk}, diskWriteRemoteStatistics, basicActivityStatistics);
+const StatisticsMapping hashDedupActivityStatistics({}, spillStatistics, diskWriteRemoteStatistics, basicActivityStatistics);
 const StatisticsMapping hashDistribActivityStatistics({StNumLocalRows, StNumRemoteRows, StSizeRemoteWrite}, basicActivityStatistics);
+const StatisticsMapping nsplitterActivityStatistics({}, spillStatistics, basicActivityStatistics);
 
 MODULE_INIT(INIT_PRIORITY_STANDARD)
 {
diff --git a/thorlcr/thorutil/thormisc.hpp b/thorlcr/thorutil/thormisc.hpp
index 2bc8f0c776d..c37a8433cde 100644
--- a/thorlcr/thorutil/thormisc.hpp
+++ b/thorlcr/thorutil/thormisc.hpp
@@ -156,6 +156,7 @@ extern graph_decl const StatisticsMapping soapcallActivityStatistics;
 extern graph_decl const StatisticsMapping indexReadFileStatistics;
 extern graph_decl const StatisticsMapping hashDedupActivityStatistics;
 extern graph_decl const StatisticsMapping hashDistribActivityStatistics;
+extern graph_decl const StatisticsMapping nsplitterActivityStatistics;
 
 class BooleanOnOff
 {
@@ -356,9 +357,14 @@ class graph_decl CFileOwner : public CSimpleInterface, implements IInterface
     }
     void noteSize(offset_t size)
     {
-        fileSize = size;
-        if (fileSizeTracker)
-            fileSizeTracker->growSize(fileSize);
+        if (fileSizeTracker && fileSize!=size)
+        {
+            if (size > fileSize)
+                fileSizeTracker->growSize(size-fileSize);
+            else
+                fileSizeTracker->shrinkSize(fileSize-size);
+            fileSize = size;
+        }
     }
     IFile &queryIFile() const { return *iFile; }
 };