Django + MySQL：保存点不存在？

本文介绍了Django + MySQL：保存点不存在？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ 我正在共享托管计划上运行一个小型Web应用程序。 我有一个工作者函数，它包含一个无限循环;该循环将检查数据库中的任务队列以执行新操作。为了击败Django的缓存并获取每一次迭代的最新信息，必须使用 c $ c $数据库错误：（1305，'SAVEPOINT s140364713719520_x1不存在'） $ p 指向 transaction.savepoint_rollback（）调用除块（参见下面的源）。 dev服务器没有这样的问题;如果在交互式shell中键入 transaction.savepoint（），则生产服务器会愉快地生成保存点ID。 这是我的代码的大纲，如果有任何帮助;我试图保持简洁。 如果有任何仁慈的Python专家，请帮助我。我真的很沮丧，虽然我认为我在做一个很好的工作，以平静的方式处理它。解决方案我有同样的偶然的错误 OperationalError：（1305，'SAVEPOINT {{name}}不存在'） Googling没有让它更清楚，除了它是一种正常并发问题。所以在开发环境中是非确定性的，很难重现。 幸运的是，它是本地化的，所以我使生产应用程序日志足够详细。 在MySQL中有一些可以隐式结束交易的操作： DDL语句（例如 CREATE TABLE ， ALTER TABLE 等）导致隐式提交。众所周知，MySQL中的DDL不是事务性的， OperationalError：（1213，尝试锁定时发现死锁;尝试重新启动事务）和 OperationalError：（1205，超过锁定等待超时;尝试重新启动事务）导致隐式回滚。 所以第二种情况确实有些正常。它可以由以下代码表示： ＃db是一个示例性数据库连接对象，其中＃ - 支持嵌套（堆叠）交易，＃ - 具有自动提交功能。 db.begin（）＃START TRANSACTION try：＃no-conflict op db.update（） db。 begin（）＃SAVEPOINT sp1 try：＃conflict op，＃eg尝试通过另一个事务更改专门锁定的行 db.update（） db.commit（）＃RELEASE SAVEPOINT sp1 除了：＃一切有趣的事情发生在这里：＃ - 更改尝试失败与OperationalError：（1213，'死锁...'），＃ - 事务回滚与所有的保存点，＃ - 下一行将尝试回滚到不再存在的保存点，＃ - 将会引发OperationalError：（1305，'SAVEPOINT sp1不存在'），＃ - 将影响原始异常。 db.rollback（）＃ROLLBACK TO SAVEPOINT sp1 raise db.commit（）＃COMMIT 除了： db。 rollback（）＃ROLLBACK raise I'm running a small Web app on a shared hosting plan.I have a "worker function" which contains an infinite loop; the loop checks a task queue in the DB for new things to do. This necessitated using @transaction.commit_manually in order to defeat Django's caching and get up-to-date info on every iteration.I recently implemented DB logging, and therefore needed to introduce using savepoints to my worker function - this way, if anything goes awry, I can rollback to a good savepoint, log to the database, and carry on until I reach the final transaction.commit()Now, unlike my development server, the production server gives me the error: DatabaseError: (1305, 'SAVEPOINT s140364713719520_x1 does not exist')pointing to a transaction.savepoint_rollback() call in an except block (see source below). The dev server has no such problems; and the production server happily yields savepoint IDs if I type transaction.savepoint() in an interactive shell.This is the outline of my code, if it'd be of any help; I've tried to keep it concise.If there's any benevolent Python gurus out there, please help me. I'm getting really frustrated over this, although I think I'm doing a fairly good job at handling it in a calm manner. 解决方案 I had the same occasionally recurring nasty error OperationalError: (1305, 'SAVEPOINT {{name}} does not exist')and Googling didn't make it clearer, except that it's sort of "normal" concurrency issue. So it's non-deterministic and hard to reproduce in development environment.Luckily it was localized, so I made the production app log enough verbose about it.In MySQL there're some operations that could implicitly end a transaction:DDL statement (e.g. CREATE TABLE, ALTER TABLE, etc.) results in implicit commit. It's well-known that DDLs in MySQL aren't transactional,OperationalError: (1213, 'Deadlock found when trying to get lock; try restarting transaction') and OperationalError: (1205, 'Lock wait timeout exceeded; try restarting transaction') result in implicit rollback.So the second case results indeed in somewhat "normal". It could be represented by the following code:# db is an exemplary database connection object, which# - supports nested (stacked) transactions,# - has autocommit on.db.begin() # START TRANSACTIONtry: # no-conflict op db.update() db.begin() # SAVEPOINT sp1 try: # conflict op, # e.g. attempt to change exclusively locked rows by another transaction db.update() db.commit() # RELEASE SAVEPOINT sp1 except: # Everything interesting happens here: # - the change attempt failed with OperationalError: (1213, 'Deadlock...'), # - the transaction is rolled back with all the savepoints, # - next line will attempt to rollback to savepoint which no longer exists, # - so will raise OperationalError: (1305, 'SAVEPOINT sp1 does not exist'), # - which will shadow the original exception. db.rollback() # ROLLBACK TO SAVEPOINT sp1 raise db.commit() # COMMITexcept: db.rollback() # ROLLBACK raise 这篇关于Django + MySQL：保存点不存在？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！