diff --git a/include/libs/stream/tstream.h b/include/libs/stream/tstream.h
index 27a9168a99..fe6a7de734 100644
--- a/include/libs/stream/tstream.h
+++ b/include/libs/stream/tstream.h
@@ -59,9 +59,10 @@ extern "C" {
 #define STREAM_EXEC_T_RESUME_TASK       (-6)
 #define STREAM_EXEC_T_ADD_FAILED_TASK   (-7)
 
-typedef struct SStreamTask   SStreamTask;
-typedef struct SStreamQueue  SStreamQueue;
-typedef struct SStreamTaskSM SStreamTaskSM;
+typedef struct SStreamTask      SStreamTask;
+typedef struct SStreamQueue     SStreamQueue;
+typedef struct SStreamTaskSM    SStreamTaskSM;
+typedef struct SStreamQueueItem SStreamQueueItem;
 
 #define SSTREAM_TASK_VER                  4
 #define SSTREAM_TASK_INCOMPATIBLE_VER     1
@@ -153,10 +154,6 @@ typedef enum EStreamTaskEvent {
 
 typedef int32_t (*__state_trans_user_fn)(SStreamTask*, void* param);
 
-typedef struct {
-  int8_t type;
-} SStreamQueueItem;
-
 typedef void    FTbSink(SStreamTask* pTask, void* vnode, void* data);
 typedef void    FSmaSink(void* vnode, int64_t smaId, const SArray* data);
 typedef int32_t FTaskExpand(void* ahandle, SStreamTask* pTask, int64_t ver);
@@ -190,13 +187,6 @@ typedef struct {
   SSDataBlock* pBlock;
 } SStreamRefDataBlock;
 
-typedef struct SStreamQueueNode SStreamQueueNode;
-
-struct SStreamQueueNode {
-  SStreamQueueItem* item;
-  SStreamQueueNode* next;
-};
-
 SStreamDataSubmit* streamDataSubmitNew(SPackedData* pData, int32_t type);
 void               streamDataSubmitDestroy(SStreamDataSubmit* pDataSubmit);
 
@@ -437,7 +427,7 @@ struct SStreamTask {
   SCheckpointInfo     chkInfo;
   STaskExec           exec;
   SDataRange          dataRange;
-  SVersionRange       step2Range;
+  SVersionRange       step2Range;     // version range used to scan wal, information in dataRange should not modified.
   SHistoryTaskInfo    hTaskInfo;
   STaskId             streamTaskId;
   STaskExecStatisInfo execInfo;
@@ -445,14 +435,11 @@ struct SStreamTask {
   TdThreadMutex       lock;           // secure the operation of set task status and puting data into inputQ
   SMsgCb*             pMsgCb;         // msg handle
   SStreamState*       pState;         // state backend
-  SArray*             pRspMsgList;
   SUpstreamInfo       upstreamInfo;
   STaskCheckInfo      taskCheckInfo;
 
   // the followings attributes don't be serialized
   SScanhistorySchedInfo schedHistoryInfo;
-
-  int32_t             numOfWaitingUpstream;
   int32_t             refCnt;
   int32_t             transferStateAlignCnt;
   struct SStreamMeta* pMeta;
diff --git a/source/libs/stream/inc/streamInt.h b/source/libs/stream/inc/streamInt.h
index 949bc2e60b..3ccb25a62a 100644
--- a/source/libs/stream/inc/streamInt.h
+++ b/source/libs/stream/inc/streamInt.h
@@ -88,6 +88,10 @@ struct SStreamQueue {
   int8_t      status;
 };
 
+struct SStreamQueueItem {
+  int8_t type;
+};
+
 typedef enum {
   EXEC_CONTINUE = 0x0,
   EXEC_AFTER_IDLE = 0x1,
diff --git a/source/libs/stream/src/streamStartHistory.c b/source/libs/stream/src/streamStartHistory.c
index 98c0d95781..fb5b5e57d4 100644
--- a/source/libs/stream/src/streamStartHistory.c
+++ b/source/libs/stream/src/streamStartHistory.c
@@ -48,9 +48,9 @@ static int32_t streamTaskSetReady(SStreamTask* pTask) {
   SStreamTaskState* p = streamTaskGetStatus(pTask);
 
   if ((p->state == TASK_STATUS__SCAN_HISTORY) && pTask->info.taskLevel != TASK_LEVEL__SOURCE) {
-    pTask->numOfWaitingUpstream = taosArrayGetSize(pTask->upstreamInfo.pList);
+    int32_t numOfUps = taosArrayGetSize(pTask->upstreamInfo.pList);
     stDebug("s-task:%s level:%d task wait for %d upstream tasks complete scan-history procedure, status:%s",
-            pTask->id.idStr, pTask->info.taskLevel, pTask->numOfWaitingUpstream, p->name);
+            pTask->id.idStr, pTask->info.taskLevel, numOfUps, p->name);
   }
 
   ASSERT(pTask->status.downstreamReady == 0);
@@ -117,18 +117,16 @@ int32_t streamTaskStartScanHistory(SStreamTask* pTask) {
   int32_t     level = pTask->info.taskLevel;
   ETaskStatus status = streamTaskGetStatus(pTask)->state;
 
-  ASSERT((pTask->status.downstreamReady == 1) && (status == TASK_STATUS__SCAN_HISTORY));
+  ASSERT((pTask->status.downstreamReady == 1) && (status == TASK_STATUS__SCAN_HISTORY) &&
+         (pTask->info.fillHistory == 1));
 
   if (level == TASK_LEVEL__SOURCE) {
     return doStartScanHistoryTask(pTask);
   } else if (level == TASK_LEVEL__AGG) {
-    if (pTask->info.fillHistory) {
-      streamSetParamForScanHistory(pTask);
-    }
+    return streamSetParamForScanHistory(pTask);
   } else if (level == TASK_LEVEL__SINK) {
     stDebug("s-task:%s sink task do nothing to handle scan-history", pTask->id.idStr);
   }
-
   return 0;
 }
 
@@ -208,27 +206,21 @@ int32_t streamTaskOnNormalTaskReady(SStreamTask* pTask) {
 }
 
 int32_t streamTaskOnScanhistoryTaskReady(SStreamTask* pTask) {
-  const char* id = pTask->id.idStr;
-
   // set the state to be ready
   streamTaskSetReady(pTask);
   streamTaskSetRangeStreamCalc(pTask);
 
   SStreamTaskState* p = streamTaskGetStatus(pTask);
-  ASSERT(p->state == TASK_STATUS__SCAN_HISTORY);
+  ASSERT((p->state == TASK_STATUS__SCAN_HISTORY) && (pTask->info.fillHistory == 1));
 
-  if (pTask->info.fillHistory == 1) {
-    stDebug("s-task:%s fill-history task enters into scan-history data stage, status:%s", id, p->name);
-    streamTaskStartScanHistory(pTask);
-  } else {
-    stDebug("s-task:%s scan wal data, status:%s", id, p->name);
-  }
+  stDebug("s-task:%s fill-history task enters into scan-history data stage, status:%s", pTask->id.idStr, p->name);
+  streamTaskStartScanHistory(pTask);
 
   // NOTE: there will be an deadlock if launch fill history here.
-//  // start the related fill-history task, when current task is ready
-//  if (HAS_RELATED_FILLHISTORY_TASK(pTask)) {
-//    streamLaunchFillHistoryTask(pTask);
-//  }
+  // start the related fill-history task, when current task is ready
+  //  if (HAS_RELATED_FILLHISTORY_TASK(pTask)) {
+  //    streamLaunchFillHistoryTask(pTask);
+  //  }
 
   return TSDB_CODE_SUCCESS;
 }
@@ -515,6 +507,8 @@ bool streamHistoryTaskSetVerRangeStep2(SStreamTask* pTask, int64_t nextProcessVe
   SVersionRange* pRange = &pTask->dataRange.range;
   ASSERT(nextProcessVer >= pRange->maxVer);
 
+  // maxVer for fill-history task is the version, where the last timestamp is acquired.
+  // it's also the maximum version to scan data in tsdb.
   int64_t walScanStartVer = pRange->maxVer + 1;
   if (walScanStartVer > nextProcessVer - 1) {
     stDebug(
diff --git a/source/libs/stream/src/streamTask.c b/source/libs/stream/src/streamTask.c
index c7e34987ab..7f5ea52f58 100644
--- a/source/libs/stream/src/streamTask.c
+++ b/source/libs/stream/src/streamTask.c
@@ -456,11 +456,6 @@ void tFreeStreamTask(SStreamTask* pTask) {
     tSimpleHashCleanup(pTask->pNameMap);
   }
 
-  if (pTask->pRspMsgList != NULL) {
-    taosArrayDestroyEx(pTask->pRspMsgList, freeItem);
-    pTask->pRspMsgList = NULL;
-  }
-
   pTask->status.pSM = streamDestroyStateMachine(pTask->status.pSM);
   streamTaskDestroyUpstreamInfo(&pTask->upstreamInfo);