Spring事务的传播行为和隔离级别
个传播行为，4个隔离级别，
Spring事务的传播行为和隔离级别
[ transaction behavior and isolated level ]
事务的传播行为和隔离级别
[ transaction behavior and isolated level ]
Spring中事务的定义：
一、Propagation ：
key属性确定代理应该给哪个方法增加事务行为。这样的属性最重要的部份是传播行为。有以下选项可供使用：
PROPAGATION_REQUIRED
- - 支持当前事务，如果当前没有事务，就新建一个事务。这是最常见的选择。
PROPAGATION_SUPPORTS
- - 支持当前事务，如果当前没有事务，就以非事务方式执行。
PROPAGATION_MANDATORY
- - 支持当前事务，如果当前没有事务，就抛出异常。
PROPAGATION_REQUIRES_NEW
- - 新建事务，如果当前存在事务，把当前事务挂起。
PROPAGATION_NOT_SUPPORTED
- - 以非事务方式执行操作，如果当前存在事务，就把当前事务挂起。
PROPAGATION_NEVER
- - 以非事务方式执行，如果当前存在事务，则抛出异常。
很多人看到事务的传播行为属性都不甚了解，我昨晚看了j2ee without ejb的时候，看到这里也不了解，甚至重新翻起数据库系统的教材书，但是也没有找到对这个的分析。今天搜索，找到一篇极好的分析文章，虽然这篇文章是重点分析PROPAGATION_REQUIRED 和 PROPAGATION_REQUIRED_NESTED的
解惑 spring 嵌套事务 /** * @date 2006-11-24 * @note 转载自http://www.javaeye.com/topic/35907?page=1 */ * * * * * * * * TransactionDefinition 接口定义* * * * * * * * * * * * * * * * * * * /** * Support a current transaction, create a new one if none exists. * Analogous to EJB transaction attribute of the same name. * This is typically the default setting of a transaction definition. */ int PROPAGATION_REQUIRED = 0; /** * Support a current transaction, execute non-transactionally if none exists. * Analogous to EJB transaction attribute of the same name. * Note: For transaction managers with transaction synchronization, * PROPAGATION_SUPPORTS is slightly different from no transaction at all, * as it defines a transaction scopp that synchronization will apply for. * As a consequence, the same resources (JDBC Connection, Hibernate Session, etc) * will be shared for the entire specified scope. Note that this depends on * the actual synchronization configuration of the transaction manager. * @see org.springframework.transaction.support.AbstractPlatformTransactionManager#setTransactionSynchronization */ int PROPAGATION_SUPPORTS = 1; /** * Support a current transaction, throw an exception if none exists. * Analogous to EJB transaction attribute of the same name. */ int PROPAGATION_MANDATORY = 2; /** * Create a new transaction, suspend the current transaction if one exists. * Analogous to EJB transaction attribute of the same name. * Note: Actual transaction suspension will not work on out-of-the-box * on all transaction managers. This in particular applies to JtaTransactionManager, * which requires the javax.transaction.TransactionManager to be * made available it to it (which is server-specific in standard J2EE). * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager */ int PROPAGATION_REQUIRES_NEW = 3; /** * Execute non-transactionally, suspend the current transaction if one exists. * Analogous to EJB transaction attribute of the same name. * Note: Actual transaction suspension will not work on out-of-the-box * on all transaction managers. This in particular applies to JtaTransactionManager, * which requires the javax.transaction.TransactionManager to be * made available it to it (which is server-specific in standard J2EE). * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager */ int PROPAGATION_NOT_SUPPORTED = 4; /** * Execute non-transactionally, throw an exception if a transaction exists. * Analogous to EJB transaction attribute of the same name. */ int PROPAGATION_NEVER = 5; /** * Execute within a nested transaction if a current transaction exists, * behave like PROPAGATION_REQUIRED else. There is no analogous feature in EJB. * Note: Actual creation of a nested transaction will only work on specific * transaction managers. Out of the box, this only applies to the JDBC * DataSourceTransactionManager when working on a JDBC 3.0 driver. * Some JTA providers might support nested transactions as well. * @see org.springframework.jdbc.datasource.DataSourceTransactionManager */ int PROPAGATION_NESTED = 6;
在这篇文章里，他用两个嵌套的例子辅助分析，我这里直接引用了。
ServiceA {
/**
* 事务属性配置为 PROPAGATION_REQUIRED
*/
@Transactional(propagation=Propagation.REQUIRED)
void methodA() {
ServiceB.methodB();
}
}
ServiceB {
/**
* 事务属性配置为 PROPAGATION_REQUIRED
*/
@Transactional(propagation=Propagation.REQUIRED)
void methodB() {
}
}
1： PROPAGATION_REQUIRED
加入当前正要执行的事务不在另外一个事务里，那么就起一个新的事务
比如说，ServiceB. methodB的事务级别定义为PROPAGATION_REQUIRED, 那么由于执行ServiceA. methodA的时候，
ServiceA. methodA已经起了事务，这时调用ServiceB. methodB，ServiceB. methodB看到自己已经运行在ServiceA. methodA
的事务内部，就不再起新的事务。而假如ServiceA. methodA运行的时候发现自己没有在事务中，他就会为自己分配一个事务。
这样，在ServiceA. methodA或者在ServiceB. methodB内的任何地方出现异常，事务都会被回滚。即使ServiceB. methodB的事务已经被
提交，但是ServiceA. methodA在接下来fail要回滚，ServiceB. methodB也要回滚
2： PROPAGATION_SUPPORTS
如果当前在事务中，即以事务的形式运行，如果当前不再一个事务中，那么就以非事务的形式运行
3： PROPAGATION_MANDATORY
必须在一个事务中运行。也就是说，他只能被一个父事务调用。否则，他就要抛出异常
4： PROPAGATION_REQUIRES_NEW
这个就比较绕口了。 比如我们设计ServiceA. methodA的事务级别为PROPAGATION_REQUIRED，ServiceB. methodB的事务级别为PROPAGATION_REQUIRES_NEW，
那么当执行到ServiceB. methodB的时候，ServiceA. methodA所在的事务就会挂起，ServiceB. methodB会起一个新的事务，等待ServiceB. methodB的事务完成以后，
他才继续执行。他与PROPAGATION_REQUIRED 的事务区别在于事务的回滚程度了。因为ServiceB. methodB是新起一个事务，那么就是存在
两个不同的事务。如果ServiceB. methodB已经提交，那么ServiceA. methodA失败回滚，ServiceB. methodB是不会回滚的。如果ServiceB. methodB失败回滚，
如果他抛出的异常被ServiceA. methodA捕获，ServiceA. methodA事务仍然可能提交。
5： PROPAGATION_NOT_SUPPORTED
当前不支持事务。比如ServiceA. methodA的事务级别是PROPAGATION_REQUIRED ，而ServiceB. methodB的事务级别是PROPAGATION_NOT_SUPPORTED ，
那么当执行到ServiceB. methodB时，ServiceA. methodA的事务挂起，而他以非事务的状态运行完，再继续ServiceA. methodA的事务。
6： PROPAGATION_NEVER
不能在事务中运行。假设ServiceA. methodA的事务级别是PROPAGATION_REQUIRED， 而ServiceB. methodB的事务级别是PROPAGATION_NEVER ，
那么ServiceB. methodB就要抛出异常了。
7： PROPAGATION_NESTED
理解Nested的关键是savepoint。他与PROPAGATION_REQUIRES_NEW的区别是，PROPAGATION_REQUIRES_NEW另起一个事务，将会与他的父事务相互独立，
而Nested的事务和他的父事务是相依的，他的提交是要等和他的父事务一块提交的。也就是说，如果父事务最后回滚，他也要回滚的。
而Nested事务的好处是他有一个savepoint。
ServiceA {
/**
* 事务属性配置为 PROPAGATION_REQUIRED
*/
@Transactional(propagation=Propagation.REQUIRED)
void methodA() {
try {
//savepoint
@Transactional(propagation=Propagation.NESTED)
ServiceB.methodB(); //PROPAGATION_NESTED 级别
} catch (SomeException) {
// 执行其他业务, 如 ServiceC.methodC();
}
}
}
也就是说ServiceB. methodB失败回滚，那么ServiceA. methodA也会回滚到savepoint点上，ServiceA. methodA可以选择另外一个分支，比如
ServiceC. methodC，继续执行，来尝试完成自己的事务。
但是这个事务并没有在EJB标准中定义。
二、Isolation Level ( 事务隔离等级) :
1、Serializable：最严格的级别，事务串行执行，资源消耗最大；
2、REPEATABLE READ：保证了一个事务不会修改已经由另一个事务读取但未提交（回滚）的数据。避免了“脏读取”和“不可重复读取”的情况，但是带来了更多的性能损失。
3、READ COMMITTED: 大多数主流数据库的默认事务等级，保证了一个事务不会读到另一个并行事务已修改但未提交的数据，避免了“脏读取”。该级别适用于大多数系统。
4、Read Uncommitted：保证了读取过程中不会读取到非法数据。隔离级别在于处理多事务的并发问题。
我们知道并行可以提高数据库的吞吐量和效率，但是并不是所有的并发事务都可以并发运行，这需要查看数据库教材的可串行化条件判断了。
这里就不阐述。
我们首先说并发中可能发生的3中不讨人喜欢的事情
1： Dirty reads
- - 读脏数据。也就是说，比如事务A的未提交（还依然缓存）的数据被事务B读走，如果事务A失败回滚，会导致事务B所读取的的数据是错误的。
2： non- repeatable reads
- - 数据不可重复读。比如事务A中两处读取数据- total- 的值。在第一读的时候，total是100，然后事务B就把total的数据改成200，事务A再读一次，结果就发现，total竟然就变成200了，造成事务A数据混乱。
3： phantom reads
- - 幻象读数据，这个和non- repeatable reads相似，也是同一个事务中多次读不一致的问题。但是non- repeatable reads的不一致是因为他所要取的数据集被改变了（比如total的数据），但是phantom reads所要读的数据的不一致却不是他所要读的数据集改变，而是他的条件数据集改变。比如Select account. id where account. name = "ppgogo*" , 第一次读去了6个符合条件的id，第二次读取的时候，由于事务b把一个帐号的名字由"dd" 改成"ppgogo1" ，结果取出来了7个数据。 Dirty reads non- repeatable reads phantom reads
Serializable 不会 不会 不会
REPEATABLE READ 不会 不会 会
READ COMMITTED 不会 会 会
Read Uncommitted 会 会 会
三、readOnly
事务属性中的readOnly标志表示对应的事务应该被最优化为只读事务。
这是一个最优化提示。在一些情况下，一些事务策略能够起到显著的最优化效果，例如在使用Object/ Relational映射工具（如：Hibernate或TopLink）时避免dirty checking（试图“刷新”）。
四、Timeout
在事务属性中还有定义“timeout”值的选项，指定事务超时为几秒。在JTA中，这将被简单地传递到J2EE服务器的事务协调程序，并据此得到相应的解释。
转载自：http://blog.chinaunix.net/u1/55983/showart_2091761.html
附:@interface Transactional
/*
* Copyright 2002-2010 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.
*/
package org.springframework.transaction.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.transaction.TransactionDefinition;
/**
* Describes transaction attributes on a method or class.
*
* <p>This annotation type is generally directly comparable to Spring's
* {@link org.springframework.transaction.interceptor.RuleBasedTransactionAttribute}
* class, and in fact {@link AnnotationTransactionAttributeSource} will directly
* convert the data to the latter class, so that Spring's transaction support code
* does not have to know about annotations. If no rules are relevant to the exception,
* it will be treated like
* {@link org.springframework.transaction.interceptor.DefaultTransactionAttribute}
* (rolling back on runtime exceptions).
*
* <p>For specific information about the semantics of this annotation's attributes,
* consider the {@link org.springframework.transaction.TransactionDefinition} and
* {@link org.springframework.transaction.interceptor.TransactionAttribute} javadocs.
*
* @author Colin Sampaleanu
* @author Juergen Hoeller
* @since 1.2
* @see org.springframework.transaction.interceptor.TransactionAttribute
* @see org.springframework.transaction.interceptor.DefaultTransactionAttribute
* @see org.springframework.transaction.interceptor.RuleBasedTransactionAttribute
*/
@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Transactional {
/**
* A qualifier value for the specified transaction.
* <p>May be used to determine the target transaction manager,
* matching the qualifier value (or the bean name) of a specific
* {@link org.springframework.transaction.PlatformTransactionManager}
* bean definition.
*/
String value() default "";
/**
* The transaction propagation type.
* Defaults to {@link Propagation#REQUIRED}.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getPropagationBehavior()
*/
Propagation propagation() default Propagation.REQUIRED;
/**
* The transaction isolation level.
* Defaults to {@link Isolation#DEFAULT}.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getIsolationLevel()
*/
Isolation isolation() default Isolation.DEFAULT;
/**
* The timeout for this transaction.
* Defaults to the default timeout of the underlying transaction system.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getTimeout()
*/
int timeout() default TransactionDefinition.TIMEOUT_DEFAULT;
/**
* <code>true</code> if the transaction is read-only.
* Defaults to <code>false</code>.
* <p>This just serves as a hint for the actual transaction subsystem;
* it will <i>not necessarily</i> cause failure of write access attempts.
* A transaction manager which cannot interpret the read-only hint will
* <i>not</i> throw an exception when asked for a read-only transaction.
* @see org.springframework.transaction.interceptor.TransactionAttribute#isReadOnly()
*/
boolean readOnly() default false;
/**
* Defines zero (0) or more exception {@link Class classes}, which must be a
* subclass of {@link Throwable}, indicating which exception types must cause
* a transaction rollback.
* <p>This is the preferred way to construct a rollback rule, matching the
* exception class and subclasses.
* <p>Similar to {@link org.springframework.transaction.interceptor.RollbackRuleAttribute#RollbackRuleAttribute(Class clazz)}
*/
Class<? extends Throwable>[] rollbackFor() default {};
/**
* Defines zero (0) or more exception names (for exceptions which must be a
* subclass of {@link Throwable}), indicating which exception types must cause
* a transaction rollback.
* <p>This can be a substring, with no wildcard support at present.
* A value of "ServletException" would match
* {@link javax.servlet.ServletException} and subclasses, for example.
* <p><b>NB: </b>Consider carefully how specific the pattern is, and whether
* to include package information (which isn't mandatory). For example,
* "Exception" will match nearly anything, and will probably hide other rules.
* "java.lang.Exception" would be correct if "Exception" was meant to define
* a rule for all checked exceptions. With more unusual {@link Exception}
* names such as "BaseBusinessException" there is no need to use a FQN.
* <p>Similar to {@link org.springframework.transaction.interceptor.RollbackRuleAttribute#RollbackRuleAttribute(String exceptionName)}
*/
String[] rollbackForClassName() default {};
/**
* Defines zero (0) or more exception {@link Class Classes}, which must be a
* subclass of {@link Throwable}, indicating which exception types must <b>not</b>
* cause a transaction rollback.
* <p>This is the preferred way to construct a rollback rule, matching the
* exception class and subclasses.
* <p>Similar to {@link org.springframework.transaction.interceptor.NoRollbackRuleAttribute#NoRollbackRuleAttribute(Class clazz)}
*/
Class<? extends Throwable>[] noRollbackFor() default {};
/**
* Defines zero (0) or more exception names (for exceptions which must be a
* subclass of {@link Throwable}) indicating which exception types must <b>not</b>
* cause a transaction rollback.
* <p>See the description of {@link #rollbackForClassName()} for more info on how
* the specified names are treated.
* <p>Similar to {@link org.springframework.transaction.interceptor.NoRollbackRuleAttribute#NoRollbackRuleAttribute(String exceptionName)}
*/
String[] noRollbackForClassName() default {};
}
enum Propagation:
/*
* Copyright 2002-2009 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.
*/
package org.springframework.transaction.annotation;
import org.springframework.transaction.TransactionDefinition;
/**
* Enumeration that represents transaction propagation behaviors for use
* with the {@link Transactional} annotation, corresponding to the
* {@link TransactionDefinition} interface.
*
* @author Colin Sampaleanu
* @author Juergen Hoeller
* @since 1.2
*/
public enum Propagation {
/**
* Support a current transaction, create a new one if none exists.
* Analogous to EJB transaction attribute of the same name.
* <p>This is the default setting of a transaction annotation.
*/
REQUIRED(TransactionDefinition.PROPAGATION_REQUIRED),
/**
* Support a current transaction, execute non-transactionally if none exists.
* Analogous to EJB transaction attribute of the same name.
* <p>Note: For transaction managers with transaction synchronization,
* PROPAGATION_SUPPORTS is slightly different from no transaction at all,
* as it defines a transaction scope that synchronization will apply for.
* As a consequence, the same resources (JDBC Connection, Hibernate Session, etc)
* will be shared for the entire specified scope. Note that this depends on
* the actual synchronization configuration of the transaction manager.
* @see org.springframework.transaction.support.AbstractPlatformTransactionManager#setTransactionSynchronization
*/
SUPPORTS(TransactionDefinition.PROPAGATION_SUPPORTS),
/**
* Support a current transaction, throw an exception if none exists.
* Analogous to EJB transaction attribute of the same name.
*/
MANDATORY(TransactionDefinition.PROPAGATION_MANDATORY),
/**
* Create a new transaction, suspend the current transaction if one exists.
* Analogous to EJB transaction attribute of the same name.
* <p>Note: Actual transaction suspension will not work on out-of-the-box
* on all transaction managers. This in particular applies to JtaTransactionManager,
* which requires the <code>javax.transaction.TransactionManager</code> to be
* made available it to it (which is server-specific in standard J2EE).
* @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
*/
REQUIRES_NEW(TransactionDefinition.PROPAGATION_REQUIRES_NEW),
/**
* Execute non-transactionally, suspend the current transaction if one exists.
* Analogous to EJB transaction attribute of the same name.
* <p>Note: Actual transaction suspension will not work on out-of-the-box
* on all transaction managers. This in particular applies to JtaTransactionManager,
* which requires the <code>javax.transaction.TransactionManager</code> to be
* made available it to it (which is server-specific in standard J2EE).
* @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
*/
NOT_SUPPORTED(TransactionDefinition.PROPAGATION_NOT_SUPPORTED),
/**
* Execute non-transactionally, throw an exception if a transaction exists.
* Analogous to EJB transaction attribute of the same name.
*/
NEVER(TransactionDefinition.PROPAGATION_NEVER),
/**
* Execute within a nested transaction if a current transaction exists,
* behave like PROPAGATION_REQUIRED else. There is no analogous feature in EJB.
* <p>Note: Actual creation of a nested transaction will only work on specific
* transaction managers. Out of the box, this only applies to the JDBC
* DataSourceTransactionManager when working on a JDBC 3.0 driver.
* Some JTA providers might support nested transactions as well.
* @see org.springframework.jdbc.datasource.DataSourceTransactionManager
*/
NESTED(TransactionDefinition.PROPAGATION_NESTED);
private final int value;
Propagation(int value) { this.value = value; }
public int value() { return this.value; }
}