基于GTID的复制
简介
基于GTID的复制是MySQL 5.6后新增的复制方式.
GTID (global transaction identifier) 即全局事务ID, 保证了在每个在主库上提交的事务在集群中有一个唯一的ID.
在原来基于日志的复制中, 从库需要告知主库要从哪个偏移量进行增量同步, 如果指定错误会造成数据的遗漏, 从而造成数据的不一致.
而基于GTID的复制中, 从库会告知主库已经执行的事务的GTID的值, 然后主库会将所有未执行的事务的GTID的列表返回给从库. 并且可以保证同一个事务只在指定的从库执行一次.
实战
1、在主库上建立复制账户并授予权限
基于GTID的复制会自动地将没有在从库执行的事务重放, 所以不要在其他从库上建立相同的账号. 如果建立了相同的账户, 有可能造成复制链路的错误.
mysql> create user 'repl'@'172.%' identified by '123456';
注意在生产上的密码必须依照相关规范以达到一定的密码强度, 并且规定在从库上的特定网段上才能访问主库.
mysql> grant replication slave on *.* to 'repl'@'172.%';
查看用户
mysql> select user, host from mysql.user; +-----------+-----------+ | user | host | +-----------+-----------+ | prontera | % | | root | % | | mysql.sys | localhost | | root | localhost | +-----------+-----------+ 4 rows in set (0.00 sec)
查看授权
mysql> show grants for repl@'172.%'; +--------------------------------------------------+ | Grants for repl@172.% | +--------------------------------------------------+ | GRANT REPLICATION SLAVE ON *.* TO 'repl'@'172.%' | +--------------------------------------------------+ 1 row in set (0.00 sec)
2、配置主库服务器
[mysqld] log_bin = /var/log/mysql/mysql-bin log_bin_index = /var/log/mysql/mysql-bin.index binlog_format = row server_id = 101 gtid_mode = ON enforce_gtid_consistency = ON #log_slave_updates = ON
NOTE: 把日志与数据分开是个好习惯, 最好能放到不同的数据分区
enforce_gtid_consistency 强制GTID一致性, 启用后以下命令无法再使用
create table ... select ...
mysql> create table dept select * from departments; ERROR 1786 (HY000): Statement violates GTID consistency: CREATE TABLE ... SELECT.
因为实际上是两个独立事件, 所以只能将其拆分先建立表, 然后再把数据插入到表中
create temporary table
事务内部不能创建临时表
mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> create temporary table dept(id int); ERROR 1787 (HY000): Statement violates GTID consistency: CREATE TEMPORARY TABLE and DROP TEMPORARY TABLE can only be executed outside transactional context. These statements are also not allowed in a function or trigger because functions and triggers are also considered to be multi-statement transactions.
同一事务中更新事务表与非事务表(MyISAM)
mysql> CREATE TABLE `dept_innodb` (id INT(11) UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT); Query OK, 0 rows affected (0.04 sec) mysql> CREATE TABLE `dept_myisam` (id INT(11) UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT) ENGINE = `MyISAM`; Query OK, 0 rows affected (0.03 sec) mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> insert into dept_innodb(id) value(1); Query OK, 1 row affected (0.00 sec) mysql> insert into dept_myisam(id) value(1); ERROR 1785 (HY000): Statement violates GTID consistency: Updates to non-transactional tables can only be done in either autocommitted statements or single-statement transactions, and never in the same statement as updates to transactional tables.
所以建议选择Innodb作为默认的数据库引擎.
log_slave_updates 该选项在MySQL 5.6版本时基于GTID的复制是必须的, 但是其增大了从服务器的IO负载, 而在MySQL 5.7中该选项已经不是必须项
3、配置从库服务器
master_info_repository 与relay_log_info_repository
在MySQL 5.6.2之前, slave记录的master信息以及slave应用binlog的信息存放在文件中, 即master.info与relay-log.info. 在5.6.2版本之后, 允许记录到table中. 对应的表分别为mysql.slave_master_info与mysql.slave_relay_log_info, 且这两个表均为innodb引擎表.
[mysqld] log_bin = /var/log/mysql/mysql-bin log_bin_index = /var/log/mysql/mysql-bin.index server_id = 102 # slaves relay_log = /var/log/mysql/relay-bin relay_log_index = /var/log/mysql/relay-bin.index relay_log_info_file = /var/log/mysql/relay-bin.info enforce_gtid_consistency = ON log_slave_updates = ON read_only = ON master_info_repository = TABLE relay_log_info_repository = TABLE
4、从库数据初始化 - [optional]
先在主库上备份数据
复制代码 代码如下:
mysqldump --single-transaction --master-data=2 --triggers --routines --all-databases --events -u root -p > backup.sql
—master-data=2 该选项将当前服务器的binlog的位置和文件名追加到输出文件中(show master status). 如果为1, 将偏移量拼接到CHANGE MASTER 命令. 如果为2, 输出的偏移量信息将会被注释。
--all-databases 因为基于GTID的复制会记录全部的事务, 所以要构建一个完整的dump这个选项是推荐的
常见错误
当从库导入SQL的时候出现
复制代码 代码如下:
ERROR 1840 (HY000) at line 24: @@GLOBAL.GTID_PURGED can only be set when @@GLOBAL.GTID_EXECUTED is empty.
此时进入从库的MySQL Command Line, 使用reset master即可
5、启动基于GTID的复制
现有master@172.20.0.2和slave@172.20.0.3, 并且已经通过mysqldump将数据同步至从库slave中. 现在在从服务器slave上配置复制链路
mysql> change master to master_host='master', master_user='repl', master_password='123456', master_auto_position=1; Query OK, 0 rows affected, 2 warnings (0.06 sec)
启动复制
mysql> start slave;
启动成功后查看slave的状态
mysql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Queueing master event to the relay log
Master_Host: master
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000002
Read_Master_Log_Pos: 12793692
Relay_Log_File: relay-bin.000002
Relay_Log_Pos: 1027
Relay_Master_Log_File: mysql-bin.000002
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: 814
Relay_Log_Space: 12794106
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: 5096
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: 101
Master_UUID: a9fd4765-ec70-11e6-b543-0242ac140002
Master_Info_File: mysql.slave_master_info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Reading event from the relay log
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set: a9fd4765-ec70-11e6-b543-0242ac140002:1-39
Executed_Gtid_Set: a9fd4765-ec70-11e6-b543-0242ac140002:1-4
Auto_Position: 1
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
当Slave_IO_Running, Slave_SQL_Running为YES,
且Slave_SQL_Running_State 为Slave has read all relay log; waiting for more updates时表示成功构建复制链路
6、总结
优点
- 因为不用手工设置日志偏移量, 可以很方便地进行故障转移
- 如果启用log_slave_updates那么从库不会丢失主库上的任何修改
缺点
- 对执行的SQL有一定限制
- 仅支持MySQL 5.6之后的版本, 而且不建议使用早期5.6版本
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