diff --git a/src/rootserver/ddl_task/ob_column_redefinition_task.cpp b/src/rootserver/ddl_task/ob_column_redefinition_task.cpp
index 57f1b3dd4..95785ddcf 100644
--- a/src/rootserver/ddl_task/ob_column_redefinition_task.cpp
+++ b/src/rootserver/ddl_task/ob_column_redefinition_task.cpp
@@ -142,6 +142,10 @@ int ObColumnRedefinitionTask::wait_data_complement(const ObDDLTaskStatus next_ta
   } else if (ObDDLTaskStatus::REDEFINITION != task_status_) {
     ret = OB_STATE_NOT_MATCH;
     LOG_WARN("task status not match", K(ret), K(task_status_));
+  } else if (OB_UNLIKELY(snapshot_version_ <= 0)) {
+    is_build_replica_end = true; // switch to fail.
+    ret = OB_ERR_UNEXPECTED;
+    LOG_WARN("unexpected snapshot", K(ret), KPC(this));
   } else if (!is_sstable_complete_task_submitted_ && OB_FAIL(send_build_single_replica_request())) {
     LOG_WARN("fail to send build single replica request", K(ret));
   } else if (is_sstable_complete_task_submitted_ && OB_FAIL(check_build_single_replica(is_build_replica_end))) {
diff --git a/src/rootserver/ddl_task/ob_constraint_task.cpp b/src/rootserver/ddl_task/ob_constraint_task.cpp
index 5df1c55d7..5c14b92c4 100644
--- a/src/rootserver/ddl_task/ob_constraint_task.cpp
+++ b/src/rootserver/ddl_task/ob_constraint_task.cpp
@@ -711,6 +711,9 @@ int ObConstraintTask::validate_constraint_valid()
   if (OB_UNLIKELY(!is_inited_)) {
     ret = OB_NOT_INIT;
     LOG_WARN("ObConstraintTask has not been inited", K(ret));
+  } else if (OB_UNLIKELY(snapshot_version_ <= 0)) {
+    ret = OB_ERR_UNEXPECTED;
+    LOG_WARN("unexpected snapshot", K(ret), KPC(this));
   } else if (OB_FAIL(check_replica_end(is_check_replica_end))) {
     LOG_WARN("check build replica end", K(ret));
   } else {
diff --git a/src/rootserver/ddl_task/ob_ddl_task.cpp b/src/rootserver/ddl_task/ob_ddl_task.cpp
index bb5749a6d..5a663a9fb 100644
--- a/src/rootserver/ddl_task/ob_ddl_task.cpp
+++ b/src/rootserver/ddl_task/ob_ddl_task.cpp
@@ -815,13 +815,14 @@ int ObDDLTask::update_task_record_status_and_msg(common::ObISQLClient &proxy, co
   return ret;
 }
 
-int ObDDLTask::switch_status(ObDDLTaskStatus new_status, const bool enable_flt, const int ret_code)
+int ObDDLTask::switch_status(const ObDDLTaskStatus new_status, const bool enable_flt, const int ret_code)
 {
   int ret = OB_SUCCESS;
   int tmp_ret = OB_SUCCESS;
   bool is_cancel = false;
   int real_ret_code = ret_code;
   bool is_tenant_dropped = false;
+  ObDDLTaskStatus real_new_status = new_status;
   const ObDDLTaskStatus old_status = task_status_;
   const bool error_need_retry = OB_SUCCESS != ret_code && is_error_need_retry(ret_code);
   if (OB_TMP_FAIL(SYS_TASK_STATUS_MGR.is_task_cancel(trace_id_, is_cancel))) {
@@ -831,11 +832,11 @@ int ObDDLTask::switch_status(ObDDLTaskStatus new_status, const bool enable_flt,
     real_ret_code = (OB_SUCCESS == ret_code || error_need_retry) ? OB_CANCELED : ret_code;
   } else if (SUCCESS == old_status || error_need_retry) {
     LOG_INFO("error code found, but execute again", K(ret_code), K(ret_code_), K(old_status), K(new_status), K(err_code_occurence_cnt_));
-    new_status = old_status;
+    real_new_status = old_status;
     real_ret_code = OB_SUCCESS;
   }
   ret_code_ = OB_SUCCESS == ret_code_ ? real_ret_code : ret_code_;
-  ObDDLTaskStatus real_new_status = ret_code_ != OB_SUCCESS ? FAIL : new_status;
+  real_new_status = OB_SUCCESS != real_ret_code ? FAIL : real_new_status;
   ObMySQLTransaction trans;
   ObRootService *root_service = nullptr;
   if (OB_ISNULL(root_service = GCTX.root_service_)) {
@@ -862,7 +863,7 @@ int ObDDLTask::switch_status(ObDDLTaskStatus new_status, const bool enable_flt,
       ret_code_ = OB_CANCELED;
     } else if (table_task_status == SUCCESS && old_status != table_task_status) {
       real_new_status = SUCCESS;
-    } else if (old_status == new_status) {
+    } else if (old_status == real_new_status) {
       // do nothing
     } else {
       if (OB_DDL_TASK_ENABLE_TRACING && enable_flt) {
@@ -872,7 +873,7 @@ int ObDDLTask::switch_status(ObDDLTaskStatus new_status, const bool enable_flt,
         }
       } else if (OB_FAIL(ObDDLTaskRecordOperator::update_task_status(
               trans, tenant_id_, task_id_, static_cast<int64_t>(real_new_status)))) {
-        LOG_WARN("update task status failed", K(ret), K(task_id_), K(new_status));
+        LOG_WARN("update task status failed", K(ret), K(task_id_), K(real_new_status));
       }
       if (OB_SUCC(ret)) {
         if (OB_FAIL(ObDDLTaskRecordOperator::update_ret_code(trans, tenant_id_, task_id_, ret_code_))) {
diff --git a/src/rootserver/ddl_task/ob_ddl_task.h b/src/rootserver/ddl_task/ob_ddl_task.h
index f724befd4..afc78b0e2 100644
--- a/src/rootserver/ddl_task/ob_ddl_task.h
+++ b/src/rootserver/ddl_task/ob_ddl_task.h
@@ -418,7 +418,7 @@ public:
   const ObString &get_ddl_stmt_str() const { return ddl_stmt_str_; }
   int set_ddl_stmt_str(const ObString &ddl_stmt_str);
   int convert_to_record(ObDDLTaskRecord &task_record, common::ObIAllocator &allocator);
-  int switch_status(share::ObDDLTaskStatus new_status, const bool enable_flt, const int ret_code);
+  int switch_status(const share::ObDDLTaskStatus new_status, const bool enable_flt, const int ret_code);
   int refresh_status();
   int refresh_schema_version();
   int remove_task_record();
diff --git a/src/rootserver/ddl_task/ob_index_build_task.cpp b/src/rootserver/ddl_task/ob_index_build_task.cpp
index e669bcca4..a78c2dca7 100644
--- a/src/rootserver/ddl_task/ob_index_build_task.cpp
+++ b/src/rootserver/ddl_task/ob_index_build_task.cpp
@@ -841,6 +841,9 @@ int ObIndexBuildTask::wait_data_complement()
     LOG_WARN("not init", K(ret));
   } else if (ObDDLTaskStatus::REDEFINITION != task_status_) {
     LOG_WARN("task status not match", K(ret), K(task_status_));
+  } else if (OB_UNLIKELY(snapshot_version_ <= 0)) {
+    ret = OB_ERR_UNEXPECTED;
+    LOG_WARN("unexpected snapshot", K(ret), KPC(this));
   }
   bool is_request_end = false;
 
diff --git a/src/rootserver/ddl_task/ob_table_redefinition_task.cpp b/src/rootserver/ddl_task/ob_table_redefinition_task.cpp
index 055757a99..ab5d8f16b 100644
--- a/src/rootserver/ddl_task/ob_table_redefinition_task.cpp
+++ b/src/rootserver/ddl_task/ob_table_redefinition_task.cpp
@@ -310,6 +310,10 @@ int ObTableRedefinitionTask::table_redefinition(const ObDDLTaskStatus next_task_
   if (OB_UNLIKELY(!is_inited_)) {
     ret = OB_NOT_INIT;
     LOG_WARN("ObTableRedefinitionTask has not been inited", K(ret));
+  } else if (OB_UNLIKELY(snapshot_version_ <= 0)) {
+    is_build_replica_end = true; // switch to fail.
+    ret = OB_ERR_UNEXPECTED;
+    LOG_WARN("unexpected snapshot", K(ret), KPC(this));
   }
 
   if (OB_SUCC(ret) && !is_build_replica_end && 0 == build_replica_request_time_) {