MySQL 主从复制是指数据可以从一个 MySQL 数据库服务器主节点复制到一个或多个从节点。MySQL 默认采用异步复制方式;从节点可以复制主数据库中的所有数据库或者特定的数据库，或者特定的表.

1. 安装指定版本

yum install -y http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm
yum install -y mysql-community*5.7.30-1.el7.x86_64

2. 初始化账号

set global validate_password_policy=0; set global validate_password_length=4;
alter user user() identified by 'root';
update mysql.user set host='%' where user='root';
flush privileges;

1. 修改 mysqld 配置文件

[mysqld]
character-set-server=utf8
collation-server=utf8_general_ci
max_connections = 2000
server-id=1
log-bin=mysql-binlog
binlog_format = ROW
binlog_row_image = minimal
; 仅记录数据库 demo01 的二进制日志 binlog
binlog-do-db = demo01

systemctl restart mysqld

2. 创建复制账号

grant replication slave on _._ to 'repl'@'%' identified by '123456';
flush privileges;

3. 查看主库状态

show master status\G;

*************************** 1. row ***************************
             File: mysql-binlog.000002
         Position: 306
     Binlog_Do_DB: demo01
 Binlog_Ignore_DB:
Executed_Gtid_Set:
1 row in set (0.00 sec)

1. 修改 mysqld 配置文件

[mysqld]
character-set-server=utf8
collation-server=utf8_general_ci
max_connections = 2000

server-id=2
log-bin=mysql-binlog
binlog_format = ROW
binlog_row_image = minimal
master_info_repository = TABLE
relay_log_info_repository = TABLE
; 当 relay-log 损坏时, 可根据当前slave端sql线程回放的位置, 重新从master上获取日志
relay_log_recovery = 1

; 备注:
; mysql slave端二进制日志没有其它用途，其实可以不必开启从端 binlog

2. 设置主从复制时的元数据(master 同步主机账号及 binlog 文件和位置)

mysql> change master to
master_host="192.168.31.17",
master_port=3306,
master_user="repl",
master_password="123456",
master_log_file="mysql-binlog.000002",
master_log_pos=306;

; 设置从库只读, 并启动slave
mysql> set global super_read_only=1;
mysql> start slave;

3. 查看状态

show slave status\G;

*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.31.17
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-binlog.000002
          Read_Master_Log_Pos: 306
               Relay_Log_File: c8-relay-bin.000002
                Relay_Log_Pos: 323
        Relay_Master_Log_File: mysql-binlog.000002
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              Replicate_Do_DB:
          Replicate_Ignore_DB:
           Replicate_Do_Table:
       Replicate_Ignore_Table:
      Replicate_Wild_Do_Table:
  Replicate_Wild_Ignore_Table:
                   Last_Errno: 0
                   Last_Error:
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 306
              Relay_Log_Space: 527
              Until_Condition: None
               Until_Log_File:
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File:
           Master_SSL_CA_Path:
              Master_SSL_Cert:
            Master_SSL_Cipher:
               Master_SSL_Key:
        Seconds_Behind_Master: 0  # slave 端落后于 master 端多少秒
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error:
               Last_SQL_Errno: 0
               Last_SQL_Error:
  Replicate_Ignore_Server_Ids:
             Master_Server_Id: 1
                  Master_UUID: 7aa006de-1b3f-11eb-842d-525400f46c59
             Master_Info_File: mysql.slave_master_info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates
           Master_Retry_Count: 86400
                  Master_Bind:
      Last_IO_Error_Timestamp:
     Last_SQL_Error_Timestamp:
               Master_SSL_Crl:
           Master_SSL_Crlpath:
           Retrieved_Gtid_Set:
            Executed_Gtid_Set:
                Auto_Position: 0
         Replicate_Rewrite_DB:
                 Channel_Name:
           Master_TLS_Version:
1 row in set (0.00 sec)

主要参数项说明

• slave io thread 按照 Master_Log_File、Read_Master_Log_Pos 位置读取主库的 binlog，并写入到本地 relay log
• slave sql thread 按照 Relay_Log_File、Relay_Log_Pos 位置进行 realy log 的回放

从服务器 sql 线程执行状态

• Waiting for the next event in relay log 该状态是读取 relay log 之前的初始状态
• Reading event from the relay log 该状态表示此线程已经在 relay log 中读取了一个事件准备执行
• Making temp file 该状态表示此线程正在执行 LOAD_DATA_INFILE 并且正在创建一个临时文件来保存从服务器将要读取的数据
• Slave has read all relay log; waiting for the slave I/O thread to update it 该线程已经处理完了 relay log 中的所有事件，现在正在等待 slave /O 线程更新 relay log 文件
• Waiting for slave mutex on exit 当线程停止的时候会短暂的出现该情况
• updating # 表示正在更新
• Opening tables
• Sending data

Master 端建库建表, 看 slave 端是否同步

master 端

-- 查看 slave 情况
show slave hosts;
show master status\G;

create database demo01;
create database demo02;
use demo01;
create table user(
id int auto_increment,
name varchar(16) not null,
age int(16) not null,
primary key(id)
)engine=innodb charset=utf8;



-- 插入入数据
insert into user(name,age) values('tom',31),('user1', 18),('user2', 16),('user3', 33),('user4', 12);

-- 查看 二进制文件
show binary logs;
+---------------------+-----------+
| Log_name            | File_size |
+---------------------+-----------+
| mysql-binlog.000001 |       177 |
| mysql-binlog.000002 |      1079 |
+---------------------+-----------+
2 rows in set (0.00 sec)

-- 查看 二进制事件
show binlog events in 'mysql-binlog.000002';
+---------------------+------+----------------+-----------+-------------+--------------------------------------+
| Log_name            | Pos  | Event_type     | Server_id | End_log_pos | Info      |
+---------------------+------+----------------+-----------+-------------+--------------------------------------+
| mysql-binlog.000002 |    4 | Format_desc    |         1 |         123 | Server ver: 5.7.30-log, Binlog ver: 4|
| mysql-binlog.000002 |  123 | Previous_gtids |         1 |         154 | |
| mysql-binlog.000002 |  154 | Anonymous_Gtid |         1 |         219 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS'|
| mysql-binlog.000002 |  219 | Query          |         1 |         306 | flush privileges |
| mysql-binlog.000002 |  306 | Anonymous_Gtid |         1 |         371 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS'|
| mysql-binlog.000002 |  371 | Query          |         1 |         471 | create database demo01|
| mysql-binlog.000002 |  471 | Anonymous_Gtid |         1 |         536 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS'|
| mysql-binlog.000002 |  536 | Query          |         1 |         748 | use `demo01`; create table user(
id int auto_increment,
name varchar(16) not null,
age int(16) not null,
primary key(id)
)engine=innodb charset=utf8 |
| mysql-binlog.000002 |  748 | Anonymous_Gtid |         1 |         813 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS'|
| mysql-binlog.000002 |  813 | Query          |         1 |         887 | BEGIN|
| mysql-binlog.000002 |  887 | Table_map      |         1 |         940 | table_id: 108 (demo01.user)|
| mysql-binlog.000002 |  940 | Write_rows     |         1 |        1048 | table_id: 108 flags: STMT_END_F|
| mysql-binlog.000002 | 1048 | Xid            |         1 |        1079 | COMMIT /* xid=24 */|
+---------------------+------+----------------+-----------+-------------+--------------------------------------+
13 rows in set (0.00 sec)

-- 二进制事件位置 Pos 813 ~ 1048 执行的是如下插入操作
insert into user(name,age) values('tom',31),('user1', 18),('user2', 16),('user3', 33),('user4', 12);

slave 端

-- 从端查看是否同步
show databases;

-- 查看指定数据是否同步
use demo01;
select * from user;
+----+-------+-----+
| id | name  | age |
+----+-------+-----+
|  1 | tom   |  31 |
|  2 | user1 |  18 |
|  3 | user2 |  16 |
|  4 | user3 |  33 |
|  5 | user4 |  12 |
+----+-------+-----+
5 rows in set (0.01 sec)