事務傳播實戰(zhàn)

事務具有四個特性 ——ACID。其中 A 代表原子性，意思是一個事務要么成功（將結果寫入數據庫），要么失敗（不對數據庫有任何影響）。這種方式在一個事務單打獨斗的時候是一個非常好的做法，但是如果在一個批量任務里（假設包含 1000 個獨立的任務），前面的 999 個任務都非常順利、完美、漂亮、酷斃且成功的執(zhí)行了，等到執(zhí)行最后一個的時候，結果這個任務非常悲催、很是不幸的失敗了。這時候 Spring 對著前面 999 個成功執(zhí)行的任務大手一揮說：兄弟們，我們有一個任務失敗了，現在全體恢復原狀！如果這樣的話，那可真是「一頓操作猛如虎，定睛一看原地杵」。

在 Spring 中， 當一個方法調用另外一個方法時，可以讓事務采取不同的策略工作，如新建事務或者掛起當前事務等，這便是事務的傳播行為。Spring 為我們提供了七種傳播行為的策略，通過枚舉類 Propagation 定義，源碼如下：

package org.springframework.transaction.annotation; ? import org.springframework.transaction.TransactionDefinition; ? public enum Propagation { ?/*** 需要事務，它是默認傳播行為，如果當前存在事務，就沿用當前事務，* 去否則新建一個事務運行內部方法*/REQUIRED(TransactionDefinition.PROPAGATION_REQUIRED), ?/*** 支持事務，如果當前存在事務，就沿用當前事務，* 如果不存在，則繼續(xù)采用無事務的方式運行內部方法*/SUPPORTS(TransactionDefinition.PROPAGATION_SUPPORTS), ?/*** 必須使用事務，如果當前沒有事務，則會拋出異常，* 如果存在當前事務，則沿用當前事務*/MANDATORY(TransactionDefinition.PROPAGATION_MANDATORY), ?/*** 無論當前事務是否存在，都會創(chuàng)建新事務運行方法，* 這樣新事務就可以擁有新的鎖和隔離級別等特性，與當前事務相互獨立*/REQUIRES_NEW(TransactionDefinition.PROPAGATION_REQUIRES_NEW), ?/*** 不支持事務，當前存在事務時，將掛起事務，運行方法*/NOT_SUPPORTED(TransactionDefinition.PROPAGATION_NOT_SUPPORTED), ?/*** 不支持事務，如果當前方法存在事務，則拋出異常，否則繼續(xù)使用無事務機制運行*/NEVER(TransactionDefinition.PROPAGATION_NEVER), ?/** * 在當前方法調用內部方法時，如果內部方法發(fā)生異常，* 只回滾內部方法執(zhí)行過的 SQL ，而不回滾當前方法的事務*/NESTED(TransactionDefinition.PROPAGATION_NESTED); ?...... ? }

本文會研究一些常用場景的事務傳播機制，文中代碼只是突出了關鍵代碼，并不完整，完整代碼請參考文章末尾的鏈接。對照代碼食用更好！

準備兩張表

CREATE TABLE `student` (`id` int(11) NOT NULL AUTO_INCREMENT,`name` varchar(255) DEFAULT NULL,`age` int(255) DEFAULT NULL,PRIMARY KEY (`id`) ) ? CREATE TABLE `course` (`id` int(11) NOT NULL AUTO_INCREMENT,`name` varchar(255) DEFAULT NULL,PRIMARY KEY (`id`) )

REQUIRED(同生共死)

結論：一旦發(fā)生回滾，所有接口都回滾

內層失敗場景

//StudentServiceImpl.java @Transactional(propagation = Propagation.REQUIRED) public class StudentServiceImpl implements StudentService{@Autowiredprivate CourseService courseService;@Resourceprivate StudentMapper studentMapper;@Overridepublic int insert(Student record) {int insert = studentMapper.insert(record);courseService.deleteByPrimaryKey(1);return insert;} } ? // CourseServiceImpl.java @Transactional(propagation = Propagation.REQUIRED) @Service public class CourseServiceImpl implements CourseService{public int deleteByPrimaryKey(Integer id) {int res = 1 / 0; //內層事務失敗return courseMapper.deleteByPrimaryKey(id);} ?//創(chuàng)建事務 - Creating new transaction with name [com.cxf.data.service.impl.StudentServiceImpl.insert]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT //給當前事務獲取一個數據庫連接 - Acquired Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] for JDBC transaction//切換連接為手動提交- Switching JDBC Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] to manual commit- ==> Preparing: insert into student (`name`, age) values (?, ?) - ==> Parameters: zhangsan(String), null- <== Updates: 1 //加入當前事務 - Participating in existing transaction //加入事務失敗，標記當前事務回滾- Participating transaction failed - marking existing transaction as rollback-only- Setting JDBC transaction [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] rollback-only //回滾 - Initiating transaction rollback- Rolling back JDBC transaction on Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] //釋放連接- Releasing JDBC Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] after transaction

外層失敗場景

//StudentServiceImpl.java @Transactional(propagation = Propagation.REQUIRED) public class StudentServiceImpl implements StudentService{@Autowiredprivate CourseService courseService;@Resourceprivate StudentMapper studentMapper;@Overridepublic int insert(Student record) {int insert = studentMapper.insert(record);int res = 1 / 0; //外層事務失敗courseService.deleteByPrimaryKey(1);return insert;} } ? // CourseServiceImpl.java @Transactional(propagation = Propagation.REQUIRED) @Service public class CourseServiceImpl implements CourseService{public int deleteByPrimaryKey(Integer id) {return courseMapper.deleteByPrimaryKey(id);} ? ?

日志如下

//創(chuàng)建事務 - Creating new transaction with name [com.cxf.data.service.impl.StudentServiceImpl.insert]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT HikariPool-1 - Starting... HikariPool-1 - Start completed. - Acquired Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] for JDBC transaction - Switching JDBC Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] to manual commit //回滾 - Initiating transaction rollback - Rolling back JDBC transaction on Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] - Releasing JDBC Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] after transaction

REQUIRES_NEW(不受外層影響)

當內部方法的傳播行為設置為 REQUIRES_NEW 時，內部方法會先將外部方法的事務掛起，然后開啟一個新的事務，等內部方法執(zhí)行完后再提交外層事務。

結論：

內部回滾會導致外部事務也回滾

外層回滾不影響內層的提交

內層失敗場景

@Transactional(propagation = Propagation.REQUIRES_NEW) @Service public class CourseServiceImpl implements CourseService{ ?public int deleteByPrimaryKey(Integer id) {int res = 1 / 0;return courseMapper.deleteByPrimaryKey(id);}

日志輸出如下

//創(chuàng)建事務 - Creating new transaction with name [com.cxf.data.service.impl.StudentServiceImpl.insert]: PROPAGATION_REQUIRED,ISOLATION_DEFAULTHikariPool-1 - Starting...HikariPool-1 - Start completed.- Acquired Connection [HikariProxyConnection@1700751834 wrapping com.mysql.cj.jdbc.ConnectionImpl@43b5021c] for JDBC transaction- Switching JDBC Connection [HikariProxyConnection@1700751834 wrapping com.mysql.cj.jdbc.ConnectionImpl@43b5021c] to manual commit//掛起當前事務，創(chuàng)建新事務- Suspending current transaction, creating new transaction with name [com.cxf.data.service.impl.CourseServiceImpl.deleteByPrimaryKey]- Acquired Connection [HikariProxyConnection@1888400144 wrapping com.mysql.cj.jdbc.ConnectionImpl@6ebc9573] for JDBC transaction- Switching JDBC Connection [HikariProxyConnection@1888400144 wrapping com.mysql.cj.jdbc.ConnectionImpl@6ebc9573] to manual commit//回滾- Initiating transaction rollback- Rolling back JDBC transaction on Connection [HikariProxyConnection@1888400144 wrapping com.mysql.cj.jdbc.ConnectionImpl@6ebc9573]- Releasing JDBC Connection [HikariProxyConnection@1888400144 wrapping com.mysql.cj.jdbc.ConnectionImpl@6ebc9573] after transaction //內部事務回滾完成后重新喚醒掛起的事務 - Resuming suspended transaction after completion of inner transaction //執(zhí)行回滾- Initiating transaction rollback- Rolling back JDBC transaction on Connection [HikariProxyConnection@1700751834 wrapping com.mysql.cj.jdbc.ConnectionImpl@43b5021c]- Releasing JDBC Connection [HikariProxyConnection@1700751834 wrapping com.mysql.cj.jdbc.ConnectionImpl@43b5021c] after transaction

外層失敗場景

外層失敗不影響內層事務的成功提交

//StudentServiceImpl.java @Transactional(propagation = Propagation.REQUIRED) public class StudentServiceImpl implements StudentService{@Autowiredprivate CourseService courseService;@Resourceprivate StudentMapper studentMapper;@Overridepublic int insert(Student record) {int insert = studentMapper.insert(record);courseService.deleteByPrimaryKey(1);int res = 1 / 0; //外層事務失敗return insert;} } ? // CourseServiceImpl.java @Transactional(propagation = Propagation.REQUIRED) @Service public class CourseServiceImpl implements CourseService{public int deleteByPrimaryKey(Integer id) {return courseMapper.deleteByPrimaryKey(id);}

日志如下

//創(chuàng)建事務 - Creating new transaction with name [com.cxf.data.service.impl.StudentServiceImpl.insert]: PROPAGATION_REQUIRES_NEW,ISOLATION_DEFAULT- Acquired Connection [HikariProxyConnection@674667952 wrapping com.mysql.cj.jdbc.ConnectionImpl@30893e08] for JDBC transaction- Switching JDBC Connection [HikariProxyConnection@674667952 wrapping com.mysql.cj.jdbc.ConnectionImpl@30893e08] to manual commit- ==> Preparing: insert into student (`name`, age) values (?, ?) - ==> Parameters: zhangsan(String), null- <== Updates: 1//掛起當前事務，并創(chuàng)建一個新事務- Suspending current transaction, creating new transaction with name [com.cxf.data.service.impl.CourseServiceImpl.deleteByPrimaryKey]- Acquired Connection [HikariProxyConnection@1857852787 wrapping com.mysql.cj.jdbc.ConnectionImpl@1e977098] for JDBC transaction- Switching JDBC Connection [HikariProxyConnection@1857852787 wrapping com.mysql.cj.jdbc.ConnectionImpl@1e977098] to manual commit Preparing: delete from course where id = ? arameters: 1(Integer)Updates: 1//提交內層事務--- 注意，內層成功了，通過查看數據庫發(fā)現記錄被成功刪除- Initiating transaction commit- Committing JDBC transaction on Connection [HikariProxyConnection@1857852787 wrapping com.mysql.cj.jdbc.ConnectionImpl@1e977098]- Releasing JDBC Connection [HikariProxyConnection@1857852787 wrapping com.mysql.cj.jdbc.ConnectionImpl@1e977098] after transaction- Resuming suspended transaction after completion of inner transaction//回滾外層事務 - Initiating transaction rollback- Rolling back JDBC transaction on Connection [HikariProxyConnection@674667952 wrapping com.mysql.cj.jdbc.ConnectionImpl@30893e08]- Releasing JDBC Connection [HikariProxyConnection@674667952 wrapping com.mysql.cj.jdbc.ConnectionImpl@30893e08] after transaction

NESTED(不受內層影響)

當內部方法的傳播行為設置為 NESTED 時，內部方法會開啟一個新的嵌套事務

每個 NESTED 事務執(zhí)行前會將當前操作保存下來，叫做 savepoint （保存點），如果當前 NESTED 事務執(zhí)行失敗，則回滾到之前的保存點，以便之前的執(zhí)行結果不受當前 NESTED 事務的影響，從而內層方法回滾，則并不影響外層方法的提交。

NESTED 事務在外部事務提交以后自己才會提交。

外層為REQUIRED

內層失敗場景

結論： 內層回滾不影響外層的執(zhí)行

//StudentServiceImpl.java @Transactional(propagation = Propagation.REQUIRED) public class StudentServiceImpl implements StudentService{ ?public int insert(Student record) {int insert = studentMapper.insert(record);courseService.deleteByPrimaryKey(1);return insert;} //CourseServiceImpl.java @Transactional(propagation = Propagation.NESTED)//注意事務傳播機制的修改 @Service public class CourseServiceImpl implements CourseService{ ?@Overridepublic int deleteByPrimaryKey(Integer id) {int res = 1 / 0; //內層失敗return courseMapper.deleteByPrimaryKey(id);}

日志如下

//創(chuàng)建事務 - Creating new transaction with name [com.cxf.data.service.impl.StudentServiceImpl.insert]: PROPAGATION_REQUIRED,ISOLATION_DEFAULTHikariPool-1 - Starting...HikariPool-1 - Start completed.- Acquired Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] for JDBC transaction- Switching JDBC Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] to manual commit- ==> Preparing: insert into student (`name`, age) values (?, ?) - ==> Parameters: zhangsan(String), null- <== Updates: 1//創(chuàng)建嵌套事務, 掛起外層事務- Creating nested transaction with name [com.cxf.data.service.impl.CourseServiceImpl.deleteByPrimaryKey]//嵌套事務回滾到savepoint- Rolling back transaction to savepoint- Initiating transaction rollback- Rolling back JDBC transaction on Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] //繼續(xù)完成外層事務- Releasing JDBC Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] after transaction

外層失敗場景

外層失敗會導致內層回滾

//StudentServiceImpl.java @Transactional(propagation = Propagation.REQUIRED) public class StudentServiceImpl implements StudentService{ ?public int insert(Student record) {int insert = studentMapper.insert(record);courseService.deleteByPrimaryKey(1);int res = 1 / 0; //外層失敗return insert;} //CourseServiceImpl.java @Transactional(propagation = Propagation.NESTED)//注意事務傳播機制的修改 @Service public class CourseServiceImpl implements CourseService{ ?@Overridepublic int deleteByPrimaryKey(Integer id) {return courseMapper.deleteByPrimaryKey(id);}

日志如下

//新建事務 - Creating new transaction with name [com.cxf.data.service.impl.StudentServiceImpl.insert]: PROPAGATION_REQUIRED,ISOLATION_DEFAULTHikariPool-1 - Starting...HikariPool-1 - Start completed.- Acquired Connection [HikariProxyConnection@247334525 wrapping com.mysql.cj.jdbc.ConnectionImpl@3a4ab7f7] for JDBC transaction- Switching JDBC Connection [HikariProxyConnection@247334525 wrapping com.mysql.cj.jdbc.ConnectionImpl@3a4ab7f7] to manual commit- ==> Preparing: insert into student (`name`, age) values (?, ?) - ==> Parameters: zhangsan(String), null- <== Updates: 1//創(chuàng)建內嵌事務- Creating nested transaction with name [com.cxf.data.service.impl.CourseServiceImpl.deleteByPrimaryKey] Preparing: delete from course where id = ? arameters: 1(Integer)Updates: 1//釋放savepoint - Releasing transaction savepoint//內嵌事務回滾- Initiating transaction rollback- Rolling back JDBC transaction on Connection [HikariProxyConnection@247334525 wrapping com.mysql.cj.jdbc.ConnectionImpl@3a4ab7f7]- Releasing JDBC Connection [HikariProxyConnection@247334525 wrapping com.mysql.cj.jdbc.ConnectionImpl@3a4ab7f7] after transaction

查看數據庫發(fā)現外層失敗會導致內層回滾。

MANDATORY

必須在一個已有的事務中執(zhí)行，否則報錯

如果外層NOT_SUPPORTED，而內層是MANDATORY，則會拋異常

Should roll back transaction but cannot - no transaction available org.springframework.transaction.IllegalTransactionStateException: No existing transaction found for transaction marked with propagation 'mandatory'

NEVEL

必須在一個沒有的事務中執(zhí)行，否則報錯

SUPPORTS

如果其他bean調用這個方法時，其他bean聲明了事務，則就用這個事務，如果沒有聲明事務，那就不用事務

外層使用REQUIRED，內層使用SUPPORTS

//創(chuàng)建事務 - Creating new transaction with name [com.cxf.data.service.impl.StudentServiceImpl.insert]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT- Acquired Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] for JDBC transaction- Switching JDBC Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] to manual commit- ==> Preparing: insert into student (`name`, age) values (?, ?) - ==> Parameters: zhangsan(String), null- <== Updates: 1 //加入已有事務 - Participating in existing transaction- Participating transaction failed - marking existing transaction as rollback-only- Setting JDBC transaction [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] rollback-only- Initiating transaction rollback- Rolling back JDBC transaction on Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d]- Releasing JDBC Connection [HikariProxyConnection@2096598149 wrapping com.mysql.cj.jdbc.ConnectionImpl@ebe067d] after transaction

總結

區(qū)別

REQUIRES_NEW 最為簡單，不管當前有無事務，它都會開啟一個全新事務，既不影響外部事務，也不會影響其他內部事務，真正的井水不犯河水，堅定而獨立。

REQUIRED 在沒有外部事務的情況下，會開啟一個事務，不影響其他內部事務；而當存在外部事務的情況下，則會與外部事務還有其他內部事務同命運共生死。有條件會直接上，沒條件是會自己創(chuàng)造條件，然后再上。

NESTED 在沒有外部事務的情況下與 REQUIRED 效果相同；而當存在外部事務的情況下，則與外部事務生死與共，但與其他內部事務互不相干。要么孑然一身，要么誓死追隨主公（外部事務）。

傳播

REQUIRED(同生共死)

當兩個方法的傳播機制都是REQUIRED時，如果一旦發(fā)生回滾，兩個方法都會回滾

REQUIRES_NEW(內層可獨立提交)

當內層方法傳播機制為REQUIRES_NEW，會開啟一個新的事務，并單獨提交方法，所以外層方法的回滾并不影響內層方法事務提交

NESTED(外層可單獨提交)
當外層方法為REQUIRED，內層方法為NESTED時，內層方法開啟一個嵌套事務；
當外層方法回滾時，內層方法也會回滾；反之，如果內層方法回滾，則并不影響外層方法的提交

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