diff --git a/source/common/src/tdatablock.c b/source/common/src/tdatablock.c
index b2f03fa7ba..887a110831 100644
--- a/source/common/src/tdatablock.c
+++ b/source/common/src/tdatablock.c
@@ -632,7 +632,10 @@ int32_t blockDataToBuf(char* buf, const SSDataBlock* pBlock) {
         pStart += colSize;
       }
     } else {
-      memcpy(pStart, pCol->pData, dataSize);
+      if (dataSize != 0) {
+        // ubsan reports error if pCol->pData==NULL && dataSize==0
+        memcpy(pStart, pCol->pData, dataSize);
+      }
       pStart += dataSize;
     }
   }
@@ -684,8 +687,10 @@ int32_t blockDataFromBuf(SSDataBlock* pBlock, const char* buf) {
         return TSDB_CODE_FAILED;
       }
     }
-
-    memcpy(pCol->pData, pStart, colLength);
+    if (colLength != 0) {
+      // ubsan reports error if colLength==0 && pCol->pData == 0
+      memcpy(pCol->pData, pStart, colLength);
+    }
     pStart += colLength;
   }
 
diff --git a/source/libs/executor/inc/executorInt.h b/source/libs/executor/inc/executorInt.h
index 9c41eb2bf0..5baf0978cd 100644
--- a/source/libs/executor/inc/executorInt.h
+++ b/source/libs/executor/inc/executorInt.h
@@ -232,19 +232,20 @@ typedef struct STableMergeScanInfo {
   int32_t         tableEndIndex;
   bool            hasGroupId;
   uint64_t        groupId;
-  SArray*         queryConds;  // array of queryTableDataCond
   STableScanBase  base;
   int32_t         bufPageSize;
   uint32_t        sortBufSize;  // max buffer size for in-memory sort
   SArray*         pSortInfo;
   SSortHandle*    pSortHandle;
   SSDataBlock*    pSortInputBlock;
+  SSDataBlock*    pReaderBlock;
   int64_t         startTs;  // sort start time
   SArray*         sortSourceParams;
   SLimitInfo      limitInfo;
   int64_t         numOfRows;
   SScanInfo       scanInfo;
   int32_t         scanTimes;
+  int32_t         readIdx;
   SSDataBlock*    pResBlock;
   SSampleExecInfo sample;  // sample execution info
   SSortExecInfo   sortExecInfo;
diff --git a/source/libs/executor/inc/tsort.h b/source/libs/executor/inc/tsort.h
index 627aa825c6..538a9f18f6 100644
--- a/source/libs/executor/inc/tsort.h
+++ b/source/libs/executor/inc/tsort.h
@@ -26,6 +26,7 @@ extern "C" {
 enum {
   SORT_MULTISOURCE_MERGE = 0x1,
   SORT_SINGLESOURCE_SORT = 0x2,
+  SORT_BLOCK_TS_MERGE = 0x3
 };
 
 typedef struct SMultiMergeSource {
@@ -53,6 +54,12 @@ typedef struct SMsortComparParam {
   int32_t numOfSources;
   SArray* orderInfo;  // SArray<SBlockOrderInfo>
   bool    cmpGroupId;
+
+  int32_t sortType;
+  // the following field to speed up when sortType == SORT_BLOCK_TS_MERGE
+  int32_t tsSlotId;
+  int32_t order;
+  __compar_fn_t cmpFn;
 } SMsortComparParam;
 
 typedef struct SSortHandle  SSortHandle;
@@ -70,8 +77,8 @@ typedef int32_t (*_sort_merge_compar_fn_t)(const void* p1, const void* p2, void*
  * @return
  */
 SSortHandle* tsortCreateSortHandle(SArray* pOrderInfo, int32_t type, int32_t pageSize, int32_t numOfPages,
-                                   SSDataBlock* pBlock, const char* idstr, uint64_t maxRows, uint32_t maxTupleLength,
-                                   uint32_t sortBufSize);
+                                   SSDataBlock* pBlock, const char* idstr, uint64_t pqMaxRows, uint32_t pqMaxTupleLength,
+                                   uint32_t pqSortBufSize);
 
 void tsortSetForceUsePQSort(SSortHandle* pHandle);
 
@@ -110,6 +117,10 @@ int32_t tsortSetFetchRawDataFp(SSortHandle* pHandle, _sort_fetch_block_fn_t fetc
  */
 int32_t tsortSetComparFp(SSortHandle* pHandle, _sort_merge_compar_fn_t fp);
 
+/**
+ * 
+*/
+void tsortSetMergeLimit(SSortHandle* pHandle, int64_t mergeLimit);
 /**
  *
  */
diff --git a/source/libs/executor/src/scanoperator.c b/source/libs/executor/src/scanoperator.c
index f1de80ec4c..810f9709f5 100644
--- a/source/libs/executor/src/scanoperator.c
+++ b/source/libs/executor/src/scanoperator.c
@@ -13,8 +13,6 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
-// clang-format off
-
 #include "executorInt.h"
 #include "filter.h"
 #include "function.h"
@@ -55,8 +53,7 @@ typedef struct STableMergeScanSortSourceParam {
   SOperatorInfo* pOperator;
   int32_t        readerIdx;
   uint64_t       uid;
-  SSDataBlock*   inputBlock;
-  STsdbReader*   dataReader;
+  STsdbReader*   reader;
 } STableMergeScanSortSourceParam;
 
 typedef struct STableCountScanOperatorInfo {
@@ -2734,32 +2731,17 @@ static SSDataBlock* getTableDataBlockImpl(void* param) {
   SExecTaskInfo*                  pTaskInfo = pOperator->pTaskInfo;
   SStorageAPI* pAPI = &pTaskInfo->storageAPI;
 
-  int32_t                         readIdx = source->readerIdx;
-  SSDataBlock*                    pBlock = source->inputBlock;
+  SSDataBlock*                    pBlock = pInfo->pReaderBlock;
   int32_t                         code = 0;
 
-  SQueryTableDataCond* pQueryCond = taosArrayGet(pInfo->queryConds, readIdx);
-
   int64_t      st = taosGetTimestampUs();
-  void*        p = tableListGetInfo(pInfo->base.pTableListInfo, readIdx + pInfo->tableStartIndex);
-  SReadHandle* pHandle = &pInfo->base.readHandle;
-  if (NULL == source->dataReader) {
-    code = pAPI->tsdReader.tsdReaderOpen(pHandle->vnode, pQueryCond, p, 1, pBlock, (void**)&source->dataReader, GET_TASKID(pTaskInfo), false, NULL);
-    if (code != 0) {
-      T_LONG_JMP(pTaskInfo->env, code);
-    }
-  }
-
-  pInfo->base.dataReader = source->dataReader;
-  STsdbReader* reader = pInfo->base.dataReader;
   bool         hasNext = false;
-  qTrace("tsdb/read-table-data: %p, enter next reader", reader);
 
+  STsdbReader* reader = pInfo->base.dataReader;
   while (true) {
     code = pAPI->tsdReader.tsdNextDataBlock(reader, &hasNext);
     if (code != 0) {
       pAPI->tsdReader.tsdReaderReleaseDataBlock(reader);
-      pInfo->base.dataReader = NULL;
       T_LONG_JMP(pTaskInfo->env, code);
     }
 
@@ -2769,7 +2751,6 @@ static SSDataBlock* getTableDataBlockImpl(void* param) {
 
     if (isTaskKilled(pTaskInfo)) {
       pAPI->tsdReader.tsdReaderReleaseDataBlock(reader);
-      pInfo->base.dataReader = NULL;
       T_LONG_JMP(pTaskInfo->env, pTaskInfo->code);
     }
 
@@ -2779,12 +2760,6 @@ static SSDataBlock* getTableDataBlockImpl(void* param) {
       continue;
     }
 
-    if (pQueryCond->order == TSDB_ORDER_ASC) {
-      pQueryCond->twindows.skey = pBlock->info.window.ekey + 1;
-    } else {
-      pQueryCond->twindows.ekey = pBlock->info.window.skey - 1;
-    }
-
     uint32_t status = 0;
     code = loadDataBlock(pOperator, &pInfo->base, pBlock, &status);
     //    code = loadDataBlockFromOneTable(pOperator, pTableScanInfo, pBlock, &status);
@@ -2806,16 +2781,9 @@ static SSDataBlock* getTableDataBlockImpl(void* param) {
     pOperator->resultInfo.totalRows += pBlock->info.rows;
     pInfo->base.readRecorder.elapsedTime += (taosGetTimestampUs() - st) / 1000.0;
 
-    qTrace("tsdb/read-table-data: %p, close reader", reader);
-    pInfo->base.dataReader = NULL;
     return pBlock;
   }
 
-  pAPI->tsdReader.tsdReaderClose(source->dataReader);
-  source->dataReader = NULL;
-  pInfo->base.dataReader = NULL;
-  blockDataDestroy(source->inputBlock);
-  source->inputBlock = NULL;
   return NULL;
 }
 
@@ -2851,6 +2819,8 @@ int32_t dumpQueryTableCond(const SQueryTableDataCond* src, SQueryTableDataCond*
 int32_t startGroupTableMergeScan(SOperatorInfo* pOperator) {
   STableMergeScanInfo* pInfo = pOperator->info;
   SExecTaskInfo*       pTaskInfo = pOperator->pTaskInfo;
+  SReadHandle* pHandle = &pInfo->base.readHandle;
+  SStorageAPI* pAPI = &pTaskInfo->storageAPI;
 
   {
     size_t  numOfTables = tableListGetSize(pInfo->base.pTableListInfo);
@@ -2867,53 +2837,29 @@ int32_t startGroupTableMergeScan(SOperatorInfo* pOperator) {
   int32_t tableStartIdx = pInfo->tableStartIndex;
   int32_t tableEndIdx = pInfo->tableEndIndex;
 
-  pInfo->base.dataReader = NULL;
-
-  // todo the total available buffer should be determined by total capacity of buffer of this task.
-  // the additional one is reserved for merge result
-  // pInfo->sortBufSize = pInfo->bufPageSize * (tableEndIdx - tableStartIdx + 1 + 1);
-  int32_t kWay = (TSDB_MAX_BYTES_PER_ROW * 2) / (pInfo->pResBlock->info.rowSize);
-  if (kWay >= 128) {
-    kWay = 128;
-  } else if (kWay <= 2) {
-    kWay = 2;
-  } else {
-    int i = 2;
-    while (i * 2 <= kWay) i = i * 2;
-    kWay = i;
-  }
-
-  pInfo->sortBufSize = pInfo->bufPageSize * (kWay + 1);
+  pInfo->sortBufSize = 2048 * pInfo->bufPageSize;
   int32_t numOfBufPage = pInfo->sortBufSize / pInfo->bufPageSize;
-  pInfo->pSortHandle = tsortCreateSortHandle(pInfo->pSortInfo, SORT_MULTISOURCE_MERGE, pInfo->bufPageSize, numOfBufPage,
+  pInfo->pSortHandle = tsortCreateSortHandle(pInfo->pSortInfo, SORT_BLOCK_TS_MERGE, pInfo->bufPageSize, numOfBufPage,
                                              pInfo->pSortInputBlock, pTaskInfo->id.str, 0, 0, 0);
-
+  int64_t mergeLimit = -1;
+  if (pInfo->limitInfo.limit.limit != -1 || pInfo->limitInfo.limit.offset != -1) {
+    mergeLimit = pInfo->limitInfo.limit.limit + pInfo->limitInfo.limit.offset;
+  }                                             
+  tsortSetMergeLimit(pInfo->pSortHandle, mergeLimit);
   tsortSetFetchRawDataFp(pInfo->pSortHandle, getTableDataBlockImpl, NULL, NULL);
 
   // one table has one data block
   int32_t numOfTable = tableEndIdx - tableStartIdx + 1;
-  pInfo->queryConds = taosArrayInit(numOfTable, sizeof(SQueryTableDataCond));
 
-  for (int32_t i = 0; i < numOfTable; ++i) {
-    STableMergeScanSortSourceParam param = {0};
-    param.readerIdx = i;
-    param.pOperator = pOperator;
-    param.inputBlock = createOneDataBlock(pInfo->pResBlock, false);
+  STableMergeScanSortSourceParam param = {0};
+  param.pOperator = pOperator;
+  STableKeyInfo* startKeyInfo = tableListGetInfo(pInfo->base.pTableListInfo, tableStartIdx);
+  pAPI->tsdReader.tsdReaderOpen(pHandle->vnode, &pInfo->base.cond, startKeyInfo, numOfTable, pInfo->pReaderBlock, (void**)&pInfo->base.dataReader, GET_TASKID(pTaskInfo), false, NULL);
 
-    taosArrayPush(pInfo->sortSourceParams, &param);
-
-    SQueryTableDataCond cond;
-    dumpQueryTableCond(&pInfo->base.cond, &cond);
-    taosArrayPush(pInfo->queryConds, &cond);
-  }
-
-  for (int32_t i = 0; i < numOfTable; ++i) {
-    SSortSource*                    ps = taosMemoryCalloc(1, sizeof(SSortSource));
-    STableMergeScanSortSourceParam* param = taosArrayGet(pInfo->sortSourceParams, i);
-    ps->param = param;
-    ps->onlyRef = true;
-    tsortAddSource(pInfo->pSortHandle, ps);
-  }
+  SSortSource* ps = taosMemoryCalloc(1, sizeof(SSortSource));
+  ps->param = &param;
+  ps->onlyRef = true;
+  tsortAddSource(pInfo->pSortHandle, ps);
 
   int32_t code = tsortOpen(pInfo->pSortHandle);
 
@@ -2929,8 +2875,6 @@ int32_t stopGroupTableMergeScan(SOperatorInfo* pOperator) {
   SExecTaskInfo*       pTaskInfo = pOperator->pTaskInfo;
   SStorageAPI*         pAPI = &pTaskInfo->storageAPI;
 
-  int32_t numOfTable = taosArrayGetSize(pInfo->queryConds);
-
   SSortExecInfo sortExecInfo = tsortGetSortExecInfo(pInfo->pSortHandle);
   pInfo->sortExecInfo.sortMethod = sortExecInfo.sortMethod;
   pInfo->sortExecInfo.sortBuffer = sortExecInfo.sortBuffer;
@@ -2938,24 +2882,14 @@ int32_t stopGroupTableMergeScan(SOperatorInfo* pOperator) {
   pInfo->sortExecInfo.readBytes += sortExecInfo.readBytes;
   pInfo->sortExecInfo.writeBytes += sortExecInfo.writeBytes;
 
-  for (int32_t i = 0; i < numOfTable; ++i) {
-    STableMergeScanSortSourceParam* param = taosArrayGet(pInfo->sortSourceParams, i);
-    blockDataDestroy(param->inputBlock);
-    pAPI->tsdReader.tsdReaderClose(param->dataReader);
-    param->dataReader = NULL;
+  if (pInfo->base.dataReader != NULL) {
+    pAPI->tsdReader.tsdReaderClose(pInfo->base.dataReader);
+    pInfo->base.dataReader = NULL;
   }
-  taosArrayClear(pInfo->sortSourceParams);
 
   tsortDestroySortHandle(pInfo->pSortHandle);
   pInfo->pSortHandle = NULL;
 
-  for (int32_t i = 0; i < taosArrayGetSize(pInfo->queryConds); i++) {
-    SQueryTableDataCond* cond = taosArrayGet(pInfo->queryConds, i);
-    taosMemoryFree(cond->colList);
-  }
-  taosArrayDestroy(pInfo->queryConds);
-  pInfo->queryConds = NULL;
-
   resetLimitInfoForNextGroup(&pInfo->limitInfo);
   return TSDB_CODE_SUCCESS;
 }
@@ -2968,28 +2902,32 @@ SSDataBlock* getSortedTableMergeScanBlockData(SSortHandle* pHandle, SSDataBlock*
   SExecTaskInfo*       pTaskInfo = pOperator->pTaskInfo;
 
   blockDataCleanup(pResBlock);
-
+  STupleHandle* pTupleHandle = NULL;
   while (1) {
-    STupleHandle* pTupleHandle = tsortNextTuple(pHandle);
-    if (pTupleHandle == NULL) {
-      break;
+    while (1) {
+      pTupleHandle = tsortNextTuple(pHandle);
+      if (pTupleHandle == NULL) {
+        break;
+      }
+
+      appendOneRowToDataBlock(pResBlock, pTupleHandle);
+      if (pResBlock->info.rows >= capacity) {
+        break;
+      }
     }
 
-    appendOneRowToDataBlock(pResBlock, pTupleHandle);
-    if (pResBlock->info.rows >= capacity) {
-      break;
+    if (tsortIsClosed(pHandle)) {
+      terrno = TSDB_CODE_TSC_QUERY_CANCELLED;
+      T_LONG_JMP(pOperator->pTaskInfo->env, terrno);
     }
+
+    bool limitReached = applyLimitOffset(&pInfo->limitInfo, pResBlock, pTaskInfo);
+    qDebug("%s get sorted row block, rows:%" PRId64 ", limit:%" PRId64, GET_TASKID(pTaskInfo), pResBlock->info.rows,
+          pInfo->limitInfo.numOfOutputRows);
+    if (pTupleHandle == NULL || limitReached || pResBlock->info.rows > 0) {
+      break;
+    }  
   }
-
-  if (tsortIsClosed(pHandle)) {
-    terrno = TSDB_CODE_TSC_QUERY_CANCELLED;
-    T_LONG_JMP(pOperator->pTaskInfo->env, terrno);
-  }
-
-  bool limitReached = applyLimitOffset(&pInfo->limitInfo, pResBlock, pTaskInfo);
-  qDebug("%s get sorted row block, rows:%" PRId64 ", limit:%" PRId64, GET_TASKID(pTaskInfo), pResBlock->info.rows,
-         pInfo->limitInfo.numOfOutputRows);
-
   return (pResBlock->info.rows > 0) ? pResBlock : NULL;
 }
 
@@ -3053,14 +2991,7 @@ void destroyTableMergeScanOperatorInfo(void* param) {
   STableMergeScanInfo* pTableScanInfo = (STableMergeScanInfo*)param;
   cleanupQueryTableDataCond(&pTableScanInfo->base.cond);
 
-  int32_t numOfTable = taosArrayGetSize(pTableScanInfo->queryConds);
-
-  for (int32_t i = 0; i < numOfTable; i++) {
-    STableMergeScanSortSourceParam* p = taosArrayGet(pTableScanInfo->sortSourceParams, i);
-    blockDataDestroy(p->inputBlock);
-    pTableScanInfo->base.readerAPI.tsdReaderClose(p->dataReader);
-    p->dataReader = NULL;
-  }
+  int32_t numOfTable = taosArrayGetSize(pTableScanInfo->sortSourceParams);
 
   pTableScanInfo->base.readerAPI.tsdReaderClose(pTableScanInfo->base.dataReader);
   pTableScanInfo->base.dataReader = NULL;
@@ -3069,16 +3000,11 @@ void destroyTableMergeScanOperatorInfo(void* param) {
   tsortDestroySortHandle(pTableScanInfo->pSortHandle);
   pTableScanInfo->pSortHandle = NULL;
 
-  for (int i = 0; i < taosArrayGetSize(pTableScanInfo->queryConds); i++) {
-    SQueryTableDataCond* pCond = taosArrayGet(pTableScanInfo->queryConds, i);
-    taosMemoryFree(pCond->colList);
-  }
-
-  taosArrayDestroy(pTableScanInfo->queryConds);
   destroyTableScanBase(&pTableScanInfo->base, &pTableScanInfo->base.readerAPI);
 
   pTableScanInfo->pResBlock = blockDataDestroy(pTableScanInfo->pResBlock);
   pTableScanInfo->pSortInputBlock = blockDataDestroy(pTableScanInfo->pSortInputBlock);
+  pTableScanInfo->pReaderBlock = blockDataDestroy(pTableScanInfo->pReaderBlock);
 
   taosArrayDestroy(pTableScanInfo->pSortInfo);
   taosMemoryFreeClear(param);
@@ -3140,6 +3066,8 @@ SOperatorInfo* createTableMergeScanOperatorInfo(STableScanPhysiNode* pTableScanN
   pInfo->base.scanFlag = MAIN_SCAN;
   pInfo->base.readHandle = *readHandle;
 
+  pInfo->readIdx = -1;
+
   pInfo->base.limitInfo.limit.limit = -1;
   pInfo->base.limitInfo.slimit.limit = -1;
   pInfo->base.pTableListInfo = pTableListInfo;
@@ -3162,6 +3090,8 @@ SOperatorInfo* createTableMergeScanOperatorInfo(STableScanPhysiNode* pTableScanN
   pInfo->pSortInputBlock = createOneDataBlock(pInfo->pResBlock, false);
   initLimitInfo(pTableScanNode->scan.node.pLimit, pTableScanNode->scan.node.pSlimit, &pInfo->limitInfo);
 
+  pInfo->pReaderBlock = createOneDataBlock(pInfo->pResBlock, false);
+
   int32_t  rowSize = pInfo->pResBlock->info.rowSize;
   uint32_t nCols = taosArrayGetSize(pInfo->pResBlock->pDataBlock);
   pInfo->bufPageSize = getProperSortPageSize(rowSize, nCols);
@@ -3570,6 +3500,4 @@ static void destoryTableCountScanOperator(void* param) {
 
   taosArrayDestroy(pTableCountScanInfo->stbUidList);
   taosMemoryFreeClear(param);
-}
-
-// clang-format on
+}
\ No newline at end of file
diff --git a/source/libs/executor/src/tsort.c b/source/libs/executor/src/tsort.c
index d26db6536f..30e7148736 100644
--- a/source/libs/executor/src/tsort.c
+++ b/source/libs/executor/src/tsort.c
@@ -24,6 +24,7 @@
 #include "tpagedbuf.h"
 #include "tsort.h"
 #include "tutil.h"
+#include "tsimplehash.h"
 
 struct STupleHandle {
   SSDataBlock* pBlock;
@@ -42,13 +43,15 @@ struct SSortHandle {
   int64_t        startTs;
   uint64_t       totalElapsed;
 
-  uint64_t         maxRows;
-  uint32_t         maxTupleLength;
-  uint32_t         sortBufSize;
+  uint64_t         pqMaxRows;
+  uint32_t         pqMaxTupleLength;
+  uint32_t         pqSortBufSize;
   bool             forceUsePQSort;
   BoundedQueue*    pBoundedQueue;
   uint32_t         tmpRowIdx;
 
+  int64_t          mergeLimit;
+
   int32_t           sourceId;
   SSDataBlock*      pDataBlock;
   SMsortComparParam cmpParam;
@@ -173,8 +176,8 @@ void destroyTuple(void* t) {
  * @return
  */
 SSortHandle* tsortCreateSortHandle(SArray* pSortInfo, int32_t type, int32_t pageSize, int32_t numOfPages,
-                                   SSDataBlock* pBlock, const char* idstr, uint64_t maxRows, uint32_t maxTupleLength,
-                                   uint32_t sortBufSize) {
+                                   SSDataBlock* pBlock, const char* idstr, uint64_t pqMaxRows, uint32_t pqMaxTupleLength,
+                                   uint32_t pqSortBufSize) {
   SSortHandle* pSortHandle = taosMemoryCalloc(1, sizeof(SSortHandle));
 
   pSortHandle->type = type;
@@ -183,10 +186,10 @@ SSortHandle* tsortCreateSortHandle(SArray* pSortInfo, int32_t type, int32_t page
   pSortHandle->pSortInfo = pSortInfo;
   pSortHandle->loops = 0;
 
-  pSortHandle->maxTupleLength = maxTupleLength;
-  if (maxRows != 0) {
-    pSortHandle->sortBufSize = sortBufSize;
-    pSortHandle->maxRows = maxRows;
+  pSortHandle->pqMaxTupleLength = pqMaxTupleLength;
+  if (pqMaxRows != 0) {
+    pSortHandle->pqSortBufSize = pqSortBufSize;
+    pSortHandle->pqMaxRows = pqMaxRows;
   }
   pSortHandle->forceUsePQSort = false;
 
@@ -194,10 +197,18 @@ SSortHandle* tsortCreateSortHandle(SArray* pSortInfo, int32_t type, int32_t page
     pSortHandle->pDataBlock = createOneDataBlock(pBlock, false);
   }
 
+  pSortHandle->mergeLimit = -1;
+
   pSortHandle->pOrderedSource = taosArrayInit(4, POINTER_BYTES);
   pSortHandle->cmpParam.orderInfo = pSortInfo;
   pSortHandle->cmpParam.cmpGroupId = false;
-
+  pSortHandle->cmpParam.sortType = type;
+  if (type == SORT_BLOCK_TS_MERGE) {
+    SBlockOrderInfo* pOrder = TARRAY_GET_ELEM(pSortInfo, 0);
+    pSortHandle->cmpParam.tsSlotId = pOrder->slotId;
+    pSortHandle->cmpParam.order = pOrder->order;
+    pSortHandle->cmpParam.cmpFn = (pOrder->order == TSDB_ORDER_ASC) ? compareInt64Val : compareInt64ValDesc;
+  }
   tsortSetComparFp(pSortHandle, msortComparFn);
 
   if (idstr != NULL) {
@@ -469,11 +480,14 @@ static int32_t adjustMergeTreeForNextTuple(SSortSource* pSource, SMultiwayMergeT
     if (pHandle->type == SORT_SINGLESOURCE_SORT) {
       pSource->pageIndex++;
       if (pSource->pageIndex >= taosArrayGetSize(pSource->pageIdList)) {
+        qDebug("adjust merge tree. %d source completed %d", *numOfCompleted, pSource->pageIndex);
         (*numOfCompleted) += 1;
         pSource->src.rowIndex = -1;
         pSource->pageIndex = -1;
         pSource->src.pBlock = blockDataDestroy(pSource->src.pBlock);
       } else {
+        if (pSource->pageIndex % 512 == 0) qDebug("begin source %p page %d", pSource, pSource->pageIndex);
+
         int32_t* pPgId = taosArrayGet(pSource->pageIdList, pSource->pageIndex);
 
         void*   pPage = getBufPage(pHandle->pBuf, *pPgId);
@@ -486,7 +500,6 @@ static int32_t adjustMergeTreeForNextTuple(SSortSource* pSource, SMultiwayMergeT
         if (code != TSDB_CODE_SUCCESS) {
           return code;
         }
-
         releaseBufPage(pHandle->pBuf, pPage);
       }
     } else {
@@ -497,6 +510,7 @@ static int32_t adjustMergeTreeForNextTuple(SSortSource* pSource, SMultiwayMergeT
       if (pSource->src.pBlock == NULL) {
         (*numOfCompleted) += 1;
         pSource->src.rowIndex = -1;
+        qDebug("adjust merge tree. %d source completed", *numOfCompleted);
       }
     }
   }
@@ -577,53 +591,63 @@ int32_t msortComparFn(const void* pLeft, const void* pRight, void* param) {
     }
   }
 
-  for (int32_t i = 0; i < pInfo->size; ++i) {
-    SBlockOrderInfo* pOrder = TARRAY_GET_ELEM(pInfo, i);
-    SColumnInfoData* pLeftColInfoData = TARRAY_GET_ELEM(pLeftBlock->pDataBlock, pOrder->slotId);
+  if (pParam->sortType == SORT_BLOCK_TS_MERGE) {
+    SColumnInfoData* pLeftColInfoData = TARRAY_GET_ELEM(pLeftBlock->pDataBlock, pParam->tsSlotId);
+    SColumnInfoData* pRightColInfoData = TARRAY_GET_ELEM(pRightBlock->pDataBlock, pParam->tsSlotId);
+    int64_t*            left1 = (int64_t*)(pLeftColInfoData->pData) + pLeftSource->src.rowIndex;
+    int64_t*            right1 =  (int64_t*)(pRightColInfoData->pData) + pRightSource->src.rowIndex;
 
-    bool leftNull = false;
-    if (pLeftColInfoData->hasNull) {
-      if (pLeftBlock->pBlockAgg == NULL) {
-        leftNull = colDataIsNull_s(pLeftColInfoData, pLeftSource->src.rowIndex);
-      } else {
-        leftNull =
-            colDataIsNull(pLeftColInfoData, pLeftBlock->info.rows, pLeftSource->src.rowIndex, pLeftBlock->pBlockAgg[i]);
+    int ret = pParam->cmpFn(left1, right1);
+    return ret;
+  } else {
+    for (int32_t i = 0; i < pInfo->size; ++i) {
+      SBlockOrderInfo* pOrder = TARRAY_GET_ELEM(pInfo, i);
+      SColumnInfoData* pLeftColInfoData = TARRAY_GET_ELEM(pLeftBlock->pDataBlock, pOrder->slotId);
+      SColumnInfoData* pRightColInfoData = TARRAY_GET_ELEM(pRightBlock->pDataBlock, pOrder->slotId);
+
+      bool leftNull = false;
+      if (pLeftColInfoData->hasNull) {
+        if (pLeftBlock->pBlockAgg == NULL) {
+          leftNull = colDataIsNull_s(pLeftColInfoData, pLeftSource->src.rowIndex);
+        } else {
+          leftNull = colDataIsNull(pLeftColInfoData, pLeftBlock->info.rows, pLeftSource->src.rowIndex,
+                                   pLeftBlock->pBlockAgg[i]);
+        }
       }
-    }
 
-    SColumnInfoData* pRightColInfoData = TARRAY_GET_ELEM(pRightBlock->pDataBlock, pOrder->slotId);
-    bool             rightNull = false;
-    if (pRightColInfoData->hasNull) {
-      if (pRightBlock->pBlockAgg == NULL) {
-        rightNull = colDataIsNull_s(pRightColInfoData, pRightSource->src.rowIndex);
-      } else {
-        rightNull = colDataIsNull(pRightColInfoData, pRightBlock->info.rows, pRightSource->src.rowIndex,
-                                  pRightBlock->pBlockAgg[i]);
+      bool rightNull = false;
+      if (pRightColInfoData->hasNull) {
+        if (pRightBlock->pBlockAgg == NULL) {
+          rightNull = colDataIsNull_s(pRightColInfoData, pRightSource->src.rowIndex);
+        } else {
+          rightNull = colDataIsNull(pRightColInfoData, pRightBlock->info.rows, pRightSource->src.rowIndex,
+                                    pRightBlock->pBlockAgg[i]);
+        }
       }
-    }
 
-    if (leftNull && rightNull) {
-      continue;  // continue to next slot
-    }
+      if (leftNull && rightNull) {
+        continue;  // continue to next slot
+      }
 
-    if (rightNull) {
-      return pOrder->nullFirst ? 1 : -1;
-    }
+      if (rightNull) {
+        return pOrder->nullFirst ? 1 : -1;
+      }
 
-    if (leftNull) {
-      return pOrder->nullFirst ? -1 : 1;
-    }
+      if (leftNull) {
+        return pOrder->nullFirst ? -1 : 1;
+      }
 
-    void* left1 = colDataGetData(pLeftColInfoData, pLeftSource->src.rowIndex);
-    void* right1 = colDataGetData(pRightColInfoData, pRightSource->src.rowIndex);
+      void* left1 = colDataGetData(pLeftColInfoData, pLeftSource->src.rowIndex);
+      void* right1 = colDataGetData(pRightColInfoData, pRightSource->src.rowIndex);
 
-    __compar_fn_t fn = getKeyComparFunc(pLeftColInfoData->info.type, pOrder->order);
+      __compar_fn_t fn = getKeyComparFunc(pLeftColInfoData->info.type, pOrder->order);
 
-    int ret = fn(left1, right1);
-    if (ret == 0) {
-      continue;
-    } else {
-      return ret;
+      int ret = fn(left1, right1);
+      if (ret == 0) {
+        continue;
+      } else {
+        return ret;
+      }
     }
   }
   return 0;
@@ -668,6 +692,7 @@ static int32_t doInternalMergeSort(SSortHandle* pHandle) {
 
     // Only *numOfInputSources* can be loaded into buffer to perform the external sort.
     for (int32_t i = 0; i < sortGroup; ++i) {
+      qDebug("internal merge sort pass %d group %d. num input sources %d ", t, i, numOfInputSources);
       pHandle->sourceId += 1;
 
       int32_t end = (i + 1) * numOfInputSources - 1;
@@ -690,13 +715,15 @@ static int32_t doInternalMergeSort(SSortHandle* pHandle) {
         return code;
       }
 
+      int nMergedRows = 0;
+
       SArray* pPageIdList = taosArrayInit(4, sizeof(int32_t));
       while (1) {
         if (tsortIsClosed(pHandle)) {
           code = terrno = TSDB_CODE_TSC_QUERY_CANCELLED;
           return code;
         }
-        
+
         SSDataBlock* pDataBlock = getSortedBlockDataInner(pHandle, &pHandle->cmpParam, numOfRows);
         if (pDataBlock == NULL) {
           break;
@@ -720,8 +747,12 @@ static int32_t doInternalMergeSort(SSortHandle* pHandle) {
 
         setBufPageDirty(pPage, true);
         releaseBufPage(pHandle->pBuf, pPage);
+        nMergedRows += pDataBlock->info.rows;
 
         blockDataCleanup(pDataBlock);
+        if ((pHandle->mergeLimit != -1) && (nMergedRows >= pHandle->mergeLimit)) {
+          break;
+        }        
       }
 
       sortComparCleanup(&pHandle->cmpParam);
@@ -769,39 +800,285 @@ int32_t getProperSortPageSize(size_t rowSize, uint32_t numOfCols) {
   return pgSize;
 }
 
-static int32_t createInitialSources(SSortHandle* pHandle) {
-  size_t sortBufSize = pHandle->numOfPages * pHandle->pageSize;
+static int32_t createPageBuf(SSortHandle* pHandle) {
+  if (pHandle->pBuf == NULL) {
+    if (!osTempSpaceAvailable()) {
+      terrno = TSDB_CODE_NO_DISKSPACE;
+      qError("create page buf failed since %s, tempDir:%s", terrstr(), tsTempDir);
+      return terrno;
+    }
+
+    int32_t code = createDiskbasedBuf(&pHandle->pBuf, pHandle->pageSize, pHandle->numOfPages * pHandle->pageSize,
+                                      "tableBlocksBuf", tsTempDir);
+    dBufSetPrintInfo(pHandle->pBuf);
+    if (code != TSDB_CODE_SUCCESS) {
+      return code;
+    }
+  }
+  return 0;
+}
+
+typedef struct SBlkMergeSupport {
+  int64_t** aTs;
+  int32_t* aRowIdx;
+  int32_t order;
+} SBlkMergeSupport;
+
+static int32_t blockCompareTsFn(const void* pLeft, const void* pRight, void* param) {
+  int32_t left = *(int32_t*)pLeft;
+  int32_t right = *(int32_t*)pRight;
+
+  SBlkMergeSupport* pSup = (SBlkMergeSupport*)param;
+  if (pSup->aRowIdx[left] == -1) {
+    return 1;
+  } else if (pSup->aRowIdx[right] == -1) {
+    return -1;
+  }
+
+  int64_t leftTs = pSup->aTs[left][pSup->aRowIdx[left]];
+  int64_t rightTs = pSup->aTs[right][pSup->aRowIdx[right]];
+
+  int32_t ret = leftTs>rightTs ? 1 : ((leftTs < rightTs) ? -1 : 0);
+  if (pSup->order == TSDB_ORDER_DESC) {
+    ret = -1 * ret;
+  }
+  return ret;
+}
+
+static int32_t appendDataBlockToPageBuf(SSortHandle* pHandle, SSDataBlock* blk, SArray* aPgId) {
+  int32_t pageId = -1;
+  void*   pPage = getNewBufPage(pHandle->pBuf, &pageId);
+  taosArrayPush(aPgId, &pageId);
+
+  int32_t size = blockDataGetSize(blk) + sizeof(int32_t) + taosArrayGetSize(blk->pDataBlock) * sizeof(int32_t);
+  ASSERT(size <= getBufPageSize(pHandle->pBuf));
+
+  blockDataToBuf(pPage, blk);
+
+  setBufPageDirty(pPage, true);
+  releaseBufPage(pHandle->pBuf, pPage);
+
+  return 0;
+}
+
+static int32_t getPageBufIncForRow(SSDataBlock* blk, int32_t row, int32_t rowIdxInPage) {
+  int sz = 0;
+  int numCols = taosArrayGetSize(blk->pDataBlock);
+  if (!blk->info.hasVarCol) {
+    sz += numCols * ((rowIdxInPage & 0x7) == 0 ? 1: 0);
+    sz += blockDataGetRowSize(blk);
+  } else {
+    for (int32_t i = 0; i < numCols; ++i) {
+      SColumnInfoData* pColInfoData = TARRAY_GET_ELEM(blk->pDataBlock, i);
+      if (IS_VAR_DATA_TYPE(pColInfoData->info.type)) {
+        if (pColInfoData->varmeta.offset[row] != -1) {
+          char* p = colDataGetData(pColInfoData, row);
+          sz += varDataTLen(p);
+        }
+
+        sz += sizeof(pColInfoData->varmeta.offset[0]);
+      } else {
+        sz += pColInfoData->info.bytes;
+
+        if (((rowIdxInPage) & 0x07) == 0) {
+          sz += 1; // bitmap
+        }
+      }
+    }    
+  }
+  return sz;
+}
+
+static int32_t sortBlocksToExtSource(SSortHandle* pHandle, SArray* aBlk, SBlockOrderInfo* order, SArray* aExtSrc) {
+  int pgHeaderSz = sizeof(int32_t) + sizeof(int32_t) * taosArrayGetSize(pHandle->pDataBlock->pDataBlock);
+  int32_t rowCap = blockDataGetCapacityInRow(pHandle->pDataBlock, pHandle->pageSize, pgHeaderSz);
+  blockDataEnsureCapacity(pHandle->pDataBlock, rowCap);
+  blockDataCleanup(pHandle->pDataBlock);
+  int32_t numBlks = taosArrayGetSize(aBlk);
+
+  SBlkMergeSupport sup;
+  sup.aRowIdx = taosMemoryCalloc(numBlks, sizeof(int32_t));
+  sup.aTs = taosMemoryCalloc(numBlks, sizeof(int64_t*));
+  sup.order = order->order;
+  for (int i = 0; i < numBlks; ++i) {
+    SSDataBlock* blk = taosArrayGetP(aBlk, i);
+    SColumnInfoData* col = taosArrayGet(blk->pDataBlock, order->slotId);
+    sup.aTs[i] = (int64_t*)col->pData;
+    sup.aRowIdx[i] = 0;
+  }
+
+  int32_t totalRows = 0;
+  for (int i = 0; i < numBlks; ++i) {
+    SSDataBlock* blk = taosArrayGetP(aBlk, i);
+    totalRows += blk->info.rows;
+  }
+
+  SArray* aPgId = taosArrayInit(8, sizeof(int32_t));
+
+  SMultiwayMergeTreeInfo* pTree = NULL;        
+  tMergeTreeCreate(&pTree, taosArrayGetSize(aBlk), &sup, blockCompareTsFn);
+  int32_t nRows = 0;
+  int32_t nMergedRows = 0;
+  bool mergeLimitReached = false;
+  size_t blkPgSz = pgHeaderSz;
+
+  while (nRows < totalRows) {
+    int32_t minIdx = tMergeTreeGetChosenIndex(pTree);
+    SSDataBlock* minBlk = taosArrayGetP(aBlk, minIdx);
+    int32_t minRow = sup.aRowIdx[minIdx];
+    int32_t bufInc = getPageBufIncForRow(minBlk, minRow, pHandle->pDataBlock->info.rows);
+
+    if (blkPgSz <= pHandle->pageSize && blkPgSz + bufInc > pHandle->pageSize) {
+        appendDataBlockToPageBuf(pHandle, pHandle->pDataBlock, aPgId);
+        nMergedRows += pHandle->pDataBlock->info.rows;
+
+        blockDataCleanup(pHandle->pDataBlock);
+        blkPgSz = pgHeaderSz;
+        bufInc = getPageBufIncForRow(minBlk, minRow, 0);
+        if ((pHandle->mergeLimit != -1) && (nMergedRows >= pHandle->mergeLimit)) {
+          mergeLimitReached = true;
+          break;
+        }        
+    }
+    blockDataEnsureCapacity(pHandle->pDataBlock, pHandle->pDataBlock->info.rows + 1);
+    appendOneRowToDataBlock(pHandle->pDataBlock, minBlk, &minRow);
+    blkPgSz += bufInc;
+
+    ++nRows;
+
+    if (sup.aRowIdx[minIdx] == minBlk->info.rows - 1) {
+      sup.aRowIdx[minIdx] = -1;
+    } else {
+      ++sup.aRowIdx[minIdx];
+    }
+    tMergeTreeAdjust(pTree, tMergeTreeGetAdjustIndex(pTree));
+  }
+  if (pHandle->pDataBlock->info.rows > 0) {
+    if (!mergeLimitReached) {
+      appendDataBlockToPageBuf(pHandle, pHandle->pDataBlock, aPgId);
+      nMergedRows += pHandle->pDataBlock->info.rows;
+    }
+    blockDataCleanup(pHandle->pDataBlock);
+  }
+  SSDataBlock* pMemSrcBlk = createOneDataBlock(pHandle->pDataBlock, false);
+  doAddNewExternalMemSource(pHandle->pBuf, aExtSrc, pMemSrcBlk, &pHandle->sourceId, aPgId);
+
+  taosMemoryFree(sup.aRowIdx);
+  taosMemoryFree(sup.aTs);
+
+  tMergeTreeDestroy(&pTree);
+
+  return 0;
+}
+
+static int32_t createBlocksMergeSortInitialSources(SSortHandle* pHandle) {
+  SBlockOrderInfo* pOrder = taosArrayGet(pHandle->pSortInfo, 0);
+  size_t           nSrc = taosArrayGetSize(pHandle->pOrderedSource);
+  SArray*          aExtSrc = taosArrayInit(nSrc, POINTER_BYTES);
+
+  size_t maxBufSize = pHandle->numOfPages * pHandle->pageSize;
+  createPageBuf(pHandle);
+
+  SSortSource* pSrc = taosArrayGetP(pHandle->pOrderedSource, 0);
+  int32_t      szSort = 0;
+
+  SArray* aBlkSort = taosArrayInit(8, POINTER_BYTES);
+  SSHashObj* mUidBlk = tSimpleHashInit(64, taosGetDefaultHashFunction(TSDB_DATA_TYPE_UBIGINT));
+  while (1) {
+    SSDataBlock* pBlk = pHandle->fetchfp(pSrc->param);
+
+    if (pBlk != NULL) {
+      szSort += blockDataGetSize(pBlk);
+
+      void* ppBlk = tSimpleHashGet(mUidBlk, &pBlk->info.id.uid, sizeof(pBlk->info.id.uid));
+      if (ppBlk != NULL) {
+        SSDataBlock* tBlk = *(SSDataBlock**)(ppBlk);
+        blockDataMerge(tBlk, pBlk);
+      } else {
+        SSDataBlock* tBlk = createOneDataBlock(pBlk, true);
+        tSimpleHashPut(mUidBlk, &pBlk->info.id.uid, sizeof(pBlk->info.id.uid), &tBlk, POINTER_BYTES);
+        taosArrayPush(aBlkSort, &tBlk);
+      }
+    }
+
+    if ((pBlk != NULL && szSort > maxBufSize) || (pBlk == NULL && szSort > 0)) {
+      tSimpleHashClear(mUidBlk);
+
+      int64_t p = taosGetTimestampUs();
+      sortBlocksToExtSource(pHandle, aBlkSort, pOrder, aExtSrc);
+      int64_t el = taosGetTimestampUs() - p;
+      pHandle->sortElapsed += el;
+
+      for (int i = 0; i < taosArrayGetSize(aBlkSort); ++i) {
+        blockDataDestroy(taosArrayGetP(aBlkSort, i));
+      }
+      taosArrayClear(aBlkSort);
+      szSort = 0;
+      qDebug("source %zu created", taosArrayGetSize(aExtSrc));
+    }
+    if (pBlk == NULL) {
+      break;
+    };
+  }
+  tSimpleHashCleanup(mUidBlk);
+  taosArrayDestroy(aBlkSort);
+  tsortClearOrderdSource(pHandle->pOrderedSource, NULL, NULL);
+  taosArrayAddAll(pHandle->pOrderedSource, aExtSrc);
+  taosArrayDestroy(aExtSrc);
+
+  pHandle->type = SORT_SINGLESOURCE_SORT;
+  return 0;
+}
+
+static int32_t createBlocksQuickSortInitialSources(SSortHandle* pHandle) {
   int32_t code = 0;
+  size_t  sortBufSize = pHandle->numOfPages * pHandle->pageSize;
 
-  if (pHandle->type == SORT_SINGLESOURCE_SORT) {
-    SSortSource** pSource = taosArrayGet(pHandle->pOrderedSource, 0);
-    SSortSource*  source = *pSource;
-    *pSource = NULL;
+  SSortSource** pSource = taosArrayGet(pHandle->pOrderedSource, 0);
+  SSortSource*  source = *pSource;
+  *pSource = NULL;
 
-    tsortClearOrderdSource(pHandle->pOrderedSource, NULL, NULL);
+  tsortClearOrderdSource(pHandle->pOrderedSource, NULL, NULL);
 
-    while (1) {
-      SSDataBlock* pBlock = pHandle->fetchfp(source->param);
-      if (pBlock == NULL) {
-        break;
+  while (1) {
+    SSDataBlock* pBlock = pHandle->fetchfp(source->param);
+    if (pBlock == NULL) {
+      break;
+    }
+
+    if (pHandle->pDataBlock == NULL) {
+      uint32_t numOfCols = taosArrayGetSize(pBlock->pDataBlock);
+      pHandle->pageSize = getProperSortPageSize(blockDataGetRowSize(pBlock), numOfCols);
+
+      // todo, number of pages are set according to the total available sort buffer
+      pHandle->numOfPages = 1024;
+      sortBufSize = pHandle->numOfPages * pHandle->pageSize;
+      pHandle->pDataBlock = createOneDataBlock(pBlock, false);
+    }
+
+    if (pHandle->beforeFp != NULL) {
+      pHandle->beforeFp(pBlock, pHandle->param);
+    }
+
+    code = blockDataMerge(pHandle->pDataBlock, pBlock);
+    if (code != TSDB_CODE_SUCCESS) {
+      if (source->param && !source->onlyRef) {
+        taosMemoryFree(source->param);
       }
-
-      if (pHandle->pDataBlock == NULL) {
-        uint32_t numOfCols = taosArrayGetSize(pBlock->pDataBlock);
-        pHandle->pageSize = getProperSortPageSize(blockDataGetRowSize(pBlock), numOfCols);
-
-        // todo, number of pages are set according to the total available sort buffer
-        pHandle->numOfPages = 1024;
-        sortBufSize = pHandle->numOfPages * pHandle->pageSize;
-        pHandle->pDataBlock = createOneDataBlock(pBlock, false);
+      if (!source->onlyRef && source->src.pBlock) {
+        blockDataDestroy(source->src.pBlock);
+        source->src.pBlock = NULL;
       }
+      taosMemoryFree(source);
+      return code;
+    }
 
-      if (pHandle->beforeFp != NULL) {
-        pHandle->beforeFp(pBlock, pHandle->param);
-      }
-
-      code = blockDataMerge(pHandle->pDataBlock, pBlock);
-      if (code != TSDB_CODE_SUCCESS) {
+    size_t size = blockDataGetSize(pHandle->pDataBlock);
+    if (size > sortBufSize) {
+      // Perform the in-memory sort and then flush data in the buffer into disk.
+      int64_t p = taosGetTimestampUs();
+      code = blockDataSort(pHandle->pDataBlock, pHandle->pSortInfo);
+      if (code != 0) {
         if (source->param && !source->onlyRef) {
           taosMemoryFree(source->param);
         }
@@ -809,74 +1086,67 @@ static int32_t createInitialSources(SSortHandle* pHandle) {
           blockDataDestroy(source->src.pBlock);
           source->src.pBlock = NULL;
         }
+
         taosMemoryFree(source);
         return code;
       }
 
-      size_t size = blockDataGetSize(pHandle->pDataBlock);
-      if (size > sortBufSize) {
-        // Perform the in-memory sort and then flush data in the buffer into disk.
-        int64_t p = taosGetTimestampUs();
-        code = blockDataSort(pHandle->pDataBlock, pHandle->pSortInfo);
-        if (code != 0) {
-          if (source->param && !source->onlyRef) {
-            taosMemoryFree(source->param);
-          }
-          if (!source->onlyRef && source->src.pBlock) {
-            blockDataDestroy(source->src.pBlock);
-            source->src.pBlock = NULL;
-          }
-
-          taosMemoryFree(source);
-          return code;
-        }
-
-        int64_t el = taosGetTimestampUs() - p;
-        pHandle->sortElapsed += el;
-        if (pHandle->maxRows > 0) blockDataKeepFirstNRows(pHandle->pDataBlock, pHandle->maxRows);
-        code = doAddToBuf(pHandle->pDataBlock, pHandle);
-        if (code != TSDB_CODE_SUCCESS) {
-          return code;
-        }
-      }
-    }
-
-    if (source->param && !source->onlyRef) {
-      taosMemoryFree(source->param);
-    }
-
-    taosMemoryFree(source);
-
-    if (pHandle->pDataBlock != NULL && pHandle->pDataBlock->info.rows > 0) {
-      size_t size = blockDataGetSize(pHandle->pDataBlock);
-
-      // Perform the in-memory sort and then flush data in the buffer into disk.
-      int64_t p = taosGetTimestampUs();
-
-      code = blockDataSort(pHandle->pDataBlock, pHandle->pSortInfo);
-      if (code != 0) {
-        return code;
-      }
-
-      if (pHandle->maxRows > 0) blockDataKeepFirstNRows(pHandle->pDataBlock, pHandle->maxRows);
       int64_t el = taosGetTimestampUs() - p;
       pHandle->sortElapsed += el;
-
-      // All sorted data can fit in memory, external memory sort is not needed. Return to directly
-      if (size <= sortBufSize && pHandle->pBuf == NULL) {
-        pHandle->cmpParam.numOfSources = 1;
-        pHandle->inMemSort = true;
-
-        pHandle->loops = 1;
-        pHandle->tupleHandle.rowIndex = -1;
-        pHandle->tupleHandle.pBlock = pHandle->pDataBlock;
-        return 0;
-      } else {
-        code = doAddToBuf(pHandle->pDataBlock, pHandle);
+      if (pHandle->pqMaxRows > 0) blockDataKeepFirstNRows(pHandle->pDataBlock, pHandle->pqMaxRows);
+      code = doAddToBuf(pHandle->pDataBlock, pHandle);
+      if (code != TSDB_CODE_SUCCESS) {
+        return code;
       }
     }
   }
 
+  if (source->param && !source->onlyRef) {
+    taosMemoryFree(source->param);
+  }
+
+  taosMemoryFree(source);
+
+  if (pHandle->pDataBlock != NULL && pHandle->pDataBlock->info.rows > 0) {
+    size_t size = blockDataGetSize(pHandle->pDataBlock);
+
+    // Perform the in-memory sort and then flush data in the buffer into disk.
+    int64_t p = taosGetTimestampUs();
+
+    code = blockDataSort(pHandle->pDataBlock, pHandle->pSortInfo);
+    if (code != 0) {
+      return code;
+    }
+
+    if (pHandle->pqMaxRows > 0) blockDataKeepFirstNRows(pHandle->pDataBlock, pHandle->pqMaxRows);
+    int64_t el = taosGetTimestampUs() - p;
+    pHandle->sortElapsed += el;
+
+    // All sorted data can fit in memory, external memory sort is not needed. Return to directly
+    if (size <= sortBufSize && pHandle->pBuf == NULL) {
+      pHandle->cmpParam.numOfSources = 1;
+      pHandle->inMemSort = true;
+
+      pHandle->loops = 1;
+      pHandle->tupleHandle.rowIndex = -1;
+      pHandle->tupleHandle.pBlock = pHandle->pDataBlock;
+      return 0;
+    } else {
+      code = doAddToBuf(pHandle->pDataBlock, pHandle);
+    }
+  }
+  return code;
+}
+
+static int32_t createInitialSources(SSortHandle* pHandle) {
+  int32_t code = 0;
+
+  if (pHandle->type == SORT_SINGLESOURCE_SORT) {
+    code = createBlocksQuickSortInitialSources(pHandle);
+  } else if (pHandle->type == SORT_BLOCK_TS_MERGE) {
+    code = createBlocksMergeSortInitialSources(pHandle);
+  }
+  qDebug("%zu sources created", taosArrayGetSize(pHandle->pOrderedSource));
   return code;
 }
 
@@ -923,6 +1193,10 @@ void tsortSetClosed(SSortHandle* pHandle) {
   atomic_store_8(&pHandle->closed, 2);
 }
 
+void tsortSetMergeLimit(SSortHandle* pHandle, int64_t mergeLimit) {
+  pHandle->mergeLimit = mergeLimit;
+}
+
 int32_t tsortSetFetchRawDataFp(SSortHandle* pHandle, _sort_fetch_block_fn_t fetchFp, void (*fp)(SSDataBlock*, void*),
                                void* param) {
   pHandle->fetchfp = fetchFp;
@@ -1002,8 +1276,8 @@ void tsortSetForceUsePQSort(SSortHandle* pHandle) {
 static bool tsortIsPQSortApplicable(SSortHandle* pHandle) {
   if (pHandle->type != SORT_SINGLESOURCE_SORT) return false;
   if (tsortIsForceUsePQSort(pHandle)) return true;
-  uint64_t maxRowsFitInMemory = pHandle->sortBufSize / (pHandle->maxTupleLength + sizeof(char*));
-  return maxRowsFitInMemory > pHandle->maxRows;
+  uint64_t maxRowsFitInMemory = pHandle->pqSortBufSize / (pHandle->pqMaxTupleLength + sizeof(char*));
+  return maxRowsFitInMemory > pHandle->pqMaxRows;
 }
 
 static bool tsortPQCompFn(void* a, void* b, void* param) {
@@ -1049,7 +1323,7 @@ static int32_t tupleComparFn(const void* pLeft, const void* pRight, void* param)
 }
 
 static int32_t tsortOpenForPQSort(SSortHandle* pHandle) {
-  pHandle->pBoundedQueue = createBoundedQueue(pHandle->maxRows, tsortPQCompFn, destroyTuple, pHandle);
+  pHandle->pBoundedQueue = createBoundedQueue(pHandle->pqMaxRows, tsortPQCompFn, destroyTuple, pHandle);
   if (NULL == pHandle->pBoundedQueue) return TSDB_CODE_OUT_OF_MEMORY;
   tsortSetComparFp(pHandle, tupleComparFn);