diff --git a/source/common/src/tdatablock.c b/source/common/src/tdatablock.c
index f51023189dc8854f2a2d5233953e88e1b548a2b2..9f5a247d76e1ae26668597602eec8391cb0ad6bd 100644
--- a/source/common/src/tdatablock.c
+++ b/source/common/src/tdatablock.c
@@ -542,8 +542,10 @@ int32_t blockDataToBuf(char* buf, const SSDataBlock* pBlock) {
 }
 
 int32_t blockDataFromBuf(SSDataBlock* pBlock, const char* buf) {
-  pBlock->info.rows = *(int32_t*)buf;
+  int32_t numOfRows = *(int32_t*) buf;
+  blockDataEnsureCapacity(pBlock, numOfRows);
 
+  pBlock->info.rows = numOfRows;
   size_t      numOfCols = taosArrayGetSize(pBlock->pDataBlock);
   const char* pStart = buf + sizeof(uint32_t);
 
@@ -589,6 +591,7 @@ int32_t blockDataFromBuf(SSDataBlock* pBlock, const char* buf) {
   return TSDB_CODE_SUCCESS;
 }
 
+// todo remove this
 int32_t blockDataFromBuf1(SSDataBlock* pBlock, const char* buf, size_t capacity) {
   pBlock->info.rows = *(int32_t*)buf;
   pBlock->info.groupId = *(uint64_t*)(buf + sizeof(int32_t));
diff --git a/source/libs/executor/src/tfill.c b/source/libs/executor/src/tfill.c
index c008c7c4a9d0fec83188ae3eee55144242125db3..959c03a3b1464dc7e6f6fb42ba098d3e7e2b609b 100644
--- a/source/libs/executor/src/tfill.c
+++ b/source/libs/executor/src/tfill.c
@@ -53,8 +53,8 @@ static void setNullRow(SSDataBlock* pBlock, int64_t ts, int32_t rowIndex) {
   // the first are always the timestamp column, so start from the second column.
   for (int32_t i = 0; i < taosArrayGetSize(pBlock->pDataBlock); ++i) {
     SColumnInfoData* p = taosArrayGet(pBlock->pDataBlock, i);
-    if (p->info.type == TSDB_DATA_TYPE_TIMESTAMP) {
-        colDataAppend(p, rowIndex, (const char*)&ts, false);
+    if (p->info.type == TSDB_DATA_TYPE_TIMESTAMP) {  // handle timestamp
+      colDataAppend(p, rowIndex, (const char*)&ts, false);
     } else {
       colDataAppendNULL(p, rowIndex);
     }
@@ -83,15 +83,20 @@ static void doFillOneRow(SFillInfo* pFillInfo, SSDataBlock* pBlock, SSDataBlock*
   if (pFillInfo->type == TSDB_FILL_PREV) {
     SArray* p = FILL_IS_ASC_FILL(pFillInfo) ? pFillInfo->prev : pFillInfo->next;
 
-    for (int32_t i = 1; i < pFillInfo->numOfCols; ++i) {
+    for (int32_t i = 0; i < pFillInfo->numOfCols; ++i) {
       SFillColInfo* pCol = &pFillInfo->pFillCol[i];
       if (TSDB_COL_IS_TAG(pCol->flag)) {
         continue;
       }
 
-      SGroupKeys*      pKey = taosArrayGet(p, i);
       SColumnInfoData* pDstColInfoData = taosArrayGet(pBlock->pDataBlock, GET_DEST_SLOT_ID(pCol));
-      doSetVal(pDstColInfoData, index, pKey);
+
+      if (pDstColInfoData->info.type == TSDB_DATA_TYPE_TIMESTAMP) {
+        colDataAppend(pDstColInfoData, index, (const char*)&ts, false);
+      } else {
+        SGroupKeys* pKey = taosArrayGet(p, i);
+        doSetVal(pDstColInfoData, index, pKey);
+      }
     }
   } else if (pFillInfo->type == TSDB_FILL_NEXT) {
     SArray* p = FILL_IS_ASC_FILL(pFillInfo) ? pFillInfo->next : pFillInfo->prev;
@@ -264,9 +269,8 @@ static int32_t fillResultImpl(SFillInfo* pFillInfo, SSDataBlock* pBlock, int32_t
       assert(pFillInfo->currentKey == ts);
 
       if (pFillInfo->type == TSDB_FILL_NEXT && (pFillInfo->index + 1) < pFillInfo->numOfRows) {
-        ++pFillInfo->index;
-        copyCurrentRowIntoBuf(pFillInfo, pFillInfo->index, pFillInfo->next);
-        --pFillInfo->index;
+        int32_t nextRowIndex = pFillInfo->index + 1;
+        copyCurrentRowIntoBuf(pFillInfo, nextRowIndex, pFillInfo->next);
       }
 
       // assign rows to dst buffer
diff --git a/source/libs/function/src/builtinsimpl.c b/source/libs/function/src/builtinsimpl.c
index e622c0c1af457588a0f46b2fe9c2b4f948b582e8..97cb1f0ee112966412e777909387a3f6ad66aa67 100644
--- a/source/libs/function/src/builtinsimpl.c
+++ b/source/libs/function/src/builtinsimpl.c
@@ -3461,9 +3461,16 @@ void doAddIntoResult(SqlFunctionCtx* pCtx, void* pData, int32_t rowIndex, SSData
   }
 }
 
+/*
+ * +------------------------------------+--------------+--------------+
+ * |            null bitmap             |              |              |
+ * |(n columns, one bit for each column)| src column #1| src column #2|
+ * +------------------------------------+--------------+--------------+
+ */
 void saveTupleData(SqlFunctionCtx* pCtx, int32_t rowIndex, const SSDataBlock* pSrcBlock, STuplePos* pPos) {
   SFilePage* pPage = NULL;
 
+  // todo refactor: move away
   int32_t completeRowSize = pCtx->subsidiaries.num * sizeof(bool);
   for (int32_t j = 0; j < pCtx->subsidiaries.num; ++j) {
     SqlFunctionCtx* pc = pCtx->subsidiaries.pCtx[j];
@@ -3476,12 +3483,15 @@ void saveTupleData(SqlFunctionCtx* pCtx, int32_t rowIndex, const SSDataBlock* pS
   } else {
     pPage = getBufPage(pCtx->pBuf, pCtx->curBufPage);
     if (pPage->num + completeRowSize > getBufPageSize(pCtx->pBuf)) {
+      // current page is all used, let's prepare a new buffer page
+      releaseBufPage(pCtx->pBuf, pPage);
       pPage = getNewBufPage(pCtx->pBuf, 0, &pCtx->curBufPage);
       pPage->num = sizeof(SFilePage);
     }
   }
 
   pPos->pageId = pCtx->curBufPage;
+  pPos->offset = pPage->num;
 
   // keep the current row data, extract method
   int32_t offset = 0;
@@ -3509,7 +3519,6 @@ void saveTupleData(SqlFunctionCtx* pCtx, int32_t rowIndex, const SSDataBlock* pS
     offset += pCol->info.bytes;
   }
 
-  pPos->offset = pPage->num;
   pPage->num += completeRowSize;
 
   setBufPageDirty(pPage, true);
@@ -4839,7 +4848,7 @@ static void doReservoirSample(SqlFunctionCtx* pCtx, SSampleInfo* pInfo, char* da
   if (pInfo->numSampled < pInfo->samples) {
     sampleAssignResult(pInfo, data, pInfo->numSampled);
     if (pCtx->subsidiaries.num > 0) {
-      saveTupleData(pCtx, index, pCtx->pSrcBlock, pInfo->tuplePos + pInfo->numSampled * sizeof(STuplePos));
+      saveTupleData(pCtx, index, pCtx->pSrcBlock, &pInfo->tuplePos[pInfo->numSampled]);
     }
     pInfo->numSampled++;
   } else {
@@ -4847,7 +4856,7 @@ static void doReservoirSample(SqlFunctionCtx* pCtx, SSampleInfo* pInfo, char* da
     if (j < pInfo->samples) {
       sampleAssignResult(pInfo, data, j);
       if (pCtx->subsidiaries.num > 0) {
-        copyTupleData(pCtx, index, pCtx->pSrcBlock, pInfo->tuplePos + j * sizeof(STuplePos));
+        copyTupleData(pCtx, index, pCtx->pSrcBlock, &pInfo->tuplePos[j]);
       }
     }
   }
@@ -4885,7 +4894,7 @@ int32_t sampleFinalize(SqlFunctionCtx* pCtx, SSDataBlock* pBlock) {
   int32_t currentRow = pBlock->info.rows;
   for (int32_t i = 0; i < pInfo->numSampled; ++i) {
     colDataAppend(pCol, currentRow + i, pInfo->data + i * pInfo->colBytes, false);
-    setSelectivityValue(pCtx, pBlock, pInfo->tuplePos + i * sizeof(STuplePos), currentRow + i);
+    setSelectivityValue(pCtx, pBlock, &pInfo->tuplePos[i], currentRow + i);
   }
 
   return pInfo->numSampled;