diff --git a/include/common/tcommon.h b/include/common/tcommon.h
index c0eb53d8ca..16653ebfee 100644
--- a/include/common/tcommon.h
+++ b/include/common/tcommon.h
@@ -70,7 +70,7 @@ typedef struct SDataBlockInfo {
   uint64_t    groupId;  // no need to serialize
   int16_t     numOfCols;
   int16_t     hasVarCol;
-  int16_t     capacity;
+  int32_t     capacity;
 } SDataBlockInfo;
 
 typedef struct SSDataBlock {
diff --git a/include/common/tdatablock.h b/include/common/tdatablock.h
index 71e2e4fba3..0d5262fe29 100644
--- a/include/common/tdatablock.h
+++ b/include/common/tdatablock.h
@@ -183,7 +183,7 @@ static FORCE_INLINE void colDataAppendDouble(SColumnInfoData* pColumnInfoData, u
 }
 
 int32_t colDataAppend(SColumnInfoData* pColumnInfoData, uint32_t currentRow, const char* pData, bool isNull);
-int32_t colDataMergeCol(SColumnInfoData* pColumnInfoData, uint32_t numOfRow1, const SColumnInfoData* pSource,
+int32_t colDataMergeCol(SColumnInfoData* pColumnInfoData, uint32_t numOfRow1, int32_t* capacity, const SColumnInfoData* pSource,
                         uint32_t numOfRow2);
 int32_t colDataAssign(SColumnInfoData* pColumnInfoData, const SColumnInfoData* pSource, int32_t numOfRows);
 int32_t blockDataUpdateTsWindow(SSDataBlock* pDataBlock);
diff --git a/source/common/src/tdatablock.c b/source/common/src/tdatablock.c
index 4a6fef4626..e703063dfa 100644
--- a/source/common/src/tdatablock.c
+++ b/source/common/src/tdatablock.c
@@ -168,13 +168,6 @@ static void doBitmapMerge(SColumnInfoData* pColumnInfoData, int32_t numOfRow1, c
 
   uint32_t total = numOfRow1 + numOfRow2;
 
-  if (BitmapLen(numOfRow1) < BitmapLen(total)) {
-    char*    tmp = taosMemoryRealloc(pColumnInfoData->nullbitmap, BitmapLen(total));
-    uint32_t extend = BitmapLen(total) - BitmapLen(numOfRow1);
-    memset(tmp + BitmapLen(numOfRow1), 0, extend);
-    pColumnInfoData->nullbitmap = tmp;
-  }
-
   uint32_t remindBits = BitPos(numOfRow1);
   uint32_t shiftBits = 8 - remindBits;
 
@@ -209,10 +202,9 @@ static void doBitmapMerge(SColumnInfoData* pColumnInfoData, int32_t numOfRow1, c
   }
 }
 
-int32_t colDataMergeCol(SColumnInfoData* pColumnInfoData, uint32_t numOfRow1, const SColumnInfoData* pSource,
-                        uint32_t numOfRow2) {
+int32_t colDataMergeCol(SColumnInfoData* pColumnInfoData, uint32_t numOfRow1, int32_t* capacity,
+                        const SColumnInfoData* pSource, uint32_t numOfRow2) {
   ASSERT(pColumnInfoData != NULL && pSource != NULL && pColumnInfoData->info.type == pSource->info.type);
-
   if (numOfRow2 == 0) {
     return numOfRow1;
   }
@@ -221,14 +213,19 @@ int32_t colDataMergeCol(SColumnInfoData* pColumnInfoData, uint32_t numOfRow1, co
     pColumnInfoData->hasNull = pSource->hasNull;
   }
 
+  uint32_t finalNumOfRows = numOfRow1 + numOfRow2;
   if (IS_VAR_DATA_TYPE(pColumnInfoData->info.type)) {
     // Handle the bitmap
-    char* p = taosMemoryRealloc(pColumnInfoData->varmeta.offset, sizeof(int32_t) * (numOfRow1 + numOfRow2));
-    if (p == NULL) {
-      return TSDB_CODE_OUT_OF_MEMORY;
+    if (finalNumOfRows > *capacity) {
+      char* p = taosMemoryRealloc(pColumnInfoData->varmeta.offset, sizeof(int32_t) * (numOfRow1 + numOfRow2));
+      if (p == NULL) {
+        return TSDB_CODE_OUT_OF_MEMORY;
+      }
+
+      *capacity = finalNumOfRows;
+      pColumnInfoData->varmeta.offset = (int32_t*)p;
     }
 
-    pColumnInfoData->varmeta.offset = (int32_t*)p;
     for (int32_t i = 0; i < numOfRow2; ++i) {
       if (pSource->varmeta.offset[i] == -1) {
         pColumnInfoData->varmeta.offset[i + numOfRow1] = -1;
@@ -253,15 +250,27 @@ int32_t colDataMergeCol(SColumnInfoData* pColumnInfoData, uint32_t numOfRow1, co
     memcpy(pColumnInfoData->pData + oldLen, pSource->pData, len);
     pColumnInfoData->varmeta.length = len + oldLen;
   } else {
-    doBitmapMerge(pColumnInfoData, numOfRow1, pSource, numOfRow2);
+    if (finalNumOfRows > *capacity) {
+      char* tmp = taosMemoryRealloc(pColumnInfoData->pData, finalNumOfRows * pColumnInfoData->info.bytes);
+      if (tmp == NULL) {
+        return TSDB_CODE_VND_OUT_OF_MEMORY;
+      }
 
-    int32_t newSize = (numOfRow1 + numOfRow2) * pColumnInfoData->info.bytes;
-    char*   tmp = taosMemoryRealloc(pColumnInfoData->pData, newSize);
-    if (tmp == NULL) {
-      return TSDB_CODE_VND_OUT_OF_MEMORY;
+      pColumnInfoData->pData = tmp;
+
+      if (BitmapLen(numOfRow1) < BitmapLen(finalNumOfRows)) {
+        char*    btmp = taosMemoryRealloc(pColumnInfoData->nullbitmap, BitmapLen(finalNumOfRows));
+        uint32_t extend = BitmapLen(finalNumOfRows) - BitmapLen(numOfRow1);
+        memset(btmp + BitmapLen(numOfRow1), 0, extend);
+
+        pColumnInfoData->nullbitmap = btmp;
+      }
+
+      *capacity = finalNumOfRows;
     }
 
-    pColumnInfoData->pData = tmp;
+    doBitmapMerge(pColumnInfoData, numOfRow1, pSource, numOfRow2);
+
     int32_t offset = pColumnInfoData->info.bytes * numOfRow1;
     memcpy(pColumnInfoData->pData + offset, pSource->pData, pSource->info.bytes * numOfRow2);
   }
@@ -350,29 +359,22 @@ int32_t blockDataUpdateTsWindow(SSDataBlock* pDataBlock) {
 // if pIndexMap = NULL, merger one column by on column
 int32_t blockDataMerge(SSDataBlock* pDest, const SSDataBlock* pSrc, SArray* pIndexMap) {
   assert(pSrc != NULL && pDest != NULL);
+  int32_t capacity = pDest->info.capacity;
 
-  int32_t numOfCols = pDest->info.numOfCols;
-  for (int32_t i = 0; i < numOfCols; ++i) {
+  for (int32_t i = 0; i < pDest->info.numOfCols; ++i) {
     int32_t mapIndex = i;
-    if(pIndexMap) {
+    if (pIndexMap) {
       mapIndex = *(int32_t*)taosArrayGet(pIndexMap, i);
     }
+
     SColumnInfoData* pCol2 = taosArrayGet(pDest->pDataBlock, i);
     SColumnInfoData* pCol1 = taosArrayGet(pSrc->pDataBlock, mapIndex);
 
-    uint32_t oldLen = colDataGetLength(pCol2, pDest->info.rows);
-    uint32_t newLen = colDataGetLength(pCol1, pSrc->info.rows);
-
-    int32_t newSize = oldLen + newLen;
-    char*   tmp = taosMemoryRealloc(pCol2->pData, newSize);
-    if (tmp != NULL) {
-      pCol2->pData = tmp;
-      colDataMergeCol(pCol2, pDest->info.rows, pCol1, pSrc->info.rows);
-    } else {
-      return TSDB_CODE_VND_OUT_OF_MEMORY;
-    }
+    capacity = pDest->info.capacity;
+    colDataMergeCol(pCol2, pDest->info.rows, &capacity, pCol1, pSrc->info.rows);
   }
 
+  pDest->info.capacity = capacity;
   pDest->info.rows += pSrc->info.rows;
   return TSDB_CODE_SUCCESS;
 }
diff --git a/source/libs/executor/src/executorimpl.c b/source/libs/executor/src/executorimpl.c
index f55d2acf28..4fabe128a8 100644
--- a/source/libs/executor/src/executorimpl.c
+++ b/source/libs/executor/src/executorimpl.c
@@ -1197,7 +1197,7 @@ int32_t projectApplyFunctions(SExprInfo* pExpr, SSDataBlock* pResult, SSDataBloc
     if (pExpr[k].pExpr->nodeType == QUERY_NODE_COLUMN) {  // it is a project query
       SColumnInfoData* pColInfoData = taosArrayGet(pResult->pDataBlock, outputSlotId);
       if (pResult->info.rows > 0 && !createNewColModel) {
-        colDataMergeCol(pColInfoData, pResult->info.rows, pfCtx->input.pData[0], pfCtx->input.numOfRows);
+        colDataMergeCol(pColInfoData, pResult->info.rows, &pResult->info.capacity, pfCtx->input.pData[0], pfCtx->input.numOfRows);
       } else {
         colDataAssign(pColInfoData, pfCtx->input.pData[0], pfCtx->input.numOfRows);
       }
@@ -1225,7 +1225,7 @@ int32_t projectApplyFunctions(SExprInfo* pExpr, SSDataBlock* pResult, SSDataBloc
       scalarCalculate(pExpr[k].pExpr->_optrRoot.pRootNode, pBlockList, &dest);
 
       int32_t startOffset = createNewColModel ? 0 : pResult->info.rows;
-      colDataMergeCol(pResColData, startOffset, &idata, dest.numOfRows);
+      colDataMergeCol(pResColData, startOffset, &pResult->info.capacity, &idata, dest.numOfRows);
 
       numOfRows = dest.numOfRows;
       taosArrayDestroy(pBlockList);
@@ -1266,7 +1266,7 @@ int32_t projectApplyFunctions(SExprInfo* pExpr, SSDataBlock* pResult, SSDataBloc
         }
 
         int32_t startOffset = createNewColModel ? 0 : pResult->info.rows;
-        colDataMergeCol(pResColData, startOffset, &idata, dest.numOfRows);
+        colDataMergeCol(pResColData, startOffset, &pResult->info.capacity, &idata, dest.numOfRows);
 
         numOfRows = dest.numOfRows;
         taosArrayDestroy(pBlockList);
@@ -7168,7 +7168,6 @@ int32_t getOperatorExplainExecInfo(SOperatorInfo* operatorInfo, SExplainExecInfo
 
 static SSDataBlock* doMergeJoin(struct SOperatorInfo* pOperator, bool* newgroup) {
   SJoinOperatorInfo* pJoinInfo = pOperator->info;
-  //  SOptrBasicInfo* pInfo = &pJoinInfo->binfo;
 
   SSDataBlock* pRes = pJoinInfo->pRes;
   blockDataCleanup(pRes);