环境：
- 192.168.205.17: as master server
- 192.168.205.27: as slave server
- 192.168.205.37: as slave server
版本：
- OS: centos 7 1810 with mini install
- mariadb-5.5.60
目地：
默认情况下，MySQL的复制功能是异步的，异步复制可以提供最佳的性能，主库把binlog日志发送给从库即结束，并不验证从库是否接收完毕。这意味着当主服务器或从服务器端发生故障时，有可能从服务器没有接收到主服务器发送过来的binlog日志，这就会造成主服务器和从服务器的数据不一致，甚至在恢复时造成数据的丢失, 半同步解决了性能和数据安全综合，在同步从服务器时只要有一个从服务器确认同步完成，即返回结果，不用等到全部复制完成，这样解决了数据同步复制时要等所有从服务器返回结果，实现了最佳性能和数据安全的结合
步骤：
- 安装数据库在所有服务器，初始化运行以下脚本
[root@master ~]#cat /data/maridb_yum.sh rpm -q mariadb-server ||yum install -y mariadb-server mkdir /data/{mysql,logs} chown mysql:mysql /data/{mysql,logs} sed -i '/\[mysqld\]/a log-bin=/data/logs/bin' /etc/my.cnf sed -i '/\[mysqld\]/a innodb_file_per_table = on' /etc/my.cnf sed -i '/\[mysqld\]/a skip_name_resolve = on' /etc/my.cnf sed -i 's@(datadir=).*@\1/data/mysql@' /etc/my.cnf - 修改配置文件
[root@master ~]#vi /etc/my.cnf [mysqld] server-id=17 [root@slave1 ~]#vi /etc/my.cnf [mysqld] server-id=27 [root@slave2 ~]#vi /etc/my.cnf [mysqld] server-id=37 - 主服务器上建立同步帐号及，记录位置或备份主服器恢复从服务器二选一
MariaDB [(none)]> grant replication slave on *.* to repluser@'192.168.205.%' identified by 'centos'; MariaDB [(none)]> show master logs; +------------+-----------+ | Log_name | File_size | +------------+-----------+ | bin.000001 | 30373 | | bin.000002 | 1038814 | | bin.000003 | 406 | +------------+-----------+ 3 rows in set (0.00 sec) -
从服务器上修改change master to，并启用slave
MariaDB [(none)]> CHANGE MASTER TO -> MASTER_HOST='192.168.205.17', -> MASTER_USER='repluser', -> MASTER_PASSWORD='centos', -> MASTER_PORT=3306, -> MASTER_LOG_FILE='bin.000003', -> MASTER_LOG_POS=406; Query OK, 0 rows affected (0.01 sec) MariaDB [(none)]> start slave; Query OK, 0 rows affected (0.00 sec) MariaDB [(none)]> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 192.168.205.17 Master_User: repluser Master_Port: 3306 Connect_Retry: 60 Master_Log_File: bin.000003 Read_Master_Log_Pos: 406 Relay_Log_File: mariadb-relay-bin.000002 Relay_Log_Pos: 523 Relay_Master_Log_File: bin.000003 Slave_IO_Running: Yes Slave_SQL_Running: Yes - 要启用主从的半同步复制需要安装一个插件
[root@centos7 data]#rpm -ql mariadb-server /usr/lib64/mysql/plugin/semisync_master.so /usr/lib64/mysql/plugin/semisync_slave.so - 在数据库中可以查看那些插件安装
MariaDB [(none)]> show plugins; - 在主服务器上安装插件
MariaDB [(none)]> install plugin rpl_semi_sync_master soname 'semisync_master.so'; Query OK, 0 rows affected (0.00 sec) MariaDB [(none)]> show plugins; … | rpl_semi_sync_master | ACTIVE | REPLICATION | semisync_master.so | GPL | +--------------------------------+----------+--------------------+--------------------+---------+ 43 rows in set (0.00 sec) - 查看半同步的状态
MariaDB [(none)]> show global variables like '%semi%' ; +------------------------------------+-------+ | Variable_name | Value | +------------------------------------+-------+ | rpl_semi_sync_master_enabled | OFF | #半同步默认off | rpl_semi_sync_master_timeout | 10000 | #超时毫秒，10秒 | rpl_semi_sync_master_trace_level | 32 | | rpl_semi_sync_master_wait_no_slave | ON | +------------------------------------+-------+ 4 rows in set (0.00 sec) - 启用半同步
MariaDB [(none)]> set global rpl_semi_sync_master_enabled=on; Query OK, 0 rows affected (0.00 sec) - 查看半同步状态信息
MariaDB [(none)]> show global status like '%semi%'; +--------------------------------------------+-------+ | Variable_name | Value | +--------------------------------------------+-------+ | Rpl_semi_sync_master_clients | 0 | | Rpl_semi_sync_master_net_avg_wait_time | 0 | | Rpl_semi_sync_master_net_wait_time | 0 | | Rpl_semi_sync_master_net_waits | 0 | | Rpl_semi_sync_master_no_times | 0 | | Rpl_semi_sync_master_no_tx | 0 | | Rpl_semi_sync_master_status | ON | | Rpl_semi_sync_master_timefunc_failures | 0 | | Rpl_semi_sync_master_tx_avg_wait_time | 0 | | Rpl_semi_sync_master_tx_wait_time | 0 | | Rpl_semi_sync_master_tx_waits | 0 | | Rpl_semi_sync_master_wait_pos_backtraverse | 0 | | Rpl_semi_sync_master_wait_sessions | 0 | | Rpl_semi_sync_master_yes_tx | 0 | +--------------------------------------------+-------+ 14 rows in set (0.00 sec) - 在所有的从节点安装slave semi插件；
MariaDB [(none)]> install plugin rpl_semi_sync_slave soname 'semisync_slave.so'; Query OK, 0 rows affected (0.00 sec) MariaDB [(none)]> show plugins; … | rpl_semi_sync_slave | ACTIVE | REPLICATION | semisync_slave.so | GPL | +--------------------------------+----------+--------------------+-------------------+---------+ 43 rows in set (0.00 sec) -
查看slave的半同步状态，并启用，并需要重新启动线程，再查看半同步状态是on才可以
MariaDB [(none)]> show global variables like '%semi%'; +---------------------------------+-------+ | Variable_name | Value | +---------------------------------+-------+ | rpl_semi_sync_slave_enabled | OFF | | rpl_semi_sync_slave_trace_level | 32 | +---------------------------------+-------+ 2 rows in set (0.00 sec) MariaDB [(none)]> set global rpl_semi_sync_slave_enabled=on; Query OK, 0 rows affected (0.00 sec) MariaDB [(none)]> show global variables like '%semi%'; +---------------------------------+-------+ | Variable_name | Value | +---------------------------------+-------+ | rpl_semi_sync_slave_enabled | ON | | rpl_semi_sync_slave_trace_level | 32 | +---------------------------------+-------+ 2 rows in set (0.00 sec) MariaDB [(none)]> stop slave; Query OK, 0 rows affected (0.00 sec) MariaDB [(none)]> start slave; Query OK, 0 rows affected (0.00 sec) MariaDB [(none)]> show global status like '%semi%'; +----------------------------+-------+ | Variable_name | Value | +----------------------------+-------+ | Rpl_semi_sync_slave_status | ON | +----------------------------+-------+ 1 row in set (0.00 sec) - 此时查看主节点的状态
MariaDB [(none)]> show global status like '%semi%'; +--------------------------------------------+-------+ | Variable_name | Value | +--------------------------------------------+-------+ | Rpl_semi_sync_master_clients | 2 | | Rpl_semi_sync_master_net_avg_wait_time | 0 | | Rpl_semi_sync_master_net_wait_time | 0 | | Rpl_semi_sync_master_net_waits | 0 | | Rpl_semi_sync_master_no_times | 0 | | Rpl_semi_sync_master_no_tx | 0 | | Rpl_semi_sync_master_status | ON | | Rpl_semi_sync_master_timefunc_failures | 0 | | Rpl_semi_sync_master_tx_avg_wait_time | 0 | | Rpl_semi_sync_master_tx_wait_time | 0 | | Rpl_semi_sync_master_tx_waits | 0 | | Rpl_semi_sync_master_wait_pos_backtraverse | 0 | | Rpl_semi_sync_master_wait_sessions | 0 | | Rpl_semi_sync_master_yes_tx | 0 | +--------------------------------------------+-------+ 14 rows in set (0.00 sec) - 测试，在主节点上创建一个库
MariaDB [(none)]> create database db1; Query OK, 1 row affected (0.00 sec) - 在从节点上可以看到同步
MariaDB [(none)]> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | db1 | | mysql | | performance_schema | | test | +--------------------+ 5 rows in set (0.00 sec) - 此进我们把slave1停掉,在主节点创建数据库，显示可以成功, 只会复制到slave2节点上
[root@slave1 ~]#systemctl stop mariadb MariaDB [(none)]> create database db2; Query OK, 1 row affected (0.01 sec) MariaDB [(none)]> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | db1 | | db2 | | mysql | | performance_schema | | test | +--------------------+ 6 rows in set (0.00 sec) - 如果全部停掉从节点，再从主节点创建数据库，会等10秒才会显示成功
[root@slave2 ~]#systemctl stop mariadb; MariaDB [(none)]> create database db3; Query OK, 1 row affected (10.00 sec) - 将两个服务器再重新启动后，查看数据也会同步
[root@slave1 ~]#systemctl start mariadb MariaDB [(none)]> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | db1 | | db2 | | db3 | | mysql | | performance_schema | | test | +--------------------+ 7 rows in set (0.00 sec)