例項是程序與記憶體的一個概述，所謂MySQL多例項，就是在伺服器上啟動多個相同的MySQL程序，執行在不同的埠（如3306，3307，3308），通過不同的埠對外提供服務。

由於MySQL在一個例項下面可以建立多個數據庫，所以通常在一臺伺服器上只要安裝一個MySQL例項即可滿足使用。但在實際使用中，因為伺服器硬體資源充足，或者業務需要（比如在一臺伺服器上建立開發資料庫和測試資料庫），往往會在一臺伺服器上建立多個例項。

（二）MySQL部署多例項的方法

MySQL多例項部署主要有以下兩種方式：

• 使用官方自帶的mysqld_multi來配置管理，特點是使用同一份MySQL配置檔案，這種方式屬於集中式管理，管理起來較為方便；
• 使用單獨的MySQL配置檔案來單獨配置例項，這種方式邏輯簡單，資料庫之間沒有關聯。

本文將對第一種方式進行環境搭建學習。

（三）實驗環境

作業系統   ：CentOS Linux release 7.4.1708 (Core)

資料庫版本：5.7.24-log

預計劃安裝4個MySQL例項，規劃資訊為：

（四）實驗過程

（4.1）在安裝MySQL之前，需要解除安裝伺服器自帶的MySQL包和MySQL資料庫分支mariadb的包

[root@masterdb ~]# rpm -qa|grep mysql
[root@masterdb ~]# rpm -qa |grep mariadb
mariadb-libs-5.5.56-2.el7.x86_64

[root@masterdb ~]# rpm -e mariadb-libs-5.5.56-2.el7.x86_64 --nodeps

（4.2）依賴包安裝

MySQL對libaio 庫有依賴性。如果未在本地安裝該庫，則資料目錄初始化和隨後的伺服器啟動步驟將失敗 、

# install library
[root@mysql mysql]# yum install libaio

對於MySQL 5.7.19和更高版本：通用Linux版本中增加了對非統一記憶體訪問（NUMA）的支援，該版本現在對libnuma庫具有依賴性 。

# install library 
[root@mysql mysql]# yum install libnuma

（4.3）建立使用者和使用者組

[root@masterdb ~]# groupadd mysql
[root@masterdb ~]# useradd -r -g mysql -s /bin/false mysql

（4.4）解壓安裝包

[root@masterdb ~]# cd /usr/local/
[root@masterdb local]# tar xzvf /root/mysql-5.7.24-linux-glibc2.12-x86_64.tar.gz

# 修改解壓檔名，與前面定義的basedir相同
[root@masterdb local]# mv mysql-5.7.24-linux-glibc2.12-x86_64/ mysql

最終解壓結果如下：

[root@masterdb mysql]# ls -l
 total 36
 drwxr-xr-x  2 root root   4096 Mar 28 13:48 bin
 -rw-r--r--  1 7161 31415 17987 Oct  4  2018 COPYING
 drwxr-xr-x  2 root root     55 Mar 28 13:48 docs
 drwxr-xr-x  3 root root   4096 Mar 28 13:48 include
 drwxr-xr-x  5 root root    230 Mar 28 13:48 lib
 drwxr-xr-x  4 root root     30 Mar 28 13:48 man
 -rw-r--r--  1 7161 31415  2478 Oct  4  2018 README
 drwxr-xr-x 28 root root   4096 Mar 28 13:48 share
 drwxr-xr-x  2 root root     90 Mar 28 13:48 support-files

（4.5）建立資料檔案存放路徑

[root@masterdb mysql]# mkdir -p /mysql/{3306,3307,3308,3309}/data
[root@masterdb mysql]# chown -R mysql:mysql /mysql 
[root@masterdb mysql]# cd /mysql
[root@masterdb mysql]# tree
.
├── 3306
│   └── data
├── 3307
│   └── data
├── 3308
│   └── data
└── 3309
    └── data

（4.6）建立MySQL引數配置檔案

[root@masterdb mysql]# vim /etc/my.cnf 

[mysqld]
user=mysql
basedir = /usr/local/mysql

[mysqld_multi]
mysqld=/usr/local/mysql/bin/mysqld_safe
mysqladmin=/usr/local/mysql/bin/mysqladmin
log=/usr/local/mysql/mysqld_multi.log

[mysqld3306]
mysqld=mysqld
mysqladmin=mysqladmin
datadir=/mysql/3306/data
port=3306
server_id=3306
socket=/tmp/mysql_3306.sock
log-error = /mysql/3306/error_3306.log

[mysqld3307]
mysqld=mysqld
mysqladmin=mysqladmin
datadir=/mysql/3307/data
port=3307
server_id=3307
socket=/tmp/mysql_3307.sock
log-error=/mysql/3307/error_3307.log

[mysqld3308]
mysqld=mysqld
mysqladmin=mysqladmin
datadir=/mysql/3308/data
port=3308
server_id=3308
socket=/tmp/mysql_3308.sock
log-error=/mysql/3308/error_3308.log

[mysqld3309]
mysqld=mysqld
mysqladmin=mysqladmin
datadir=/mysql/3309/data
port=3309
server_id=3309
socket=/tmp/mysql_3309.sock
log-error = /mysql/3309/error_3309.log

（4.7）初始化資料庫

注意，初始化例項的最後一行記錄了root的初始密碼

# 初始化3306例項
[root@masterdb mysql]# /usr/local/mysql/bin/mysqld --defaults-file=/etc/my.cnf --initialize --basedir=/usr/local/mysql/ --datadir=/mysql/3306/data
2020-03-28T06:10:28.484174Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2020-03-28T06:10:28.689102Z 0 [Warning] InnoDB: New log files created, LSN=45790
2020-03-28T06:10:28.723881Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
2020-03-28T06:10:28.781205Z 0 [Warning] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: d29ad574-70ba-11ea-a38f-000c29fb6200.
2020-03-28T06:10:28.782195Z 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.
2020-03-28T06:10:28.783078Z 1 [Note] A temporary password is generated for root@localhost: YuJ6Bi=PtqCJ


# 初始化3307例項 
[root@masterdb mysql]# /usr/local/mysql/bin/mysqld --defaults-file=/etc/my.cnf --initialize --basedir=/usr/local/mysql/ --datadir=/mysql/3307/data
2020-03-28T06:10:45.598676Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2020-03-28T06:10:45.793277Z 0 [Warning] InnoDB: New log files created, LSN=45790
2020-03-28T06:10:45.829673Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
2020-03-28T06:10:45.886255Z 0 [Warning] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: dcccdb2f-70ba-11ea-a565-000c29fb6200.
2020-03-28T06:10:45.887571Z 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.
2020-03-28T06:10:45.890477Z 1 [Note] A temporary password is generated for root@localhost: &s)nYg.e4qx#
[root@masterdb mysql]# 


# 初始化3308例項
[root@masterdb mysql]# /usr/local/mysql/bin/mysqld --defaults-file=/etc/my.cnf --initialize --basedir=/usr/local/mysql/ --datadir=/mysql/3308/data
2020-03-28T06:10:55.237714Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2020-03-28T06:10:55.442794Z 0 [Warning] InnoDB: New log files created, LSN=45790
2020-03-28T06:10:55.479012Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
2020-03-28T06:10:55.534839Z 0 [Warning] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: e28d1d57-70ba-11ea-a5c4-000c29fb6200.
2020-03-28T06:10:55.535622Z 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.
2020-03-28T06:10:55.536387Z 1 [Note] A temporary password is generated for root@localhost: Mz<kr!vsh1yj
[root@masterdb mysql]# 


# 初始化3309例項
[root@masterdb mysql]# /usr/local/mysql/bin/mysqld --defaults-file=/etc/my.cnf --initialize --basedir=/usr/local/mysql/ --datadir=/mysql/3309/data
2020-03-28T06:11:05.644331Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2020-03-28T06:11:05.840498Z 0 [Warning] InnoDB: New log files created, LSN=45790
2020-03-28T06:11:05.879941Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
2020-03-28T06:11:05.936262Z 0 [Warning] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: e8c03ed2-70ba-11ea-a8fb-000c29fb6200.
2020-03-28T06:11:05.937179Z 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.
2020-03-28T06:11:05.937877Z 1 [Note] A temporary password is generated for root@localhost: K.KLa30i-sv3

（4.8）環境變了設定

添加了環境變數，作業系統才能夠自己找到mysql、mysqld_multi等命令的位置

[root@masterdb mysql]# vim /etc/profil
# 在檔案末尾新增下面資訊
export PATH=/usr/local/mysql/bin:$PATH

#使環境變數生效
[root@masterdb mysql]# source /etc/profile

（4.9）使用mysqld_multi管理多例項

# 使用mysqld_multi啟動3306埠的例項
[root@masterdb mysql]# mysqld_multi start 3306

# 使用mysqld_multi啟動全部例項
[root@masterdb mysql]# mysqld_multi start

# 使用mysqld_multi檢視例項狀態
[root@masterdb mysql]# mysqld_multi report
Reporting MySQL servers
MySQL server from group: mysqld3306 is running
MySQL server from group: mysqld3307 is running
MySQL server from group: mysqld3308 is running
MySQL server from group: mysqld3309 is running

使用mysqld_multi關閉例項較為麻煩，需要配置密碼，因此如何關閉各個例項，見後面章節：（六）關閉多例項資料庫 。

（五）訪問多例項資料庫

（5.1）登入MySQL資料庫

在安裝完成並啟動資料庫後，需要去訪問各個MySQL例項，這裡非常有意思，經常會發現無法連線到資料庫上，我們不妨看一下幾種連線方式：

連線方式一：使用伺服器IP地址，無法連線。這裡還是比較好理解的，MySQL建立完成後，資料庫賬號root@localhost只允許本地連線，引數“-h”後面用伺服器IP被認為了遠端連線，因此無法登陸

[root@masterdb mysql]# mysql -uoot -p -h192.168.10.11 -P3306
Enter password: 
ERROR 1130 (HY000): Host 'masterdb' is not allowed to connect to this MySQL server

連線方式二：使用localhost訪問資料庫，無法連線。我覺得有些匪夷所思，可以看到，MySQL例項使用的socket檔案不對

[root@masterdb mysql]# mysql -uroot -p -hlocalhost -P3306
Enter password: 
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

連線方式三：使用127.0.0.1訪問資料庫，可以連線。有些難以理解，理論上127.0.0.1和localhost是對應的，127.0.0.1可以訪問資料庫，但是localhost卻無法訪問

[root@masterdb mysql]# mysql -uroot -p -h127.0.0.1 -P3306
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 7
Server version: 5.7.24 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, 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.

mysql> exit
Bye

連線方式四：使用socket檔案連線，可以正常訪問

[root@masterdb mysql]# mysql -S /tmp/mysql_3306.sock -p 
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.7.24

Copyright (c) 2000, 2018, 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.

mysql>

（5.2）修改資料庫root@localhost密碼

初次登陸MySQL資料庫，需要修改root密碼，否則無法正常使用

[root@masterdb mysql]# mysql -S /tmp/mysql_3306.sock -p 
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.7.24

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

-- 無法查詢
mysql> show databases;
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.

-- 修改root@localhost使用者的密碼
mysql> alter user  root@localhost identified by '123456';
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

mysql> exit
Bye

（六）關閉多例項資料庫

（6.1）直接使用mysqld_multi來關閉例項

使用mysqld_multi關閉多例項資料庫目前來看比較麻煩，需要在my.cnf檔案的[mysqld_multi]模組裡面配置使用者密碼，並且各個資料庫的使用者密碼都需要相同，否則無法關閉。

我們可以看一下使用mysqld_multi來關閉資料庫例項的日誌：

[root@masterdb mysql]# cat /usr/local/mysql/mysqld_multi.log 

# 當執行：mysqld_multi report時，顯示所有資料庫均在執行
Reporting MySQL servers
MySQL server from group: mysqld3306 is running
MySQL server from group: mysqld3307 is running
MySQL server from group: mysqld3308 is running
MySQL server from group: mysqld3309 is running
mysqld_multi log file version 2.16; run: Sat Mar 28 14:55:16 2020


# 當執行：mysqld_multi stopt時，mysqld_multi會呼叫mysqladmin去關閉資料庫，使用的是[mysqld_multi]裡面配置的賬號密碼，此時3306的密碼是正確的，

# 其它都是錯誤的，因此3306關閉成功，而其它埠的例項因為密碼錯誤而連線資料庫失敗，自然沒有關閉資料庫
Stopping MySQL servers

mysqladmin: [Warning] Using a password on the command line interface can be insecure.
mysqladmin: [Warning] Using a password on the command line interface can be insecure.
mysqladmin: connect to server at 'localhost' failed
error: 'Access denied for user 'root'@'localhost' (using password: YES)'
mysqladmin: [Warning] Using a password on the command line interface can be insecure.
mysqladmin: connect to server at 'localhost' failed
error: 'Access denied for user 'root'@'localhost' (using password: YES)'
mysqladmin: [Warning] Using a password on the command line interface can be insecure.
mysqladmin: connect to server at 'localhost' failed
error: 'Access denied for user 'root'@'localhost' (using password: YES)'
mysqld_multi log file version 2.16; run: Sat Mar 28 14:55:21 2020

# 結果：僅僅關閉了密碼正確的3306埠資料庫
Reporting MySQL servers
MySQL server from group: mysqld3306 is not running
MySQL server from group: mysqld3307 is running
MySQL server from group: mysqld3308 is running
MySQL server from group: mysqld3309 is running
mysqld_multi log file version 2.16; run: Sat Mar 28 14:58:07 2020

既然知道了mysqld_multi是呼叫mysqladmin來關閉資料庫的，那最好的辦法還是直接使用mysqladmin來關閉各個資料庫了，下面演示使用mysqladmin來關閉資料庫例項。

（6.2）使用mysqladmin來關閉例項

[root@masterdb mysql]# mysqld_multi report
Reporting MySQL servers
MySQL server from group: mysqld3306 is running
MySQL server from group: mysqld3307 is running
MySQL server from group: mysqld3308 is running
MySQL server from group: mysqld3309 is running
[root@masterdb mysql]# 
[root@masterdb mysql]# 
[root@masterdb mysql]# cd
[root@masterdb ~]# mysqladmin -h127.0.0.1 -uroot -p -P3306 shutdown 
Enter password: 
[root@masterdb ~]# 
[root@masterdb ~]# mysqladmin -h127.0.0.1 -uroot -p -P3307 shutdown 
Enter password: 
[root@masterdb ~]# mysqld_multi report
Reporting MySQL servers
MySQL server from group: mysqld3306 is not running
MySQL server from group: mysqld3307 is not running
MySQL server from group: mysqld3308 is running
MySQL server from group: mysqld3309 is running

最終關閉了3306和3307資料庫。

【結束】