MySQL半同步复制详细描述
程序员文章站
2022-03-28 19:44:02
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...
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：
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。