更新后从另一个事务中可见，这是MySQL MVCC中的错误吗？

我的情况如下：

CREATE TABLE test (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, value INT DEFAULT 0);
INSERT INTO test (id, value) VALUES (1, 10);

会话A

START TRANSACTION;
SELECT value FROM test WHERE id = 1;
  10

UPDATE test SET value = value + 2 WHERE id = 1;
SELECT value FROM test WHERE id = 1;
  12
COMMIT;

会话B

START TRANSACTION;
SELECT value FROM test WHERE id = 1;
  10

SELECT value FROM test WHERE id = 1;
  10

UPDATE test SET value = value + 3 WHERE id = 1;

SELECT value FROM test WHERE id = 1;
  15

UPDATE test SET value = value + 3 WHERE id = 1;

会话A

START TRANSACTION;
SELECT value FROM test WHERE id = 1;
  10

UPDATE test SET value = value + 2 WHERE id = 1;
SELECT value FROM test WHERE id = 1;
  12
COMMIT;

会话B

START TRANSACTION;
SELECT value FROM test WHERE id = 1;
  10

SELECT value FROM test WHERE id = 1;
  10

UPDATE test SET value = value + 3 WHERE id = 1;

SELECT value FROM test WHERE id = 1;
  15

UPDATE test SET value = value + 3 WHERE id = 1;

这里我得到了预期的结果，因为会话B有一个行

id=1

的独立副本，即会话A的提交在这里不可见

但当我更新此行时，隔离会中断：

会话B

START TRANSACTION;
SELECT value FROM test WHERE id = 1;
  10

SELECT value FROM test WHERE id = 1;
  10

UPDATE test SET value = value + 3 WHERE id = 1;

SELECT value FROM test WHERE id = 1;
  15

UPDATE test SET value = value + 3 WHERE id = 1;

根据这段关于MVCC的视频（15'00），此更新应该被拒绝。但是MySQL接受了这个更新

会话B

START TRANSACTION;
SELECT value FROM test WHERE id = 1;
  10

SELECT value FROM test WHERE id = 1;
  10

UPDATE test SET value = value + 3 WHERE id = 1;

SELECT value FROM test WHERE id = 1;
  15

UPDATE test SET value = value + 3 WHERE id = 1;

因此，此选择得到了一个意外的结果：会话A的提交在会话B中可见

我的MySQL版本是5.7.26，隔离级别是可重复读取的

==更新===

本案例与MariaDB 10.4.10和RocksDB发动机的预期一样有效

在会话B中

START TRANSACTION;
SELECT value FROM test WHERE id = 1;
  10

SELECT value FROM test WHERE id = 1;
  10

UPDATE test SET value = value + 3 WHERE id = 1;

SELECT value FROM test WHERE id = 1;
  15

UPDATE test SET value = value + 3 WHERE id = 1;

它回来了

ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction (snapshot conflict)

---

在InnoDB中，锁定语句不遵守可重复读取隔离

锁始终影响行的最新提交版本。因此，它们的行为就好像您使用了READ-COMMITTED

这会影响

更新

和

删除

，以及锁定读取，如

选择…进行更新

---

但一旦您更新了一行，新版本将在事务中可见。

似乎

REPEATABLE-READ

不适用于这种“REPEATABLE-Write”场景。我将隔离级别更改为可序列化，并按预期工作：MVCC似乎未启用，行已锁定。