【DB笔试面试733】在Oracle中，RAC中REMOTE_LISTENER的作用是什么？

小麦苗DBA宝典

发布于 2020-01-20 16:59:37

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发布于 2020-01-20 16:59:37

文章被收录于专栏：小麦苗的DB宝专栏小麦苗的DB宝专栏

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题目部分

在Oracle中，RAC中REMOTE_LISTENER的作用是什么？

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答案部分

REMOTE_LISTENER参数主要用于RAC环境中监听器的远程注册，监听器的远程注册主要用于实现负载均衡。通常情况下，客户端发出的连接请求会首先被LOCAL_LISTENER接收，然后由Master Instance来决定当前的连接请求应该由哪个目标Instance发出Server Process响应这个连接请求。在启用了负载均衡的情形下，Master Instance会将请求转发到负载较小的实例。如果此时Remote_Listener中指定的实例负载较小，那么当前的请求会被重定向到负载较小的Instance中来建立连接，派生服务器进程进行相应连接。

在RAC环境下不管是使用了默认的TCP和1521还是其他协议都建议配置LOCAL_LISTENER。REMOTE_LISTENER参数在RAC环境下非常重要，是服务器实现负载均衡的一个工具。在服务器端的连接中，Oracle NET通过remote_listener确定当前RAC中的远程监听和实例，以便分发连接。

RAC环境中的监听器可以分为本地监听器和SCAN监听器，分别对应LOCAL_LISTENER和REMOTE_LISTENER参数：

LOCAL LISTENER:本地监听器只能监听到运行在本节点上的数据库。RAC的每个节点上都会有独立的本地监听器，它会监听该节点的Public IP和VIP，而每个节点的实例在启动的时候也会向本地监听器进行注册，当然它也会向SCAN监听器注册，当VIP或者Public IP有连接请求的时候，本地监听器就接受处理并和本地实例建立连接。如果某个节点故障，那么其上面的VIP会进行漂移，但本地监听器并不会产生漂移。

本地监听器对应的设置参数为LOCAL_LISTENER。这个参数控制着本地监听器的注册，因为本地监听器的工作机制关系，通过本地监听器的数据库连接请求只会连接到本地节点的实例上。

SCAN LISTENER:SCAN监听器可以监听到集群中运行的所有数据库，它是实现SCAN负载均衡的原理所在。如果RAC上有三个SCAN VIP，那么SCAN监听器也有三个，它们各自监听SCAN VIP的连接请求。SCAN监听器跟着SCAN VIP随机分配到节点服务器上，如果某个节点发生故障，那么运行在此节点上的SCAN VIP会进行漂移，这时候SCAN监听器也跟着漂移到正常的节点上，继续为SCAN VIP监听连接请求。当PMON进程下次动态更新实例信息到该SCAN监听器之后，它又重新接收客户端的连接。这和VIP产生漂移的时候是有所区别的。

SCAN监听器对应的设置参数为REMOTE_LISTENER。通过设置这个参数，任何数据库实例都会向SCAN监听器注册，主要用于注册远程数据库实例，所以SCAN监听器能够负载均衡地分发连接请求到节点本地监听器上，也就是连接到其本地节点上实例上。

修改远程监听参数REMOTE_LISTENER，值为“SCAN Name:port”：

alter system set remote_listener='raclhr-11gR2-scan:1521' sid='*';

修改远程监听端口scan端口：

srvctl modify scan_listener -p 1522

有关SCAN监听器的其它命令：

[root@raclhr-11gR2-N2 ~]# srvctl -h | grep scan_listener
Usage: srvctl add scan_listener [-l <lsnr_name_prefix>] [-s] [-p [TCP:]<port>[/IPC:<key>][/NMP:<pipe_name>][/TCPS:<s_port>] [/SDP:<port>]] 
Usage: srvctl config scan_listener [-i <ordinal_number>]
Usage: srvctl start scan_listener [-n <node_name>] [-i <ordinal_number>]
Usage: srvctl stop scan_listener [-i <ordinal_number>] [-f]
Usage: srvctl relocate scan_listener -i <ordinal_number> [-n <node_name>]
Usage: srvctl status scan_listener [-i <ordinal_number>] [-v]
Usage: srvctl enable scan_listener [-i <ordinal_number>]
Usage: srvctl disable scan_listener [-i <ordinal_number>]
Usage: srvctl modify scan_listener {-u|-p [TCP:]<port>[/IPC:<key>][/NMP:<pipe_name>][/TCPS:<s_port>] [/SDP:<port>]} 
Usage: srvctl remove scan_listener [-f] [-y]
[root@raclhr-11gR2-N2 ~]#

查看现有的监听器：

[oracle@raclhr-11gR2-N2 ~]$ ps -ef|grep tns
root        15     2  0 09:55 ?        00:00:00 [netns]
grid     18138     1  0 10:38 ?        00:00:00 /u01/app/11.2.0/grid/bin/tnslsnr LISTENER_SCAN1 -inherit
grid     18168     1  0 10:38 ?        00:00:00 /u01/app/11.2.0/grid/bin/tnslsnr LISTENER -inherit
oracle   19184 18645  0 11:05 pts/2    00:00:00 grep tns
[oracle@raclhr-11gR2-N2 ~]$ 
[root@raclhr-11gR2-N2 ~]# lsnrctl status LISTENER_SCAN1

LSNRCTL for Linux: Version 11.2.0.3.0 - Production on 05-JUN-2018 10:48:12

Copyright (c) 1991, 2011, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN1)))
STATUS of the LISTENER
------------------------
Alias                     LISTENER_SCAN1
Version                   TNSLSNR for Linux: Version 11.2.0.3.0 - Production
Start Date                05-JUN-2018 10:38:02
Uptime                    0 days 0 hr. 10 min. 10 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Listener Parameter File   /u01/app/11.2.0/grid/network/admin/listener.ora
Listener Log File         /u01/app/11.2.0/grid/log/diag/tnslsnr/raclhr-11gR2-N2/listener_scan1/alert/log.xml
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER_SCAN1)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.59.174)(PORT=1521)))
Services Summary...
Service "+ASM" has 2 instance(s).
  Instance "+ASM1", status READY, has 1 handler(s) for this service...
  Instance "+ASM2", status READY, has 1 handler(s) for this service...
Service "lhrrac1" has 2 instance(s).
  Instance "lhrrac11", status READY, has 1 handler(s) for this service...
  Instance "lhrrac12", status READY, has 1 handler(s) for this service...
Service "lhrrac1XDB" has 2 instance(s).
  Instance "lhrrac11", status READY, has 1 handler(s) for this service...
  Instance "lhrrac12", status READY, has 1 handler(s) for this service...
The command completed successfully
[root@raclhr-11gR2-N2 ~]# lsnrctl status LISTENER 

LSNRCTL for Linux: Version 11.2.0.3.0 - Production on 05-JUN-2018 11:22:08

Copyright (c) 1991, 2011, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER)))
STATUS of the LISTENER
------------------------
Alias                     LISTENER
Version                   TNSLSNR for Linux: Version 11.2.0.3.0 - Production
Start Date                05-JUN-2018 10:38:07
Uptime                    0 days 0 hr. 44 min. 1 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Listener Parameter File   /u01/app/11.2.0/grid/network/admin/listener.ora
Listener Log File         /u01/app/grid/diag/tnslsnr/raclhr-11gR2-N2/listener/alert/log.xml
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.59.171)(PORT=1521)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.59.173)(PORT=1521)))
Services Summary...
Service "+ASM" has 1 instance(s).
  Instance "+ASM2", status READY, has 1 handler(s) for this service...
Service "lhrrac1" has 1 instance(s).
  Instance "lhrrac12", status READY, has 1 handler(s) for this service...
Service "lhrrac1XDB" has 1 instance(s).
  Instance "lhrrac12", status READY, has 1 handler(s) for this service...
The command completed successfully

当然，SCAN Listener也可以进行静态监听，如下所示：

[root@raclhr-11gR2-N2 .oracle]# cat /u01/app/11.2.0/grid/network/admin/listener.ora
LISTENER_SCAN1=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN1))))                # line added by Agent
LISTENER=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER))))            # line added by Agent
ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER=ON              # line added by Agent
ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER_SCAN1=ON                # line added by Agent

LISTENER_SCAN1 =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.59.174)(PORT = 1521))
    )
  )

SID_LIST_LISTENER_SCAN1 =
(SID_LIST =
    (SID_DESC =
     (GLOBAL_DBNAME = lhrrac1)
     (ORACLE_HOME = /u01/app/oracle/product/11.2.0/dbhome_1)
     (SID_NAME = lhrrac12)
    )
    (SID_DESC =
     (GLOBAL_DBNAME = lhrrac1)
     (ORACLE_HOME = /u01/app/oracle/product/11.2.0/dbhome_1)
     (SID_NAME = lhrrac11)
    )
 )
[root@raclhr-11gR2-N2 .oracle]# lsnrctl reload listener_scan1                      

LSNRCTL for Linux: Version 11.2.0.3.0 - Production on 05-JUN-2018 13:46:13

Copyright (c) 1991, 2011, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.59.174)(PORT=1521)))
The command completed successfully
[root@raclhr-11gR2-N2 .oracle]# lsnrctl status listener_scan1                      

LSNRCTL for Linux: Version 11.2.0.3.0 - Production on 05-JUN-2018 13:46:19

Copyright (c) 1991, 2011, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.59.174)(PORT=1521)))
STATUS of the LISTENER
------------------------
Alias                     listener_scan1
Version                   TNSLSNR for Linux: Version 11.2.0.3.0 - Production
Start Date                05-JUN-2018 13:41:04
Uptime                    0 days 0 hr. 5 min. 14 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Listener Parameter File   /u01/app/11.2.0/grid/network/admin/listener.ora
Listener Log File         /u01/app/11.2.0/grid/log/diag/tnslsnr/raclhr-11gR2-N2/listener_scan1/alert/log.xml
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.59.174)(PORT=1521)))
Services Summary...
Service "+ASM" has 2 instance(s).
  Instance "+ASM1", status READY, has 1 handler(s) for this service...
  Instance "+ASM2", status READY, has 1 handler(s) for this service...
Service "lhrrac1" has 4 instance(s).
  Instance "lhrrac11", status UNKNOWN, has 1 handler(s) for this service...
  Instance "lhrrac11", status READY, has 1 handler(s) for this service...
  Instance "lhrrac12", status UNKNOWN, has 1 handler(s) for this service...
  Instance "lhrrac12", status READY, has 1 handler(s) for this service...
Service "lhrrac1XDB" has 2 instance(s).
  Instance "lhrrac11", status READY, has 1 handler(s) for this service...
  Instance "lhrrac12", status READY, has 1 handler(s) for this service...
Service "lhrxxt" has 2 instance(s).
  Instance "lhrrac11", status READY, has 1 handler(s) for this service...
  Instance "lhrrac12", status READY, has 1 handler(s) for this service...
The command completed successfully

本文选自《Oracle程序员面试笔试宝典》，作者：小麦苗

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