throw out schema error when sequence schema is not found

src/rootserver/ob_ddl_service.cpp

@@ -14667,7 +14667,7 @@ int ObDDLService::do_modify_system_variable(
   char value_buf[BUF_SIZE];
   ObString new_value(modify_var.get_value());
 
-  if (0 == MEMCMP(modify_var.get_name().ptr(), PARALLEL_MAX_SERVERS, modify_var.get_name().length())) {
+  if (0 == STRNCMP(modify_var.get_name().ptr(), PARALLEL_MAX_SERVERS, modify_var.get_name().length())) {
     // If the value of parallel_max_servers exceeds the maximum allowed by unit, reduce the configuration
     LOG_INFO("parallel_max_servers update", K(modify_var));
     common::ObArray<share::ObUnitInfo> units;

src/share/schema/ob_schema_getter_guard.cpp

@@ -5011,8 +5011,9 @@ int ObSchemaGetterGuard::get_sequence_schema(
   } else if (OB_FAIL(get_schema_v2(SEQUENCE_SCHEMA, sequence_id, sequence_schema))) {
     LOG_WARN("get sequence schema failed", K(sequence_id), K(ret));
   } else if (OB_ISNULL(sequence_schema)) {
-    ret = OB_ERR_UNEXPECTED;
-    LOG_WARN("NULL ptr", K(ret), K(sequence_id));
+    ret = OB_SCHEMA_ERROR;
+    LOG_WARN("sequence schema not exists", K(ret), K(sequence_id),
+             "pure_sequence_id", extract_pure_id(sequence_id));
   }
   return ret;
 }
@@ -5357,7 +5358,7 @@ int ObSchemaGetterGuard::check_tablegroup_exist(const uint64_t tablegroup_id, bo
   return ret;
 }
 
-/* https://docs.oracle.com/cd/E18283_01/server.112/e17118/sql_elements008.htm
+/*
  * Within a namespace, no two objects can have the same name.
    In oracle mode, the following schema objects share one namespace:
    Tables(create, rename, flashback)