一、原理

　　mysql的主从数据同步是一个异步复制过程，需要master开启bin-log日志功能，bin-log记录了master库中的增、删、修改、更新操作的sql语句，整个过程需要开启3个线程，分别是master开启I/O线程，slave开启I/O线程和SQL线程

　　1、在slave服务器上执行start slave命令开启主从复制开关，主从复制开始进行，slave I/O线程会通过master创建的授权用户连接上master，并请求master从指定文件和位置之后发送bin-log日志内容

　　2、master接收请求后，master I/O线程更加slave发送的指定bin-log日志position点之后的内容，然后返回给slave的I/O线程；返回的信息中除了bin-log日志外，还有在master服务器记录的新的bin-log文件名及新的bin-log中的下一个指定更新位置（position）

　　3、slave I/O线程接收信息后，将接收的日志内容一次添加到slave端的relay-log（中继日志）文件（mysql-relay-bin.xxxxxx）的最末端，并将读取到的master端的bin-log文件名和position点记录到master.info文件中，以便下次读取时能够告知master从相应的bin-log文件名及最后一个position点开始发起请求

　　4、slave SQL 线程检测到relay-log中I/O线程新增加的内容有更新，会立即分析relay-log日志中的内容，将解析的sql语句按顺序在slave里执行，并记录应用中继日志的文件名及位置点在relay-log.info中，执行成功后slave库与master库数据保持一致

　　总结

　　　　主从复制是异步的逻辑的SQL语句级的复制

　　　　复制时，主库有一个I/O线程，从库有两个线程，I/O和SQL线程

　　　　作为复制的所有mysql节点server-id都不能相同

　　　　bin-log文件只记录对数据库有更改的sql语句（数据库内容的变更），不记录任何查询（select，slow）语句

　　原理流程图如下：

 

　　主从复制条件

　　　　开启binlog功能

　　　　主库要建立账号

　　　　从库要配置master.info

　　　　start slave 开启复制功能

 

 

二、环境

　　master：192.168.216.52

　　slave:192.168.216.53

mariadb版本10.2.24

[root@web2 ~]# rpm -qa Maria*MariaDB-server-10.2.24-1.el7.centos.x86_64MariaDB-compat-10.2.24-1.el7.centos.x86_64MariaDB-common-10.2.24-1.el7.centos.x86_64MariaDB-client-10.2.24-1.el7.centos.x86_64[root@web2 ~]#

 

三、安装配置

　　1、添加mariadb，yum源

　　　　

[root@web2 ~]# cat /etc/yum.repos.d/mariadb.repo [mariadb]name = MariaDBbaseurl = https://mirrors.ustc.edu.cn/mariadb/yum/10.2/centos7-amd64/gpgkey=https://mirrors.ustc.edu.cn/mariadb/yum/RPM-GPG-KEY-MariaDBgpgcheck=1

　　2、这里yum安装

　　　两台机器都安装

　　　　yum install  mariadb-server

　　3、初始化mariadb，可以忽略

　　　　参考： 

　　4、配置master

 

-------------------修改配置文件（红色部分关键，其他为优化）

[root@web2 my.cnf.d]# cat server.cnf## These groups are read by MariaDB server.# Use it for options that only the server (but not clients) should see## See the examples of server my.cnf files in /usr/share/mysql/## this is read by the standalone daemon and embedded servers[server]# this is only for the mysqld standalone daemon[mysqld]server-id=1log-bin=mysql-bin#binlog-do-db=liting#binlog-ignore-db=mysqlsync_binlog=1binlog_checksum = nonebinlog_format = mixedport = 3306socket  = /var/lib/mysql/mysql.sockskip-external-lockingkey_buffer_size = 256MBmax_allowed_packet      = 1MBtable_open_cache        = 256sort_buffer_size        = 1MBread_buffer_size        = 1MBread_rnd_buffer_size    = 4MBmyisam_sort_buffer_size = 64MBthread_cache_size       = 8query_cache_size        = 16MBthread_concurrency      = 8[mysqldump]quickmax_allowed_packet      = 16MB[mysql]no-auto-rehash[myisamchk]key_buffer_size         = 128MBsort_buffer_size        = 128MBread_buffer             = 2MBwrite_buffer            = 2MB[mysqlhotcopy]interactive-timeout## * Galera-related settings#[galera]# Mandatory settings#wsrep_on=ON#wsrep_provider=#wsrep_cluster_address=#binlog_format=row#default_storage_engine=InnoDB#innodb_autoinc_lock_mode=2## Allow server to accept connections on all interfaces.##bind-address=0.0.0.0## Optional setting#wsrep_slave_threads=1#innodb_flush_log_at_trx_commit=0# this is only for embedded server[embedded]# This group is only read by MariaDB servers, not by MySQL.# If you use the same .cnf file for MySQL and MariaDB,# you can put MariaDB-only options here[mariadb]# This group is only read by MariaDB-10.2 servers.# If you use the same .cnf file for MariaDB of different versions,# use this group for options that older servers don't understand[mariadb-10.2][root@web2 my.cnf.d]# 　　

 

----------------------授权 

grant replication slave,replication client on *.* to 'tongbu'@'%' identified by '123456';

----------------------查看bin-log及position点

MariaDB [test3]> show master status;+------------------+----------+--------------+------------------+| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |+------------------+----------+--------------+------------------+| mysql-bin.000003 |      320|              |                  |+------------------+----------+--------------+------------------+1 row in set (0.00 sec)

 

　　5、配置slave

 

--------------------修改配置

[root@web3 my.cnf.d]# cat server.cnf ## These groups are read by MariaDB server.# Use it for options that only the server (but not clients) should see## See the examples of server my.cnf files in /usr/share/mysql/## this is read by the standalone daemon and embedded servers[server]# this is only for the mysqld standalone daemon[mysqld]socket = /var/lib/mysql/mysql.sockport    = 3306skip-external-lockingkey_buffer_size =256MBmax_allowed_packet      = 1MBtable_open_cache        = 256sort_buffer_size        = 1MBread_buffer_size        = 1MBread_rnd_buffer_size    = 4MBmyisam_sort_buffer_size = 64MBthread_cache_size       = 8query_cache_size        = 16MBthread_concurrency      = 8server-id               = 2## * Galera-related settings#[galera]# Mandatory settings#wsrep_on=ON#wsrep_provider=#wsrep_cluster_address=#binlog_format=row#default_storage_engine=InnoDB#innodb_autoinc_lock_mode=2## Allow server to accept connections on all interfaces.##bind-address=0.0.0.0## Optional setting#wsrep_slave_threads=1#innodb_flush_log_at_trx_commit=0# this is only for embedded server[embedded]# This group is only read by MariaDB servers, not by MySQL.# If you use the same .cnf file for MySQL and MariaDB,# you can put MariaDB-only options here[mariadb]# This group is only read by MariaDB-10.2 servers.# If you use the same .cnf file for MariaDB of different versions,# use this group for options that older servers don't understand[mariadb-10.2][root@web3 my.cnf.d]#

[root@web3 my.cnf.d]# cat mysql-clients.cnf      #[mysql][mysqlcheck][mysqldump]也可以写在这个文件里，master我是都卸载server.cnf里面了## These groups are read by MariaDB command-line tools# Use it for options that affect only one utility#[mysql]no-auto-rehash[mysql_upgrade][mysqladmin][mysqlbinlog][mysqlcheck]key_buffer_size         = 128MBsort_buffer_size        = 128MBread_buffer             = 2MBwrite_buffer            = 2MB[mysqldump]quickmax_allowed_packet      = 16MB[mysqlimport][mysqlshow][mysqlslap][mysqlhotcopy]interactive-timeout[root@web3 my.cnf.d]#

---------------------slave进入mysql设置

　　slave指定master ip、用户名、密码、bin-log文件名、position（下面标记红色部分）

[root@web3 my.cnf.d]#  mysqlWelcome to the MariaDB monitor.  Commands end with ; or \g.Your MariaDB connection id is 12Server version: 10.2.24-MariaDB MariaDB ServerCopyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.MariaDB [(none)]> change master to master_host='192.168.216.52',master_user='tongbu',master_password='123456',master_log_file='mysql-bin.000003',master_log_pos=320;MariaDB [(none)]> master_host='192.168.216.52',master_user='tongbu',master_password='123456',master_log_file='mysql-bin.000003',master_log_pos=320;

　MariaDB [(none)]> slave start;

 

 

　　

---------------查看状态正常状态如下：（正常状态关注标记紫色部分)

MariaDB [(none)]> show slave status\G*************************** 1. row ***************************Slave_IO_State: Waiting for master to send eventMaster_Host: 192.168.216.52Master_User: tongbuMaster_Port: 3306Connect_Retry: 60Master_Log_File: mysql-bin.000004Read_Master_Log_Pos: 593Relay_Log_File: web3-relay-bin.000006Relay_Log_Pos: 828Relay_Master_Log_File: mysql-bin.000004Slave_IO_Running: YesSlave_SQL_Running: YesReplicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 0Last_Error: Skip_Counter: 0Exec_Master_Log_Pos: 593Relay_Log_Space: 1136Until_Condition: NoneUntil_Log_File: Until_Log_Pos: 0Master_SSL_Allowed: NoMaster_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: 0Master_SSL_Verify_Server_Cert: NoLast_IO_Errno: 0Last_IO_Error: Last_SQL_Errno: 0Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 1Master_SSL_Crl: Master_SSL_Crlpath: Using_Gtid: NoGtid_IO_Pos: Replicate_Do_Domain_Ids: Replicate_Ignore_Domain_Ids: Parallel_Mode: conservativeSQL_Delay: 0SQL_Remaining_Delay: NULLSlave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it1 row in set (0.00 sec) 需要关注如下几点 引用：

#  1）Slave_IO_Running：该参数可作为io_thread的监控项，Yes表示io_thread的和主库连接正常并能实施复制工作，No则说明与主库通讯异常，多数情况是由主从间网络引起的问题；    2）Slave_SQL_Running：该参数代表sql_thread是否正常，YES表示正常，NO表示执行失败，具体就是语句是否执行通过，常会遇到主键重复或是某个表不存在。    3）Seconds_Behind_Master：是通过比较sql_thread执行的event的timestamp和io_thread复制好的event的timestamp(简写为ts)进行比较，而得到的这么一个差值；         NULL—表示io_thread或是sql_thread有任何一个发生故障，也就是该线程的Running状态是No，而非Yes。         0 — 该值为零，是我们极为渴望看到的情况，表示主从复制良好，可以认为lag不存在。         正值 — 表示主从已经出现延时，数字越大表示从库落后主库越多。         负值 — 几乎很少见，我只是听一些资深的DBA说见过，其实，这是一个BUG值，该参数是不支持负值的，也就是不应该出现。　　

 

　　6、测试，master创建一个test3的库及t1的表

 

[root@web2 my.cnf.d]# mysql -uroot -pEnter password: Welcome to the MariaDB monitor.  Commands end with ; or \g.Your MariaDB connection id is 11Server version: 10.2.24-MariaDB-log MariaDB ServerCopyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.MariaDB [(none)]> MariaDB [(none)]> create database test3;Query OK, 1 row affected (0.00 sec)MariaDB [(none)]> use test3;Database changedMariaDB [test3]> create table t1(id varchar(20),name varchar(20));Query OK, 0 rows affected (0.02 sec)MariaDB [test3]> show tables;+-----------------+| Tables_in_test3 |+-----------------+| t1              |+-----------------+1 row in set (0.00 sec)MariaDB [test3]>

　　

---------------slave查看已经同步过来了

MariaDB [(none)]> show databases;+--------------------+| Database           |+--------------------+| information_schema || mysql              || performance_schema || test               || test3              |+--------------------+5 rows in set (0.00 sec)MariaDB [(none)]>

 

 

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