半同步复制搭建过程

主库：
mysql> install plugin rpl_semi_sync_master soname 'semisync_master.so';
Query OK, 0 rows affected (0.01 sec)

mysql> select plugin_name,plugin_status from information_schema.plugins where plugin_name like '%semi%';
+----------------------+---------------+
| plugin_name          | plugin_status |
+----------------------+---------------+
| rpl_semi_sync_master | ACTIVE        |
+----------------------+---------------+
1 row in set (0.00 sec)

备库：
mysql> install plugin rpl_semi_sync_slave soname 'semisync_slave.so';
Query OK, 0 rows affected (0.01 sec)

mysql> select plugin_name,plugin_status from information_schema.plugins where plugin_name like '%semi%';
+----------------------+---------------+
| plugin_name          | plugin_status |
+----------------------+---------------+
| rpl_semi_sync_slave  | ACTIVE        |
+----------------------+---------------+
2 rows in set (0.00 sec)
建议主从把这个2个插件都安装上

主库：
mysql> set global rpl_semi_sync_master_enabled=1;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like '%rpl_semi%';
+-------------------------------------------+------------+
| Variable_name                             | Value      |
+-------------------------------------------+------------+
| rpl_semi_sync_master_enabled              | ON         |
| rpl_semi_sync_master_timeout              | 10000      |
| rpl_semi_sync_master_trace_level          | 32         |
| rpl_semi_sync_master_wait_for_slave_count | 1          |
| rpl_semi_sync_master_wait_no_slave        | ON         |
| rpl_semi_sync_master_wait_point           | AFTER_SYNC |
| rpl_semi_sync_slave_enabled               | OFF        |
| rpl_semi_sync_slave_trace_level           | 32         |
+-------------------------------------------+------------+
8 rows in set (0.00 sec)

启用从库的半同步插件：
mysql> set global rpl_semi_sync_slave_enabled=1;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like '%rpl_semi%';
+-------------------------------------------+------------+
| Variable_name                             | Value      |
+-------------------------------------------+------------+
| rpl_semi_sync_master_enabled              | OFF        |
| rpl_semi_sync_master_timeout              | 10000      |
| rpl_semi_sync_master_trace_level          | 32         |
| rpl_semi_sync_master_wait_for_slave_count | 1          |
| rpl_semi_sync_master_wait_no_slave        | ON         |
| rpl_semi_sync_master_wait_point           | AFTER_SYNC |
| rpl_semi_sync_slave_enabled               | ON         |
| rpl_semi_sync_slave_trace_level           | 32         |
+-------------------------------------------+------------+
8 rows in set (0.01 sec)

mysql> show status like '%semi%status%';
+-----------------------------+-------+
| Variable_name               | Value |
+-----------------------------+-------+
| Rpl_semi_sync_master_status | ON    |
| Rpl_semi_sync_slave_status  | OFF   |
+-----------------------------+-------+
2 rows in set (0.01 sec)

mysql> 

mysql> show status like '%semi%status%';
+-----------------------------+-------+
| Variable_name               | Value |
+-----------------------------+-------+
| Rpl_semi_sync_slave_status  | OFF   |
+-----------------------------+-------+
2 rows in set (0.01 sec)
mysql> 

mysql> stop slave io_thread;
Query OK, 0 rows affected, 2 warnings (0.00 sec)

mysql> start slave io_thread;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql>  show status like '%semi%status%';
+-----------------------------+-------+
| Variable_name               | Value |
+-----------------------------+-------+
| Rpl_semi_sync_master_status | OFF   |
| Rpl_semi_sync_slave_status  | ON    |
+-----------------------------+-------+
2 rows in set (0.00 sec)
现在从库半同步插件启用了

#for master
rpl_semi_sync_master_enabled = 1
rpl_semi_sync_master_timeout = 1000

#for slave
rpl_semi_sync_slave_enabled = 1

mysql> show status like '%semi%tx%';
+---------------------------------------+-------+
| Variable_name                         | Value |
+---------------------------------------+-------+
| Rpl_semi_sync_master_no_tx            | 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_yes_tx           | 0     |
+---------------------------------------+-------+
5 rows in set (0.00 sec)

mysql> use ww_xxx
Database changed
mysql> create table test(id int);
Query OK, 0 rows affected (0.03 sec)

mysql> insert into test values (4),(6),(9),(10);
Query OK, 4 rows affected (0.02 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> select * from test;
+------+
| id   |
+------+
|    4 |
|    6 |
|    9 |
|   10 |
+------+
4 rows in set (0.00 sec)

mysql> show status like '%semi%tx%';
+---------------------------------------+-------+
| Variable_name                         | Value |
+---------------------------------------+-------+
| Rpl_semi_sync_master_no_tx            | 0     |
| Rpl_semi_sync_master_tx_avg_wait_time | 358   |
| Rpl_semi_sync_master_tx_wait_time     | 716   |
| Rpl_semi_sync_master_tx_waits         | 2     |
| Rpl_semi_sync_master_yes_tx           | 2     |
+---------------------------------------+-------+
5 rows in set (0.00 sec)

mysql> 

Rpl_semi_sync_master_yes_tx 成功收到slave ack的事务数量 可以看出有2个事务通过半同步复制进行的
停止备库的io_thread线程,在主库执行事务
mysql> insert into test values(100);
Query OK, 1 row affected (10.01 sec)
mysql>
可以看到语句执行10s 等待备库ack响应超时这也证明半同步复制生效了
超时之后转换为异步复制了
mysql> show status like '%semi%status%';
+-----------------------------+-------+
| Variable_name               | Value |
+-----------------------------+-------+
| Rpl_semi_sync_master_status | OFF   |
| Rpl_semi_sync_slave_status  | OFF   |
+-----------------------------+-------+
2 rows in set (0.00 sec)

启动io_thread，恢复复制连接，主库从异步复制提升为半同步复制
mysql> show status like '%semi%status%';
+-----------------------------+-------+
| Variable_name               | Value |
+-----------------------------+-------+
| Rpl_semi_sync_master_status | ON    |
| Rpl_semi_sync_slave_status  | OFF   |
+-----------------------------+-------+
2 rows in set (0.00 sec)