MySQL主从介绍

MySQL主从叫做Replication、AB复制，A和B做主从后，在A上写数据。B上也会同步A的数据，两者实现实时同步

MySQL是基于binlog日志来同步的，主上必须开启binlog才能进行主从同步，同步过程大概有三个步骤

(1)主将数据操作更改的记录到binlog中

(2)主从之间同步比较binlog的事件记录，A将事件记录到binlog里，从同步到本地后也会在本机上记录一个relaylog的文件

(3)从根据relaylog里面的事件记录来执行同步

主上有一个log dump的线程，用来和从的I/O线程传递binlog

从上会有两个线程，其中I/O线程用于同步binlog的记录并产生relaylog记录，另一个SQL线程用来执行relaylog中的事务，把SQL数据在主上按大小、改变、来一一同步

主从同步有两种场景模式

主-从：主负责所有的数据查询和更改，从只负责数据的备份，只起到备份的作用

主写-从读：主负责数据来源的存储和修改，不用于数据查询。从不仅起到实时备份的作用，还对外部提供查询数据的访问，这样可以减小主数据库的访问压力

主从数据库准备

安装mysql数据库可以参考另一篇文章

对mysql的编译安装参数参考：

[root@localhost mysql-5.7.22]# cmake . -DCMALE_INSTALL_PREFIX=/usr/local/mysql -DMYSQL_DATADIR=/var/mysql/data -DSYSCONFDIR=/etc -DWITH_MYISAM_STORAGE_ENGINE=1 -DWITH_INNOBASE_STORAGE_ENGINE=1 -DWITH_ARCHIVE_STORAGE_ENGINE=1 -DMYSQL_UNIX_ADDR=/usr/local/mysql/mysql.sock -DWITH_PARTITION_STORAGE_ENGINE=1 -DEXTRA_CHARSETS=all -DDEFAULT_CHARSET=utf8 -DDEFAULT_COLLATION=utf8_general_ci -DWITH-SYSTEMD=1 -DWITH_BOOST=/usr/local/boost

-----------------------省略过程----------------------

-- CMAKE_C_LINK_FLAGS:

-- CMAKE_CXX_LINK_FLAGS:

-- CMAKE_C_FLAGS_RELWITHDEBINFO: -O3 -g -fabi-version=2 -fno-omit-frame-pointer -fno-strict-aliasing -DDBUG_OFF

-- CMAKE_CXX_FLAGS_RELWITHDEBINFO: -O3 -g -fabi-version=2 -fno-omit-frame-pointer -fno-strict-aliasing -DDBUG_OFF

-- Configuring done

-- Generating done

-- Build files have been written to: /usr/local/src/mysql-5.7.22

[root@localhost mysql-5.7.22]# echo $?

0

结果无报错，继续make编译

[root@localhost mysql-5.7.22]# make

Scanning dependencies of target abi_check

[ 0%] Built target abi_check

Scanning dependencies of target INFO_SRC

[ 0%] Built target INFO_SRC

Scanning dependencies of target INFO_BIN

[ 0%] Built target INFO_BIN

Scanning dependencies of target zlib

----------------省略过程------------------------

[ 99%] Building C object libmysqld/examples/CMakeFiles/mysql_client_test_embedded.dir/__/__/testclients/mysql_client_test.c.o

[ 99%] Linking CXX executable mysql_client_test_embedded

[ 99%] Built target mysql_client_test_embedded

Scanning dependencies of target my_safe_process

[100%] Building CXX object mysql-test/lib/My/SafeProcess/CMakeFiles/my_safe_process.dir/safe_process.cc.o

[100%] Linking CXX executable my_safe_process

[100%] Built target my_safe_process

[root@localhost mysql-5.7.22]# aecho $?

0

安装无报错，完成最后安装make install

-----------------------过程省略---------------------

-- Installing: /usr/local/mysql/support-files/mysqld_multi.server

-- Installing: /usr/local/mysql/support-files/mysql-log-rotate

-- Installing: /usr/local/mysql/support-files/magic

-- Installing: /usr/local/mysql/share/aclocal/mysql.m4

-- Installing: /usr/local/mysql/support-files/mysql.server

[root@localhost mysql-5.7.22]# echo $?

0

基本的安装完成，接下来就是配置mysql的启动和配置项

递归指定mysql所属用户和所属组的权限

[root@localhost ]# chown -R mysql:mysql /usr/local/mysql/

数据库的初始化

编译好的数据库进行初始化，其中mysql初始化信息中包含一个随机生成的密码

[root@localhost mysql-5.7.22]# /usr/local/mysql/bin/mysqld --initialize --user=mysql --basedir=/usr/local/mysql --datadir=/usr/local/mysql/data

2018-07-28T09:08:42.088874Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).

2018-07-28T09:08:42.590615Z 0 [Warning] InnoDB: New log files created, LSN=45790

2018-07-28T09:08:42.861362Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.

2018-07-28T09:08:42.955937Z 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: d342a57c-9245-11e8-bf5e-080027a7f9c2.

2018-07-28T09:08:42.965634Z 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.

2018-07-28T09:08:42.966858Z 1 [Note] A temporary password is generated for root@localhost: tHuQg=%M!12j

my.cnf和/etc/init.d/mysqld文件

拷贝服务启动文件，并修改my.cnf配置文件。指定mysql安装路径和存储数据的路径及添加系统服务

[root@localhost ]# cp /usr/local/src/mysql-5.7.22/support-files/mysql.server /etc/init.d/mysqld

[root@localhost ]# vim /etc/init.d/mysqld

~

basedir=/usr/local/mysql/

datadir=/usr/local/mysql/data/

~

[root@localhost ]# chmod +x /etc/init.d/mysqld

[root@localhost ]# ls -l /etc/init.d/mysqld

-rwxr-xr-x 1 root root 10609 7月 28 17:21 /etc/init.d/mysqld

[root@localhost ]# chkconfig --add mysqld

[root@localhost ]# chkconfig --list

注意：该输出结果只显示 SysV 服务，并不包含原生 systemd 服务。SysV 配置数据可能被原生 systemd 配置覆盖。

如果您想列出 systemd 服务,请执行 'systemctl list-unit-files'。

欲查看对特定 target 启用的服务请执行

'systemctl list-dependencies [target]'。

mysqld 0:关  1:关 2:开 3:开 4:开 5:开 6:关

netconsole 0:关  1:关 2:关 3:关 4:关 5:关 6:关

network 0:关 1:关 2:开 3:开 4:开 5:开 6:关

编辑my.cnf的mysql配置文件，log-error是记录启动时报错的错误信息。在报错pid的错误中，有尝试把basedir = 的配置给注释掉，然后mysql能正常启动了，查看错误日志记录，日志记录报错unknown variable /usr/local/mysql/ 未知的变量路径，说明my.cnf指定的路径有问题，这里我直接注释掉basedir这个路径，然后启动成功

[root@localhost ]# less /etc/my.cnf

[mysqld]

basedir = /usr/local/mysql/

datadir = /usr/local/mysql/data

port = 3306

character-set-server = utf8

explicit_defaults_for_timestamp = true

# socket = /var/run/mysqld/mysqld.sock

# Disabling symbolic-links is recommended to prevent assorted security risks

symbolic-links=0

# Settings user and group are ignored when systemd is used.

# If you need to run mysqld under a different user or group,

# customize your systemd unit file for mariadb according to the

# instructions in http://fedoraproject.org/wiki/Systemd

[mysqld_safe]

log-error=/var/log/mariadb/mariadb.log

pid-file=/var/run/mariadb/mariadb.pid

log-error = /data/mysql/logs/error.log

#

# include all files from the config directory

#

!includedir /etc/my.cnf.d

mysql的启动过程

添加完成跟随系统启动后，启动mysql服务：

[root@localhost ]# /etc/init.d/mysqld start

Starting MySQL.2018-07-28T09:23:23.822700Z mysqld_safe error: log-error set to '/var/log/mariadb/mariadb.log', however file don't exists. Create writable for user 'mysql'.

ERROR! The server quit without updating PID file (/usr/local/mysql/data/localhost.pid).

根据报错提示创建了mysql的日志文件，然后再尝试启动

[root@localhost ]# mkdir -p /var/log/mariadb/mariadb

[root@localhost ]# touch /var/log/mariadb/mariadb.log

[root@localhost ]# chown -R mysql:mysql /var/log/mariadb/mariadb

再次尝试启动mysql服务，并启动成功

[root@localhost support-files]# /etc/init.d/mysqld start

Starting MySQL. SUCCESS!

[root@localhost support-files]# ps -aux |grep mysql

root 21812 0.0 0.1 113312 1636 pts/0 S 17:28 0:00 /bin/sh /usr/local/mysql//bin/mysqld_safe --datadir=/usr/local/mysq/data --pid-file=/usr/local/mysql/data/localhost.pid

mysql 22000 1.7 16.3 1112372 166604 pts/0 Sl 17:28 0:00 /usr/local/mysql/bin/mysqld --basedir=/usr/local/mysql/ --datadir=/usr/local/mysql/data --plugin-dir=/usr/local/mysql//lib/plugin --user=mysql --log-error=/var/log/mariadb/mariadb.log --pid-file=/usr/local/mysql/data/localhost.pid --port=3306

root 22030 0.0 0.0 112724 976 pts/0 R+ 17:28 0:00 grep --color=auto mysql

将mysql命令写入系统文件中，这样就能在命令行中直接使用mysql这个命令了

[root@localhost mysql]# echo "export PATH=$PATH:/usr/local/mysql/bin/" >>/etc/profile

[root@localhost mysql]# source /etc/profile

[root@localhost mysql]# echo "/usr/local/mysql/lib/" >>/etc/ld.so.conf

[root@localhost mysql]# ldconfig

建立master和slave的主从通信

步骤一

master主配置

清除iptables防火墙规则，由于没有清除iptables。导致进来的数据被转发重定向到其他IP地址上了

[root@aaa ~]# iptables -nvL

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)

pkts bytes target prot opt in out source destination

4811 348K ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED

1 84 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0

4 324 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0

2 104 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22

13467 1028K REJECT all -- * * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)

pkts bytes target prot opt in out source destination

0 0 REJECT all -- * * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT 3311 packets, 1476K bytes)

pkts bytes target prot opt in out source destination

[root@aaa ~]# iptables -F

安装完mysql后，对my.cnf配置文件进行修改，添加binlog日志的记录，指定主从运行时的serverID。

修改my.cnf，添加binlog日志的产生配置并指定mysql的运行server级别ID

如果只同步或不同步的库，就需要在my.cnf中指定不同步或同步的库

#binlog-do-db=db1        #只针对指定库同步

#binlog-ignore-db=mysql    针对某些库不同步

[root@aaa /]# vim /etc/my.cnf

[mysqld]

basedir = /usr/local/mysql/

datadir = /usr/local/mysql/data

port = 3306

character-set-server = utf8

explicit_defaults_for_timestamp = true

server-id = 10

log-bin = zidingyi

在数据库中创建一个从数据库使用访问的授权用户，用于从在master中读取数据并进行同步的作用

mysql> grant replication slave on *.* to 'repl'@192.168.1.220 identified by 'xiangchen' ;

Query OK, 0 rows affected, 1 warning (0.00 sec)

查看主数据库中的binlog存储的值，这个是用于记录数据存储大小的记录的，如果数据表发生读写变化，这里也会发生改变。在主从同步前需要在主库锁表停止数据库读写。file是指定生成binlog文件的名称，Position是数据存储的变化值，通过这个值来进行同步，这个值也表达了binlog文件的改变大小

mysql> show master status;

+-----------------+----------+--------------+------------------+-------------------+

| File           | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |

+-----------------+----------+--------------+------------------+-------------------+

| zidingyi.000001 | 1108     |             |                 |                   |

+-----------------+----------+--------------+------------------+-------------------+

1 row in set (0.00 sec)

将主库锁表暂时禁止读取写入

mysql> flush tables with read lock;

Query OK, 0 rows affected (0.01 sec)

步骤二

slave从配置

slave角色上同样需要清除iptables规则，以免主从之间无法通信

slave从上配置my.cnf，修改server-id，这个id不能小于主上的配置，数值越小优先级越高。从服务器的my.cnf不需要配置log-bin，因为是slave的角色，所以只需要从master那里同步数据即可

[root@Huaching-2 ~]# vim /etc/my.cnf

[mysqld]

#bashdir = /usr/local/mysql/

datadir = /data/mysql

port = 3306

character-set-server = utf8

explicit_defaults_for_timestamp = true

server-id = 20

重启后登入从数据库中，先暂停slave的角色，并在数据库中写入与master通信的一些信息(binlog记录的数值)。

master_log_file是指定主上生成binlog文件的名称，slave会通过这个名称去找对应的binlog文件。

master_log_pos是指定master数据存储的变化值，通过这个值来进行同步，这个值也表达了binlog文件的改变大小

[root@Huaching-2 ~]# /etc/init.d/mysqld restart

Shutting down MySQL.. SUCCESS!

Starting MySQL.. SUCCESS!

mysql> stop slave ;

Query OK, 0 rows affected (0.01 sec)

mysql> change master to master_host='192.168.1.234', master_port=3306, master_user='slave', master_password='xiangchen', master_log_file='zidingyi.000001', master_log_pos=1108;

Query OK, 0 rows affected, 2 warnings (0.02 sec)

步骤三

解除master表锁和启动slave角色，进行数据同步

设置好master和slave的授权和访问账户设置后，解除master的表锁和启动slave的角色，并把master中的库拷贝到slave中，这样才能够保证启动同步时两边数据的一致性

在解除master的表锁之前，拷贝master数据到slave中，忽略明文密码的警告

[root@aaa ~]# mysqldump -uroot -ppwd@123 mysql2 > my2.db

mysqldump: [Warning] Using a password on the command line interface can be insecure.

[root@aaa ~]# mysqldump -uroot -ppwd@123 zrlog > zrlog.db

mysqldump: [Warning] Using a password on the command line interface can be insecure.

将以db结尾的后缀备份文件通过scp、rzsz或者ftp等方法传输到slave上，slave在库中需要创建需要恢复库的一个空库，用于数据导入

mysql> create database mysql2;

Query OK, 0 rows affected (0.02 sec)

mysql> create database zrlog;

Query OK, 0 rows affected (0.02 sec)

mysql> exit

Bye

[root@Huaching-2 ~]# mysql -uroot -ppwd@123 mysql2 < my2.db

[root@Huaching-2 ~]# mysql -uroot -ppwd@123 zrlog < zrlog.db

master上可以把数据表锁解除掉，让主数据库可以正常读写访问

mysql> unlock tables;

mysql> flush privileges;

在从数据库启用slave的角色，并与master数据库进行数据同步(数据同步前两个数据库数据必须一致，否则同步会造成数据不一样的情况发生)

mysql> start slave;

Query OK, 0 rows affected (0.00 sec)

查看主从同步的信息，这里主要关注 Slave_IO_Running: Yes和 Slave_SQL_Running: Yes这两个值，一个表示是否和master正常通信的状态，Slave_IO是和master的IO进程通信的一个线程，yes表示在正常运行。另一个是表示SQL执行是否在监听状态

mysql> show slave status\G;

*************************** 1. row ***************************

Slave_IO_State: Waiting for master to send event

Master_Host: 192.168.1.234

Master_User: slave

Master_Port: 3306

Connect_Retry: 60

Master_Log_File: zidingyi.000001

Read_Master_Log_Pos: 1108

Relay_Log_File: Huaching-2-relay-bin.000002

Relay_Log_Pos: 319

Relay_Master_Log_File: zidingyi.000001

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: 1108

Relay_Log_Space: 531

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

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: 10

Master_UUID: 9174f3d7-9c9a-11e8-88a9-08002733edda

Master_Info_File: /data/mysql/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:

测试主从同步

master和slave的my.cnf中使用的同步配置

master的my.cnf中可以指定同步时排除或者只同步某些库

#binlog-do-db=db1        #只针对指定库同步

#binlog-ignore-db=mysql    针对某些库不同步

slave角色配置针对某些库完全记录执行，不会忽略掉binlog中某条SQL执行语句

replicate_wild_do_table=   支持通配符，统配库，如user.

replicate_wild_ignore_table=   表示这个配置里的内容会被忽略执行

不建议使用以下的配置参数，因为匹配同步的库也有可能会被忽略不去执行

匹配库

replicate_do_db=

replicate_ignore_db=

匹配表

replicate_do_table=

replicate_ignore_table=

在主上查询库的操作，查询主从数据是否一致，相同的库、相同的表

mysql> use mysql2

Database changed

mysql> select count(*) from user;

+----------+

| count(*) |

+----------+

| 6       |

+----------+

1 row in set (0.00 sec)

slave从上的查询结果

mysql> use mysql2

Database changed

mysql> select count(*) from user;

+----------+

| count(*) |

+----------+

| 6       |

+----------+

1 row in set (0.00 sec)

在主上清空这个数据表的内容并查看数据表的行数

mysql> truncate table user;

Query OK, 0 rows affected (0.00 sec)

mysql> select count(*) from user;

+----------+

| count(*) |

+----------+

| 0       |

+----------+

1 row in set (0.00 sec)

slave从上只执行查询数据表行数的操作，结果是会把同样的数据执行同步过来

mysql> select count(*) from user;

+----------+

| count(*) |

+----------+

| 0       |

+----------+

1 row in set (0.00 sec)

如果发生在从上删除表删除库的操作，此时master主上如果误执行了slave上被删除的内容的话，还会造成主从同步发生问题，只能通过重新在slave上指定position的值来进行同步了。这种误操作会破坏主从之间的同步

从删除某些内容后再次同步时发生的报错信息

Last_ SQL_ Error: Error 'Can't drop database 'user'; database doesn't exist' on query. Default database: 'user'. Query: 'drop database user'