在使用MySQL数据库时，有时会出现ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction 这样的报错。而在一个事务中，如果其中一条sql执行时出现此报错，对本事务的其他脚本是否有影响呢，后面如果执行commit操作，报错之前语句的结果是否成功呢？ 这个结果与隔离级别以及innodb_rollback_on_timeout参数设置有关。
注： MySQL默认隔离级别为 REPEATABLE-READ，innodb_rollback_on_timeout为OFF，本文基于innodb表（支持事务）进行测试。
1. 准备工作
1.1 测试环境
MySQL 8.0
1.2 创建测试表及预备数据
创建一张测试表，并插入一条记录
mysql> use testdb;
Database changed
mysql> create table test1(id int primary key,name varchar(20));
Query OK, 0 rows affected (0.01 sec)
mysql> insert into test1 values(1,'1wdrt5');
Query OK, 1 row affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
+----+--------+
1 row in set (0.00 sec)
下面将根据不同的隔离级别及innodb_rollback_on_timeout启停情况进行测试。
2. 测试过程
2.1 隔离级别REPEATABLE-READ & innodb_rollback_on_timeout =OFF
a) 测试过程：
| session A |
session B |
|
mysql> begin;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1 where id=1 for update;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
+----+--------+
1 row in set (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
+----+--------+
2 rows in set (0.00 sec)
|
mysql> begin;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
+----+--------+
1 row in set (0.00 sec)
mysql> insert into test1 values(2,'2edft6');
Query OK, 1 row affected (0.00 sec)
mysql> delete from test1 where id=1;
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
mysql> commit;
Query OK, 0 rows affected (0.02 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
+----+--------+
2 rows in set (0.00 sec)
|
b） 测试结果：
隔离级别REPEATABLE-READ & innodb_rollback_on_timeout =OFF （2个参数均为默认值）的情况下，即使事务中有超时回滚报错，超时前的sql不会回滚，依旧执行成功。
2.2 隔离级别为READ-COMMITTED & innodb_rollback_on_timeout =OFF
a) 测试过程
| session A |
session B |
|
mysql> show global variables like 'transaction_isolation';
+-----------------------+----------------+
| Variable_name | Value |
+-----------------------+----------------+
| transaction_isolation | READ-COMMITTED |
+-----------------------+----------------+
1 row in set (0.01 sec)
mysql> use testdb;
Database changed
mysql> begin ;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
+----+--------+
2 rows in set (0.00 sec)
mysql> select * from test1 where id =1 for update;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
+----+--------+
1 row in set (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
| 3 | 3eft6 |
+----+--------+
3 rows in set (0.00 sec)
|
mysql> begin;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
+----+--------+
2 rows in set (0.00 sec)
mysql> insert into test1 values(3,'3eft6');
Query OK, 1 row affected (0.00 sec)
mysql> delete from test1 where id=1;
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
| 3 | 3eft6 |
+----+--------+
3 rows in set (0.00 sec)
|
b）测试结果：
隔离级别为READ-COMMITTED & innodb_rollback_on_timeout =OFF 情况下，即使事务中有超时回滚报错，超时前的sql不会回滚，依旧执行成功，同2者均为默认值的情况。
2.3 隔离级别REPEATABLE-READ & innodb_rollback_on_timeout =ON
注： innodb_rollback_on_timeout不能在线修改，需要修改配置文件后重启生效
测试过程：
a) 修改配置文件，重启数据库
在my.cnf文件里添加innodb_rollback_on_timeout=on 再重启数据库即可生效
mysql> show global variables like 'transaction_isolation';
+-----------------------+-----------------+
| Variable_name | Value |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
+-----------------------+-----------------+
1 row in set (0.00 sec)
mysql> show global variables like 'innodb_rollback_on_timeout';
+----------------------------+-------+
| Variable_name | Value |
+----------------------------+-------+
| innodb_rollback_on_timeout | ON |
+----------------------------+-------+
1 row in set (0.00 sec)
b) 事务测试过程
| session A |
session B |
|
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
| 3 | 3eft6 |
+----+--------+
3 rows in set (0.00 sec)
mysql> select * from test1 where id=1 for update;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
+----+--------+
1 row in set (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
| 3 | 3eft6 |
+----+--------+
3 rows in set (0.00 sec)
|
mysql> use testdb;
Database changed
mysql> begin;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
| 3 | 3eft6 |
+----+--------+
3 rows in set (0.00 sec)
mysql> insert into test1 values(4,'4rgy7');
Query OK, 1 row affected (0.00 sec)
mysql> delete from test1 where id=1;
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
| 3 | 3eft6 |
+----+--------+
3 rows in set (0.00 sec)
|
c) 测试结果：
隔离级别REPEATABLE-READ & innodb_rollback_on_timeout =ON 的情况下，事务中有超时回滚报错时，超时前sql也会回滚。
2.4 隔离级别为READ-COMMITTED & innodb_rollback_on_timeout =ON
a) 参数调整
mysql> set global transaction_isolation='READ-COMMITTED';
mysql> exit
# 重新登录
mysql> show global variables like 'transaction_isolation';
+-----------------------+----------------+
| Variable_name | Value |
+-----------------------+----------------+
| transaction_isolation | READ-COMMITTED |
+-----------------------+----------------+
1 row in set (0.00 sec)
mysql> show global variables like 'innodb_rollback_on_timeout';
+----------------------------+-------+
| Variable_name | Value |
+----------------------------+-------+
| innodb_rollback_on_timeout | ON |
+----------------------------+-------+
1 row in set (0.00 sec)
b) 测试过程
| session A |
session B |
|
mysql> use testdb;
Database changed
mysql> begin;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
| 3 | 3eft6 |
+----+--------+
3 rows in set (0.00 sec)
mysql> select * from test1 where id =1 for update;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
+----+--------+
1 row in set (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
| 3 | 3eft6 |
| 5 | 5thu8 |
+----+--------+
4 rows in set (0.00 sec)
|
mysql> use testdb;
Database changed
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
| 3 | 3eft6 |
+----+--------+
3 rows in set (0.00 sec)
mysql> insert into test1 values(5,'5thu8');
Query OK, 1 row affected (0.01 sec)
mysql> delete from test1 where id =1;
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test1;
+----+--------+
| id | name |
+----+--------+
| 1 | 1wdrt5 |
| 2 | 2edft6 |
| 3 | 3eft6 |
| 5 | 5thu8 |
+----+--------+
4 rows in set (0.00 sec)
|
c) 测试结果
隔离级别为READ-COMMITTED & innodb_rollback_on_timeout =ON的情况下，即使事务中有超时回滚报错，超时前的sql不会回滚，依旧执行成功，同2者均为默认值的情况。
3. 小结
在MySQL8.0 中,仅有在隔离级别为READ-COMMITTED & innodb_rollback_on_timeout =ON情况下，事务中有超时回滚报错时，超时前sql也会回滚。
| 隔离级别 |
innodb_rollback_on_timeout |
结果 |
| REPEATABLE-READ |
OFF |
超时回滚前的SQL不会自动回滚 |
| READ-COMMITTED |
OFF |
超时回滚前的SQL不会自动回滚 |
| REPEATABLE-READ |
ON |
超时回滚前的SQL会自动回滚 |
| READ-COMMITTED |
ON |
超时回滚前的SQL不会自动回滚 |
TIPS：
1) 测试过程中可以查看information_schema.innodb_trx表观察事务情况，在不同的版本中事务情况不一样.例如，隔离级别REPEATABLE-READ & innodb_rollback_on_timeout=on的情况下，MySQL5.6 中整个事务回滚后会自动创建一个事务，而MySQL5.7则不会再自动创建事务。
2) 在生产环境使用中,建议将innodb_rollback_on_timeout 设置为ON。应用程序一定要做好事务控制，在一个事务出现异常时必须进行显式rollback
