diff --git a/source/dnode/vnode/src/tsdb/tsdbMergeTree.c b/source/dnode/vnode/src/tsdb/tsdbMergeTree.c
index d4af0422d7..d9d60442ff 100644
--- a/source/dnode/vnode/src/tsdb/tsdbMergeTree.c
+++ b/source/dnode/vnode/src/tsdb/tsdbMergeTree.c
@@ -404,7 +404,7 @@ void tLDataIterNextBlock(SLDataIter *pIter, const char *idStr) {
     tsdbDebug("try next last file block:%d from %d, trigger by uid:%" PRIu64 ", file index:%d, %s", pIter->iSttBlk,
               oldIndex, pIter->uid, pIter->iStt, idStr);
   } else {
-    tsdbDebug("no more last block qualified, uid:%" PRIu64 ", file index::%d, %s", pIter->uid, oldIndex, idStr);
+    tsdbDebug("no more last block qualified, uid:%" PRIu64 ", file index:%d, %s", pIter->uid, oldIndex, idStr);
   }
 }
 
diff --git a/source/dnode/vnode/src/tsdb/tsdbRead.c b/source/dnode/vnode/src/tsdb/tsdbRead.c
index 4c5b87559e..fd19e552c1 100644
--- a/source/dnode/vnode/src/tsdb/tsdbRead.c
+++ b/source/dnode/vnode/src/tsdb/tsdbRead.c
@@ -44,6 +44,7 @@ typedef struct SBlockIndex {
 typedef struct STableBlockScanInfo {
   uint64_t  uid;
   TSKEY     lastKey;
+  TSKEY     lastKeyInStt;       // last accessed key in stt
   SMapData  mapData;            // block info (compressed)
   SArray*   pBlockList;         // block data index list, SArray<SBlockIndex>
   SIterInfo iter;               // mem buffer skip list iterator
@@ -192,7 +193,7 @@ static TSDBROW* getValidMemRow(SIterInfo* pIter, const SArray* pDelList, STsdbRe
 static int32_t  doMergeRowsInFileBlocks(SBlockData* pBlockData, STableBlockScanInfo* pScanInfo, STsdbReader* pReader,
                                         SRowMerger* pMerger);
 static int32_t  doMergeRowsInLastBlock(SLastBlockReader* pLastBlockReader, STableBlockScanInfo* pScanInfo, int64_t ts,
-                                       SRowMerger* pMerger, SVersionRange* pVerRange);
+                                       SRowMerger* pMerger, SVersionRange* pVerRange, const char* id);
 static int32_t  doMergeRowsInBuf(SIterInfo* pIter, uint64_t uid, int64_t ts, SArray* pDelList, SRowMerger* pMerger,
                                  STsdbReader* pReader);
 static int32_t  doAppendRowFromTSRow(SSDataBlock* pBlock, STsdbReader* pReader, SRow* pTSRow,
@@ -402,9 +403,11 @@ static SHashObj* createDataBlockScanInfo(STsdbReader* pTsdbReader, SBlockInfoBuf
     if (ASCENDING_TRAVERSE(pTsdbReader->order)) {
       int64_t skey = pTsdbReader->window.skey;
       pScanInfo->lastKey = (skey > INT64_MIN) ? (skey - 1) : skey;
+      pScanInfo->lastKeyInStt = skey;
     } else {
       int64_t ekey = pTsdbReader->window.ekey;
       pScanInfo->lastKey = (ekey < INT64_MAX) ? (ekey + 1) : ekey;
+      pScanInfo->lastKeyInStt = ekey;
     }
 
     taosHashPut(pTableMap, &pScanInfo->uid, sizeof(uint64_t), &pScanInfo, POINTER_BYTES);
@@ -1795,21 +1798,18 @@ static bool nextRowFromLastBlocks(SLastBlockReader* pLastBlockReader, STableBloc
 
   while (1) {
     bool hasVal = tMergeTreeNext(&pLastBlockReader->mergeTree);
-    if (!hasVal) {
+    if (!hasVal) { // the next value will be the accessed key in stt
+      pScanInfo->lastKeyInStt += step;
       return false;
     }
 
     TSDBROW row = tMergeTreeGetRow(&pLastBlockReader->mergeTree);
     TSDBKEY k = TSDBROW_KEY(&row);
-    if (hasBeenDropped(pScanInfo->delSkyline, &pScanInfo->lastBlockDelIndex, &k, pLastBlockReader->order, pVerRange)) {
-      pScanInfo->lastKey = k.ts;
-    } else {
+    pScanInfo->lastKeyInStt = k.ts;
+
+    if (!hasBeenDropped(pScanInfo->delSkyline, &pScanInfo->lastBlockDelIndex, &k, pLastBlockReader->order, pVerRange)) {
       // the qualifed ts may equal to k.ts, only a greater version one.
       // here we need to fallback one step.
-      if (pScanInfo->lastKey == k.ts) {
-        pScanInfo->lastKey -= step;
-      }
-
       return true;
     }
   }
@@ -1949,7 +1949,7 @@ static int32_t doMergeBufAndFileRows(STsdbReader* pReader, STableBlockScanInfo*
           return code;
         }
       }
-      doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLast, &merge, &pReader->verRange);
+      doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLast, &merge, &pReader->verRange, pReader->idStr);
     }
 
     if (minKey == k.ts) {
@@ -1997,7 +1997,7 @@ static int32_t doMergeBufAndFileRows(STsdbReader* pReader, STableBlockScanInfo*
           return code;
         }
       }
-      doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLast, &merge, &pReader->verRange);
+      doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLast, &merge, &pReader->verRange, pReader->idStr);
     }
 
     if (minKey == key) {
@@ -2050,7 +2050,7 @@ static int32_t doMergeFileBlockAndLastBlock(SLastBlockReader* pLastBlockReader,
 
       TSDBROW fRow1 = tMergeTreeGetRow(&pLastBlockReader->mergeTree);
       tsdbRowMerge(&merge, &fRow1);
-      doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLastBlock, &merge, &pReader->verRange);
+      doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLastBlock, &merge, &pReader->verRange, pReader->idStr);
 
       code = tsdbRowMergerGetRow(&merge, &pTSRow);
       if (code != TSDB_CODE_SUCCESS) {
@@ -2068,7 +2068,7 @@ static int32_t doMergeFileBlockAndLastBlock(SLastBlockReader* pLastBlockReader,
       return code;
     }
 
-    doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLastBlock, &merge, &pReader->verRange);
+    doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLastBlock, &merge, &pReader->verRange, pReader->idStr);
 
     // merge with block data if ts == key
     if (tsLastBlock == pBlockData->aTSKEY[pDumpInfo->rowIndex]) {
@@ -2121,7 +2121,7 @@ static int32_t mergeFileBlockAndLastBlock(STsdbReader* pReader, SLastBlockReader
         TSDBROW fRow1 = tMergeTreeGetRow(&pLastBlockReader->mergeTree);
         tsdbRowMerge(&merge, &fRow1);
 
-        doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, ts, &merge, &pReader->verRange);
+        doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, ts, &merge, &pReader->verRange, pReader->idStr);
 
         code = tsdbRowMergerGetRow(&merge, &pTSRow);
         if (code != TSDB_CODE_SUCCESS) {
@@ -2230,7 +2230,7 @@ static int32_t doMergeMultiLevelRows(STsdbReader* pReader, STableBlockScanInfo*
         }
       }
 
-      doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLast, &merge, &pReader->verRange);
+      doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLast, &merge, &pReader->verRange, pReader->idStr);
     }
 
     if (minKey == ik.ts) {
@@ -2321,7 +2321,7 @@ static int32_t doMergeMultiLevelRows(STsdbReader* pReader, STableBlockScanInfo*
           return code;
         }
       }
-      doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLast, &merge, &pReader->verRange);
+      doMergeRowsInLastBlock(pLastBlockReader, pBlockScanInfo, tsLast, &merge, &pReader->verRange, pReader->idStr);
     }
 
     if (minKey == key) {
@@ -2472,9 +2472,9 @@ static bool initLastBlockReader(SLastBlockReader* pLBlockReader, STableBlockScan
   int32_t     step = ASCENDING_TRAVERSE(pLBlockReader->order) ? 1 : -1;
   STimeWindow w = pLBlockReader->window;
   if (ASCENDING_TRAVERSE(pLBlockReader->order)) {
-    w.skey = pScanInfo->lastKey + step;
+    w.skey = pScanInfo->lastKeyInStt;
   } else {
-    w.ekey = pScanInfo->lastKey + step;
+    w.ekey = pScanInfo->lastKeyInStt;
   }
 
   tsdbDebug("init last block reader, window:%" PRId64 "-%" PRId64 ", uid:%" PRIu64 ", %s", w.skey, w.ekey,
@@ -3568,13 +3568,16 @@ int32_t doMergeRowsInFileBlocks(SBlockData* pBlockData, STableBlockScanInfo* pSc
 }
 
 int32_t doMergeRowsInLastBlock(SLastBlockReader* pLastBlockReader, STableBlockScanInfo* pScanInfo, int64_t ts,
-                               SRowMerger* pMerger, SVersionRange* pVerRange) {
+                               SRowMerger* pMerger, SVersionRange* pVerRange, const char* idStr) {
   while (nextRowFromLastBlocks(pLastBlockReader, pScanInfo, pVerRange)) {
     int64_t next1 = getCurrentKeyInLastBlock(pLastBlockReader);
     if (next1 == ts) {
       TSDBROW fRow1 = tMergeTreeGetRow(&pLastBlockReader->mergeTree);
       tsdbRowMerge(pMerger, &fRow1);
     } else {
+      tsdbTrace("uid:%" PRIu64 " last del index:%d, del range:%d, lastKeyInStt:%" PRId64 ", %s", pScanInfo->uid,
+                pScanInfo->lastBlockDelIndex, (int32_t)taosArrayGetSize(pScanInfo->delSkyline), pScanInfo->lastKeyInStt,
+                idStr);
       break;
     }
   }
@@ -3937,6 +3940,17 @@ int32_t tsdbSetTableList(STsdbReader* pReader, const void* pTableList, int32_t n
     pInfo->uid = pList[i].uid;
     pUidList->tableUidList[i] = pList[i].uid;
 
+    // todo extract method
+    if (ASCENDING_TRAVERSE(pReader->order)) {
+      int64_t skey = pReader->window.skey;
+      pInfo->lastKey = (skey > INT64_MIN) ? (skey - 1) : skey;
+      pInfo->lastKeyInStt = skey;
+    } else {
+      int64_t ekey = pReader->window.ekey;
+      pInfo->lastKey = (ekey < INT64_MAX) ? (ekey + 1) : ekey;
+      pInfo->lastKeyInStt = ekey;
+    }
+
     taosHashPut(pReader->status.pTableMap, &pInfo->uid, sizeof(uint64_t), &pInfo, POINTER_BYTES);
   }
 
@@ -4721,8 +4735,12 @@ int32_t tsdbReaderReset(STsdbReader* pReader, SQueryTableDataCond* pCond) {
   return code;
 }
 
-static int32_t getBucketIndex(int32_t startRow, int32_t bucketRange, int32_t numOfRows) {
-  return (numOfRows - startRow) / bucketRange;
+static int32_t getBucketIndex(int32_t startRow, int32_t bucketRange, int32_t numOfRows, int32_t numOfBucket) {
+  int32_t bucketIndex = (numOfRows - startRow) / bucketRange;
+  if (bucketIndex == numOfBucket) {
+    bucketIndex -= 1;
+  }
+  return bucketIndex;
 }
 
 int32_t tsdbGetFileBlocksDistInfo(STsdbReader* pReader, STableBlockDistInfo* pTableBlockInfo) {
@@ -4731,8 +4749,9 @@ int32_t tsdbGetFileBlocksDistInfo(STsdbReader* pReader, STableBlockDistInfo* pTa
   pTableBlockInfo->totalRows = 0;
   pTableBlockInfo->numOfVgroups = 1;
 
-  // find the start data block in file
+  const int32_t numOfBucket = 20.0;
 
+  // find the start data block in file
   tsdbAcquireReader(pReader);
   if (pReader->suspended) {
     tsdbReaderResume(pReader);
@@ -4743,7 +4762,7 @@ int32_t tsdbGetFileBlocksDistInfo(STsdbReader* pReader, STableBlockDistInfo* pTa
   pTableBlockInfo->defMinRows = pc->minRows;
   pTableBlockInfo->defMaxRows = pc->maxRows;
 
-  int32_t bucketRange = ceil((pc->maxRows - pc->minRows) / 20.0);
+  int32_t bucketRange = ceil((pc->maxRows - pc->minRows) / numOfBucket);
 
   pTableBlockInfo->numOfFiles += 1;
 
@@ -4781,7 +4800,7 @@ int32_t tsdbGetFileBlocksDistInfo(STsdbReader* pReader, STableBlockDistInfo* pTa
 
       pTableBlockInfo->totalSize += pBlock->aSubBlock[0].szBlock;
 
-      int32_t bucketIndex = getBucketIndex(pTableBlockInfo->defMinRows, bucketRange, numOfRows);
+      int32_t bucketIndex = getBucketIndex(pTableBlockInfo->defMinRows, bucketRange, numOfRows, numOfBucket);
       pTableBlockInfo->blockRowsHisto[bucketIndex]++;
 
       hasNext = blockIteratorNext(&pStatus->blockIter, pReader->idStr);
diff --git a/tests/pytest/util/dnodes.py b/tests/pytest/util/dnodes.py
index ddb3bfaa26..360843c46c 100644
--- a/tests/pytest/util/dnodes.py
+++ b/tests/pytest/util/dnodes.py
@@ -45,6 +45,8 @@ class TDSimClient:
             "supportVnodes": "1024",
             "enableQueryHb": "1",
             "telemetryReporting": "0",
+            "tqDebugflag": "135",
+            "wDebugflag":"135",
         }
 
     def getLogDir(self):
diff --git a/tests/script/tsim/parser/sliding.sim b/tests/script/tsim/parser/sliding.sim
index b9353e2c61..45a49fbc4e 100644
--- a/tests/script/tsim/parser/sliding.sim
+++ b/tests/script/tsim/parser/sliding.sim
@@ -49,9 +49,23 @@ while $i < $tbNum
     $nchar = $nchar . $c
     $nchar = $nchar . '
 
-    sql insert into $tb values ($tstart , $c , $c , $c , $c , $c , $c , $c , $binary , $nchar )
-    $tstart = $tstart + 30
-    $x = $x + 1
+    $next = $tstart + 30
+    $f = $x + 1
+    $c1 = $f / 100
+    $c1 = $c1 * 100
+    $c1 = $f - $c1
+
+    $binary1 = ' . binary
+    $binary1 = $binary1 . $c1
+    $binary1 = $binary1 . '
+
+    $nchar1 = ' . nchar
+    $nchar1 = $nchar1 . $c1
+    $nchar1 = $nchar1 . '
+
+    sql insert into $tb values ($tstart , $c , $c , $c , $c , $c , $c , $c , $binary , $nchar ) ($next , $c1 , $c1 , $c1 , $c1 , $c1 , $c1 , $c1 , $binary1 , $nchar1 )
+    $tstart = $tstart + 60
+    $x = $x + 2
   endw
 
   $i = $i + 1