mysql半同步开启

开启半同步复制

#在有的高可用架构下，master和slave需同时启动，以便在切换后能继续使用半同步复制

/etc/my.cnf

plugin-load = "rpl_semi_sync_master=semisync_master.so;rpl_semi_sync_slave=semisync_slave.so"
rpl-semi-sync-master-enabled = 1
rpl-semi-sync-slave-enabled = 1

查看半同步是否在运行

master：
mysql> show status like 'Rpl_semi_sync_master_status';
+-----------------------------+-------+
| Variable_name              | Value |
+-----------------------------+-------+
| Rpl_semi_sync_master_status | ON    |
+-----------------------------+-------+

slave：
mysql> show status like 'Rpl_semi_sync_slave_status';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| Rpl_semi_sync_slave_status | ON    |
+----------------------------+-------+

重启slave上的IO线程使半同步生效

mysql> stop slave io_thread;

mysql> start slave io_thread;
#如果没有重启，则默认还是异步复制，重启后，slave会在master上注册为半同步复制的slave角色。

半同步复制测试

master:
mysql> create database db;
mysql> use db
Database changed
mysql> create table t1(id int);
mysql> insert into t1 values(1);
mysql> select * from t1;
+------+| id  |+------+|    1 |+------+1 row in set (0.00 sec)
slave:
mysql> select * from db.t1;
+------+| id  |+------+|    1 |+------+1 row in set (0.00 sec)

#可以看到数据很快同步到了从库上，下面关闭io_thread测试
slave：
mysql> stop slave io_thread;
Query OK, 0 rows affected (0.00 sec)

master：
mysql> insert into t1 values(2);  #此处有一个10s的超时等待时间，超时后转为异步插入
Query OK, 1 row affected (10.11 sec)
mysql> show status like 'Rpl_semi_sync_master_status';  #半同步已失效
+-----------------------------+-------+| Variable_name              | Value |
+-----------------------------+-------+| Rpl_semi_sync_master_status | OFF  |
+-----------------------------+-------+


slave：
mysql> show status like 'Rpl_semi_sync_slave_status';  #从库的半同步也失效
+----------------------------+-------+| Variable_name              | Value |
+----------------------------+-------+| Rpl_semi_sync_slave_status | OFF  |
+----------------------------+-------+1 row in set (0.01 sec)

slave：
mysql> start slave io_thread;  #从库开启io线程
Query OK, 0 rows affected (0.00 sec)

master：
mysql> show status like 'Rpl_semi_sync_master_status';  #又重新转为半同步复制
+-----------------------------+-------+| Variable_name              | Value |
+-----------------------------+-------+| Rpl_semi_sync_master_status | ON    |
+-----------------------------+-------+1 row in set (0.00 sec)

slave：
mysql> select * from db.t1;  #从库上数据已同步 
+------+| id |+------+| 1 || 2 |+------+2 rows in set (0.00 sec)