并发情况下数据校验-基于数据库实现
- 数据库行锁
- 原理
- 实际操作
- 数据准备
- 开启事务，更新数据
- 项目实战
- 项目配置
- 多线程测试
在开发过程中，我们会遇到校验数据的唯一性，数据更新之后是否超过设置的阈值等等。并发情况下数据校验常见方式有使用分布式锁，数据库行锁等。本章介绍并发情况下使用数据库进行数据校验，常见的场景有:
- 金额扣减
- 抽奖奖品数量扣减
- 库存扣减
数据库行锁
原理
mysql数据库锁
悲观锁&乐观锁
Mysql 如何解决并发更新同一行数据
MySql MVCC 详解
实际操作
mysql 的默认引擎 InnoDB 支持行锁的，本节使用 Mysql 数据库来说明数据库行锁
数据准备
- 创建金额表
create table t_amount (
id int primary key auto_increment,
total_amount decimal(10,2) not null default 0,
used_amount decimal(10,2) not null default 0
) charset = utf8mb4;
- 插入测试数据
insert into t_amount(total_amount, used_amount) values(100, 0);
- 查询数据表
mysql> select * from t_amount;
+----+--------------+-------------+
| id | total_amount | used_amount |
+----+--------------+-------------+
| 1 | 100.00 | 0.00 |
+----+--------------+-------------+
1 row in set (0.00 sec)
开启事务，更新数据
- 打开2个终端，开启事务
start transaction;
start transaction 语句有啥作用？可以使用 help start transaction 命令查看
mysql> help start transaction
Name: 'START TRANSACTION'
Description:
Syntax:
START TRANSACTION
[transaction_characteristic [, transaction_characteristic] ...]
transaction_characteristic:
WITH CONSISTENT SNAPSHOT
| READ WRITE
| READ ONLY
BEGIN [WORK]
COMMIT [WORK] [AND [NO] CHAIN] [[NO] RELEASE]
ROLLBACK [WORK] [AND [NO] CHAIN] [[NO] RELEASE]
SET autocommit = {0 | 1}
These statements provide control over use of transactions:
o START TRANSACTION or BEGIN start a new transaction.
o COMMIT commits the current transaction, making its changes permanent.
o ROLLBACK rolls back the current transaction, canceling its changes.
o SET autocommit disables or enables the default autocommit mode for
the current session.
By default, MySQL runs with autocommit mode enabled. This means that as
soon as you execute a statement that updates (modifies) a table, MySQL
stores the update on disk to make it permanent. The change cannot be
rolled back.
To disable autocommit mode implicitly for a single series of
statements, use the START TRANSACTION statement:
START TRANSACTION;
SELECT @A:=SUM(salary) FROM table1 WHERE type=1;
UPDATE table2 SET summary=@A WHERE type=1;
COMMIT;
With START TRANSACTION, autocommit remains disabled until you end the
transaction with COMMIT or ROLLBACK. The autocommit mode then reverts
to its previous state.
START TRANSACTION permits several modifiers that control transaction
characteristics. To specify multiple modifiers, separate them by
commas.
o The WITH CONSISTENT SNAPSHOT modifier starts a consistent read for
storage engines that are capable of it. This applies only to InnoDB.
The effect is the same as issuing a START TRANSACTION followed by a
SELECT from any InnoDB table. See
http://dev.mysql.com/doc/refman/8.0/en/innodb-consistent-read.html.
The WITH CONSISTENT SNAPSHOT modifier does not change the current
transaction isolation level, so it provides a consistent snapshot
only if the current isolation level is one that permits a consistent
read. The only isolation level that permits a consistent read is
REPEATABLE READ. For all other isolation levels, the WITH CONSISTENT
SNAPSHOT clause is ignored. A warning is generated when the WITH
CONSISTENT SNAPSHOT clause is ignored.
o The READ WRITE and READ ONLY modifiers set the transaction access
mode. They permit or prohibit changes to tables used in the
transaction. The READ ONLY restriction prevents the transaction from
modifying or locking both transactional and nontransactional tables
that are visible to other transactions; the transaction can still
modify or lock temporary tables.
MySQL enables extra optimizations for queries on InnoDB tables when
the transaction is known to be read-only. Specifying READ ONLY
ensures these optimizations are applied in cases where the read-only
status cannot be determined automatically. See
http://dev.mysql.com/doc/refman/8.0/en/innodb-performance-ro-txn.html
for more information.
If no access mode is specified, the default mode applies. Unless the
default has been changed, it is read/write. It is not permitted to
specify both READ WRITE and READ ONLY in the same statement.
In read-only mode, it remains possible to change tables created with
the TEMPORARY keyword using DML statements. Changes made with DDL
statements are not permitted, just as with permanent tables.
For additional information about transaction access mode, including
ways to change the default mode, see [HELP ISOLATION].
If the read_only system variable is enabled, explicitly starting a
transaction with START TRANSACTION READ WRITE requires the
CONNECTION_ADMIN or SUPER privilege.
*Important*:
Many APIs used for writing MySQL client applications (such as JDBC)
provide their own methods for starting transactions that can (and
sometimes should) be used instead of sending a START TRANSACTION
statement from the client. See
http://dev.mysql.com/doc/refman/8.0/en/connectors-apis.html, or the
documentation for your API, for more information.
To disable autocommit mode explicitly, use the following statement:
SET autocommit=0;
After disabling autocommit mode by setting the autocommit variable to
zero, changes to transaction-safe tables (such as those for InnoDB or
NDB (http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster.html)) are
not made permanent immediately. You must use COMMIT to store your
changes to disk or ROLLBACK to ignore the changes.
autocommit is a session variable and must be set for each session. To
disable autocommit mode for each new connection, see the description of
the autocommit system variable at
http://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html.
BEGIN and BEGIN WORK are supported as aliases of START TRANSACTION for
initiating a transaction. START TRANSACTION is standard SQL syntax, is
the recommended way to start an ad-hoc transaction, and permits
modifiers that BEGIN does not.
The BEGIN statement differs from the use of the BEGIN keyword that
starts a BEGIN ... END compound statement. The latter does not begin a
transaction. See [HELP BEGIN END].
*Note*:
Within all stored programs (stored procedures and functions, triggers,
and events), the parser treats BEGIN [WORK] as the beginning of a BEGIN
... END block. Begin a transaction in this context with START
TRANSACTION instead.
The optional WORK keyword is supported for COMMIT and ROLLBACK, as are
the CHAIN and RELEASE clauses. CHAIN and RELEASE can be used for
additional control over transaction completion. The value of the
completion_type system variable determines the default completion
behavior. See
http://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html.
The AND CHAIN clause causes a new transaction to begin as soon as the
current one ends, and the new transaction has the same isolation level
as the just-terminated transaction. The new transaction also uses the
same access mode (READ WRITE or READ ONLY) as the just-terminated
transaction. The RELEASE clause causes the server to disconnect the
current client session after terminating the current transaction.
Including the NO keyword suppresses CHAIN or RELEASE completion, which
can be useful if the completion_type system variable is set to cause
chaining or release completion by default.
URL: http://dev.mysql.com/doc/refman/8.0/en/commit.html
默认情况下， mysql 会自动自提交事务，执行 start transaction 不会自动提交事务，需要执行 commit 才会提交事务
- 执行更新数据SQL语句
终端1执行更新已使用金额（used_amount）语句，终端1不提交事务，终端2也执行同样的sql语句
update t_amount set used_amount = used_amount + 2.11 where id = 1;
可以看到终端2的更新卡在这里不动了，此时这行数据已经被终端1锁住了，等待一段时间之后，发现终端2报错了
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
锁等待时间超时，重新开始事务。mysql 锁的超时时间是可以设置的，参考博客mysql修改数据库锁超时时间。
mysql> show variables like 'innodb_lock_wait_timeout';
+--------------------------+-------+
| Variable_name | Value |
+--------------------------+-------+
| innodb_lock_wait_timeout | 50 |
+--------------------------+-------+
1 row in set, 1 warning (0.20 sec)
查询出锁等待超时时间为50秒。再次在终端2中执行更新sql，在行锁等待时间范围内，提交终端1的事务，此时终端2获取到行锁，可以更新数据了
3. 校验超过总金额SQL语句
该步骤模拟实际操作中，多个线程并发更新使用金额（used_amount）,但是需要保证使用金额小于总金额（total_amount）。使用2个终端，分别开启事务，更新使用金额，在where条件之后校验是否小于等于总金额
mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)
mysql> update t_amount set used_amount = used_amount + 50 where id = 1 and used_amount + 50 <= total_amount;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
终端1执行commit; 之后，可以发现终端2在获取到行锁之后，更新的数据为0条Rows matched: 0 Changed: 0 Warnings: 0, 在业务代码中可以根据jdbc返回的update结果来确定是否更新成功了
查看此时的金额数据，发现使用金额小于总金额√
项目实战
在实际的项目使用多线程来测试并发情况下的数据校验，本节使用MyBatis框架来更新数据。
项目配置
- mybatis 配置文件 mybatis-config.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!--
Copyright 2009-2017 the original author or authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!-- autoMappingBehavior should be set in each test case -->
<properties resource="templates/db.properties"/>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC">
<property name="" value=""/>
</transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${driverClassName}"/>
<property name="url" value="${jdbcUrl}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mapper/AmountMapper.xml"/>
</mappers>
</configuration>
- 数据库配置文件 db.properties
driverClassName=com.mysql.cj.jdbc.Driver
jdbcUrl=jdbc:mysql://localhost:3306/bootdo?useUnicode=true&characterEncoding=utf-8&serverTimezone=UTC
username=chengdu
password=chengdu
- 相关代码文件
AmountMapper.xml 文件
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.scd.mapper.AmountMapper">
<update id="updateUsedAmount">
update t_amount set used_amount = used_amount + #{usedAmount}
where id = 1 and used_amount + #{usedAmount} <![CDATA[<=]]> total_amount
</update>
</mapper>
AmountMapper.java 文件
package com.scd.mapper;
import java.math.BigDecimal;
public interface AmountMapper {
int updateUsedAmount(BigDecimal updateUsedAmount);
}
多线程测试
测试类 AmountTest.java
package com.scd.amount;
import com.scd.mapper.AmountMapper;
import com.scd.sql.SqlTest;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.Reader;
import java.math.BigDecimal;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class AmountTest {
private static final Logger LOGGER = LoggerFactory.getLogger(SqlTest.class);
private SqlSessionFactory sqlSessionFactory;
@Before
public void setUp() throws Exception {
String resource = "templates/mybatis-config.xml";
Reader reader = Resources.getResourceAsReader(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
}
@Test
public void testUpdateUsedAmount() {
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
AmountMapper amountMapper = sqlSession.getMapper(AmountMapper.class);
int updated = amountMapper.updateUsedAmount(new BigDecimal("50.22"));
if (updated == 0) {
LOGGER.info("当前使用金额大于总金额");
} else {
LOGGER.info("更新成功");
}
}
}
@Test
public void testMultiThreadUpdate() {
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(5, 5, 1,
TimeUnit.HOURS,
new ArrayBlockingQueue<>(100));
CountDownLatch countDownLatch = new CountDownLatch(5);
for (int i = 0; i < 5; i++) {
threadPoolExecutor.execute(() -> {
try (SqlSession sqlSession = sqlSessionFactory.openSession(false)) {
AmountMapper amountMapper = sqlSession.getMapper(AmountMapper.class);
int updated = amountMapper.updateUsedAmount(new BigDecimal("20"));
sqlSession.commit();
if (updated == 0) {
LOGGER.info("当前使用金额大于总金额, 执行完成时间 " + System.currentTimeMillis());
} else {
LOGGER.info("更新成功, 执行完成时间 " + System.currentTimeMillis());
}
} finally {
countDownLatch.countDown();
}
});
}
try {
countDownLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
执行 testMultiThreadUpdate 方法，可以看到有部分线程更新成功，有些线程由于超过总金额未更新成功
17:47:43.540 [main] DEBUG org.apache.ibatis.logging.LogFactory - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
17:47:43.568 [main] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
17:47:43.568 [main] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
17:47:43.568 [main] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
17:47:43.568 [main] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
17:47:43.732 [pool-1-thread-1] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Opening JDBC Connection
17:47:43.732 [pool-1-thread-3] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Opening JDBC Connection
17:47:43.732 [pool-1-thread-2] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Opening JDBC Connection
17:47:43.732 [pool-1-thread-5] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Opening JDBC Connection
17:47:43.732 [pool-1-thread-4] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Opening JDBC Connection
17:47:44.772 [pool-1-thread-1] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - Created connection 1212136459.
17:47:44.772 [pool-1-thread-1] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@483fbc0b]
17:47:44.776 [pool-1-thread-1] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - ==> Preparing: update t_amount set used_amount = used_amount + ? where id = 1 and used_amount + ? <= total_amount
17:47:44.792 [pool-1-thread-4] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - Created connection 538640972.
17:47:44.792 [pool-1-thread-4] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@201b024c]
17:47:44.792 [pool-1-thread-4] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - ==> Preparing: update t_amount set used_amount = used_amount + ? where id = 1 and used_amount + ? <= total_amount
17:47:44.804 [pool-1-thread-4] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - ==> Parameters: 20(BigDecimal), 20(BigDecimal)
17:47:44.804 [pool-1-thread-1] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - ==> Parameters: 20(BigDecimal), 20(BigDecimal)
17:47:44.812 [pool-1-thread-4] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - <== Updates: 1
17:47:44.812 [pool-1-thread-4] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Committing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@201b024c]
17:47:44.816 [pool-1-thread-5] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - Created connection 149901742.
17:47:44.816 [pool-1-thread-5] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@8ef51ae]
17:47:44.816 [pool-1-thread-5] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - ==> Preparing: update t_amount set used_amount = used_amount + ? where id = 1 and used_amount + ? <= total_amount
17:47:44.816 [pool-1-thread-5] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - ==> Parameters: 20(BigDecimal), 20(BigDecimal)
17:47:44.824 [pool-1-thread-2] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - Created connection 529041956.
17:47:44.824 [pool-1-thread-2] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@1f888a24]
17:47:44.824 [pool-1-thread-2] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - ==> Preparing: update t_amount set used_amount = used_amount + ? where id = 1 and used_amount + ? <= total_amount
17:47:44.828 [pool-1-thread-2] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - ==> Parameters: 20(BigDecimal), 20(BigDecimal)
17:47:44.836 [pool-1-thread-3] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - Created connection 1100293226.
17:47:44.836 [pool-1-thread-3] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@4195246a]
17:47:44.836 [pool-1-thread-3] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - ==> Preparing: update t_amount set used_amount = used_amount + ? where id = 1 and used_amount + ? <= total_amount
17:47:44.836 [pool-1-thread-3] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - ==> Parameters: 20(BigDecimal), 20(BigDecimal)
17:47:44.967 [pool-1-thread-4] INFO com.scd.sql.SqlTest - 更新成功, 执行完成时间 1708854464967
17:47:44.967 [pool-1-thread-1] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - <== Updates: 1
17:47:44.967 [pool-1-thread-4] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@201b024c]
17:47:44.967 [pool-1-thread-1] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Committing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@483fbc0b]
17:47:44.967 [pool-1-thread-4] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@201b024c]
17:47:44.967 [pool-1-thread-4] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - Returned connection 538640972 to pool.
17:47:45.033 [pool-1-thread-5] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - <== Updates: 0
17:47:45.033 [pool-1-thread-1] INFO com.scd.sql.SqlTest - 更新成功, 执行完成时间 1708854465033
17:47:45.033 [pool-1-thread-1] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@483fbc0b]
17:47:45.033 [pool-1-thread-5] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Committing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@8ef51ae]
17:47:45.033 [pool-1-thread-1] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@483fbc0b]
17:47:45.033 [pool-1-thread-2] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - <== Updates: 0
17:47:45.033 [pool-1-thread-1] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - Returned connection 1212136459 to pool.
17:47:45.033 [pool-1-thread-5] INFO com.scd.sql.SqlTest - 当前使用金额大于总金额, 执行完成时间 1708854465033
17:47:45.033 [pool-1-thread-2] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Committing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@1f888a24]
17:47:45.033 [pool-1-thread-5] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@8ef51ae]
17:47:45.033 [pool-1-thread-5] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@8ef51ae]
17:47:45.033 [pool-1-thread-2] INFO com.scd.sql.SqlTest - 当前使用金额大于总金额, 执行完成时间 1708854465033
17:47:45.033 [pool-1-thread-5] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - Returned connection 149901742 to pool.
17:47:45.033 [pool-1-thread-3] DEBUG com.scd.mapper.AmountMapper.updateUsedAmount - <== Updates: 0
17:47:45.033 [pool-1-thread-3] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Committing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@4195246a]
17:47:45.033 [pool-1-thread-2] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@1f888a24]
17:47:45.033 [pool-1-thread-3] INFO com.scd.sql.SqlTest - 当前使用金额大于总金额, 执行完成时间 1708854465033
17:47:45.033 [pool-1-thread-3] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@4195246a]
17:47:45.033 [pool-1-thread-2] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@1f888a24]
17:47:45.033 [pool-1-thread-2] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - Returned connection 529041956 to pool.
17:47:45.037 [pool-1-thread-3] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction - Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@4195246a]
17:47:45.037 [pool-1-thread-3] DEBUG org.apache.ibatis.datasource.pooled.PooledDataSource - Returned connection 1100293226 to pool.
查询数据表t_amount
未执行多线程测试方法之前 used_amount 的金额为 54.22， 执行完成之后，通过运行日志可以确定有2个线程执行成功了，使用金额变成了94.22
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