是否支持
mysql> select @@have_dynamic_loading;
+------------------------+
| @@have_dynamic_loading |
+------------------------+
| YES |
+------------------------+
1 row in set (0.00 sec)
mysql>
2.查看插件
[root@192 /]# ll /usr/local/mysql/lib/plugin/
semisync_master.so
semisync_slave.so
在主库上安装：
mysql> install plugin rpl_semi_sync_master SONAME "semisync_master.so";
Query OK, 0 rows affected (0.03 sec)
再从库上安装：
mysql> install plugin rpl_semi_sync_slave SONAME "semisync_slave.so";
Query OK, 0 rows affected (0.02 sec)
检查：
mysql> select * from mysql.plugin;
+----------------------+--------------------+
| name | dl |
+----------------------+--------------------+
| rpl_semi_sync_master | semisync_master.so |
+----------------------+--------------------+
mysql> select * from mysql.plugin;
+---------------------+-------------------+
| name | dl |
+---------------------+-------------------+
| rpl_semi_sync_slave | semisync_slave.so |
+---------------------+-------------------+
3.在主库和从库上配置参数打开半同步：
主库
mysql> set global rpl_semi_sync_master_enabled = 1;
Query OK, 0 rows affected (0.00 sec)
mysql> set global rpl_semi_sync_master_timeout = 3000;
Query OK, 0 rows affected (0.00 sec)
从库
mysql> set global rpl_semi_sync_slave_enabled = 1;
Query OK, 0 rows affected (0.00 sec)
由于之前是异步复制，所以要重新启动下I/O线程：
mysql> stop slave io_thread; start slave io_thread;
Query OK, 0 rows affected (0.07 sec)
Query OK, 0 rows affected (0.01 sec)
回到主库，查看半同步的一些状态值：
mysql> show status like "%semi_sync%";
+--------------------------------------------+-------+
| Variable_name | Value |
+--------------------------------------------+-------+
| Rpl_semi_sync_master_clients | 1 |
| 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 |
+--------------------------------------------+-------+
执行一个事务再次查看：
mysql> show status like "%semi_sync%";
+--------------------------------------------+-------+
| Variable_name | Value |
+--------------------------------------------+-------+
| Rpl_semi_sync_master_clients | 1 |
| Rpl_semi_sync_master_net_avg_wait_time | 1072 |
| Rpl_semi_sync_master_net_wait_time | 1072 |
| Rpl_semi_sync_master_net_waits | 1 |
| 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 | 1 |
+--------------------------------------------+-------+
如果超时会自动降级为异步，从库正常会恢复到半同步。
