再来理解一下杀手级新特性：gtid

1.一个事务，就会给一个gtid编号。来看看例子：

mysql> show master status;+---------------+----------+--------------+------------------+------------------------------------------------+| File          | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set                              |+---------------+----------+--------------+------------------+------------------------------------------------+| binlog.000017 |    58105 |              |                  | b526042e-89a7-11e8-bddb-000c29d7d637:1-1304086 |+---------------+----------+--------------+------------------+------------------------------------------------+1 row in set (0.00 sec)mysql> insert into student(id) values(5);Query OK, 1 row affected (0.01 sec)mysql> show master status;+---------------+----------+--------------+------------------+------------------------------------------------+| File          | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set                              |+---------------+----------+--------------+------------------+------------------------------------------------+| binlog.000017 |    58432 |              |                  | b526042e-89a7-11e8-bddb-000c29d7d637:1-1304087 |+---------------+----------+--------------+------------------+------------------------------------------------+1 row in set (0.00 sec)mysql> begin      -> ;Query OK, 0 rows affected (0.00 sec)mysql> insert into student(id) values(6);Query OK, 1 row affected (0.00 sec)mysql> insert into student(id) values(7);Query OK, 1 row affected (0.00 sec)mysql> commit;Query OK, 0 rows affected (0.01 sec)mysql> show master status;+---------------+----------+--------------+------------------+------------------------------------------------+| File          | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set                              |+---------------+----------+--------------+------------------+------------------------------------------------+| binlog.000017 |    58918 |              |                  | b526042e-89a7-11e8-bddb-000c29d7d637:1-1304088 |+---------------+----------+--------------+------------------+------------------------------------------------+1 row in set (0.00 sec)mysql> begin ;Query OK, 0 rows affected (0.00 sec)mysql> insert into student(id) values(8);Query OK, 1 row affected (0.00 sec)mysql> rollback;Query OK, 0 rows affected (0.00 sec)mysql> show master status;+---------------+----------+--------------+------------------+------------------------------------------------+| File          | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set                              |+---------------+----------+--------------+------------------+------------------------------------------------+| binlog.000017 |    58918 |              |                  | b526042e-89a7-11e8-bddb-000c29d7d637:1-1304088 |+---------------+----------+--------------+------------------+------------------------------------------------+1 row in set (0.00 sec)mysql> quitBye[root@yw-gz-hd-test-211 ~]# cat /data/mysql3308/auto.cnf [auto]server-uuid=b526042e-89a7-11e8-bddb-000c29d7d637

仔细看看上面的例子，当前gtid：b526042e-89a7-11e8-bddb-000c29d7d637:1304086，然后我插入一条数据，执行一个事务，gtid加1，变成b526042e-89a7-11e8-bddb-000c29d7d637:1304087，然后我用begin commit,标志另外一个事务，插入2条数据，gtid加1，变成b526042e-89a7-11e8-bddb-000c29d7d637:1304088，然后我rollback，gtid不加1.

到这里，我们停下来，思考一下。。。。。。。。。。。

gtid是什么东东？明白了吧，有所领悟了吧。

2.为什么说gtid能避免重复执行，避免丢数据呢？

来看下下面这个例子：

mysql> SET @@SESSION.GTID_NEXT= 'b526042e-89a7-11e8-bddb-000c29d7d637:1304076'/*!*/;Query OK, 0 rows affected (0.00 sec)mysql> select * from student where id=4;+----+------+------+---------+---------+---------------------+---------------------+| id | name | age  | textcol | blobcol | birday              | birday2             |+----+------+------+---------+---------+---------------------+---------------------+|  4 | 3    |    3 | 3       | NULL    | 2018-07-25 10:42:29 | 2018-07-25 10:42:33 |+----+------+------+---------+---------+---------------------+---------------------+1 row in set (0.00 sec)mysql> CREATE TABLE `student` (    -> `id`  int NOT NULL AUTO_INCREMENT ,    -> `name`  varchar(255) NULL ,    -> `age`  int NULL ,    -> `textcol`  text NULL ,    -> `blobcol`  blob NULL ,    -> `birday`  timestamp NULL ON UPDATE CURRENT_TIMESTAMP ,    -> `birday2`  datetime NULL ON UPDATE CURRENT_TIMESTAMP ,    -> PRIMARY KEY (`id`)    -> )    -> ;Query OK, 0 rows affected (0.00 sec)mysql> show master status;+---------------+----------+--------------+------------------+------------------------------------------------+| File          | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set                              |+---------------+----------+--------------+------------------+------------------------------------------------+| binlog.000017 |    58105 |              |                  | b526042e-89a7-11e8-bddb-000c29d7d637:1-1304086 |+---------------+----------+--------------+------------------+------------------------------------------------+1 row in set (0.00 sec)mysql> insert into studnet(id) values(5);ERROR 1837 (HY000): When @@SESSION.GTID_NEXT is set to a GTID, you must explicitly set it to a different value after a COMMIT or ROLLBACK. Please check GTID_NEXT variable manual page for detailed explanation. Current @@SESSION.GTID_NEXT is 'b526042e-89a7-11e8-bddb-000c29d7d637:1304076'.

这个信息量有点大。一点点理解，首先我

SET @@SESSION.GTID_NEXT= 'b526042e-89a7-11e8-bddb-000c29d7d637:1304076'

但是当前gtid是b526042e-89a7-11e8-bddb-000c29d7d637:1-1304086 。什么意思，就是说1304076 事务包含在1-1304086。也就是说，这个事务已经执行了，不需要再执行了。理解了吗？

思考一下。。。。。。。。。

这个理解通了，你就会发现，为什么我发布了一个create table 命令，查询返回Query OK, 0 rows affected (0.00 sec)

就是什么作用也没有。意思就是说，这个命令create table 我已经执行过了，所以不需要执行。

再来看看错误：ERROR 1837 (HY000): When @@SESSION.GTID_NEXT is set to a GTID, you must explicitly set it to a different value after a COMMIT or ROLLBACK. Please check GTID_NEXT variable manual page for detailed explanation. Current @@SESSION.GTID_NEXT is 'b526042e-89a7-11e8-bddb-000c29d7d637:1304076'.

意思就是说，你每执行一个命令，都必须先执行 set @@SESSION.GTID_NEXT = xxxxx。

为什么会这样呢？

思考一下。。。。。。