什么是GTID呢， 简而言之，就是全局事务ID(global transaction identifier )，最初由google实现，官方MySQL在5.6才加入该功能。
GTID是事务提交时创建分配的唯一标识符，所有事务均与GTID一一映射。
GTID的格式类似于：
5882bfb0-c936-11e4-a843-000c292dc103:1
这个字符串，用“：”分开，前面表示这个服务器的server_uuid，这是一个128位的随机字符串，在第一次启动时生成（函数generate_server_uuid），对应的variables是只读变量server_uuid。 它能以极高的概率保证全局唯一性，并存到文件
DATADIR/auto.cnf中。因此要注意保护这个文件不要被删除或修改。
第二部分是一个自增的事务ID号，事务id号+server_uuid来唯一标示一个事务。
mysql> show global variables like '%gtid%';+--------------------------+------------------------------------------+| Variable_name | Value |+--------------------------+------------------------------------------+| enforce_gtid_consistency | ON || gtid_executed | 5882bfb0-c936-11e4-a843-000c292dc103:1-6 || gtid_mode | ON || gtid_owned | || gtid_purged | |+--------------------------+------------------------------------------+5 rows in set (0.00 sec)mysql> show global variables like '%uuid%';+---------------+--------------------------------------+| Variable_name | Value |+---------------+--------------------------------------+| server_uuid | 5882bfb0-c936-11e4-a843-000c292dc103 |+---------------+--------------------------------------+1 row in set (0.00 sec)shell> cat auto.cnf [auto]server-uuid=5882bfb0-c936-11e4-a843-000c292dc103设置GTID复制
同步主从数据
mysql> SET @@global.read_only = ON;Query OK, 0 rows affected (0.01 sec)
停止所有数据库
shell> mysqladmin -u root -p shutdown
设置开发GTID模式并启动所有数据库
shell> vi my.cnf 添加如下内容================================================================[mysqld]gtid_mode=ONlog-slave-updates=ONenforce-gtid-consistency=ON #强制GTID的一致性================================================================
从库指定主库
mysql> CHANGE MASTER TO -> MASTER_HOST = host, -> MASTER_PORT = port, -> MASTER_USER = user, -> MASTER_PASSWORD = password, -> MASTER_AUTO_POSITION = 1;mysql> START SLAVE;Query OK, 0 rows affected (0.04 sec)
禁止read-only模式
mysql> SET @@global.read_only = OFF;Query OK, 0 rows affected (0.00 sec)
GTID 模式实例和非GTID模式实例是不能进行复制的，要求非常严格，要么都是GTID，要么都不是
gtid_mode 是只读的，要改变状态必须1)关闭实例、2)修改配置文件、3) 重启实例
更新非事务引擎表
在同一事务中更新事务表与非事务表将导致多个GTIDs分配给同一事务
mysql> cretea table tt (id int) engine=myisam;mysql> insert into tt values(1),(2);mysql> cretea table t (id int) engine=innodb;mysql> insert into t values(1),(2);mysql> set autocommit = 0；mysql> begin；mysql> update t set id = 3 where id =2;Query OK, 1 row affected (0.00 sec)Rows matched: 1 Changed: 1 Warnings: 0mysql> update tt set id = 3 where id =2;ERROR 1785 (HY000): When @@GLOBAL.ENFORCE_GTID_CONSISTENCY = 1, 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.
CREATE TABLE … SELECT statements
不安全的基于语句复制，实际是两个独立的事件，一个用于建表，一个用于向新表插入源表数据。
mysql> create table t engine=innodb as select * from tt;ERROR 1786 (HY000): CREATE TABLE ... SELECT is forbidden when @@GLOBAL.ENFORCE_GTID_CONSISTENCY = 1.
临时表
事务内部不能执行创建删除临时表语句，但可以在事务外执行，但必须设置set autocommit = 1
mysql> create temporary table tttt(id int);ERROR 1787 (HY000): When @@GLOBAL.ENFORCE_GTID_CONSISTENCY = 1, the statements CREATE TEMPORARY TABLE and DROP TEMPORARY TABLE can be executed in a non-transactional context only, and require that AUTOCOMMIT = 1.mysql> set autocommit = 1;Query OK, 0 rows affected (0.00 sec)mysql> create temporary table tttt(id int);Query OK, 0 rows affected (0.04 sec)
不执行不支持的语句
启用--enforce-gtid-consistency选项启动GTID模式，上述不支持的语句将会返回错误。
a. 忽略复制错误
当备库复制出错时，传统的跳过错误的方法是设置sql_slave_skip_counter,然后再START SLAVE。
但如果打开了GTID，就会设置失败：
mysql> stop slave;Query OK, 0 rows affected (0.03 sec)mysql> set global sql_slave_skip_counter = 1;ERROR 1858 (HY000): sql_slave_skip_counter can not be set when the server is running with @@GLOBAL.GTID_MODE = ON.Instead, for each transaction that you want to skip, generate an empty transaction with the same GTID as the transaction
提示的错误信息告诉我们，可以通过生成一个空事务来跳过错误的事务。
我们手动产生一个备库复制错误：
[slave]mysql> alter table t add primary key pk_id(id);Query OK, 2 rows affected (0.12 sec)Records: 2 Duplicates: 0 Warnings: 0mysql> insert into t values(1);mysql> insert into t values(4);mysql> insert into t values(5);mysql> show master status ;+-------------------+----------+--------------+------------------+-------------------------------------------+| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |+-------------------+----------+--------------+------------------+-------------------------------------------+| mysql-info.000004 | 914 | | | 5882bfb0-c936-11e4-a843-000c292dc103:1-17 |+-------------------+----------+--------------+------------------+-------------------------------------------+1 row in set (0.00 sec)mysql> show slave status \G*************************** 1. row *************************** ... Slave_IO_Running: Yes lave_SQL_Running: No Last_Errno: 1062 Last_Error: Could not execute Write_rows event on table db_test.t; Duplicate entry '1' for key 'PRIMARY', Error_code: 1062; handler error HA_ERR_FOUND_DUPP_KEY; the event's master log mysql-info.000004, end_log_pos 401 Retrieved_Gtid_Set: 5882bfb0-c936-11e4-a843-000c292dc103:1-15 Executed_Gtid_Set: 5882bfb0-c936-11e4-a843-000c292dc103:1-14, f1e6584a-c935-11e4-a840-000c29348dbe:1 Auto_Position: 11 row in set (0.00 sec)mysql> SET @@SESSION.GTID_NEXT= '5882bfb0-c936-11e4-a843-000c292dc103:15';Query OK, 0 rows affected (0.00 sec)mysql> begin;Query OK, 0 rows affected (0.00 sec)mysql> commit;Query OK, 0 rows affected (0.00 sec)mysql> SET SESSION GTID_NEXT = AUTOMATIC;mysql> start slave;mysql> show slave status\G*************************** 1. row *************************** Slave_IO_Running: Yes Slave_SQL_Running: Yes Last_Errno: 0 Retrieved_Gtid_Set: 5882bfb0-c936-11e4-a843-000c292dc103:1-17 Executed_Gtid_Set: 5882bfb0-c936-11e4-a843-000c292dc103:1-17, f1e6584a-c935-11e4-a840-000c29348dbe:1 Auto_Position: 11 row in set (0.00 sec)
再查看show slave status，就会发现错误事务已经被跳过了。这种方法的原理很简单，空事务产生的GTID加入到GTID_EXECUTED中，
这相当于告诉备库，这个GTID对应的事务已经执行了，此时主从数据不一致。
上一篇：MySQL 5.7.9 GA稳定版新特性有哪些
下一篇：怎么解决MySQL元数据锁导致的会话等待
gtid mysql
