Database Change Notification的一个例子

ORACLE提供的Databas Change Notification特性让我们可以通过Register的形式告诉数据库，
用户对某些表的内容改变感兴趣。最常用的地方是，在数据发生变化后，刷新Mid-Tier的数据
Cache.摘录一段文档内容
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Database Change Notification is a feature that enables client applications to register
queries with the database and receive notifications in response to DML or DDL
changes on the objects associated with the queries. The notifications are published by
the database when the DML or DDL transaction commits.
During registration, the application specifies a notification handler and associates a set
of interesting queries with the notification handler. A notification handler can be either
a server side PL/SQL procedure or a client side C callback. Registrations are created
on all objects referenced during the execution of the queries. The notification handler
is invoked when a transaction subsequently changes any of the registered objects and
commits.
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使用的对象以及关系
        sys.chnf$_desc <-- sys.chnf$_tdesc <-- sys.chnf$_rdesc

SQL> desc sys.chnf$_desc
Element          Type                  
---------------- ---------------------
REGISTRATION_ID  NUMBER               
TRANSACTION_ID   RAW(8)               
DBNAME           VARCHAR2(30)         
EVENT_TYPE       NUMBER               
NUMTABLES        NUMBER               
TABLE_DESC_ARRAY SYS.CHNF$_TDESC_ARRAY

SQL> desc sys.chnf$_tdesc
Element        Type                  
-------------- ---------------------
OPFLAGS        NUMBER               
TABLE_NAME     VARCHAR2(64)         
NUMROWS        NUMBER               
ROW_DESC_ARRAY SYS.CHNF$_RDESC_ARRAY

SQL> desc sys.chnf$_rdesc
Element Type           
------- --------------
OPFLAGS NUMBER         
ROW_ID  VARCHAR2(2000)

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下面提供一个简单的例子（首先满足系统权限要求）
CONNECT / AS SYSDBA;
GRANT CHANGE NOTIFICATION TO T2;
GRANT EXECUTE ON DBMS_CHANGE_NOTIFICATION TO T2;
-- 如果有必要，设置参数job_queue_processes为非零（默认就是非零）
ALTER SYSTEM SET job_queue_processes=4;

------------------------------------------------------------------------------
-- create sample data
------------------------------------------------------------------------------
create table ntfn_batch as select rb.* from rps_batch rb where rb.id = 2730006;

create table ntfn_trans as
select rt.*
  from rps_transaction rt
where rt.original_rps_batch_id = 2730006
order by rt.id;

------------------------------------------------------------------------------
-- create message table
------------------------------------------------------------------------------
drop table ntfn_msg;
create table ntfn_msg
(
  ora_trans raw(8),
  tab_name  varchar2(30),
  row_id    varchar2(2000),
  dt        date default sysdate
);

------------------------------------------------------------------------------
-- create procedure to process the callback when notification occurs
------------------------------------------------------------------------------
/*
You can create a PL/SQL stored procedure that the database server invokes in
response to a change to a registered object. The procedure that receives the notification
must have the following signature, where schema_name is the name of the database
schema and proc_name is the name of the stored procedure:

PROCEDURE schema_name.proc_name( ntfnds IN SYS.CHNF$_DESC )
经过测试，这里的参数名称都必须一致 ntfnds
*/

create or replace procedure ntfs_callback(ntfnds in sys.chnf$_desc) is
  l_event_type   number;
  l_ora_trans_id raw(8);
  l_numtables    number;
  l_op_flag      number;
  l_tab_name     varchar2(100);
  l_numrows      number;
  l_row_id       varchar2(2000);
begin
  l_event_type   := ntfnds.event_type;
  l_ora_trans_id := ntfnds.transaction_id;
  l_numtables    := ntfnds.numtables;

  -- only concern table change
  if l_event_type = dbms_change_notification.EVENT_OBJCHANGE then
    -- loop each table
    for i in 1 .. l_numtables loop
      --------------------------------------------------
      -- usually we call UTL_HTTP to send a notification
      -- to WEB Server, and here we only use some tables
      --------------------------------------------------
      l_op_flag  := ntfnds.table_desc_array(i).opflags;
      l_tab_name := ntfnds.table_desc_array(i).table_name;
      -- get table name without schema name
      l_tab_name := substr(l_tab_name, instr(l_tab_name, '.') + 1);
   
      if bitand(l_op_flag, dbms_change_notification.ALL_ROWS) = 1 then
        -- no certain rowid
        insert into ntfn_msg
          (ora_trans, tab_name)
        values
          (l_ora_trans_id, l_tab_name);
      else
        -- loop each row in this table
        l_numrows := ntfnds.table_desc_array(i).numrows;
        for j in 1 .. l_numrows loop
          l_row_id := ntfnds.table_desc_array(i).row_desc_array(j).row_id;
          insert into ntfn_msg
            (ora_trans, tab_name, row_id)
          values
            (l_ora_trans_id, l_tab_name, l_row_id);
        end loop; -- end loop row
      end if;
    end loop; -- end loop table
  end if;

  commit;
end;
/

------------------------------------------------------------------------------
-- procession for registration and deregister
------------------------------------------------------------------------------
-- registration
declare
  l_reg_info sys.chnf$_reg_info;
  l_reg_id number;
  l_qosflags number;
  l_temp number;
begin
  l_qosflags := dbms_change_notification.QOS_ROWIDS;
  l_reg_info := sys.chnf$_reg_info('ntfs_callback',l_qosflags,0,0,0);
  l_reg_id := dbms_change_notification.NEW_REG_START(l_reg_info);
  -- register tables
  select count(1) into l_temp from ntfn_batch b, ntfn_trans t where b.id = t.original_rps_batch_id;  
  dbms_change_notification.REG_END;
end;
/

-- check register result
select r.regid,r.table_name from user_change_notification_regs r;

-- deregister
declare
  l_reg_id number := 23;
begin
  dbms_change_notification.DEREGISTER(l_reg_id);
end;
/  


------------------------------------------------------------------------------
-- do some change and check result after commit
------------------------------------------------------------------------------
update ntfn_batch b set b.rps_application_id=b.rps_application_id where rownum = 1;
commit;
update ntfn_batch b set b.rps_application_id=b.rps_application_id;
commit;
update ntfn_trans t set t.t2_identifier = t.t2_identifier;
commit;

select to_char(m.dt, 'yyyy-mm-dd hh24:mi:ss') dt,
       m.ora_trans,
       m.tab_name,
       m.row_id
  from ntfn_msg m
order by 1, 3, 4;

SQL>
SQL> select to_char(m.dt, 'yyyy-mm-dd hh24:mi:ss') dt,
  2         m.ora_trans,
  3         m.tab_name,
  4         m.row_id
  5    from ntfn_msg m
  6   order by 1, 3, 4;

DT                  ORA_TRANS        TAB_NAME                       ROW_ID
------------------- ---------------- ------------------------------ --------------------------------------------------------------------------------
2007-10-26 17:23:16 08004100D20D0100 NTFN_BATCH                     AAFCIbAAHAAAM5AAAA
2007-10-26 17:23:46 0A0061003ED50000 NTFN_BATCH                     AAFCIbAAHAAAM5AAAA
2007-10-26 17:24:26 0400200065D30000 NTFN_TRANS                     AAFCIcAAHAAAM8IAAA
2007-10-26 17:24:26 0400200065D30000 NTFN_TRANS                     AAFCIcAAHAAAM8IAAB
2007-10-26 17:24:26 0400200065D30000 NTFN_TRANS                     AAFCIcAAHAAAM8IAAC
2007-10-26 17:24:26 0400200065D30000 NTFN_TRANS                     AAFCIcAAHAAAM8IAAD
2007-10-26 17:24:26 0400200065D30000 NTFN_TRANS                     AAFCIcAAHAAAM8IAAE
2007-10-26 17:24:26 0400200065D30000 NTFN_TRANS                     AAFCIcAAHAAAM8IAAF

8 rows selected

从这个结果可以分析出
        执行了3个事务（简称1，2，3）
        事务1，2更改了NTFN_BATCH，事务3更改了NTFN_TRANS