在DG容灾的体系中，监听作为主备库的通信通道，至关重要。这里我们尝试一下，把监听切断，会导致什么后果呢？

----查看主备库的监听状态：

---主库监听状态：

[oracle@host01 ~]$ lsnrctl status

LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 12-MAR-2017 15:14:59

Copyright (c) 1991, 2013, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=host01)(PORT=1521)))

TNS-12541: TNS:no listener

 TNS-12560: TNS:protocol adapter error

  TNS-00511: No listener

   Linux Error: 111: Connection refused

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1521)))

TNS-12541: TNS:no listener

 TNS-12560: TNS:protocol adapter error

  TNS-00511: No listener

   Linux Error: 111: Connection refused

[oracle@host01 ~]$

---备库监听状态：

[oracle@oracle ~]$ lsnrctl status

LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 12-MAR-2017 15:15:05

Copyright (c) 1991, 2013, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=oracle)(PORT=1521)))

TNS-12541: TNS:no listener

 TNS-12560: TNS:protocol adapter error

  TNS-00511: No listener

   Linux Error: 111: Connection refused

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1521)))

TNS-12541: TNS:no listener

 TNS-12560: TNS:protocol adapter error

  TNS-00511: No listener

   Linux Error: 111: Connection refused

[oracle@oracle ~]$

----查看主备库的切换状态：

---主库：

SQL>  select open_mode,protection_mode,switchover_status,database_role from v$database;

OPEN_MODE            PROTECTION_MODE      SWITCHOVER_STATUS    DATABASE_ROLE

-------------------- -------------------- -------------------- ----------------

READ WRITE           MAXIMUM PERFORMANCE  FAILED DESTINATION   PRIMARY

---备库：

SQL>  select open_mode,protection_mode,switchover_status,database_role from v$database;

OPEN_MODE            PROTECTION_MODE      SWITCHOVER_STATUS    DATABASE_ROLE

-------------------- -------------------- -------------------- ----------------

READ ONLY            MAXIMUM PERFORMANCE  NOT ALLOWED          PHYSICAL STANDBY

----查看主备库当前最大日志号：

---主库最大日志号：

SQL> select max(sequence#), to_char(max(first_time),'yyyy-mm-dd hh24:mi:ss') from v$log_history where thread#=1

  2   and RESETLOGS_TIME = (select max(a.RESETLOGS_TIME) from v$log_history a);

MAX(SEQUENCE#) TO_CHAR(MAX(FIRST_T

-------------- -------------------

           154 2017-03-12 15:11:35

---备库最大日志号：

SQL> select max(sequence#), to_char(max(first_time),'yyyy-mm-dd hh24:mi:ss') from v$log_history where thread#=1

  2   and RESETLOGS_TIME = (select max(a.RESETLOGS_TIME) from v$log_history a); 

MAX(SEQUENCE#) TO_CHAR(MAX(FIRST_T

-------------- -------------------

           152 2017-03-12 12:45:17

----启动主备库的监听：

--主库监听启动：

[oracle@host01 ~]$ lsnrctl start

LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 12-MAR-2017 15:27:05

Copyright (c) 1991, 2013, Oracle.  All rights reserved.

Starting /u01/app/oracle/product/11.2.0/dbhome_1/bin/tnslsnr: please wait...

TNSLSNR for Linux: Version 11.2.0.4.0 - Production

System parameter file is /u01/app/oracle/product/11.2.0/dbhome_1/network/admin/listener.ora

Log messages written to /u01/app/oracle/diag/tnslsnr/host01/listener/alert/log.xml

Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=host01)(PORT=1521)))

Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=host01)(PORT=1521)))

STATUS of the LISTENER

------------------------

Alias                     LISTENER

Version                   TNSLSNR for Linux: Version 11.2.0.4.0 - Production

Start Date                12-MAR-2017 15:27:07

Uptime                    0 days 0 hr. 0 min. 0 sec

Trace Level               off

Security                  ON: Local OS Authentication

SNMP                      OFF

Listener Parameter File   /u01/app/oracle/product/11.2.0/dbhome_1/network/admin/listener.ora

Listener Log File         /u01/app/oracle/diag/tnslsnr/host01/listener/alert/log.xml

Listening Endpoints Summary...

  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=host01)(PORT=1521)))

  (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))

Services Summary...

Service "ORA11GR2" has 1 instance(s).

  Instance "ORA11GR2", status UNKNOWN, has 1 handler(s) for this service...

Service "SBDB" has 1 instance(s).

  Instance "SBDB", status UNKNOWN, has 1 handler(s) for this service...

The command completed successfully

[oracle@host01 ~]$

--主库注册监听：

SQL> alter system register;

System altered.

--备库监听启动：

[oracle@oracle ~]$ lsnrctl start 

LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 12-MAR-2017 15:27:24 

Copyright (c) 1991, 2013, Oracle.  All rights reserved.

Starting /u01/app/oracle/product/11.2.0/dbhome_1/bin/tnslsnr: please wait...

TNSLSNR for Linux: Version 11.2.0.4.0 - Production

System parameter file is /u01/app/oracle/product/11.2.0/dbhome_1/network/admin/listener.ora

Log messages written to /u01/app/oracle/diag/tnslsnr/oracle/listener/alert/log.xml

Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=oracle)(PORT=1521)))

Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=oracle)(PORT=1521)))

STATUS of the LISTENER

------------------------

Alias                     LISTENER

Version                   TNSLSNR for Linux: Version 11.2.0.4.0 - Production

Start Date                12-MAR-2017 15:27:26

Uptime                    0 days 0 hr. 0 min. 0 sec

Trace Level               off

Security                  ON: Local OS Authentication

SNMP                      OFF

Listener Parameter File   /u01/app/oracle/product/11.2.0/dbhome_1/network/admin/listener.ora

Listener Log File         /u01/app/oracle/diag/tnslsnr/oracle/listener/alert/log.xml

Listening Endpoints Summary...

  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=oracle)(PORT=1521)))

  (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))

Services Summary...

Service "ENMO.oracle.com" has 1 instance(s).

  Instance "ENMO", status UNKNOWN, has 1 handler(s) for this service...

Service "ORA11GR2" has 1 instance(s).

  Instance "ORA11GR2", status UNKNOWN, has 1 handler(s) for this service...

The command completed successfully

[oracle@oracle ~]$

--备库注册监听：

SQL> alter system register;

System altered.

----再次查看主库的切换状态：

SQL> select open_mode,protection_mode,switchover_status,database_role from v$database;

OPEN_MODE            PROTECTION_MODE      SWITCHOVER_STATUS    DATABASE_ROLE

-------------------- -------------------- -------------------- ----------------

READ WRITE           MAXIMUM PERFORMANCE  TO STANDBY           PRIMARY

---再次查看备库的切换状态：

SQL> select open_mode,protection_mode,switchover_status,database_role from v$database; 

OPEN_MODE            PROTECTION_MODE      SWITCHOVER_STATUS    DATABASE_ROLE

-------------------- -------------------- -------------------- ----------------

READ ONLY            MAXIMUM PERFORMANCE  NOT ALLOWED          PHYSICAL STANDBY

#当监听打开后，主备库就相互接通，并确定主备库的关系以及切换状态。 

----备库引用主库传输的归档日志：

SQL>  ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT FROM SESSION;

Database altered.

---主库切换一个日志：

SQL> alter system switch logfile;

System altered.

---再次查看主库的最大日志号：

SQL> select max(sequence#), to_char(max(first_time),'yyyy-mm-dd hh24:mi:ss') from v$log_history where thread#=1

  2   and RESETLOGS_TIME = (select max(a.RESETLOGS_TIME) from v$log_history a);

MAX(SEQUENCE#) TO_CHAR(MAX(FIRST_T

-------------- -------------------

           156 2017-03-12 15:27:37

---再次查看备库的最大日志号：

SQL> select max(sequence#), to_char(max(first_time),'yyyy-mm-dd hh24:mi:ss') from v$log_history where thread#=1

  2   and RESETLOGS_TIME = (select max(a.RESETLOGS_TIME) from v$log_history a);

MAX(SEQUENCE#) TO_CHAR(MAX(FIRST_T

-------------- -------------------

           156 2017-03-12 15:27:37

#主备库的最大日志号相同。

--我们从上面的测试可以看到：当监听不相通的时候，dataguard容灾体系中的主备库角色没有影响（已经搭建好DG的情况下），
主库备库依然保持该有的角色，但是，主备库之间，在网络不相通的情况下，不允许主备角色的切换，主库是 FAILED DESTINATION
的切换状态，备库依然是NOT ALLOWED的切换状态，主要还是受到监听不相通，主备库之间的日志传输受阻，从而不允许切换。