[20230317]关于TIME_WAIT问题.txt
--//被别人问起这个问题，服务器的网络链接出现大量TIME_WAIT连接。实际上达到怎么样量才是最严重也没有标准。
--//实际上如果不影响生产系统应用，可以完全不用理会。自己看了以前一些笔记，做一些总结，不知道对不对。
--//互联网上能找到许多图，感觉很复杂。实际上主要记住一点仅仅主动方(也就是发起方主动退出才会在发起方出现TIME_WAIT),比如：
--//对于oracle的单机数据库,正常情况下比如sqlplus通过网络连接执行sql语句正常退出，发起方在客户端，服务器不会出现TIME_WAIT
--//问题，TIME_WAIT仅仅出现在客户端。
--//在rac环境下如果应用程序使用scan ip连接，确实会在服务端出现大量的TIME_WAIT链接、因为最终的连接是vip地址。
--//所以rac环境中间件服务器尽量不要使用scan ip，直接可以使用vip配置，来减少中间环节，避免服务端出现大量TIME_WAIT的情况。
--//另外tnsping可以导致服务端出现TIME_WAIT。因为tnsping发起断开连接在服务端。
--//顺便验证自己的测试：
1.测试配置情况：
--//192.168.100.33 客户端
--//192.168.100.78 服务器
2.测试1：
--//192.168.100.33:
$ time sqlplus -s -l scott/book@192.168.100.78:1521/book <<<'select sysdate from dual;'
SCOTT@192.168.100.78:1521/book>
SYSDATE
-------------------
2023-03-21 08:46:04
real 0m0.072s
user 0m0.024s
sys 0m0.009s
$ seq 100 | xargs -IQ bash -c "netstat -tonp 2>/dev/null| grep 192.168.100.78 | ts.awk;sleep 1"
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name Timer
[2023-03-21 08:46:04] tcp 0 0 192.168.100.33:47790 192.168.100.78:1521 TIME_WAIT - timewait (59.93/0/0)
[2023-03-21 08:46:05] tcp 0 0 192.168.100.33:47790 192.168.100.78:1521 TIME_WAIT - timewait (58.87/0/0)
[2023-03-21 08:46:06] tcp 0 0 192.168.100.33:47790 192.168.100.78:1521 TIME_WAIT - timewait (57.81/0/0)
[2023-03-21 08:46:07] tcp 0 0 192.168.100.33:47790 192.168.100.78:1521 TIME_WAIT - timewait (56.75/0/0)
...
[2023-03-21 08:46:59] tcp 0 0 192.168.100.33:47790 192.168.100.78:1521 TIME_WAIT - timewait (4.84/0/0)
[2023-03-21 08:47:00] tcp 0 0 192.168.100.33:47790 192.168.100.78:1521 TIME_WAIT - timewait (3.78/0/0)
[2023-03-21 08:47:01] tcp 0 0 192.168.100.33:47790 192.168.100.78:1521 TIME_WAIT - timewait (2.72/0/0)
[2023-03-21 08:47:02] tcp 0 0 192.168.100.33:47790 192.168.100.78:1521 TIME_WAIT - timewait (1.66/0/0)
[2023-03-21 08:47:03] tcp 0 0 192.168.100.33:47790 192.168.100.78:1521 TIME_WAIT - timewait (0.60/0/0)
--//题头我加上的.注意看前面的时间,基本可以对上一般timewait=60秒.
--//你可以发现time_wait发生在客户端.
--//192.168.100.78:
$ seq 100 | xargs -IQ bash -c "netstat -tonp 2>/dev/null| grep 192.168.100.33 | ts.awk;sleep 1"
--//没有输出或者仅仅输出1行(看运气).
3.测试2：
--//先做一个简单测试:
--//192.168.100.33:
$ seq 1 | xargs -IQ -P20 tnsping 192.168.100.78 1
TNS Ping Utility for Linux: Version 10.2.0.4.0 - Production on 21-MAR-2023 09:04:07
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Copyright (c) 1997, 2007, Oracle. All rights reserved.
Used parameter files:
/u01/app/oracle/product/10.2.0/db_1/network/admin/sqlnet.ora
Used HOSTNAME adapter to resolve the alias
Attempting to contact (DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=192.168.100.78))(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.100.78)(PORT=1521)))
OK (0 msec)
--//192.168.100.33.打开另外窗口执行:
$ seq 70 | xargs -IQ bash -c "netstat -tonp 2>/dev/null| grep 192.168.100.78 | ts.awk;sleep 1"
--//没有任何输出.
--//192.168.100.78:
$ seq 70 | xargs -IQ bash -c "netstat -tonp 2>/dev/null| grep 192.168.100.33 | ts.awk;sleep 1"
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name Timer
[2023-03-21 09:04:07] tcp 0 0 192.168.100.78:1521 192.168.100.33:47918 TIME_WAIT - timewait (59.87/0/0)
~~~~~~~~~~~~~~~~~~~~~
[2023-03-21 09:04:08] tcp 0 0 192.168.100.78:1521 192.168.100.33:47918 TIME_WAIT - timewait (58.85/0/0)
[2023-03-21 09:04:09] tcp 0 0 192.168.100.78:1521 192.168.100.33:47918 TIME_WAIT - timewait (57.83/0/0)
...
[2023-03-21 09:05:04] tcp 0 0 192.168.100.78:1521 192.168.100.33:47918 TIME_WAIT - timewait (3.78/0/0)
[2023-03-21 09:05:05] tcp 0 0 192.168.100.78:1521 192.168.100.33:47918 TIME_WAIT - timewait (2.76/0/0)
[2023-03-21 09:05:06] tcp 0 0 192.168.100.78:1521 192.168.100.33:47918 TIME_WAIT - timewait (1.74/0/0)
[2023-03-21 09:05:07] tcp 0 0 192.168.100.78:1521 192.168.100.33:47918 TIME_WAIT - timewait (0.72/0/0)
--//题头我加上的,注意看时间,基本能对上.
--//你可以发现time_wait发生在服务端.
4.测试3:
--//192.168.100.33:
$ seq 10000 | xargs -IQ -P20 tnsping 192.168.100.78 100 > /dev/null
--//相当于瞬间执行1000000次tnsping 。
--//192.168.100.78:
$ netstat -tonp 2>/dev/null | grep 192.168.100.33 | wc -l
61919
--//192.168.100.33:
$ time sqlplus -s -l scott/book@192.168.100.78:1521/book <<<'select sysdate from dual;'
SYSDATE
-------------------
2023-03-21 09:43:51
real 0m0.077s
user 0m0.023s
sys 0m0.011s
--//执行并不慢.另另外一个方面也说明出现大量time_wait问题不会太大.
--//192.168.100.33端也出现少量time_wait,我估计端口占用问题或者从192.168.100.33发出太多的tnsping，根本发不出去。
$ netstat -tonp| grep 192.168.100.78|head -10
(Not all processes could be identified, non-owned process info
will not be shown, you would have to be root to see it all.)
tcp 0 0 192.168.100.33:40585 192.168.100.78:1521 TIME_WAIT - timewait (40.32/0/0)
tcp 0 0 192.168.100.33:40615 192.168.100.78:1521 TIME_WAIT - timewait (40.34/0/0)
tcp 0 0 192.168.100.33:40645 192.168.100.78:1521 TIME_WAIT - timewait (40.36/0/0)
tcp 0 0 192.168.100.33:40657 192.168.100.78:1521 TIME_WAIT - timewait (40.37/0/0)
tcp 0 0 192.168.100.33:40682 192.168.100.78:1521 TIME_WAIT - timewait (40.38/0/0)
tcp 0 0 192.168.100.33:40932 192.168.100.78:1521 TIME_WAIT - timewait (40.55/0/0)
tcp 0 0 192.168.100.33:40033 192.168.100.78:1521 TIME_WAIT - timewait (39.94/0/0)
tcp 0 0 192.168.100.33:40194 192.168.100.78:1521 TIME_WAIT - timewait (40.05/0/0)
tcp 0 0 192.168.100.33:39479 192.168.100.78:1521 TIME_WAIT - timewait (39.56/0/0)
tcp 0 0 192.168.100.33:39048 192.168.100.78:1521 TIME_WAIT - timewait (39.27/0/0)
$ netstat -tonp| grep 192.168.100.78|wc
249 2241 32094
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