Java 在高负载情况下未连接DatabaseAccessor

我在追查应用程序中“EclipseLink-4005（..）DatabaseAccessor not connected”错误的罪魁祸首时遇到了一个问题。它是一个独立的应用程序（不是web应用程序），多个线程连接到同一个db（Oracle）。我们使用EclipseLink 2.4.2及其带有默认设置的内部连接池。事务在应用程序中进行管理，可以嵌套。该应用程序在大多数情况下工作正常，但偶尔会在高负载下出现“EclipseLink-4005（..）DatabaseAccessor not connected”（未连接数据库访问器）错误

我能够在我们的测试环境中重现错误，但无法理解在什么条件下可能发生错误。有些事务是长时间运行的。是否有可能其中一些线程超时，导致相应的会话注销，并导致另一个线程出错

下面是示例堆栈跟踪：

Exception [EclipseLink-4005] (Eclipse Persistence Services - 2.4.2.v20130514-5956486): org.eclipse.persistence.exceptions.DatabaseException
Exception Description: DatabaseAccessor not connected.
    at org.eclipse.persistence.exceptions.DatabaseException.databaseAccessorNotConnected(DatabaseException.java:116)
    at org.eclipse.persistence.internal.databaseaccess.DatasourceAccessor.incrementCallCount(DatasourceAccessor.java:309)
    at org.eclipse.persistence.internal.databaseaccess.DatasourceAccessor.beginTransaction(DatasourceAccessor.java:238)
    at org.eclipse.persistence.internal.sessions.AbstractSession.basicBeginTransaction(AbstractSession.java:526)
    at org.eclipse.persistence.sessions.server.ClientSession.addWriteConnection(ClientSession.java:693)
    at org.eclipse.persistence.sessions.server.ServerSession.acquireClientConnection(ServerSession.java:246)
    at org.eclipse.persistence.sessions.server.ClientSession.getAccessor(ClientSession.java:333)
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.getAccessor(UnitOfWorkImpl.java:1867)
    at org.eclipse.persistence.internal.jpa.EntityManagerImpl.unwrap(EntityManagerImpl.java:2540)
    (..)

及

如果你需要更多的信息，请告诉我。我很高兴与大家分享，因为我现在没有想法了

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启用EclipseLink日志记录后的更多信息

在日志中，我发现一个连接在错误发生前不久就断开了（见下文）。我的第一个想法是，这是因为它被标记为无效（使用DatabaseAccessor.setIsValid），但在错误发生之前发生的唯一问题是30分钟前抛出的OptimisticLockException，并且应用程序对它进行了优雅的处理。此外，在接下来的半小时内，同样的连接会被愉快地使用，所以我不认为它被标记为无效

TRACE  [2017-09-01 10:01:04.851/-0700] [Worker-659:org.eclipse.persistence.transaction] [ ] 2017-09-01 10:01:04.851--ClientSession(436256688)--Connection(148152749)--Thread(Thread[Worker-659,5,main])-- commit transaction
TRACE  [2017-09-01 10:01:04.914/-0700] [Worker-659:org.eclipse.persistence.connection] [ ] 2017-09-01 10:01:04.914--ServerSession(441145695)--Connection(148152749)--Thread(Thread[Worker-659,5,main])-- Connection released to connection pool [default].
DEBUG  [2017-09-01 10:01:04.914/-0700] [Worker-659:org.eclipse.persistence.connection] [ ] 2017-09-01 10:01:04.914--ServerSession(441145695)--Connection(148152749)--Thread(Thread[Worker-659,5,main])-- disconnect
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.transaction] [ ] 2017-09-01 10:01:04.929--UnitOfWork(122187888)--Thread(Thread[Worker-659,5,main])-- end unit of work commit
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.transaction] [ ] 2017-09-01 10:01:04.929--UnitOfWork(122187888)--Thread(Thread[Worker-659,5,main])-- resume unit of work
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.transaction] [ ] 2017-09-01 10:01:04.929--UnitOfWork(122187888)--Thread(Thread[Worker-659,5,main])-- release unit of work
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.connection] [ ] 2017-09-01 10:01:04.929--ClientSession(436256688)--Thread(Thread[Worker-659,5,main])-- client released
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.query] [ ] 2017-09-01 10:01:04.929--UnitOfWork(122187888)--Thread(Thread[Worker-659,5,main])-- Execute query ReadAllQuery(...)
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.connection] [ ] 2017-09-01 10:01:04.929--ServerSession(441145695)--Connection(985262420)--Thread(Thread[Worker-659,5,main])-- Connection acquired from connection pool [default].
TRACE  [2017-09-01 10:01:04.961/-0700] [Worker-659:org.eclipse.persistence.connection] [ ] 2017-09-01 10:01:04.961--ServerSession(441145695)--Connection(985262420)--Thread(Thread[Worker-659,5,main])-- Connection released to connection pool [default].
WARN   [2017-09-01 10:01:04.961/-0700] [Worker-659:org.eclipse.persistence] [ ] 2017-09-01 10:01:04.961--UnitOfWork(122187888)--Thread(Thread[Worker-659,5,main])-- 
Local Exception Stack: 
Exception [EclipseLink-4005] (Eclipse Persistence Services - 2.4.2.v20130514-5956486): org.eclipse.persistence.exceptions.DatabaseException
Exception Description: DatabaseAccessor not connected.
    at org.eclipse.persistence.exceptions.DatabaseException.databaseAccessorNotConnected(DatabaseException.java:116)
    at org.eclipse.persistence.internal.databaseaccess.DatasourceAccessor.incrementCallCount(DatasourceAccessor.java:309)
    at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.basicExecuteCall(DatabaseAccessor.java:581)
    at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeCall(DatabaseAccessor.java:537)
    at org.eclipse.persistence.internal.sessions.AbstractSession.basicExecuteCall(AbstractSession.java:1805)
    at org.eclipse.persistence.sessions.server.ServerSession.executeCall(ServerSession.java:566)
(..)

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是否还有其他原因可以断开连接？

允许我回答我自己的问题，这样别人就可以从我的发现中获益

这个问题原来是由Eclipse链接中的一个bug引起的。你看，在写这篇文章的时候，它还是开着的

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在我的特殊情况下，解决方案是避免打开连接，即不要调用

EntityManager.unwrap（Connection.class）

，因为您可以在测试环境中复制它，所以请尝试打开日志以查看导致错误的情况。日志记录可能会减慢速度，因此如果它是一个时间问题，则可能更难重现，但会为您提供每种情况的确切情况。另一个要尝试的是最新的EclipseLink版本，因为自2.4.2以来，堆栈跟踪中涉及的类发生了一些变化。谢谢@Chris，我按照建议启用了日志记录。为问题添加更多信息。

TRACE  [2017-09-01 10:01:04.851/-0700] [Worker-659:org.eclipse.persistence.transaction] [ ] 2017-09-01 10:01:04.851--ClientSession(436256688)--Connection(148152749)--Thread(Thread[Worker-659,5,main])-- commit transaction
TRACE  [2017-09-01 10:01:04.914/-0700] [Worker-659:org.eclipse.persistence.connection] [ ] 2017-09-01 10:01:04.914--ServerSession(441145695)--Connection(148152749)--Thread(Thread[Worker-659,5,main])-- Connection released to connection pool [default].
DEBUG  [2017-09-01 10:01:04.914/-0700] [Worker-659:org.eclipse.persistence.connection] [ ] 2017-09-01 10:01:04.914--ServerSession(441145695)--Connection(148152749)--Thread(Thread[Worker-659,5,main])-- disconnect
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.transaction] [ ] 2017-09-01 10:01:04.929--UnitOfWork(122187888)--Thread(Thread[Worker-659,5,main])-- end unit of work commit
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.transaction] [ ] 2017-09-01 10:01:04.929--UnitOfWork(122187888)--Thread(Thread[Worker-659,5,main])-- resume unit of work
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.transaction] [ ] 2017-09-01 10:01:04.929--UnitOfWork(122187888)--Thread(Thread[Worker-659,5,main])-- release unit of work
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.connection] [ ] 2017-09-01 10:01:04.929--ClientSession(436256688)--Thread(Thread[Worker-659,5,main])-- client released
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.query] [ ] 2017-09-01 10:01:04.929--UnitOfWork(122187888)--Thread(Thread[Worker-659,5,main])-- Execute query ReadAllQuery(...)
TRACE  [2017-09-01 10:01:04.929/-0700] [Worker-659:org.eclipse.persistence.connection] [ ] 2017-09-01 10:01:04.929--ServerSession(441145695)--Connection(985262420)--Thread(Thread[Worker-659,5,main])-- Connection acquired from connection pool [default].
TRACE  [2017-09-01 10:01:04.961/-0700] [Worker-659:org.eclipse.persistence.connection] [ ] 2017-09-01 10:01:04.961--ServerSession(441145695)--Connection(985262420)--Thread(Thread[Worker-659,5,main])-- Connection released to connection pool [default].
WARN   [2017-09-01 10:01:04.961/-0700] [Worker-659:org.eclipse.persistence] [ ] 2017-09-01 10:01:04.961--UnitOfWork(122187888)--Thread(Thread[Worker-659,5,main])-- 
Local Exception Stack: 
Exception [EclipseLink-4005] (Eclipse Persistence Services - 2.4.2.v20130514-5956486): org.eclipse.persistence.exceptions.DatabaseException
Exception Description: DatabaseAccessor not connected.
    at org.eclipse.persistence.exceptions.DatabaseException.databaseAccessorNotConnected(DatabaseException.java:116)
    at org.eclipse.persistence.internal.databaseaccess.DatasourceAccessor.incrementCallCount(DatasourceAccessor.java:309)
    at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.basicExecuteCall(DatabaseAccessor.java:581)
    at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeCall(DatabaseAccessor.java:537)
    at org.eclipse.persistence.internal.sessions.AbstractSession.basicExecuteCall(AbstractSession.java:1805)
    at org.eclipse.persistence.sessions.server.ServerSession.executeCall(ServerSession.java:566)
(..)