MySQL5.7、8.0 InnoDB在 REPEATABLE-READ隔离级别下幻读问题
Posted by:
lk lk
Date: December 29, 2023 01:52AM
前提条件:
mysql5.7 Or 8.0 版本都存在此问题。存储引擎是:InnoDb,事务隔离级别是:REPEATABLE-READ
表结构、数据:
CREATE TABLE `test` (
`a` int(4) NOT NULL,
`b` int(10) DEFAULT NULL,
PRIMARY KEY (`a`),
KEY `test_b_index` (`b`)
);
insert into test values (1, 1), (2, 3), (3, 6), (4, 8);
事务A: start transaction; select * from test order by a; # 先读取整个表的数据(生成MVCC快照),只能读取到 a=1、2、3、4的数据
事务B: start transaction; insert into test values (5, 7); commit;
事务A: select * from test order by a; # 由于快照已生成,所以查询不到新插入的a=5的数据
事务A: update test set b = 6 where b > 6; # 由于快照已生成,所以查询不到新插入的a=5的数据
事务A: select * from test order by a; rollback; # 能够正常读取到数据 a=5
猜测原因:事务A的更新语句,更改了数据 a=5 的隐藏字段 DB_TRX_ID,上一次修改改数据的事务id,改成了事务A自己的事务id,所以事务A能够查询到新增数据了。
如果是以上原因,我存在疑问的是:事务A的事务id应该比事务B的事务id小,所以不应该让事务A更新到事务B新增的数据
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MySQL5.7、8.0 InnoDB在 REPEATABLE-READ隔离级别下幻读问题
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December 29, 2023 01:52AM
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