Question

我将Spring框架与DataSourceTransactionManager一起使用，我发现可重复读取隔离对Postgresql无法正常工作。根据Postgres documentation：

可重复读取事务无法修改或锁定更改的行可重复读取事务开始后的其他事务。

让我们假设我们有2个交易：T1和T2。假设这种情况：

T1 begin - ＆gt; T2 begin - ＆gt; T2 update row - ＆gt; T2 commit - ＆gt; T1 update the same row - ＆gt; T1 commit

应回滚事务T1并显示消息

错误：由于并发更新而无法序列化访问

但T1已提交并覆盖T2更新。我在Spring中做了一个简单的例子来演示它：

SQL：

CREATE TABLE tab
(
  id bigint NOT NULL,
  name character varying(50),
  CONSTRAINT tab_pkey PRIMARY KEY (id )
)
INSERT INTO tab(id, name) VALUES (1, 'name');

DataSource配置：

 <?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:context="http://www.springframework.org/schema/context"
        xmlns:jdbc="http://www.springframework.org/schema/jdbc"
        xmlns:tx="http://www.springframework.org/schema/tx"
        xmlns:jpa="http://www.springframework.org/schema/data/jpa"
        xsi:schemaLocation="http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.1.xsd
            http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
            http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.1.xsd
            http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
            http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd">

        <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
            <property name="driverClassName" value="${jdbc.driverClassName}" />
            <property name="url" value="${jdbc.url}" />
            <property name="username" value="${jdbc.username}" />
            <property name="password" value="${jdbc.password}" />
        </bean>
        <bean id="transactionManager"
            class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource"></property>
        </bean>
        <tx:annotation-driven transaction-manager="transactionManager" />
        <context:annotation-config />

        <bean
            class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"
            id="property">
            <property name="location" value="classpath:database.properties"></property>
        </bean>
        <bean id="service" class="com.kulig.db_test.ServiceImpl">
            <constructor-arg ref="dataSource"></constructor-arg>
        </bean>
    </beans>

服务界面：

public interface Service {
            public void dosth(String name);
            public void dosth2(String name);    
        }

服务接口的实现：

public class ServiceImpl extends JdbcTemplate implements Service {
    public ServiceImpl(DataSource dataSource) {
        super(dataSource);
    }
    String sqlQuery="update tab set name=? where id=?";
    @Transactional(isolation=Isolation.REPEATABLE_READ)
    public void dosth(String name) {
        System.out.println("Before waiting, "+Thread.currentThread().getName());
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Start, "+Thread.currentThread().getName());
        update(sqlQuery, name,1);
        System.out.println("Stop,"+Thread.currentThread().getName());
    }
    @Transactional(isolation=Isolation.REPEATABLE_READ)
    public void dosth2(String name) {
        System.out.println("Before waiting, "+Thread.currentThread().getName());
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Start, "+Thread.currentThread().getName());
        update(sqlQuery, name,1);
        System.out.println("Stop, "+Thread.currentThread().getName());
    }

}

主：

public class MainApp {
public static void main(String[] args) {
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("data-tx-jpa.xml");
        final Service service = applicationContext.getBean(Service.class);

        Runnable runnable1 = new Runnable() {
            public void run() {
                service.dosth("name1");
            }
        };
        Runnable runnable2 = new Runnable() {
            public void run() {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                service.dosth2("name2");

            }
        };
        Thread thread1 = new Thread(runnable1, "thread1");
        Thread thread2 = new Thread(runnable2, "thread2");
        thread1.start();
        thread2.start();

    }

}

日志：

main 2014-01-08 10:34:04,636 INFO [org.springframework.context.support.ClassPathXmlApplicationContext] - <Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@786bb78a: startup date [Wed Jan 08 10:34:04 CET 2014]; root of context hierarchy>
main 2014-01-08 10:34:04,687 INFO [org.springframework.beans.factory.xml.XmlBeanDefinitionReader] - <Loading XML bean definitions from class path resource [data-tx-jpa.xml]>
main 2014-01-08 10:34:04,967 INFO [org.springframework.beans.factory.config.PropertyPlaceholderConfigurer] - <Loading properties file from class path resource [database.properties]>
main 2014-01-08 10:34:04,998 INFO [org.springframework.beans.factory.support.DefaultListableBeanFactory] - <Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@4d8657b9: defining beans [dataSource,transactionManager,org.springframework.aop.config.internalAutoProxyCreator,org.springframework.transaction.annotation.AnnotationTransactionAttributeSource#0,org.springframework.transaction.interceptor.TransactionInterceptor#0,org.springframework.transaction.config.internalTransactionAdvisor,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.internalPersistenceAnnotationProcessor,property,service,org.springframework.context.annotation.ConfigurationClassPostProcessor.importAwareProcessor]; root of factory hierarchy>
main 2014-01-08 10:34:05,080 DEBUG [org.springframework.transaction.annotation.AnnotationTransactionAttributeSource] - <Adding transactional method 'dosth2' with attribute: PROPAGATION_REQUIRED,ISOLATION_REPEATABLE_READ; ''>
thread1 2014-01-08 10:34:05,108 DEBUG [org.springframework.transaction.annotation.AnnotationTransactionAttributeSource] - <Adding transactional method 'dosth' with attribute: PROPAGATION_REQUIRED,ISOLATION_REPEATABLE_READ; ''>
thread1 2014-01-08 10:34:05,116 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Creating new transaction with name [com.kulig.db_test.ServiceImpl.dosth]: PROPAGATION_REQUIRED,ISOLATION_REPEATABLE_READ; ''>
thread1 2014-01-08 10:34:05,180 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Acquired Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver] for JDBC transaction>
thread1 2014-01-08 10:34:05,188 DEBUG [org.springframework.jdbc.datasource.DataSourceUtils] - <Changing isolation level of JDBC Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver] to 4>
thread1 2014-01-08 10:34:05,204 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Switching JDBC Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver] to manual commit>
Before waiting, thread1
thread2 2014-01-08 10:34:06,106 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Creating new transaction with name [com.kulig.db_test.ServiceImpl.dosth2]: PROPAGATION_REQUIRED,ISOLATION_REPEATABLE_READ; ''>
thread2 2014-01-08 10:34:06,111 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Acquired Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver] for JDBC transaction>
thread2 2014-01-08 10:34:06,111 DEBUG [org.springframework.jdbc.datasource.DataSourceUtils] - <Changing isolation level of JDBC Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver] to 4>
thread2 2014-01-08 10:34:06,112 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Switching JDBC Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver] to manual commit>
Before waiting, thread2
Start, thread2
thread2 2014-01-08 10:34:11,115 DEBUG [com.kulig.db_test.ServiceImpl] - <Executing prepared SQL update>
thread2 2014-01-08 10:34:11,116 DEBUG [com.kulig.db_test.ServiceImpl] - <Executing prepared SQL statement [update tab set name=? where id=?]>
thread2 2014-01-08 10:34:11,125 DEBUG [com.kulig.db_test.ServiceImpl] - <SQL update affected 1 rows>
Stop, thread2
thread2 2014-01-08 10:34:11,127 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Initiating transaction commit>
thread2 2014-01-08 10:34:11,128 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Committing JDBC transaction on Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver]>
thread2 2014-01-08 10:34:11,149 DEBUG [org.springframework.jdbc.datasource.DataSourceUtils] - <Resetting isolation level of JDBC Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver] to 2>
thread2 2014-01-08 10:34:11,149 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Releasing JDBC Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver] after transaction>
thread2 2014-01-08 10:34:11,149 DEBUG [org.springframework.jdbc.datasource.DataSourceUtils] - <Returning JDBC Connection to DataSource>
Start, thread1
thread1 2014-01-08 10:34:15,205 DEBUG [com.kulig.db_test.ServiceImpl] - <Executing prepared SQL update>
thread1 2014-01-08 10:34:15,205 DEBUG [com.kulig.db_test.ServiceImpl] - <Executing prepared SQL statement [update tab set name=? where id=?]>
thread1 2014-01-08 10:34:15,207 DEBUG [com.kulig.db_test.ServiceImpl] - <SQL update affected 1 rows>
Stop,thread1
thread1 2014-01-08 10:34:15,207 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Initiating transaction commit>
thread1 2014-01-08 10:34:15,207 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Committing JDBC transaction on Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver]>
thread1 2014-01-08 10:34:15,233 DEBUG [org.springframework.jdbc.datasource.DataSourceUtils] - <Resetting isolation level of JDBC Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver] to 2>
thread1 2014-01-08 10:34:15,234 DEBUG [org.springframework.jdbc.datasource.DataSourceTransactionManager] - <Releasing JDBC Connection [jdbc:postgresql://localhost:5432/test, UserName=postgres, PostgreSQL Native Driver] after transaction>
thread1 2014-01-08 10:34:15,234 DEBUG [org.springframework.jdbc.datasource.DataSourceUtils] - <Returning JDBC Connection to DataSource>

bug在哪里？我做错了什么或Postgres交易不起作用？

修改这个scenerio正常工作： T1 begin - ＆gt; **T1 select row** - ＆gt; T2 begin - ＆gt; T2 update row - ＆gt; T2 commit - ＆gt; T1 update the same row - ＆gt; T1 commit

Answer 1

您正在使用非法的外部知识来说明一项交易在另一项交易之前开始。只要存在合法的行动顺序，数据库就会履行其义务，这些行动将产生与实际产生的结果相同的数据库最终结果。此法定订单不需要与您认为用秒表测量的顺序相匹配。

Answer 2

我使用Wireshark来分析我的java应用程序和PostgreSQL的通信。我注意到在发送第一个查询之前发生了交易。我认为事务在使用@Transactional注释开始方法之前开始。所以现场：

T1 begin -> T2 begin -> T2 update row -> T2 commit -> T1 update the same row -> T1 commit

不正确。我测试的真实场景是：

T2 begin -> `T2 update row` -> T2 commit -> T1 begin ->T1 update the same row -> T1 commit

要测试第一个scenerio，应在等待事务T1之前执行一些查询（例如select version()）。该查询对于在事务T2开始之前开始事务T1是必要的。在这个场景中，一切正常。

事务重复读取隔离在PostgreSQL中无法正常工作

2 个答案: