这里是环境：
- 爪哇 5
- 在 Windows 上运行 Tomcat 6.0.18 的 Web 应用程序（不确定版本）
- 数据库：SQL Server 2008 R2
- JDBC 驱动程序：jTDS 1.2.5
- 连接池提供程序：C3P0 0.9.1.2
我正在尝试调试客户遇到的问题。基本上每隔几周，我们的 Web 应用程序就会锁定在他们的服务器上，并且他们无法访问它。重新启动可以解决问题。进一步调查表明，一切都被锁定的原因是一切都在等待数据库连接返回。我认为问题可能出在 SQL Server 上，而不是 C3P0。
我相信正在发生的是 C3P0 的“空闲检查查询”正在挂起。查询是这样的：
select * from c3p0_connection_test_table
看起来此查询已运行，并且从未返回结果。这是我在线程转储中看到的内容。注意DefaultConnectionTester.activeCheckConnection()，这是空闲检查：
"com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2" daemon prio=6 tid=0x0000000007c32000 nid=0x1250 runnable [0x000000001072f000]
java.lang.Thread.State: RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:129)
at java.io.DataInputStream.readFully(DataInputStream.java:178)
at java.io.DataInputStream.readFully(DataInputStream.java:152)
at net.sourceforge.jtds.jdbc.SharedSocket.readPacket(SharedSocket.java:841)
at net.sourceforge.jtds.jdbc.SharedSocket.getNetPacket(SharedSocket.java:722)
- locked <0x000000016ac03f48> (a java.util.ArrayList)
at net.sourceforge.jtds.jdbc.ResponseStream.getPacket(ResponseStream.java:466)
at net.sourceforge.jtds.jdbc.ResponseStream.read(ResponseStream.java:103)
at net.sourceforge.jtds.jdbc.ResponseStream.peek(ResponseStream.java:88)
at net.sourceforge.jtds.jdbc.TdsCore.wait(TdsCore.java:3928)
at net.sourceforge.jtds.jdbc.TdsCore.executeSQL(TdsCore.java:1045)
- locked <0x000000016d965268> (a net.sourceforge.jtds.jdbc.TdsCore)
at net.sourceforge.jtds.jdbc.JtdsStatement.executeSQLQuery(JtdsStatement.java:465)
at net.sourceforge.jtds.jdbc.JtdsStatement.executeQuery(JtdsStatement.java:1301)
at com.mchange.v2.c3p0.impl.DefaultConnectionTester.activeCheckConnection(DefaultConnectionTester.java:73)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.testPooledConnection(C3P0PooledConnectionPool.java:374)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.refurbishIdleResource(C3P0PooledConnectionPool.java:310)
at com.mchange.v2.resourcepool.BasicResourcePool$AsyncTestIdleResourceTask.run(BasicResourcePool.java:1999)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
但是什么会导致这样一个简单的查询在从套接字读取时挂起？我不相信该表上会有任何数据库锁定，因为它完全由 C3P0 管理并且从未插入/更新。此外，任何从池中获取连接的失败尝试（如果这是挂起的原因），我希望在某个地方有一个堆栈跟踪。相反，我看到的是应用程序刚刚锁定，因为所有未来的连接请求都在等待这个“空闲检查”完成。
这是等待“空闲检查”完成的线程之一：
"http-80-3" daemon prio=6 tid=0x0000000007c33800 nid=0x122c in Object.wait() [0x000000001082d000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:579)
- locked <0x0000000167a88a60> (a com.mchange.v2.resourcepool.BasicResourcePool)
at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:477)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525)
at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
at org.springframework.orm.hibernate3.LocalDataSourceConnectionProvider.getConnection(LocalDataSourceConnectionProvider.java:81)
at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)
at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
at org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:142)
at org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:85)
at org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1354)
at org.springframework.orm.hibernate3.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:555)
at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:371)
at sun.reflect.GeneratedMethodAccessor105.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:89)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
at $Proxy15.getTransaction(Unknown Source)
at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:317)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:105)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:89)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
at $Proxy79.getCrowdProperties(Unknown Source)
at com.jamasoftware.contour.gateway.crowd.CrowdSsoServices.autoLogin(Unknown Source)
at com.jamasoftware.contour.security.AutoLoginServicesManager.autoLogin(Unknown Source)
at org.springframework.security.ui.rememberme.RememberMeProcessingFilter.doFilterHttp(RememberMeProcessingFilter.java:74)
at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
at org.springframework.security.ui.AbstractProcessingFilter.doFilterHttp(AbstractProcessingFilter.java:277)
at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
at com.jamasoftware.contour.view.filter.CheckSetupFilter.doFilter(Unknown Source)
at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
at org.springframework.security.context.HttpSessionContextIntegrationFilter.doFilterHttp(HttpSessionContextIntegrationFilter.java:235)
at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
at org.springframework.security.concurrent.ConcurrentSessionFilter.doFilterHttp(ConcurrentSessionFilter.java:99)
at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
at com.jamasoftware.contour.view.filter.ExpirationFilter.doFilter(Unknown Source)
at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
at com.jamasoftware.contour.view.filter.GzipFilter.doFilter(Unknown Source)
at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
at org.springframework.security.util.FilterChainProxy.doFilter(FilterChainProxy.java:175)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:864)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:579)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1665)
at java.lang.Thread.run(Thread.java:619)
通过查看 C3P0 的源代码，顶部的两行：
at java.lang.Object.wait(Native Method)
at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:579)
...仅在连接等待“空闲检查”时发生。
不幸的是，这是一个客户，我不能在这里报告环境的确切细节。但我可以在下次通话时向他们提出任何建议。
更新：
他们的申请今天再次被锁定。以下是我们迄今为止尝试过的事情：
- 他们已更新到最新的 jTDS 驱动程序 (1.2.5)
- 我已将
socketTimeout连接字符串上的属性设置为 300，但驱动程序在 5 分钟后仍停留在 socketRead0() 上 - 我们将活动检查查询从“select * from c3p0_connection_test_table”更改为“select 1”
- 我们在 C3P0 中添加了
unreturnedConnectionTimeoutanddebugUnreturnedConnectionStackTraces属性（不过，这些并没有捕获断开的连接）
以下是我们设置的所有 C3P0 连接属性：
<property name="minPoolSize" value="1"/>
<property name="maxPoolSize" value="30"/>
<property name="acquireIncrement" value="3"/>
<property name="automaticTestTable" value="c3p0_connection_test_table"/>
<property name="idleConnectionTestPeriod" value="30"/>
<property name="testConnectionOnCheckin" value="true"/>
<property name="testConnectionOnCheckout" value="true"/>
发生的一件奇怪的事情是，当应用程序被锁定时，我们尝试使用应用程序用户登录 SQL Server Management Studio，但它不会让我们进入（我认为这只是一个正常的超时错误）。数据库已启动并侦听端口 1433（使用 验证telnet），因此我认为这意味着已达到与数据库的最大连接数。不过，我不确定这是否有助于确定此问题的原因。
领导跟随但没有成功：
有用的答案可以要求我检查客户机器上的某些内容，或者指出可能的根本原因。无论答案如何帮助我追查到这一点，都会得到赏金。