diff --git a/source/libs/executor/src/sortoperator.c b/source/libs/executor/src/sortoperator.c
index 6201dfc9cb..c292d7e9e1 100644
--- a/source/libs/executor/src/sortoperator.c
+++ b/source/libs/executor/src/sortoperator.c
@@ -732,12 +732,13 @@ void destroyMultiwayMergeOperatorInfo(void* param) {
 
 int32_t getMultiwayMergeExplainExecInfo(SOperatorInfo* pOptr, void** pOptrExplain, uint32_t* len) {
   ASSERT(pOptr != NULL);
-  SSortExecInfo* pInfo = taosMemoryCalloc(1, sizeof(SSortExecInfo));
+  SSortExecInfo* pSortExecInfo = taosMemoryCalloc(1, sizeof(SSortExecInfo));
 
-  SMultiwayMergeOperatorInfo* pOperatorInfo = (SMultiwayMergeOperatorInfo*)pOptr->info;
+  SMultiwayMergeOperatorInfo* pInfo = (SMultiwayMergeOperatorInfo*)pOptr->info;
+
+  *pSortExecInfo = tsortGetSortExecInfo(pInfo->pSortHandle);
+  *pOptrExplain = pSortExecInfo;
 
-  *pInfo = tsortGetSortExecInfo(pOperatorInfo->pSortHandle);
-  *pOptrExplain = pInfo;
   *len = sizeof(SSortExecInfo);
   return TSDB_CODE_SUCCESS;
 }
diff --git a/source/libs/executor/src/tsort.c b/source/libs/executor/src/tsort.c
index 1c31b550c6..02f2b15a8f 100644
--- a/source/libs/executor/src/tsort.c
+++ b/source/libs/executor/src/tsort.c
@@ -831,14 +831,19 @@ uint64_t tsortGetGroupId(STupleHandle* pVHandle) { return pVHandle->pBlock->info
 SSortExecInfo tsortGetSortExecInfo(SSortHandle* pHandle) {
   SSortExecInfo info = {0};
 
-  info.sortBuffer = pHandle->pageSize * pHandle->numOfPages;
-  info.sortMethod = pHandle->inMemSort ? SORT_QSORT_T : SORT_SPILLED_MERGE_SORT_T;
-  info.loops = pHandle->loops;
+  if (pHandle == NULL) {
+    info.sortMethod = SORT_QSORT_T; // by default
+    info.sortBuffer = 2 * 1048576;  // 2mb by default
+  } else {
+    info.sortBuffer = pHandle->pageSize * pHandle->numOfPages;
+    info.sortMethod = pHandle->inMemSort ? SORT_QSORT_T : SORT_SPILLED_MERGE_SORT_T;
+    info.loops = pHandle->loops;
 
-  if (pHandle->pBuf != NULL) {
-    SDiskbasedBufStatis st = getDBufStatis(pHandle->pBuf);
-    info.writeBytes = st.flushBytes;
-    info.readBytes = st.loadBytes;
+    if (pHandle->pBuf != NULL) {
+      SDiskbasedBufStatis st = getDBufStatis(pHandle->pBuf);
+      info.writeBytes = st.flushBytes;
+      info.readBytes = st.loadBytes;
+    }
   }
 
   return info;