Oracle Streams：ORA-0001出列了吗？

Question

在生产过程中，我们偶尔会在出列消息时出现ORA-0001错误。我们使用：

1. Solaris 10
2. Oracle 10g
3. C ++应用程序
4. PROC * C with dbms_aq package for queuing operations
5. 使用XML有效负载的队列
6. 我们处理大量邮件（1K /分钟）。

为什么出列会导致ORA-0001（唯一约束）错误的任何线索？

更新：按请求添加代码。

EXEC SQL EXECUTE
DECLARE
      message_properties dbms_aq.message_properties_t;
      dequeue_options    dbms_aq.dequeue_options_t;
      message_payload xmltype;
      tmpclob clob;
      dynamic_sql_string varchar2(512);

BEGIN
dequeue_options.wait := :iReadTimeout;
dequeue_options.dequeue_mode := dbms_aq.REMOVE;
dequeue_options.visibility := dbms_aq.ON_COMMIT;


IF :iBuffered = 1 then
    dequeue_options.delivery_mode := dbms_aq.buffered;
    dequeue_options.visibility := dbms_aq.immediate;
    :iNavigationMode := 0;
END IF;

IF :iDequeueOnly = 1 and :iQueueType <> 1 THEN
    dequeue_options.dequeue_mode := dbms_aq.REMOVE_NODATA;
    dequeue_options.wait := dbms_aq.NO_WAIT;
    dequeue_options.msgid := hextoraw(:pszDequeueMsgId);
ELSE
    IF :iNavigationMode = 0 THEN
       dequeue_options.navigation := dbms_aq.FIRST_MESSAGE;
    ELSE
       dequeue_options.navigation := dbms_aq.NEXT_MESSAGE;
    END IF;
END IF;


dequeue_options.deq_condition := :pszDeqCondition;

dbms_aq.dequeue(queue_name => :pszQueueName,
      message_properties => message_properties,
      dequeue_options => dequeue_options,
      payload => message_payload,
      msgid => :msgid );
IF dequeue_options.dequeue_mode <> dbms_aq.REMOVE_NODATA THEN
        EXECUTE IMMEDIATE dynamic_sql_string USING OUT tmpclob, IN message_payload;
        :gpoXmlClob := tmpclob;
ELSE
        :gpoXmlClob := message_payload.getclobval();
END IF;
END;