要想使用半同步复制，必须满足以下几个条件：
1. MySQL 5.5及以上版本
2. 变量 have_dynamic_loading 为YES(主从都要查看)
mysql> show variables like '%have_dynamic_loading%';
+----------------------+-------+
| Variable_name | Value |
+----------------------+-------+
| have_dynamic_loading | YES |
+----------------------+-------+
1 row in set (0.00 sec)
3. 异步复制已经存在
1.首先加载插件
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主(不用具体进入某个库下):
mysql> INSTALL PLUGIN rpl_semi_sync_master SONAME 'semisync_master.so';
Query OK, 0 rows affected (0.06 sec)
从(不用具体进入某个库下):
mysql> INSTALL PLUGIN rpl_semi_sync_slave SONAME 'semisync_slave.so';
Query OK, 0 rows affected (0.05 sec)
2.查看插件是否加载成功(主从库查看方法一样)
方式1:
mysql> show plugins;
+----------------------------+----------+--------------------+--------------------+---------+
| Name | Status | Type | Library | License |
+----------------------------+----------+--------------------+--------------------+---------+
| binlog | ACTIVE | STORAGE ENGINE | NULL | GPL |
| mysql_native_password | ACTIVE | AUTHENTICATION | NULL | GPL |
| sha256_password | ACTIVE | AUTHENTICATION | NULL | GPL |
| PERFORMANCE_SCHEMA | ACTIVE | STORAGE ENGINE | NULL | GPL |
| MRG_MYISAM | ACTIVE | STORAGE ENGINE | NULL | GPL |
| MEMORY | ACTIVE | STORAGE ENGINE | NULL | GPL |
| InnoDB | ACTIVE | STORAGE ENGINE | NULL | GPL |
| INNODB_TRX | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_LOCKS | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_LOCK_WAITS | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_CMP | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_CMP_RESET | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_CMPMEM | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_CMPMEM_RESET | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_CMP_PER_INDEX | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_CMP_PER_INDEX_RESET | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_BUFFER_PAGE | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_BUFFER_PAGE_LRU | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_BUFFER_POOL_STATS | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_TEMP_TABLE_INFO | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_METRICS | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_FT_DEFAULT_STOPWORD | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_FT_DELETED | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_FT_BEING_DELETED | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_FT_CONFIG | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_FT_INDEX_CACHE | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_FT_INDEX_TABLE | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_SYS_TABLES | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_SYS_TABLESTATS | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_SYS_INDEXES | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_SYS_COLUMNS | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_SYS_FIELDS | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_SYS_FOREIGN | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_SYS_FOREIGN_COLS | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_SYS_TABLESPACES | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_SYS_DATAFILES | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| INNODB_SYS_VIRTUAL | ACTIVE | INFORMATION SCHEMA | NULL | GPL |
| CSV | ACTIVE | STORAGE ENGINE | NULL | GPL |
| MyISAM | ACTIVE | STORAGE ENGINE | NULL | GPL |
| ARCHIVE | ACTIVE | STORAGE ENGINE | NULL | GPL |
| partition | ACTIVE | STORAGE ENGINE | NULL | GPL |
| BLACKHOLE | ACTIVE | STORAGE ENGINE | NULL | GPL |
| FEDERATED | DISABLED | STORAGE ENGINE | NULL | GPL |
| ngram | ACTIVE | FTPARSER | NULL | GPL |
| rpl_semi_sync_master | ACTIVE | REPLICATION | semisync_master.so | GPL |
+----------------------------+----------+--------------------+--------------------+---------+
方式2:
mysql> SELECT PLUGIN_NAME, PLUGIN_STATUS FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_NAME LIKE '%semi%';
+----------------------+---------------+
| PLUGIN_NAME | PLUGIN_STATUS |
+----------------------+---------------+
| rpl_semi_sync_master | ACTIVE |
+----------------------+---------------+
1 row in set (0.00 sec)
3.启动半同步复制
在安装完插件后，半同步复制默认是关闭的，这时需设置参数来开启半同步
主:
mysql> SET GLOBAL rpl_semi_sync_master_enabled = 1;
从:
mysql> SET GLOBAL rpl_semi_sync_slave_enabled = 1;
以上的启动方式是在命令行操作，也可写在配置文件中。
主:
plugin-load="rpl_semi_sync_master=semisync_master.so"
rpl_semi_sync_master_enabled=1
从:
plugin-load="rpl_semi_sync_slave=semisync_slave.so"
rpl_semi_sync_slave_enabled=1
在有的高可用架构下,master和slave需同时启动,以便在切换后能继续使用半同步复制
plugin-load="rpl_semi_sync_master=semisync_master.so;rpl_semi_sync_slave=semisync_slave.so"
rpl_semi_sync_master_enabled = 1
rpl_semi_sync_slave_enabled = 1
4.重启从库上的IO线程
mysql> STOP SLAVE IO_THREAD;
mysql> START SLAVE IO_THREAD;
如果没有重启，则默认还是异步复制,重启后,slave会在master上注册为半同步复制的slave角色.
这时候mysqlerr.log会输出如下信息:
2018-04-19T05:37:58.918754Z 8 [Warning] IP address '192.168.56.93' could not be resolved: Name or service not known
2018-04-19T06:06:16.606839Z 9 [Warning] IP address '192.168.56.93' could not be resolved: Name or service not known
2018-04-19T06:06:16.621052Z 9 [Note] Start binlog_dump to master_thread_id(9) slave_server(3), pos(binlog.000006, 1700)
2018-04-19T07:20:00.109652Z 4 [Note] Slave I/O thread killed while reading event for channel ''
2018-04-19T07:20:00.109710Z 4 [Note] Slave I/O thread exiting for channel '', read up to log 'binlog.000043', position 1784
2018-04-19T07:20:07.285629Z 12 [Note] Slave
I/O thread: Start semi-sync replication to master
'repl@192.168.56.91:3306' in log 'binlog.000043' at position 1784
2018-04-19T07:20:07.285699Z 12 [Warning] Storing MySQL user name or
password information in the master info repository is not secure and is
therefore not recommended. Please consider using the USER and PASSWORD
connection options for START SLAVE; see the 'START SLAVE Syntax' in the
MySQL Manual for more information.
2018-04-19T07:20:07.293393Z 12 [Note] Slave I/O thread for channel '':
connected to master 'repl@192.168.56.91:3306',replication started in log
'binlog.000043' at position 1784
5.查看半同步是否在运行
主:
mysql> show status like 'Rpl_semi_sync_master_status';
+-----------------------------+-------+
| Variable_name | Value |
+-----------------------------+-------+
| Rpl_semi_sync_master_status | ON |
+-----------------------------+-------+
1 row in set (0.00 sec)
从:
mysql> show status like 'Rpl_semi_sync_slave_status';
+----------------------------+-------+
| Variable_name | Value |
+----------------------------+-------+
| Rpl_semi_sync_slave_status | ON |
+----------------------------+-------+
1 row in set (0.20 sec)
这两个变量常用来监控主从是否运行在半同步复制模式下。
至此,MySQL半同步复制搭建完毕~