1. 背景
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嘉定网站制作公司 * 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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