求助：c3p0不定期出现SQLException: An attempt ...异常

求助
项目采用spring2.0 + struts 1.3.5 + spring jdbc
Dao层采用spring提供的声明式事务控制
Web服务器为Tomcat 5.0.28

问题现象：
最近该项目在做系统测试，服务运行一段时间之后，c3p0-0.9.0.4出现SQLException: An attempt by a client to checkout a Connection has timed out异常信息
在出现异常的同时，采用其他的客户端连接数据库没有问题。出现该问题之后，重启Tomcat服务器又能稳定运行一段时间。

在google上未找到答案。期待热心人解答

详细异常信息


org.springframework.transaction.CannotCreateTransactionException: Could not open JDBC Connection for transaction; nested exception is java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.
Caused by: 
java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.
	at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:104)
	at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:65)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:262)
	at com.mchange.v2.c3p0.PoolBackedDataSource.getConnection(PoolBackedDataSource.java:94)
	at com.mchange.v2.c3p0.ComboPooledDataSource.getConnection(ComboPooledDataSource.java:521)
	at org.springframework.jdbc.datasource.DataSourceTransactionManager.doBegin(DataSourceTransactionManager.java:200)
	at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:350)
	at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:262)
	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:102)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:166)
	at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:630)
	at com.ge.gdc.management.dao.GDCHF0005A02Dao$$EnhancerByCGLIB$$2004b336.findMaxTimeAndMinTime(<generated>)
	at com.ge.gdc.management.service.impl.GDCHF0005A02BlogicImpl.findMaxTimeAndMinTime(GDCHF0005A02BlogicImpl.java:224)
	at com.ge.gdc.management.action.GDCHF0005A02Action.find(GDCHF0005A02Action.java:99)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:324)
	at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:280)
	at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:216)
	at org.springframework.web.struts.DelegatingActionProxy.execute(DelegatingActionProxy.java:110)
	at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
	at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
	at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
	at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157

详细异常信息


Caused by: com.mchange.v2.resourcepool.TimeoutException: internal -- timeout at awaitAcquire()
	at com.mchange.v2.resourcepool.BasicResourcePool.awaitAcquire(BasicResourcePool.java:970)
	at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:208)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:260)
	... 53 more

不了解c3p0具体是什么。

但是，从异常的字面意义上和stack trace上来看，很可能是connection pool获取的时候出现死锁或者别的问题（原因是获取connection的锁无法获得），导致无法获得连接。
[该贴被slangmgh于2007年09月05日 14:39修改过]

另外还有一种可能，就是connection没有归还到缓冲池，如果缓冲池有设最大值，但是交易过程中有connection泄漏，那么一段时间后，就会出现这个问题。

仅供参考。

谢谢了，后来通过优化数据设置的方式有一段时间基本不出现这个问题了。

今天又频繁出现这个问题，正按照你的思路在调查。

我也遇到这个问题，楼主是怎么解决的。