【MySQL】MySQL半同步复制
默认情况下,MySQL的复制是异步的,主库执行完Commit提交操作后,在主库写入BInlog后即可成功返回给客户端,无需等待BInlog传给从库。当在主库上写入一个事务并提交成功,而从库尚未得到主库推送的Binlog时,主库宕机了,从而从库可能损失该事务,造成主从库的不一致。
为了解决这个问题,MySQL引入了半同步复制。半同步复制保证了主库上的每一个Binlog都能可靠的复制到从库上,主库在每次事务提交时,并不及时反馈给前端用户,而是等待其中一个从库也接收到Binlog并成功写入中继日志后,主库才返回Commit操作成功给客户端。此时,至少有两份日志记录,一份在主库的Binlog上,另一份在至少一个从库的中继日志上,从而保证了数据的完整性。
半同步复制通过使用插件来实现,插件安装成功后,通过使用与其相关的系统变量来控制它。使用半同步复制,需要满足下面的条件:
- MySQL 5.5或以上版本;
- MySQL服务器支持动态加载插件的能力,可通过have_dynamic_loading来判断;
- 复制必须已经工作;
- 不能配置多个复制通道,半同步复制只与默认的复制通道兼容;
配置半同步复制,使用下面的命令即可:Install plugin,set global,stop slave 和start slave,下面具体演示:
本篇基于前篇:MySQL搭建主从复制环境
1、软件环境
mysql> select version();
+------------+
| version() |
+------------+
| 5.7.21-log |
+------------+
1 row in set (0.00 sec)
2、判断MySQL服务器是否支持动态加载插件mysql> select @@have_dynamic_loading;
+------------------------+
| @@have_dynamic_loading |
+------------------------+
| YES |
+------------------------+
1 row in set (0.00 sec)
3、安装主库和从库的半同步插件主库插件:/usr/local/mysql/lib/plugin/semisync_master.so
从库插件:/usr/local/mysql/lib/plugin/semisync_slave.so
主库上安装插件semisync_master.so:
mysql> install plugin rpl_semi_sync_master soname 'semisync_master.so';
Query OK, 0 rows affected (0.16 sec)
mysql> show variables like '%rpl_semi_sync%';
+-------------------------------------------+------------+
| 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 |
+-------------------------------------------+------------+
6 rows in set (0.00 sec)
mysql> select *from mysql.plugin;
+----------------------+--------------------+
| name | dl |
+----------------------+--------------------+
| rpl_semi_sync_master | semisync_master.so |
+----------------------+--------------------+
1 row in set (0.00 sec)
从库上安装插件semisync_slave.so:mysql> install plugin rpl_semi_sync_slave soname 'semisync_slave.so';
Query OK, 0 rows affected (0.11 sec)
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 (0.03 sec)
mysql> select *from mysql.plugin;
+---------------------+-------------------+
| name | dl |
+---------------------+-------------------+
| rpl_semi_sync_slave | semisync_slave.so |
+---------------------+-------------------+
1 row in set (0.00 sec)
4、分别在主从库打开半同步,默认是不打开的主库配置:
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=50000;
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like '%semi_sync%';
+-------------------------------------------+------------+
| Variable_name | Value |
+-------------------------------------------+------------+
| rpl_semi_sync_master_enabled | ON |
| rpl_semi_sync_master_timeout | 50000 |
| 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 |
+-------------------------------------------+------------+
6 rows in set (0.00 sec)
从库配置:mysql> set global rpl_semi_sync_slave_enabled=1;
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like '%semi_sync%';
+---------------------------------+-------+
| Variable_name | Value |
+---------------------------------+-------+
| rpl_semi_sync_slave_enabled | ON |
| rpl_semi_sync_slave_trace_level | 32 |
+---------------------------------+-------+
2 rows in set (0.00 sec)
注意:由于之前是异步复制,故需要重启下从库的I/O线程,如果是全新配置半同步则不需要:mysql> stop slave io_thread;start slave io_thread;
Query OK, 0 rows affected (0.02 sec)
Query OK, 0 rows affected (0.00 sec)
插入一条记录,查看主库的状态:mysql> insert into t_mm (name) values('Test Semi');
Query OK, 1 row affected (0.03 sec)
mysql> select *from t_mm;
+----+-----------+---------------------+
| id | name | cdate |
+----+-----------+---------------------+
| 2 | China | 2018-02-28 17:31:57 |
| 4 | Japon | 2018-02-28 17:31:57 |
| 6 | USA | 2018-02-28 17:31:57 |
| 7 | Alen | 2018-02-28 17:32:07 |
| 9 | Jack | 2018-02-28 17:32:07 |
| 11 | Summer | 2018-02-28 17:32:07 |
| 12 | UK | 2018-02-28 17:32:42 |
| 14 | CN | 2018-03-01 08:54:24 |
| 15 | Lilei | 2018-03-01 08:55:07 |
| 17 | Hanmeimei | 2018-03-01 09:11:55 |
| 19 | Test Semi | 2018-03-01 16:28:26 |
+----+-----------+---------------------+
11 rows in set (0.00 sec)
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 | 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 | 877 |
| Rpl_semi_sync_master_tx_wait_time | 877 |
| Rpl_semi_sync_master_tx_waits | 1 |
| Rpl_semi_sync_master_wait_pos_backtraverse | 0 |
| Rpl_semi_sync_master_wait_sessions | 0 |
| Rpl_semi_sync_master_yes_tx | 1 |
+--------------------------------------------+-------+
14 rows in set (0.00 sec)
状态值分析:Rpl_semi_sync_master_status:值为ON,表示半同步目前是打开状态;
Rpl_semi_sync_master_yes_tx:值为1,表示主库当前是有一个事务是通过半同步复制到从库;
Rpl_semi_sync_master_no_tx:值为0,表示当前没有不是半同步模式下从库及时响应的。
5、模拟网络故障,半同步转为异步复制模式
1)半同步复制在主库等待50秒超时
mysql> show variables like '%semi_sync%timeout%';
+------------------------------+-------+
| Variable_name | Value |
+------------------------------+-------+
| rpl_semi_sync_master_timeout | 50000 |
+------------------------------+-------+
1 row in set (0.01 sec)
2)模拟从库故障mysql> stop slave;
Query OK, 0 rows affected (0.01 sec)
3)主库执行一个事务并提交,主库的提交操作会阻塞50秒mysql> insert into t_mm (name) values('Block');
新开一个窗口检查当前主库线程,发现提交操作在等待从库半同步操作相应:mysql> show processlist\G;
*************************** 1. row ***************************
Id: 19
User: root
Host: localhost
db: test
Command: Query
Time: 18
State: Waiting for semi-sync ACK from slave
Info: insert into t_mm (name) values('Block')
*************************** 2. row ***************************
Id: 22
User: root
Host: localhost
db: test
Command: Query
Time: 0
State: starting
Info: show processlist
2 rows in set (0.00 sec)
ERROR:
No query specified
4)主库上等待50秒超时mysql> insert into t_mm (name) values('Block');
Query OK, 1 row affected (50.09 sec)
检查半同步状态值:mysql> show status like '%semi_sync%';
+--------------------------------------------+-------+
| Variable_name | Value |
+--------------------------------------------+-------+
| Rpl_semi_sync_master_clients | 0 |
| Rpl_semi_sync_master_net_avg_wait_time | 0 |
| Rpl_semi_sync_master_net_wait_time | 0 |
| Rpl_semi_sync_master_net_waits | 1 |
| Rpl_semi_sync_master_no_times | 1 |
| Rpl_semi_sync_master_no_tx | 1 |
| Rpl_semi_sync_master_status | OFF |
| Rpl_semi_sync_master_timefunc_failures | 0 |
| Rpl_semi_sync_master_tx_avg_wait_time | 877 |
| Rpl_semi_sync_master_tx_wait_time | 877 |
| Rpl_semi_sync_master_tx_waits | 1 |
| Rpl_semi_sync_master_wait_pos_backtraverse | 0 |
| Rpl_semi_sync_master_wait_sessions | 0 |
| Rpl_semi_sync_master_yes_tx | 1 |
+--------------------------------------------+-------+
14 rows in set (0.00 sec)
状态值分析:Rpl_semi_sync_master_status :值为OFF,表示半同步关闭,目前复制模式是异步复制;
Rpl_semi_sync_master_yes_tx :值为1,表示刚才的事务不是通过半同步完成的,不累加;
Rpl_semi_sync_master_no_tx :值为1 ,表示半同步模式下,从库没有及时响应的事务增加1个。
6、模拟异步复制自动切换为半同步模式
1)从库正常
mysql> start slave;
Query OK, 0 rows affected (0.04 sec)
2)检查从库状态,则数据同步到从库mysql> show slave status \G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 10.24.33.186
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000013
Read_Master_Log_Pos: 2892
Relay_Log_File: strong-relay-bin.000141
Relay_Log_Pos: 739
Relay_Master_Log_File: mysql-bin.000013
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 2892
Relay_Log_Space: 1536
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 1
Master_UUID: 2a3e3fd9-0587-11e8-bdb8-0800272325a8
Master_Info_File: /usr/local/mysql-5.7.21-el7-x86_64/data/master.info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set: 2a3e3fd9-0587-11e8-bdb8-0800272325a8:19-36
Executed_Gtid_Set: 2a3e3fd9-0587-11e8-bdb8-0800272325a8:1-36,
fb42b433-06fc-11e8-b91a-0800275b8da0:1-13
Auto_Position: 1
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
ERROR:
No query specified
3)检查主库半同步复制状态,表示自动切换为半同步模式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 | 2 |
| Rpl_semi_sync_master_no_times | 1 |
| Rpl_semi_sync_master_no_tx | 1 |
| Rpl_semi_sync_master_status | ON |
| Rpl_semi_sync_master_timefunc_failures | 0 |
| Rpl_semi_sync_master_tx_avg_wait_time | 877 |
| Rpl_semi_sync_master_tx_wait_time | 877 |
| Rpl_semi_sync_master_tx_waits | 1 |
| Rpl_semi_sync_master_wait_pos_backtraverse | 0 |
| Rpl_semi_sync_master_wait_sessions | 0 |
| Rpl_semi_sync_master_yes_tx | 1 |
+--------------------------------------------+-------+
14 rows in set (0.01 sec)
4)在主库测试当前模式是半同步模式mysql> insert into t_mm (name) values('Semi Mode');
Query OK, 1 row affected (0.03 sec)
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 | 3 |
| Rpl_semi_sync_master_no_times | 1 |
| Rpl_semi_sync_master_no_tx | 1 |
| Rpl_semi_sync_master_status | ON |
| Rpl_semi_sync_master_timefunc_failures | 0 |
| Rpl_semi_sync_master_tx_avg_wait_time | 1314 |
| Rpl_semi_sync_master_tx_wait_time | 2628 |
| 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)
提交一个事务后,Rpl_semi_sync_master_yes_tx 由1变为2,表示刚才的操作是通过半同步模式完成的。