diff --git a/src/sql/session/ob_sql_session_info.h b/src/sql/session/ob_sql_session_info.h
index 560d85645..061317f7f 100644
--- a/src/sql/session/ob_sql_session_info.h
+++ b/src/sql/session/ob_sql_session_info.h
@@ -125,8 +125,14 @@ public:
 struct ObContextUnit
 {
   inline void free(common::ObIAllocator &alloc) {
-    alloc.free(value_.ptr());
-    alloc.free(attribute_.ptr());
+    if (nullptr != value_.ptr()) {
+      alloc.free(value_.ptr());
+      value_.reset();
+    }
+    if (nullptr != attribute_.ptr()) {
+      alloc.free(attribute_.ptr());
+      attribute_.reset();
+    }
   }
   int deep_copy(const common::ObString &attribute,
                 const common::ObString &value,
@@ -136,6 +142,7 @@ struct ObContextUnit
       SQL_ENG_LOG(WARN, "failed to copy attribute", K(ret));
     } else if (OB_FAIL(ob_write_string(alloc, value, value_))) {
       alloc.free(attribute_.ptr());
+      attribute_.reset();
       SQL_ENG_LOG(WARN, "failed to copy value", K(ret));
     }
     return ret;
@@ -458,9 +465,11 @@ struct ObInnerContextMap {
     if (OB_NOT_NULL(context_map_)) {
       context_map_->destroy();
       alloc_.free(context_map_);
+      context_map_ = nullptr;
     }
     if (OB_NOT_NULL(context_name_.ptr())) {
       alloc_.free(context_name_.ptr());
+      context_name_.reset();
     }
   }
   int init()