Halfway through the execution of the transaction, the business system is down, what will happen to the data in the database?
The business system submitted a database dml command, but before submitting it, the system crashed. So will the data in the database be before modification or after modification? Will the connection be dropped in the database and will the data be locked? With these questions in mind, we conducted the following tests:
1. Insert a piece of data into the database
At this point, the user password in the database is: test
2. View the connection to the database
show FULL PROCESSLIST;
There is a connection at this time, which is the client connection of navicat
3. View database transactions
SELECT * FROM information_schema.INNODB_TRX;
no transaction
4. Execute the modification statement in the business system
@Transactional(rollbackFor = Exception.class)
public void update(){
UserEntity userEntity = new UserEntity();
userEntity.setId(2);
//修改数据库的用户密码为 test112
userEntity.setPassword("test112");
userMapper.updateById(userEntity);
}
@Transactional(rollbackFor = Exception.class)
public void shutdown(){
update();
try {
//模拟长事务，方便我们测试系统宕机
Thread.sleep(5000000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
@Test
public void testShutDown(){
userService.shutdown();
}
Execute the testShutDown method
5. Check the database connection again
There are a lot more connections, because I use the database connection pool in the code, and 5 connections are created by default
6. Check the database transaction again
At this point there is a running transaction and a row is locked
7. We directly kill the process of the business system
taskkill /f /pid 13964
8. Check the database connection
The database connection has been closed
9. View database transactions
business is gone
10. View data
data unchanged
Experimental parameters:
The above test was tested on a windows 10 machine, mysql version 5.7.30 community edition, using the druid connection pool
On centos 7.5, other conditions remain unchanged, and the same result as above is obtained
On windows10, use jdbc connection, do not use connection pool, other conditions remain unchanged, get the same result as above
in conclusion:
When the system submits the database dml command but does not execute the commit, the system crashes. At this time, the data in the database will not change, the database connection will be cleared, the database transaction will also be cleared, and the data will not be locked