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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”：
1alter system set remote_listener='raclhr-11gR2-scan:1521' sid='*';
修改远程监听端口scan端口：
1srvctl modify scan_listener -p 1522
有关SCAN监听器的其它命令：
1[root@raclhr-11gR2-N2 ~]# srvctl -h | grep scan_listener
2Usage: srvctl add scan_listener [-l <lsnr_name_prefix>] [-s] [-p [TCP:]<port>[/IPC:<key>][/NMP:<pipe_name>][/TCPS:<s_port>] [/SDP:<port>]]
3Usage: srvctl config scan_listener [-i <ordinal_number>]
4Usage: srvctl start scan_listener [-n <node_name>] [-i <ordinal_number>]
5Usage: srvctl stop scan_listener [-i <ordinal_number>] [-f]
6Usage: srvctl relocate scan_listener -i <ordinal_number> [-n <node_name>]
7Usage: srvctl status scan_listener [-i <ordinal_number>] [-v]
8Usage: srvctl enable scan_listener [-i <ordinal_number>]
9Usage: srvctl disable scan_listener [-i <ordinal_number>]
10Usage: srvctl modify scan_listener {-u|-p [TCP:]<port>[/IPC:<key>][/NMP:<pipe_name>][/TCPS:<s_port>] [/SDP:<port>]}
11Usage: srvctl remove scan_listener [-f] [-y]
12[root@raclhr-11gR2-N2 ~]#
查看现有的监听器：
1[oracle@raclhr-11gR2-N2 ~]$ ps -ef|grep tns 2root 15 2 0 09:55 ? 00:00:00 [netns] 3grid 18138 1 0 10:38 ? 00:00:00 /u01/app/11.2.0/grid/bin/tnslsnr LISTENER_SCAN1 -inherit 4grid 18168 1 0 10:38 ? 00:00:00 /u01/app/11.2.0/grid/bin/tnslsnr LISTENER -inherit 5oracle 19184 18645 0 11:05 pts/2 00:00:00 grep tns 6[oracle@raclhr-11gR2-N2 ~]$ 7[root@raclhr-11gR2-N2 ~]# lsnrctl status LISTENER_SCAN1 8 9LSNRCTL for Linux: Version 11.2.0.3.0 - Production on 05-JUN-2018 10:48:12 10 11Copyright (c) 1991, 2011, Oracle. All rights reserved. 12 13Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN1))) 14STATUS of the LISTENER 15------------------------ 16Alias LISTENER_SCAN1 17Version TNSLSNR for Linux: Version 11.2.0.3.0 - Production 18Start Date 05-JUN-2018 10:38:02 19Uptime 0 days 0 hr. 10 min. 10 sec 20Trace Level off 21Security ON: Local OS Authentication 22SNMP OFF 23Listener Parameter File /u01/app/11.2.0/grid/network/admin/listener.ora 24Listener Log File /u01/app/11.2.0/grid/log/diag/tnslsnr/raclhr-11gR2-N2/listener_scan1/alert/log.xml 25Listening Endpoints Summary... 26 (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER_SCAN1))) 27 (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.59.174)(PORT=1521))) 28Services Summary... 29Service "+ASM" has 2 instance(s). 30 Instance "+ASM1", status READY, has 1 handler(s) for this service... 31 Instance "+ASM2", status READY, has 1 handler(s) for this service... 32Service "lhrrac1" has 2 instance(s). 33 Instance "lhrrac11", status READY, has 1 handler(s) for this service... 34 Instance "lhrrac12", status READY, has 1 handler(s) for this service... 35Service "lhrrac1XDB" has 2 instance(s). 36 Instance "lhrrac11", status READY, has 1 handler(s) for this service... 37 Instance "lhrrac12", status READY, has 1 handler(s) for this service... 38The command completed successfully 39[root@raclhr-11gR2-N2 ~]# lsnrctl status LISTENER 40 41LSNRCTL for Linux: Version 11.2.0.3.0 - Production on 05-JUN-2018 11:22:08 42 43Copyright (c) 1991, 2011, Oracle. All rights reserved. 44 45Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER))) 46STATUS of the LISTENER 47------------------------ 48Alias LISTENER 49Version TNSLSNR for Linux: Version 11.2.0.3.0 - Production 50Start Date 05-JUN-2018 10:38:07 51Uptime 0 days 0 hr. 44 min. 1 sec 52Trace Level off 53Security ON: Local OS Authentication 54SNMP OFF 55Listener Parameter File /u01/app/11.2.0/grid/network/admin/listener.ora 56Listener Log File /u01/app/grid/diag/tnslsnr/raclhr-11gR2-N2/listener/alert/log.xml 57Listening Endpoints Summary... 58 (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER))) 59 (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.59.171)(PORT=1521))) 60 (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.59.173)(PORT=1521))) 61Services Summary... 62Service "+ASM" has 1 instance(s). 63 Instance "+ASM2", status READY, has 1 handler(s) for this service... 64Service "lhrrac1" has 1 instance(s). 65 Instance "lhrrac12", status READY, has 1 handler(s) for this service... 66Service "lhrrac1XDB" has 1 instance(s). 67 Instance "lhrrac12", status READY, has 1 handler(s) for this service... 68The command completed successfully
当然，SCAN Listener也可以进行静态监听，如下所示：
1[root@raclhr-11gR2-N2 .oracle]# cat /u01/app/11.2.0/grid/network/admin/listener.ora 2LISTENER_SCAN1=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN1)))) # line added by Agent 3LISTENER=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER)))) # line added by Agent 4ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER=ON # line added by Agent 5ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER_SCAN1=ON # line added by Agent 6 7LISTENER_SCAN1 = 8 (DESCRIPTION_LIST = 9 (DESCRIPTION = 10 (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.59.174)(PORT = 1521)) 11 ) 12 ) 13 14SID_LIST_LISTENER_SCAN1 = 15(SID_LIST = 16 (SID_DESC = 17 (GLOBAL_DBNAME = lhrrac1) 18 (ORACLE_HOME = /u01/app/oracle/product/11.2.0/dbhome_1) 19 (SID_NAME = lhrrac12) 20 ) 21 (SID_DESC = 22 (GLOBAL_DBNAME = lhrrac1) 23 (ORACLE_HOME = /u01/app/oracle/product/11.2.0/dbhome_1) 24 (SID_NAME = lhrrac11) 25 ) 26 ) 27[root@raclhr-11gR2-N2 .oracle]# lsnrctl reload listener_scan1 28 29LSNRCTL for Linux: Version 11.2.0.3.0 - Production on 05-JUN-2018 13:46:13 30 31Copyright (c) 1991, 2011, Oracle. All rights reserved. 32 33Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.59.174)(PORT=1521))) 34The command completed successfully 35[root@raclhr-11gR2-N2 .oracle]# lsnrctl status listener_scan1 36 37LSNRCTL for Linux: Version 11.2.0.3.0 - Production on 05-JUN-2018 13:46:19 38 39Copyright (c) 1991, 2011, Oracle. All rights reserved. 40 41Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.59.174)(PORT=1521))) 42STATUS of the LISTENER 43------------------------ 44Alias listener_scan1 45Version TNSLSNR for Linux: Version 11.2.0.3.0 - Production 46Start Date 05-JUN-2018 13:41:04 47Uptime 0 days 0 hr. 5 min. 14 sec 48Trace Level off 49Security ON: Local OS Authentication 50SNMP OFF 51Listener Parameter File /u01/app/11.2.0/grid/network/admin/listener.ora 52Listener Log File /u01/app/11.2.0/grid/log/diag/tnslsnr/raclhr-11gR2-N2/listener_scan1/alert/log.xml 53Listening Endpoints Summary... 54 (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.59.174)(PORT=1521))) 55Services Summary... 56Service "+ASM" has 2 instance(s). 57 Instance "+ASM1", status READY, has 1 handler(s) for this service... 58 Instance "+ASM2", status READY, has 1 handler(s) for this service... 59Service "lhrrac1" has 4 instance(s). 60 Instance "lhrrac11", status UNKNOWN, has 1 handler(s) for this service... 61 Instance "lhrrac11", status READY, has 1 handler(s) for this service... 62 Instance "lhrrac12", status UNKNOWN, has 1 handler(s) for this service... 63 Instance "lhrrac12", status READY, has 1 handler(s) for this service... 64Service "lhrrac1XDB" has 2 instance(s). 65 Instance "lhrrac11", status READY, has 1 handler(s) for this service... 66 Instance "lhrrac12", status READY, has 1 handler(s) for this service... 67Service "lhrxxt" has 2 instance(s). 68 Instance "lhrrac11", status READY, has 1 handler(s) for this service... 69 Instance "lhrrac12", status READY, has 1 handler(s) for this service... 70The 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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