MySQL登陆之socket与TCP

　　在一台测试服务器上部署了2个实例，一个端口是默认的3306，另外一个端口是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的部分参数配置以下

[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的部分参数配置以下

[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

　　两个数据库中的帐号及密码以下

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

　　当使用帐号、密码、端口的方式方式登陆到端口为3376的实例时，发现登陆的倒是3306端口的实例下

[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)]> 

　　请注意上面代码块中的红色加粗字体，这是端口为3306实例的socket文件，3376端口实例使用socket方式登陆以下：

[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)]> 

　　在须要登陆到3376端口实例下时，已经明确指定了端口，为何仍是登陆到3306端口实例下呢？ 

　　难道是由于没有加上“-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)]> 

　　能够看到，使用“-hlocalhost”是仍是登陆到3306端口实例下，如果修改成“-h IP”，又会怎么样呢？ 

[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)]> 

　　此次就能如愿登陆到所指望的3376端口实例下了。

　　小结：安装了多实例的状况下，须要登陆到特定端口实例下的方法

　　一、使用“-S” 参数，经过指定实例下的socket文件来登陆到指定的实例

　　二、使用“-h”参数，注意，这里必须是使用'TCP/IP'的方式，不能是'localhost'，由于'localhost'会使用默认的socket文件登陆

 

　　那么，为何指定了端口“-P3376”，仍是会登陆到3306端口实例下呢？ 

　　缘由是由于没有指定“-h”使用'TCP/IP'方式来登陆时，是默认使用socket方式登陆，问题又来了，是使用哪一个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

　　这个文件是在哪里指定呢？ 

[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个“my.cnf”后面的参数会覆盖前面的。

　　如果产生怀疑，能够试验一下在“~/.my.cnf”中添加以下代码

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

[client]
socket          = /tmp/mysql3306.sock

　　再查看一下mysql读取的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

　　从上面的测试就能够看出是读取socket文件的路径

　　注意：测试完以后须要改回正确的socket文件名

　　看完上面的说明，如今应该能明白为何为何指定了“-P 3376”，却登陆到了3306端口是实例下了。其实，正确的应该是这个路径“/etc/my.cnf /etc/mysql/my.cnf /usr/local/mysql/etc/my.cnf ~/.my.cnf”下的socket参数对应的是哪一个端口，就会登陆到哪一个端口的实例下。 

 

　　看完了这么多，可能仍是不明白socket是什么？ 

　　socket是用于同一台主机的进程间通信（IPC），不须要通过网络协议栈，不须要打包拆包、计算校验和、维护序号和应答等，只是将应用层数据从一个进程拷贝到另一个进程，消息既不会丢失也不会顺序错乱。可用于两个没有亲缘关系的进程，是全双工的。

 

　　以上，如有错误，请不吝指出。