diff --git a/source/common/src/tdatablock.c b/source/common/src/tdatablock.c
index 63c095ecf5904ad28675ce3c4de388556b4d62c5..33dc3a2469d79fab1035731cfeb5178f5c7a26d1 100644
--- a/source/common/src/tdatablock.c
+++ b/source/common/src/tdatablock.c
@@ -409,7 +409,7 @@ int32_t blockDataSplitRows(SSDataBlock* pBlock, bool hasVarCol, int32_t startInd
       }
     }
 
-    if (size > pageSize) {
+    if (size > pageSize) {  // pageSize must be able to hold one row
       *stopIndex = j - 1;
       ASSERT(*stopIndex >= startIndex);
 
diff --git a/source/libs/executor/src/executorimpl.c b/source/libs/executor/src/executorimpl.c
index f960993e3e9714074196d7ed359717ca93da7dac..b66107b4a708c63366abd138760ff767c9a2c247 100644
--- a/source/libs/executor/src/executorimpl.c
+++ b/source/libs/executor/src/executorimpl.c
@@ -6155,7 +6155,7 @@ SOperatorInfo* createSortOperatorInfo(SOperatorInfo* downstream, SSDataBlock* pR
     return NULL;
   }
 
-  pInfo->bufPageSize = rowSize < 1024 ? 1024 : rowSize*2;
+  pInfo->bufPageSize = rowSize < 1024 ? 1024*2 : rowSize*2; // there are headers, so pageSize = rowSize + header
 
   pInfo->sortBufSize = pInfo->bufPageSize * 16;  // TODO dynamic set the available sort buffer
   pInfo->numOfRowsInRes = 1024;
diff --git a/source/libs/executor/test/sortTests.cpp b/source/libs/executor/test/sortTests.cpp
index f1891f9c62d2140bdc5781efd1b757aa21d04a24..a89b76e81ecd03de63244c79547825fdbe83b0a7 100644
--- a/source/libs/executor/test/sortTests.cpp
+++ b/source/libs/executor/test/sortTests.cpp
@@ -287,7 +287,13 @@ TEST(testCase, external_mem_sort_Test) {
 
   for (int i = 0; i < 8; i++){
     SBlockOrderInfo oi = {0};
-    oi.order = TSDB_ORDER_ASC;
+
+    if(pInfo[i].type == TSDB_DATA_TYPE_NCHAR){
+      oi.order = TSDB_ORDER_DESC;
+    }else{
+      oi.order = TSDB_ORDER_ASC;
+    }
+
     oi.slotId = 0;
     SArray* orderInfo = taosArrayInit(1, sizeof(SBlockOrderInfo));
     taosArrayPush(orderInfo, &oi);
@@ -363,15 +369,16 @@ TEST(testCase, ordered_merge_sort_Test) {
   tsortSetFetchRawDataFp(phandle, getSingleColDummyBlock);
   tsortSetComparFp(phandle, docomp);
 
+  SGenericSource* p = static_cast<SGenericSource*>(taosMemoryCalloc(10, sizeof(SGenericSource)));
+  _info* c = static_cast<_info*>(taosMemoryCalloc(10, sizeof(_info)));
   for(int32_t i = 0; i < 10; ++i) {
-    SGenericSource* p = static_cast<SGenericSource*>(taosMemoryCalloc(1, sizeof(SGenericSource)));
-    _info* c = static_cast<_info*>(taosMemoryCalloc(1, sizeof(_info)));
-    c->count    = 1;
-    c->pageRows = 1000;
-    c->startVal = i*1000;
-
-    p->param = c;
-    tsortAddSource(phandle, p);
+    c[i].count    = 1;
+    c[i].pageRows = 1000;
+    c[i].startVal = i*1000;
+    c[i].type = TSDB_DATA_TYPE_INT;
+
+    p[i].param = c;
+    tsortAddSource(phandle, &p[i]);
   }
 
   int32_t code = tsortOpen(phandle);
@@ -388,8 +395,10 @@ TEST(testCase, ordered_merge_sort_Test) {
     ASSERT_EQ(row++, *(int32_t*) v);
 
   }
+  taosMemoryFree(p);
+  taosMemoryFree(c);
   tsortDestroySortHandle(phandle);
-  taosMemoryFree(pBlock);
+  blockDataDestroy(pBlock);
 }
 
 #endif