一、現狀記錄
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[oracle@node1 ~]$ /sbin/ifconfig
eth2 Link encap:Ethernet HWaddr 00:25:90:04:AB:6B
inet addr:192.168.9.140 Bcast:192.168.15.255 Mask:255.255.248.0
inet6 addr: fe80::225:90ff:fe04:ab6b/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:23530402 errors:0 dropped:0 overruns:0 frame:0
TX packets:10959123 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:15308483748 (14.2 GiB) TX bytes:10087987532 (9.3 GiB)
--IP地址為192.168.9.140
[oracle@node1 ~]$ more /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 ecp-db localhost.localdomain localhost
192.168.9.140 node1.srtcloud.com
--域名node1.srtcloud.com對應ip192.168.9.140
[oracle@node1 ~]$ lsnrctl status
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=node1.srtcloud.com)(PORT=1521)))
STATUS of the LISTENER
------------------------
Alias LISTENER
Version TNSLSNR for Linux: Version 10.2.0.5.0 - Production
Start Date 04-NOV-2011 09:08:51
Uptime 21 days 4 hr. 58 min. 45 sec
Trace Level off
Security ON: Local OS Authentication
SNMP OFF
Listener Parameter File /opt/oracle/product/10.2.0/db_1/network/admin/listener.ora
Listener Log File /opt/oracle/product/10.2.0/db_1/network/log/listener.log
Listening Endpoints Summary...
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=node1.srtcloud.com)(PORT=1521)))
Services Summary...
Service "ecp" has 2 instance(s).
Instance "ecp", status UNKNOWN, has 1 handler(s) for this service...
Instance "ecp", status READY, has 1 handler(s) for this service...
Service "ecpXDB" has 1 instance(s).
Instance "ecp", status READY, has 1 handler(s) for this service...
Service "ecp_XPT" has 1 instance(s).
Instance "ecp", status READY, has 1 handler(s) for this service...
Service "ora11g" has 2 instance(s).
Instance "ora11g", status UNKNOWN, has 1 handler(s) for this service...
Instance "ora11g", status READY, has 1 handler(s) for this service...
Service "ora11gXDB" has 1 instance(s).
Instance "ora11g", status READY, has 1 handler(s) for this service...
The command completed successfully
--說明:ora11g是oracle 11g，ecp是oracle 10g
--當前使用域名node1.srtcloud.com監聽
[oracle@node1 ~]$ more /opt/oracle/product/10.2.0/db_1/network/admin/tnsnames.ora
# tnsnames.ora Network Configuration File: /opt/oracle/product/10.2.0/db_1/network/admin/tnsnames.ora
# Generated by Oracle configuration tools.
ECP =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = node1.srtcloud.com)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = ecp)
)
)
ORA11G =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = node1.srtcloud.com)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = ora11g)
)
)
--tns也通過域名訪問
[oracle@node1 ~]$ more /etc/resolv.conf
nameserver 211.155.235.201
nameserver 211.155.235.188
[oracle@node1 ~]$ more /etc/nsswitch.conf |grep hosts:
hosts: files dns
--域名解析順序 |
二、數據庫正常工作分析
1、tns工作：客戶端通過tns訪問數據庫，tns配置的是域名訪問，所以需要解析，因為此刻解析的順序是先利用/etc/hosts解析，所以讀取hosts文件，獲取到ip，然后訪問對應數據庫，和監聽接觸。
2、監聽工作：監聽的是域名，其實也是通過hosts解析成ip的
3、這里能夠正常的工作，是因為hosts文件解析了域名
三、模擬數據庫訪問延遲
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[oracle@node1 ~]$ more /etc/nsswitch.conf |grep hosts:
hosts: dns files
--先使用dns服務器解析，再使用hosts文件
[oracle@node1 ~]$ more /etc/resolv.conf
nameserver 11.1.1.1
--無效的dns服務器
[oracle@node1 ~]$ sqlplus chf/xifenfei@ora11g
SQL*Plus: Release 10.2.0.5.0 - Production on Fri Nov 25 14:44:55 2011
Copyright (c) 1982, 2010, Oracle. All Rights Reserved.
--會在這里一個很長的時間等待
[oracle@node1 ~]$ lsnrctl status
LSNRCTL for Linux: Version 10.2.0.5.0 - Production on 25-NOV-2011 14:48:26
Copyright (c) 1991, 2010, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=node1.srtcloud.com)(PORT=1521)))
--也會一個長時間的等待
--問題原因:就是因為解析域名的時候，先去訪問dns服務器，因為該ip非dns服務器ip，所以會一直等待該ip超時，
--然后訪問hosts文件獲取ip地址（這個就是為什么我們登錄或者查看監聽狀態的時候，會出現如此長的時間的等待） |
其實因為dns延遲的現象有很多種，我這里只是舉了一個最簡單，比較常見的例子，在處理因dns解析的監聽延遲的問題上，可以參考下面幾點:
1、如果非特殊情況，盡可能使用ip地址在監聽和tns中
2、如果是使用域名，請盡可能使用hosts解析，解析順序配置為files優先（因為dns服務器有很多不確定，不可控因素）
3、如果一定要使用dns服務器解析，請把穩定的dns服務器配置在第一項，盡可能避免出現dns服務器不可達或者不存在該域名的現象
