MySQL GTID (四)

七. GTID的限制以及解决方案

7.1 事务中混合多个存储引擎,会产生多个GTID。

当使用GTID,在同一个事务中,更新包括了非事务引擎(MyISAM)和事务引擎(InnoDB)表的操作,就会导致多个GTID分配给同一个事务。

mysql> CREATE TABLE `t_test_myisam` (
	->   `id` int(11) NOT NULL,
	->   `name` varchar(10) DEFAULT NULL,
	->   PRIMARY KEY (`id`)
	-> ) ENGINE=MyISAM DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.01 sec)

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> update t_test set name ='aa1' where id =1;
Query OK, 1 row affected (0.04 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> insert into t_test_myisam values(1,'aa2');
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.

7.2 主从表的存储引擎不一致,会导致数据不一致。

7.3 基于GTID复制,不支持CREATE TABLE....SELECT 语句

该语句实际上被记录为两个单独的事件,一个是创建表,另一个插入数据。当事务执行该语句时,在一些情况下,这两个事件可能接收到相同的事务ID,导致插入的事件被从库跳过。

mysql> create table t_test_new as  select * from t_test;
ERROR 1786 (HY000): Statement violates GTID consistency: CREATE TABLE ... SELECT.

解决方案:

mysql> create table t_test_new like t_test;
Query OK, 0 rows affected (0.06 sec)

mysql> insert into t_test_new select * from t_test;
Query OK, 5 rows affected (0.03 sec)
Records: 5  Duplicates: 0  Warnings: 0

7.4 不支持事务里包含 CREAT TEMPORARY TABLE和DROP TEMPORARY TABLE

在 autocommit=1的情况下,可以创建临时表,MASTER创建临时表不产生GTID信息,所以不会同步到SLAVE。

#事务里
mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TEMPORARY TABLE TMP_TEST(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.

#事务外
mysql> CREATE TEMPORARY TABLE TMP_TEST(ID int);
Query OK, 0 rows affected (0.00 sec)

MySQL5.7中cache里面的机制，大体来说，binlog有两个cache来缓存事务的binlog

#存放非事务表和临时表binlog
binlog_cache_data stmt_cache;
#存放事务表binlog
binlog_cache_data trx_cache;

GTID中,会检查这两个cache,如有冲突,则抛出错误

7.5 不推荐在GTID模式的实例上进行 mysql_upgrade

归根结底,还是因为mysql_upgrade的过程中要创建或修改系统表(非事务引擎)