MySQL登陸之socket與TCP

　　在一臺測試服務器上部署了2個實例，一個端口是默認的3306，另外一個端口是3376。MySQL的版本是5.6.35

[root@MySQL56_L1 ~]# ps -ef | grep mysql | grep -v grep 
mysql    11176  9876  0 13:31 pts/1    00:00:00 /usr/local/mysql/bin/mysqld --defaults-file=/etc/my.cnf
mysql    11262  9876  0 13:34 pts/1    00:00:00 /usr/local/mysql/bin/mysqld --defaults-file=/data/mysql/mysql3376/my3376.cnf

　　my3376.cnf的部分參數配置以下

[root@MySQL56_L1 ~]# more /etc/my.cnf 

[client]
port            = 3306
socket          = /tmp/mysql.sock

# The MySQL server
[mysqld]
# Basic
port            = 3306
user        = mysql
basedir         = /usr/local/mysql
datadir         = /data/mysql/mysql3306/data
tmpdir          = /data/mysql/mysql3306/tmp
socket          = /tmp/mysql.sock

　　my3376.cnf的部分參數配置以下

[root@MySQL56_L1 ~]# more /data/mysql/mysql3376/my3376.cnf 

[client]
port            = 3376
socket          = /tmp/mysql3376.sock

# The MySQL server
[mysqld]
# Basic
port            = 3376
user        = mysql
basedir         = /usr/local/mysql
datadir         = /data/mysql/mysql3376/data
tmpdir          = /data/mysql/mysql3376/tmp
socket          = /tmp/mysql3376.sock

　　兩個數據庫中的帳號及密碼以下

(product)root@localhost [(none)]> select host, user, password from mysql.user ;  
+-----------+------+----------+
| host      | user | password |
+-----------+------+----------+
| localhost | root |          |
| 127.0.0.1 | root |          |
+-----------+------+----------+

　　當使用帳號、密碼、端口的方式方式登陸到端口爲3376的實例時，發現登陸的倒是3306端口的實例下

[root@MySQL56_L1 ~]# mysql  -uroot -p -P3376
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 5
Server version: 5.6.35-log MySQL Community Server (GPL)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

(product)root@localhost mysql.sock [(none)]> 

　　請注意上面代碼塊中的紅色加粗字體，這是端口爲3306實例的socket文件，3376端口實例使用socket方式登陸以下：

[root@MySQL56_L1 ~]# mysql -S /tmp/mysql3376.sock 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.6.35-log MySQL Community Server (GPL)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

(product)root@localhost mysql3376.sock [(none)]> 

　　在須要登陸到3376端口實例下時，已經明確指定了端口，爲何仍是登陸到3306端口實例下呢？ 

　　難道是由於沒有加上「-h」?

[root@MySQL56_L1 ~]# mysql -hlocalhost -uroot -p -P3376 
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 6
Server version: 5.6.35-log MySQL Community Server (GPL)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

(product)root@localhost mysql.sock [(none)]> 

　　能夠看到，使用「-hlocalhost」是仍是登陸到3306端口實例下，如果修改成「-h IP」，又會怎麼樣呢？ 

[root@MySQL56_L1 ~]# mysql -h127.0.0.1 -uroot -p -P3376          
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.6.35-log MySQL Community Server (GPL)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

(product)root@127.0.0.1 3376 [(none)]> 

　　此次就能如願登陸到所指望的3376端口實例下了。

　　小結：安裝了多實例的狀況下，須要登陸到特定端口實例下的方法

　　一、使用「-S」 參數，經過指定實例下的socket文件來登陸到指定的實例

　　二、使用「-h」參數，注意，這裏必須是使用'TCP/IP'的方式，不能是'localhost'，由於'localhost'會使用默認的socket文件登陸

 

　　那麼，爲何指定了端口「-P3376」，仍是會登陸到3306端口實例下呢？ 

　　緣由是由於沒有指定「-h」使用'TCP/IP'方式來登陸時，是默認使用socket方式登陸，問題又來了，是使用哪一個socket文件呢？

[root@MySQL56_L1 ~]# mysql --verbose --help | grep socket
  --protocol=name     The protocol to use for connection (tcp, socket, pipe,
  -S, --socket=name   The socket file to use for connection.
                      The buffer size for TCP/IP and socket communication.
socket /tmp/mysql.sock

　　這個文件是在哪裏指定呢？ 

[root@MySQL56_L1 ~]# mysql --verbose --help | grep my.cnf
                      order of preference, my.cnf, $MYSQL_TCP_PORT,
/etc/my.cnf /etc/mysql/my.cnf /usr/local/mysql/etc/my.cnf ~/.my.cnf 

　　注：以上的4個「my.cnf」後面的參數會覆蓋前面的。

　　如果產生懷疑，能夠試驗一下在「~/.my.cnf」中添加以下代碼

[root@MySQL56_L1 ~]# vi ~/.my.cnf  

[client]
socket          = /tmp/mysql3306.sock

　　再查看一下mysql讀取的socket文件

[root@MySQL56_L1 ~]# mysql --verbose --help | grep socket
  --protocol=name     The protocol to use for connection (tcp, socket, pipe,
  -S, --socket=name   The socket file to use for connection.
                      The buffer size for TCP/IP and socket communication.
socket /tmp/mysql3306.sock

　　從上面的測試就能夠看出是讀取socket文件的路徑

　　注意：測試完以後須要改回正確的socket文件名

　　看完上面的說明，如今應該能明白爲何爲何指定了「-P 3376」，卻登陸到了3306端口是實例下了。其實，正確的應該是這個路徑「/etc/my.cnf /etc/mysql/my.cnf /usr/local/mysql/etc/my.cnf ~/.my.cnf」下的socket參數對應的是哪一個端口，就會登陸到哪一個端口的實例下。 

 

　　看完了這麼多，可能仍是不明白socket是什麼？ 

　　socket是用於同一臺主機的進程間通信（IPC），不須要通過網絡協議棧，不須要打包拆包、計算校驗和、維護序號和應答等，只是將應用層數據從一個進程拷貝到另一個進程，消息既不會丟失也不會順序錯亂。可用於兩個沒有親緣關係的進程，是全雙工的。

 

　　以上，如有錯誤，請不吝指出。