我们的生产系统经常出现明显的僵局，我们似乎无法深入人心。我们无法跟踪任何与在线用户数量的相关性，看起来我们的可用连接似乎不足。
我们有一个Java EE应用程序通过Hibernate和c3p0连接到Oracle。我们的c3p0配置是：
minPoolSize=10
maxPoolSize=300
initialPoolSize=30
acquireIncrement=10
maxIdleTime=1800
maxStatementsPerConnection=0
numHelperThreads=5
明显的死锁日志输出总是看起来像这样：
[com.mchange.v2.async.ThreadPoolAsynchronousRunner] (Timer-1) com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@4c9f1b4d -- APPARENT DEADLOCK!!! Complete Status:
Managed Threads: 5
Active Threads: 5
Active Tasks:
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@7fe1ab86 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1)
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@38c42c01 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2)
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@572512c4 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#4)
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@42f32e8e (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0)
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@6b758ef8 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#3)
Pending Tasks:
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@72fd72e5
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@5d82535d
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@172f2ea1
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@1a9e57eb
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@20ee5a35
实际的池线程堆栈跟踪不同，我在下面添加了一些示例：
Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#4,5,jboss]
java.lang.AbstractStringBuilder.<init>(AbstractStringBuilder.java:45)
java.lang.StringBuilder.<init>(StringBuilder.java:80)
oracle.net.ns.Packet.<init>(Packet.java:513)
oracle.net.ns.ConnectPacket.<init>(ConnectPacket.java:64)
oracle.net.ns.NSProtocol.connect(NSProtocol.java:278)
oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1042)
oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:301)
oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:531)
oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:221)
oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:503)
com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:135)
com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2,5,jboss]
oracle.jdbc.driver.T4CTTIoauthenticate.processRPA(T4CTTIoauthenticate.java:491)
oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:295)
oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:186)
oracle.jdbc.driver.T4CTTIoauthenticate.doOSESSKEY(T4CTTIoauthenticate.java:390)
oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:356)
oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:531)
oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:221)
oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:503)
com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:135)
com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:1
Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1,5,jboss]
oracle.net.ns.NSProtocol.connect(NSProtocol.java:346)
oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1042)
oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:301)
oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:531)
oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:221)
oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:503)
com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:135)
com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)
com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
我们应该在何处进行调查？这是c3p0，我们的查询，我们的代码，数据库吗？
答案 0 :(得分：3)
所以，你的助手线程显然已经被Connection收购所饱和。这意味着多次尝试获取Connections既不会成功，也不会因为Exception而长时间失败。这最终是你需要调试的问题。
我首先要升级到c3p0-0.9.2.1，它使用的是＆＃34;分散的＆＃34;在收购失败时，获得节省汇集线程使用的任务。第二个建议可能是将名为numHelperThreads的c3p0配置参数增加到远高于其默认值3的值，甚至是你正在使用的5。看起来你的Threads实际上已经占据了Connection获取的各个阶段，因此增加了＆＃34; lane＆＃34;通过它可以获得连接可能会有所帮助。 [但请参阅下面的附言！]
但最终，问题将归结为为什么Connection获取完成得如此缓慢（对于宣布APPARENT DEADLOCK，没有任何收购将成功获得大约10秒的东西）。这可能是数据库或网络问题。但请尝试升级到0.9.2并增加numHelperThreads。 [numHelperThreads的默认值可能已过时;在多核计算机时代，专门用于IO绑定任务的线程池可能应该是核心数量的倍数]这些调整可能很好地解决了这个问题，或者可以提供更好的下一步查看信息。
祝你好运！P.S。我猜测你显示的线程堆栈跟踪实际上并不是在构建到APPARENT DEADLOCK期间的堆栈跟踪。因为你不知道一个APPARENT DEADLOCK即将到来，直到c3p0宣布它为止，这将很难计时。我敢打赌，在死锁中，这些堆栈跟踪彼此更相似，并且正在等待某种IO。