• 半同步复制：
  
  • 5.5集成到MySQL，以插件的形式存在，需要单独安装
  • 确保事务提交后bnog至少传输到一个从库
  • 不保证从库应用完这个事务的binlog
  • 性能有一定的降低，响应时间会更长
  • 网络异常或从库宕机，卡住主库直到超时或从库恢复

异步复制的逻辑

半同步复制的逻辑

安装
主库上

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

mysql> show plugins;
+----------------------------+----------+--------------------+--------------------+---------+
| Name                       | Status   | Type               | Library            | License |
...
| rpl_semi_sync_master       | ACTIVE   | REPLICATION        | semisync_master.so | GPL     |

从库上

mysql> install plugin rpl_semi_sync_slave soname 'semisync_slave.so';
Query OK, 0 rows affected (0.02 sec)

mysql> show plugins;
+----------------------------+----------+--------------------+-------------------+---------+
| Name                       | Status   | Type               | Library           | License |
...
| rpl_semi_sync_slave        | ACTIVE   | REPLICATION        | semisync_slave.so | GPL     |

查看semi-sync的参数

#主库
mysql> show variables like '%semi%';
+------------------------------------+-------+
| Variable_name                      | Value |
+------------------------------------+-------+
| rpl_semi_sync_master_enabled       | OFF   |
| rpl_semi_sync_master_timeout       | 10000 |#超时时间，默认10秒钟
| rpl_semi_sync_master_trace_level   | 32    |
| rpl_semi_sync_master_wait_no_slave | ON    |
+------------------------------------+-------+
4 rows in set (0.00 sec)

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

#从库
mysql> show 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)

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

重启主从复制

#从库
mysql> stop slave;
Query OK, 0 rows affected (0.01 sec)

mysql> start slave;
Query OK, 0 rows affected (0.02 sec)

mysql> show global status like '%semi%';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| Rpl_semi_sync_slave_status | ON    |
+----------------------------+-------+
1 row in set (0.01 sec)

#主库

mysql> show global status like '%semi%';
+--------------------------------------------+-------+
| Variable_name                              | Value |
+--------------------------------------------+-------+
| Rpl_semi_sync_master_clients               | 1     |#表示有一个semi—sync从库在进行复制
| 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

#主库
mysql> select * from test;
+------+------+
| id   | name |
+------+------+
|    1 | m1   |
|    2 | m2   |
|    3 | m3   |
|    4 | m4   |
+------+------+
4 rows in set (0.00 sec)

mysql> insert into test values (5,'m5');
Query OK, 1 row affected (0.00 sec)

#从库
mysql> stop slave;
Query OK, 0 rows affected (0.01 sec)

#主库
mysql> insert into test values (6,'m6');
Query OK, 1 row affected (10.00 sec)#可以看到，主库插入用了10秒钟

修改超时参数，默认的10秒钟太长了，如果从库出问题的话，那么有可能引起雪崩效应
#从库
mysql> start slave;
Query OK, 0 rows affected (0.02 sec)

#主库
mysql> set global rpl_semi_sync_master_timeout=100;
Query OK, 0 rows affected (0.00 sec)

#从库
mysql> stop slave;
Query OK, 0 rows affected (0.00 sec)

#主库

mysql> insert into test values (7,'m7');
Query OK, 1 row affected (0.10 sec)

半同步复制状态