半同步复制
MySQL的主从复制在5.5版本以前只支持异步复制，也就是说主库在执行一些事务后，是不管从库备库的进度的，这种方式最大的好处是速度快、效率高；缺点就是在主库宕机后，不能确保从库和主库的数据一致性。
半同步复制的好处就是，主库在每执行一次事务后，会等待备库接受日志后才返回给客户端，如果做的是小事务，两台主机的延迟较小，则可以实现在损失很小的性能的情况下保证零数据丢失。
原理
1）主库每执行一次事务都会先让备库读取日志，确保至少有一台备库上面的数据和自己完整
2）如果在一个timeout超时时间内主库仍旧没有收到备库的应答，则自动q切换回异步模式，保证业务运行
3）半同步复制只能保证从库读取了日志，并不能保证数据写入到了从库数据库中，还得看从库sql进程执行情况
4）如果有从库进度追赶上了主库，模式继续切换回半同步状态
环境搭建实践
MySQL半同步复制插件由谷歌提供，5.5版本以后自带可以直接使用
!！注意,两台主机实现半同步复制之前的必须已经实现主从复制 请参考博文：http://www.lichengbing.cn/archivers/82.html
mysql> show variables like ‘plugin_dir‘; +---------------+--------------------------------+ | Variable_name | Value | +---------------+--------------------------------+ | plugin_dir | /application/mysql/lib/plugin/ | #插件位置 +---------------+--------------------------------+ 1 row in set (0.00 sec)
主库安装插件
mysql> install plugin rpl_semi_sync_master soname ‘semisync_master.so‘; mysql> show variables like ‘%rpl_semi_sync%‘; #查看配置状态 +---------------------------------+-------+ | 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_master_enabled = 1; #开启Semi-sync功能 mysql> set global rpl_semi_sync_master_timeout = 10000; #设置超时时间为10秒 mysql> show variables like ‘%rpl_semi_sync%‘; +------------------------------------+-------+ | 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_no_slave | ON | +------------------------------------+-------+
加入配置文件my.cnf中
[mysqld] rpl_semi_sync_master_enabled = 1 rpl_semi_sync_master_timeout = 10000
从库
安装插件
mysql> install plugin rpl_semi_sync_slave soname ‘semisync_slave.so‘; mysql> show variables like ‘%rpl_semi_sync%‘; +---------------------------------+-------+ | 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; #开启插件 mysql> stop slave; #重启从库IO进程 mysql> start slave;
此时在主库这边可以查看半同步复制状态
mysql> show global status like ‘%rpl_semi%‘; +--------------------------------------------+-------+ | Variable_name | Value | +--------------------------------------------+-------+ | Rpl_semi_sync_master_clients | 1 | #正常连接的客户端台数 | 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 | 2 | | Rpl_semi_sync_master_no_tx | 1 | | Rpl_semi_sync_master_status | ON | #状态正常 | 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 (0.01 sec)
做几个简单的测试：主库插入一行数据
mysql> select * from test; +----+--------+ | id | name | +----+--------+ | 1 | 小明 | +----+--------+ 1 row in set (0.00 sec) mysql> insert into test values(2,‘test‘); Query OK, 1 row affected (0.00 sec) #可以看见延迟几乎可以忽略
从库这边，数据正常说明成功了~
mysql> select * from test; +----+--------+ | id | name | +----+--------+ | 1 | 小明 | | 2 | test | +----+--------+ 2 rows in set (0.00 sec)
模拟下从库故障
mysql> stop slave IO_THREAD; Query OK, 0 rows affected (0.01 sec)
我们再在主从插入数据
mysql> insert into test values(3,‘test‘); Query OK, 1 row affected (10.01 sec) #插入时间很久，10秒钟，10秒超时后，自动切换回异步复制了 mysql> show global status like ‘%rpl_semi%‘; +--------------------------------------------+-------+ | Variable_name | Value | +--------------------------------------------+-------+ | Rpl_semi_sync_master_clients | 1 | | Rpl_semi_sync_master_net_avg_wait_time | 498 | | Rpl_semi_sync_master_net_wait_time | 1495 | | Rpl_semi_sync_master_net_waits | 3 | | Rpl_semi_sync_master_no_times | 3 | | Rpl_semi_sync_master_no_tx | 2 | | Rpl_semi_sync_master_status | OFF | #关闭状态 | Rpl_semi_sync_master_timefunc_failures | 0 | | Rpl_semi_sync_master_tx_avg_wait_time | 799 | | Rpl_semi_sync_master_tx_wait_time | 1599 | | Rpl_semi_sync_master_tx_waits | 2 | | Rpl_semi_sync_master_wait_pos_backtraverse | 0 | | Rpl_semi_sync_master_wait_sessions | 0 | | Rpl_semi_sync_master_yes_tx | 2 | +--------------------------------------------+-------+ 14 rows in set (0.00 sec)
恢复IO线程
mysql> start slave IO_THREAD; Query OK, 0 rows affected (0.00 sec) mysql> show global status like ‘%rpl_semi%‘; +--------------------------------------------+-------+ | Variable_name | Value | +--------------------------------------------+-------+ | Rpl_semi_sync_master_clients | 1 | | Rpl_semi_sync_master_net_avg_wait_time | 4526 | | Rpl_semi_sync_master_net_wait_time | 18107 | | Rpl_semi_sync_master_net_waits | 4 | | Rpl_semi_sync_master_no_times | 3 | | Rpl_semi_sync_master_no_tx | 2 | | Rpl_semi_sync_master_status | ON | #重新开启了 | Rpl_semi_sync_master_timefunc_failures | 0 | | Rpl_semi_sync_master_tx_avg_wait_time | 799 | | Rpl_semi_sync_master_tx_wait_time | 1599 | | Rpl_semi_sync_master_tx_waits | 2 | | Rpl_semi_sync_master_wait_pos_backtraverse | 0 | | Rpl_semi_sync_master_wait_sessions | 0 | | Rpl_semi_sync_master_yes_tx | 2 | +--------------------------------------------+-------+ 14 rows in set (0.00 sec)
时间： 2024-12-12 13:52:11