diff --git a/thorlcr/activities/funnel/thfunnelslave.cpp b/thorlcr/activities/funnel/thfunnelslave.cpp
index db801b7b6d2..35969abd57c 100644
--- a/thorlcr/activities/funnel/thfunnelslave.cpp
+++ b/thorlcr/activities/funnel/thfunnelslave.cpp
@@ -142,6 +142,7 @@ class CParallelFunnel : implements IRowStream, public CSimpleInterface
     SimpleInterThreadQueueOf<const void, true> rows;
     Semaphore fullSem;
     size32_t totSize;
+    size32_t peakTotSize;
     unsigned waiting = 0;
     bool stopped;
     Linked<IOutputRowSerializer> serializer;
@@ -161,6 +162,8 @@ class CParallelFunnel : implements IRowStream, public CSimpleInterface
             }
             rows.enqueue(row);
             totSize += rowSize;
+            if (totSize > peakTotSize)
+                peakTotSize = totSize;
             if (totSize > FUNNEL_MIN_BUFF_SIZE)
             {
                 waiting++;
@@ -193,6 +196,8 @@ class CParallelFunnel : implements IRowStream, public CSimpleInterface
             }
             rows.enqueueMany(numRows, newRows);
             totSize += rowSizes;
+            if (totSize > peakTotSize)
+                peakTotSize = totSize;
             if (totSize > FUNNEL_MIN_BUFF_SIZE)
             {
                 waiting++;
@@ -229,6 +234,7 @@ class CParallelFunnel : implements IRowStream, public CSimpleInterface
         stopped = false;
         waiting = 0;
         totSize = 0;
+        peakTotSize = 0;
         eoss = 0;
         serializer.set(activity.queryRowSerializer());
         for (unsigned i=0; i<activity.queryNumInputs(); i++)
@@ -331,6 +337,11 @@ class CParallelFunnel : implements IRowStream, public CSimpleInterface
             fullSem.signal(numToSignal);
         return row.getClear();
     }
+    
+    size32_t getPeakRowMemory() const
+    {
+        return peakTotSize;
+    }
 
 friend class CInputHandler;
 };
@@ -562,6 +573,15 @@ class FunnelSlaveActivity : public CSlaveActivity
         calcMetaInfoSize(info, inputs);
     }
     virtual bool isGrouped() const override { return grouped; }
+    virtual void gatherActiveStats(CRuntimeStatisticCollection &activeStats) const override
+    {
+        PARENT::gatherActiveStats(activeStats);
+        if (parallelOutput)
+        {
+            CParallelFunnel *funnel = static_cast<CParallelFunnel *>(parallelOutput.get());
+            activeStats.setStatistic(StSizePeakRowMemory, funnel->getPeakRowMemory());
+        }
+    }
 };
 
 /////
diff --git a/thorlcr/activities/nsplitter/thnsplitterslave.cpp b/thorlcr/activities/nsplitter/thnsplitterslave.cpp
index f8a45eb529d..44da738447a 100644
--- a/thorlcr/activities/nsplitter/thnsplitterslave.cpp
+++ b/thorlcr/activities/nsplitter/thnsplitterslave.cpp
@@ -72,6 +72,7 @@ class CSplitterOutput : public CSimpleInterfaceOf<IStartableEngineRowStream>, pu
     virtual void stop() override;
     virtual const void *nextRow() override;
     virtual void resetEOF() { throwUnexpected(); }
+    virtual memsize_t getPeakRowMemory() const override { return 0; }
 };
 
 
@@ -407,7 +408,10 @@ class NSplitterSlaveActivity : public CSlaveActivity, implements ISharedSmartBuf
     {
         PARENT::gatherActiveStats(activeStats);
         if (sharedRowStream)
+        {
             mergeRemappedStats(activeStats, sharedRowStream, diskToTempStatsMap);
+            activeStats.setStatistic(StSizePeakRowMemory, sharedRowStream->getPeakRowMemory());
+        }
     }
 // ISharedSmartBufferCallback impl.
     virtual void paged() { pagedOut = true; }
diff --git a/thorlcr/activities/thactivityutil.cpp b/thorlcr/activities/thactivityutil.cpp
index 6aa574949b7..062efb31a63 100644
--- a/thorlcr/activities/thactivityutil.cpp
+++ b/thorlcr/activities/thactivityutil.cpp
@@ -302,6 +302,12 @@ class CRowStreamLookAhead : public CSimpleInterfaceOf<IStartableEngineRowStream>
                 throw getexception.getClear();
         }
     }
+    memsize_t getPeakRowMemory() const
+    {
+        if (smartbuf)
+            return smartbuf->getPeakRowMemory();
+        return 0;
+    }
 };
 
 
diff --git a/thorlcr/graph/thgraphslave.hpp b/thorlcr/graph/thgraphslave.hpp
index 542c73116ce..abf0854ad63 100644
--- a/thorlcr/graph/thgraphslave.hpp
+++ b/thorlcr/graph/thgraphslave.hpp
@@ -36,6 +36,7 @@
 interface IStartableEngineRowStream : extends IEngineRowStream
 {
     virtual void start() = 0;
+    virtual memsize_t getPeakRowMemory() const = 0;
 };
 
 class COutputTiming
@@ -186,6 +187,12 @@ class CThorInput : public CSimpleInterfaceOf<IInterface>
     }
     bool isFastThrough() const;
     bool suppressLookAhead() const;
+    memsize_t getPeakRowMemory() const
+    {
+        if (lookAhead && lookAheadActive)
+            return lookAhead->getPeakRowMemory();
+        return 0;
+    }
 };
 typedef IArrayOf<CThorInput> CThorInputArray;
 
@@ -229,6 +236,17 @@ class graphslave_decl CSlaveActivity : public CActivityBase, public CEdgeProgres
         offset_t peakTempSize = queryPeakTempSize();
         if (peakTempSize)
             activeStats.mergeStatistic(StSizePeakTempDisk, peakTempSize);
+        
+        // Gather peak row memory from all inputs with look-ahead
+        memsize_t totalPeakRowMemory = 0;
+        ForEachItemIn(i, inputs)
+        {
+            memsize_t inputPeak = inputs.item(i).getPeakRowMemory();
+            if (inputPeak > totalPeakRowMemory)
+                totalPeakRowMemory = inputPeak;
+        }
+        if (totalPeakRowMemory)
+            activeStats.setStatistic(StSizePeakRowMemory, totalPeakRowMemory);
     }
 public:
     IMPLEMENT_IINTERFACE_USING(CActivityBase)
diff --git a/thorlcr/thorutil/thbuf.cpp b/thorlcr/thorutil/thbuf.cpp
index 95d21791a26..c4c689f15ac 100644
--- a/thorlcr/thorutil/thbuf.cpp
+++ b/thorlcr/thorutil/thbuf.cpp
@@ -74,6 +74,7 @@ class CSmartRowBuffer: public CSimpleInterface, implements ISmartRowBuffer, impl
     CActivityBase *activity;
     ThorRowQueue *in;
     size32_t insz;
+    size32_t peakInsz;
     ThorRowQueue *out;
     CFileOwner tmpFileOwner;
     Owned<IFileIO> tempFileIO;
@@ -269,6 +270,7 @@ class CSmartRowBuffer: public CSimpleInterface, implements ISmartRowBuffer, impl
         blocksize = ((bufsize/2+0xfffff)/0x100000)*0x100000;
         numblocks = 0;
         insz = 0;
+        peakInsz = 0;
         eoi = false;
         diskfree.setown(createThreadSafeBitSet());
 
@@ -309,6 +311,8 @@ class CSmartRowBuffer: public CSimpleInterface, implements ISmartRowBuffer, impl
             diskflush();
         in->enqueue(row);
         insz += sz;
+        if (insz > peakInsz)
+            peakInsz = insz;
         if (waiting) {
             waitsem.signal();
             waiting = false;
@@ -447,6 +451,10 @@ class CSmartRowBuffer: public CSimpleInterface, implements ISmartRowBuffer, impl
         else
             return 0;
     }
+    size32_t getPeakRowMemory() const
+    {
+        return peakInsz;
+    }
 };
 
 
@@ -457,6 +465,7 @@ class CSmartRowInMemoryBuffer: public CSimpleInterface, implements ISmartRowBuff
     IThorRowInterfaces *rowIf;
     ThorRowQueue *in;
     size32_t insz;
+    size32_t peakInsz;
     SpinLock lock; // MORE: This lock is held for quite long periods.  I suspect it could be significantly optimized.
     bool waitingin;
     Semaphore waitinsem;
@@ -484,6 +493,7 @@ class CSmartRowInMemoryBuffer: public CSimpleInterface, implements ISmartRowBuff
         waitingout = false;
         blocksize = ((bufsize/2+0xfffff)/0x100000)*0x100000;
         insz = 0;
+        peakInsz = 0;
         eoi = false;
     }
 
@@ -524,6 +534,8 @@ class CSmartRowInMemoryBuffer: public CSimpleInterface, implements ISmartRowBuff
             if (!eoi) {
                 in->enqueue(row);
                 insz += sz;
+                if (insz > peakInsz)
+                    peakInsz = insz;
 #ifdef _TRACE_SMART_PUTGET
                 ActPrintLog(activity, "***putRow2(%x) insize = %d ",insz);
 #endif
@@ -649,6 +661,10 @@ class CSmartRowInMemoryBuffer: public CSimpleInterface, implements ISmartRowBuff
     {
         return 0;
     }
+    size32_t getPeakRowMemory() const
+    {
+        return peakInsz;
+    }
 };
 
 
@@ -741,6 +757,7 @@ class CCompressedSpillingRowStream: public CSimpleInterfaceOf<ISmartRowBuffer>,
     // in-memory related members
     CSPSCQueue<RowEntry> inMemRows;
     std::atomic<memsize_t> inMemRowsMemoryUsage = 0; // NB updated from writer and reader threads
+    std::atomic<memsize_t> peakInMemRowsMemoryUsage = 0;
     Semaphore moreRows;
     std::atomic<bool> readerWaitingForQ = false; // set by reader, cleared by writer
 
@@ -960,7 +977,10 @@ class CCompressedSpillingRowStream: public CSimpleInterfaceOf<ISmartRowBuffer>,
         if (queued)
         {
             trace("WRITE: Q: nextOutputRow: %" RCPF "u", nextOutputRow.load());
-            inMemRowsMemoryUsage += rowSz;
+            memsize_t newUsage = inMemRowsMemoryUsage += rowSz;
+            memsize_t currentPeak = peakInMemRowsMemoryUsage.load();
+            while (newUsage > currentPeak && !peakInMemRowsMemoryUsage.compare_exchange_weak(currentPeak, newUsage))
+                ;
             ++nextOutputRow;
             recentlyQueued = true;
         }
@@ -1111,6 +1131,10 @@ class CCompressedSpillingRowStream: public CSimpleInterfaceOf<ISmartRowBuffer>,
             v += currentOutputIFileIO->getStatistic(kind);
         return v;
     }
+    memsize_t getPeakRowMemory() const
+    {
+        return peakInMemRowsMemoryUsage.load();
+    }
 // IRowStream
     virtual const void *nextRow() override
     {
@@ -1846,6 +1870,10 @@ class CSharedWriteAheadBase : public CSimpleInterface, implements ISharedSmartBu
     {
         return 0;
     }
+    virtual memsize_t getPeakRowMemory() const override
+    {
+        return 0;
+    }
 friend class COutput;
 friend class CRowSet;
 };
@@ -2531,6 +2559,7 @@ class CSharedFullSpillingWriteAhead : public CInterfaceOf<ISharedRowStreamReader
     std::vector<Owned<COutputRowStream>> outputs;
     std::deque<std::tuple<const void *, size32_t>> rows;
     memsize_t rowsMemUsage = 0;
+    memsize_t peakRowsMemUsage = 0;
     std::atomic<rowcount_t> totalInputRowsRead = 0; // not used until spilling begins, represents count of all rows read
     rowcount_t inMemTotalRows = 0; // whilst in memory, represents count of all rows seen
     CriticalSection readAheadCS; // ensure single reader (leader), reads ahead (updates rows/totalInputRowsRead/inMemTotalRows)
@@ -2751,6 +2780,8 @@ class CSharedFullSpillingWriteAhead : public CInterfaceOf<ISharedRowStreamReader
                     size32_t sz = thorRowMemoryFootprint(serializer, row);
                     rows.emplace_back(row, sz);
                     rowsMemUsage += sz;
+                    if (rowsMemUsage > peakRowsMemUsage)
+                        peakRowsMemUsage = rowsMemUsage;
                     if ((rowsMemUsage >= options.inMemReadAheadGranularity) ||
                         (rows.size() >= options.inMemReadAheadGranularityRows))
                         break;
@@ -2813,6 +2844,10 @@ class CSharedFullSpillingWriteAhead : public CInterfaceOf<ISharedRowStreamReader
     {
         return stats.getStatisticValue(kind);
     }
+    memsize_t getPeakRowMemory() const
+    {
+        return peakRowsMemUsage;
+    }
 };
 
 ISharedRowStreamReader *createSharedFullSpillingWriteAhead(CActivityBase *_activity, unsigned numOutputs, IRowStream *_input, bool _inputGrouped, const SharedRowStreamReaderOptions &options, IThorRowInterfaces *_rowIf, const char *tempFileName, ICompressHandler *compressHandler)
diff --git a/thorlcr/thorutil/thbuf.hpp b/thorlcr/thorutil/thbuf.hpp
index 76dfa3cbcfd..948f7e2f94d 100644
--- a/thorlcr/thorutil/thbuf.hpp
+++ b/thorlcr/thorutil/thbuf.hpp
@@ -62,6 +62,7 @@ interface ISmartRowBuffer: extends IRowStream
 {
     virtual IRowWriter *queryWriter() = 0;
     virtual unsigned __int64 getStatistic(StatisticKind kind) const = 0;
+    virtual memsize_t getPeakRowMemory() const = 0;
 };
 
 class CActivityBase;
@@ -89,6 +90,7 @@ interface ISharedRowStreamReader : extends IInterface
     virtual void cancel()=0;
     virtual void reset() = 0;
     virtual unsigned __int64 getStatistic(StatisticKind kind) const = 0;
+    virtual memsize_t getPeakRowMemory() const = 0;
 };