1. 背景
* MySQL Replication默认都是异步（asynchronous），当主库在执行完一些事务后，是不会管备库的进度的。如果备库不幸落后，而更不幸的是主库此时又出现Crash（例如宕机），这时备库中的数据就是不完整的。简而言之，在主库发生故障的时候，我们无法使用备库来继续提供数据一致的服务了。
* Semi sync Replication在一定程度上保证提交的事务已经传给了至少一个备库。
* Semi sync Replication仅仅保证事务的已经传递到备库上，但是并不确保已经在备库上执行完成。
* Semi sync Replication主库等待超时(rpl_semi_sync_master_timeout)后，会自动降级为默认的异步（asynchronous）。
* MySQL 5.5版本开始支持Semi sync Replication
2. 环境
* master 服务器环境
mysql> system cat /etc/redhat-release CentOS release 6.8 (Final) mysql> system ifconfig eth0 | sed -rn '2s#^.*addr:(.*) Bca.*$#\1#gp' 172.18.0.1 mysql> show variables like 'version'; +---------------+------------+ | Variable_name | Value | +---------------+------------+ | version | 5.6.36-log | +---------------+------------+ 1 row in set (0.00 sec)
* master 服务器环境
mysql> system cat /etc/redhat-release CentOS release 6.8 (Final) mysql> system ifconfig eth0 | sed -rn '2s#^.*addr:(.*) Bca.*$#\1#gp' 172.18.4.1 mysql> show variables like 'version'; +---------------+------------+ | Variable_name | Value | +---------------+------------+ | version | 5.6.36-log | +---------------+------------+ 1 row in set (0.00 sec)
* master服务器my.cnf配置文件
[mysqld] ########basic settings######## # 主从server-id一定要设置不同 server-id = 110 port = 3306 user = mysql bind_address = 0.0.0.0 character_set_server=utf8mb4 skip_name_resolve = 1 datadir = /data/mysql_data log_error = error.log #######replication settings######## master_info_repository = TABLE relay_log_info_repository = TABLE # MySQL复制是基于binlog日志的 log_bin = bin.log sync_binlog = 1 log_slave_updates # MySQL binlog格式搭建主从时必须设置为row binlog_format = row relay_log = relay.log relay_log_recovery = 1 slave_skip_errors = ddl_exist_errors ######semi sync replication settings######## # 设置插件目录路径 plugin_dir=/usr/local/mysql/lib/plugin # 加载插件 plugin_load = "rpl_semi_sync_master=semisync_master.so;rpl_semi_sync_slave=semisync_slave.so" # 开启master semi sync replication loose_rpl_semi_sync_master_enabled = 1 # 开启slave semi sync replication loose_rpl_semi_sync_slave_enabled = 1 # 等待5秒无ack应答自动切换为异步模式 loose_rpl_semi_sync_master_timeout = 5000
* slave服务器my.cnf配置文件
[mysqld] ########basic settings######## server-id = 210 port = 3306 user = mysql bind_address = 0.0.0.0 character_set_server=utf8mb4 skip_name_resolve = 1 datadir = /data/mysql_data log_error = error.log # slave上开启只读，避免应用误写导致主从数据不一致 read_only = on #######replication settings######## master_info_repository = TABLE relay_log_info_repository = TABLE log_bin = bin.log sync_binlog = 1 log_slave_updates binlog_format = row relay_log = relay.log relay_log_recovery = 1 binlog_gtid_simple_recovery = 1 slave_skip_errors = ddl_exist_errors ######semi sync replication settings######## plugin_dir=/usr/local/mysql/lib/plugin plugin_load = "rpl_semi_sync_master=semisync_master.so;rpl_semi_sync_slave=semisync_slave.so" loose_rpl_semi_sync_master_enabled = 1 loose_rpl_semi_sync_slave_enabled = 1 loose_rpl_semi_sync_master_timeout = 5000
3. 搭建基于半同步主从
* Master 创建复制所使用的用户 [ 此处ip设置为slave服务IP或者% ]
grant replication slave on *.* to 'rpl'@'172.18.4.1' identified by '123';
* master服务器上查看binlog文件名和日志位置
mysql> show master status; +------------+----------+--------------+------------------+-------------------+ | File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set | +------------+----------+--------------+------------------+-------------------+ | bin.000003 | 1187 | | | | +------------+----------+--------------+------------------+-------------------+ 1 row in set (0.00 sec)
* slave服务器上设置master信息
未开启slave服务时，Slave_IO_Running与Slave_SQL_Running状态成No
mysql> show slave status; # 未开启复制功能时，slave状态是空的 Empty set (0.00 sec) mysql> change master to master_host='172.18.0.1',master_user='rpl',master_password='123',master_log_file='bin.000003',master_log_pos=1187; Query OK, 0 rows affected, 2 warnings (0.01 sec) mysql> show slave status\G *************************** 1. row *************************** Slave_IO_State: Master_Host: 172.18.0.1 Master_User: rpl Master_Port: 3306 Connect_Retry: 60 Master_Log_File: bin.000003 Read_Master_Log_Pos: 1187 Relay_Log_File: relay.000001 Relay_Log_Pos: 4 Relay_Master_Log_File: bin.000003 Slave_IO_Running: No Slave_SQL_Running: No 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: 1187 Relay_Log_Space: 120 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: NULL 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: 0 Master_UUID: Master_Info_File: mysql.slave_master_info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: Executed_Gtid_Set: Auto_Position: 0 1 row in set (0.00 sec)
* 开启slave服务，并查看状态
正常开启slave服务后，Slave_IO_Running与Slave_SQL_Running状态成Yes
mysql> start slave; Query OK, 0 rows affected (0.01 sec) mysql> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 172.18.0.1 Master_User: rpl Master_Port: 3306 Connect_Retry: 60 Master_Log_File: bin.000003 Read_Master_Log_Pos: 1187 Relay_Log_File: relay.000002 Relay_Log_Pos: 277 Relay_Master_Log_File: bin.000003 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: 1187 Relay_Log_Space: 440 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: 110 Master_UUID: 08ea3ca7-6dd4-11e7-a45c-00163e0432c5 Master_Info_File: mysql.slave_master_info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: Executed_Gtid_Set: Auto_Position: 0 1 row in set (0.00 sec)
* Master上查看Slave连接信息
mysql> show slave hosts; +-----------+------+------+-----------+--------------------------------------+ | Server_id | Host | Port | Master_id | Slave_UUID | +-----------+------+------+-----------+--------------------------------------+ | 210 | | 3306 | 110 | d6ceba69-6dd4-11e7-a462-00163e028c02 | +-----------+------+------+-----------+--------------------------------------+ 1 row in set (0.00 sec)
* Master上操作创建数据库与表，并插入数据
mysql> create database mytest character set utf8mb4;
Query OK, 1 row affected (0.01 sec)
mysql> use mytest;
mysql> create table users(
-> id BIGINT NOT NULL AUTO_INCREMENT,
-> name VARCHAR(255) NOT NULL,
-> sex ENUM('M', 'F') NOT NULL DEFAULT 'M',
-> age INT SIGNED NOT NULL DEFAULT '0',
-> PRIMARY KEY (id)
-> )ENGINE=INNODB DEFAULT CHARSET=utf8mb4;
Query OK, 0 rows affected (0.03 sec)
mysql> insert into users values(null, 'tom', 'M', 24), (null, 'jak', 'F', 32), (null, 'sea', 'M', 35), (null, 'lisea', 'M', 29);
Query OK, 4 rows affected (0.01 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from users;
+----+-------+-----+-----+
| id | name | sex | age |
+----+-------+-----+-----+
| 1 | tom | M | 24 |
| 2 | jak | F | 32 |
| 3 | sea | M | 35 |
| 4 | lisea | M | 29 |
+----+-------+-----+-----+
4 rows in set (0.00 sec)* Slave上查看
mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | mysql | | mytest | | performance_schema | | test | +--------------------+ 5 rows in set (0.00 sec) mysql> use mytest; Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed mysql> show tables; +------------------+ | Tables_in_mytest | +------------------+ | users | +------------------+ 1 row in set (0.00 sec) mysql> select * from users; +----+-------+-----+-----+ | id | name | sex | age | +----+-------+-----+-----+ | 1 | tom | M | 24 | | 2 | jak | F | 32 | | 3 | sea | M | 35 | | 4 | lisea | M | 29 | +----+-------+-----+-----+ 4 rows in set (0.00 sec)
4. Master/Slave传输过程
5. 总结
以需求驱动技术，技术本身没有优略之分，只有业务之分。
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