MySQL--------基于半同步复制搭建主从

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-releaseCentOS release 6.8 (Final)mysql> system ifconfig eth0  | sed -rn '2s#^.*addr:(.*)  Bca.*$#\1#gp'172.18.0.1mysql> 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-releaseCentOS release 6.8 (Final)mysql> system ifconfig eth0  | sed -rn '2s#^.*addr:(.*)  Bca.*$#\1#gp'172.18.4.1mysql> 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 = 110port = 3306user = mysqlbind_address = 0.0.0.0    character_set_server=utf8mb4skip_name_resolve = 1datadir = /data/mysql_datalog_error = error.log#######replication settings########master_info_repository = TABLErelay_log_info_repository = TABLE# MySQL复制是基于binlog日志的log_bin = bin.logsync_binlog = 1log_slave_updates# MySQL binlog格式搭建主从时必须设置为rowbinlog_format = rowrelay_log = relay.logrelay_log_recovery = 1slave_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 replicationloose_rpl_semi_sync_master_enabled = 1# 开启slave semi sync replicationloose_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 = 210port = 3306user = mysqlbind_address = 0.0.0.0character_set_server=utf8mb4skip_name_resolve = 1datadir = /data/mysql_datalog_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 = TABLErelay_log_info_repository = TABLElog_bin = bin.logsync_binlog = 1log_slave_updatesbinlog_format = rowrelay_log = relay.logrelay_log_recovery = 1binlog_gtid_simple_recovery = 1slave_skip_errors = ddl_exist_errors######semi sync replication settings########plugin_dir=/usr/local/mysql/lib/pluginplugin_load = "rpl_semi_sync_master=semisync_master.so;rpl_semi_sync_slave=semisync_slave.so"loose_rpl_semi_sync_master_enabled = 1loose_rpl_semi_sync_slave_enabled = 1loose_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: NULLMaster_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: 01 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: 0Master_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: 01 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: 0mysql> 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 namesYou can turn off this feature to get a quicker startup with -ADatabase changedmysql> 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。