diff --git a/source/libs/executor/src/scanoperator.c b/source/libs/executor/src/scanoperator.c
index 5db1e00410..23a2eb5492 100644
--- a/source/libs/executor/src/scanoperator.c
+++ b/source/libs/executor/src/scanoperator.c
@@ -31,6 +31,7 @@
 #include "thash.h"
 #include "ttypes.h"
 
+#define MULTI_READER_MAX_TABLE_NUM 5000
 #define SET_REVERSE_SCAN_FLAG(_info) ((_info)->scanFlag = REVERSE_SCAN)
 #define SWITCH_ORDER(n)              (((n) = ((n) == TSDB_ORDER_ASC) ? TSDB_ORDER_DESC : TSDB_ORDER_ASC))
 
@@ -44,6 +45,7 @@ typedef struct STableMergeScanSortSourceParam {
   int32_t        readerIdx;
   uint64_t       uid;
   SSDataBlock*   inputBlock;  
+  bool           multiReader;
   STsdbReader*   dataReader;
 } STableMergeScanSortSourceParam;
 
@@ -2595,7 +2597,7 @@ static SSDataBlock* getTableDataBlockImpl(void* param) {
   void*        p = tableListGetInfo(pTaskInfo->pTableInfoList, readIdx + pInfo->tableStartIndex);
   SReadHandle* pHandle = &pInfo->base.readHandle;
 
-  if (NULL == source->dataReader) {
+  if (NULL == source->dataReader || !source->multiReader) {
     code = tsdbReaderOpen(pHandle->vnode, pQueryCond, p, 1, pBlock, &source->dataReader, GET_TASKID(pTaskInfo));
     if (code != 0) {
       T_LONG_JMP(pTaskInfo->env, code);
@@ -2608,6 +2610,7 @@ static SSDataBlock* getTableDataBlockImpl(void* param) {
   while (tsdbNextDataBlock(reader)) {
     if (isTaskKilled(pTaskInfo)) {
       tsdbReleaseDataBlock(reader);
+      pInfo->base.dataReader = NULL;
       T_LONG_JMP(pTaskInfo->env, pTaskInfo->code);
     }
 
@@ -2641,10 +2644,18 @@ static SSDataBlock* getTableDataBlockImpl(void* param) {
     pInfo->base.readRecorder.elapsedTime += (taosGetTimestampUs() - st) / 1000.0;
 
     qTrace("tsdb/read-table-data: %p, close reader", reader);
+    if (!source->multiReader) {
+      tsdbReaderClose(pInfo->base.dataReader);
+      source->dataReader = NULL;
+    }
     pInfo->base.dataReader = NULL;
     return pBlock;
   }
 
+  if (!source->multiReader) {
+    tsdbReaderClose(pInfo->base.dataReader);
+    source->dataReader = NULL;
+  }
   pInfo->base.dataReader = NULL;
   return NULL;
 }
@@ -2716,6 +2727,7 @@ int32_t startGroupTableMergeScan(SOperatorInfo* pOperator) {
     STableMergeScanSortSourceParam param = {0};
     param.readerIdx = i;
     param.pOperator = pOperator;
+    param.multiReader = (numOfTable <= MULTI_READER_MAX_TABLE_NUM) ? true : false;
     param.inputBlock = createOneDataBlock(pInfo->pResBlock, false);
     blockDataEnsureCapacity(param.inputBlock, pOperator->resultInfo.capacity);
 
@@ -2877,6 +2889,9 @@ void destroyTableMergeScanOperatorInfo(void* param) {
     p->dataReader = NULL;
   }
 
+  tsdbReaderClose(pTableScanInfo->base.dataReader);
+  pTableScanInfo->base.dataReader = NULL;
+
   taosArrayDestroy(pTableScanInfo->sortSourceParams);
   tsortDestroySortHandle(pTableScanInfo->pSortHandle);
   pTableScanInfo->pSortHandle = NULL;