No operations allowed after connection closed with Hibernate & C3p0

Hey have been struggling with this issue for a while and not sure how to go about solving it, any input much appreciated.

I’m using Hibernate with c3p0 for connection pooling (hibernate versions: org.hibernate:hibernate-c3p0:5.2.9.Final). This is running on google AppEngine connecting to cloud SQL.

The issue is that every so often it seems like one of the connections in the pool gets closed and C3p0 keeps serving that connection. The transactions themselves are managed using @Transactional on methods, and the exception is thrown as soon as that method is hit.

Trace:

org.hibernate.TransactionException: JDBC begin transaction failed: 
at org.hibernate.resource.jdbc.internal.AbstractLogicalConnectionImplementor.begin(AbstractLogicalConnectionImplementor.java:71)
at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.begin(LogicalConnectionManage...', developerMessage='Application threw exceptionType=class org.hibernate.TransactionException'}
org.hibernate.TransactionException: JDBC begin transaction failed:
at org.hibernate.resource.jdbc.internal.AbstractLogicalConnectionImplementor.begin(AbstractLogicalConnectionImplementor.java:71)
at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.begin(LogicalConnectionManagedImpl.java:255)
at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl$TransactionDriverControlImpl.begin(JdbcResourceLocalTransactionCoordinatorImpl.java:203)
at org.hibernate.engine.transaction.internal.TransactionImpl.begin(TransactionImpl.java:56)
at com.google.inject.persist.jpa.JpaLocalTxnInterceptor.invoke(JpaLocalTxnInterceptor.java:66)
at com.backend.api.resources.UserResource.loginEmailUser(UserResource.java:191)
at com.backend.api.resources.UserResource.login(UserResource.java:93)
at sun.reflect.GeneratedMethodAccessor259.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory.lambda$static$0(ResourceMethodInvocationHandlerFactory.java:76)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:148)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:191)
at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:243)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:103)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:493)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:415)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:104)
at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:277)
at org.glassfish.jersey.internal.Errors$1.call(Errors.java:272)
at org.glassfish.jersey.internal.Errors$1.call(Errors.java:268)
at org.glassfish.jersey.internal.Errors.process(Errors.java:316)
at org.glassfish.jersey.internal.Errors.process(Errors.java:298)
at org.glassfish.jersey.internal.Errors.process(Errors.java:268)
at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:289)
at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:256)
at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:703)
at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:416)
at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:370)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:389)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:342)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:229)
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:876)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:542)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:146)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:257)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1711)
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:255)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1347)
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:203)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:480)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1678)
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:201)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1249)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:144)
at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:220)
at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:152)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
at org.eclipse.jetty.server.Server.handle(Server.java:505)
at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:370)
at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:267)
at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:305)
at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:103)
at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:117)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.runTask(EatWhatYouKill.java:333)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:310)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.tryProduce(EatWhatYouKill.java:168)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:126)
at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:366)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:781)
at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:917)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.sql.SQLNonTransientConnectionException: No operations allowed after connection closed.
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:526)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:513)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:505)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:479)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:489)
at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:66)
at com.mysql.cj.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:3782)
at com.mchange.v2.c3p0.impl.NewProxyConnection.setAutoCommit(NewProxyConnection.java:1059)
at org.hibernate.resource.jdbc.internal.AbstractLogicalConnectionImplementor.begin(AbstractLogicalConnectionImplementor.java:66)
... 63 more
Caused by: com.mysql.cj.core.exceptions.ConnectionIsClosedException: No operations allowed after connection closed.
at sun.reflect.GeneratedConstructorAccessor300.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.cj.core.exceptions.ExceptionFactory.createException(ExceptionFactory.java:54)
at com.mysql.cj.core.exceptions.ExceptionFactory.createException(ExceptionFactory.java:93)
at com.mysql.cj.core.exceptions.ExceptionFactory.createException(ExceptionFactory.java:133)
at com.mysql.cj.jdbc.ConnectionImpl.checkClosed(ConnectionImpl.java:931)
at com.mysql.cj.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:3733)
... 65 more

Both hibernate and c3p0 configs are set i persistence.xml (and based on what c3p0 logs it seems to pick them up fine)

 <property name="hibernate.cache.provider_class" value="org.hibernate.cache.NoCacheProvider"/>
            <property name="hibernate.connection.provider_class" value="org.hibernate.c3p0.internal.C3P0ConnectionProvider" />
            <property name="hibernate.id.new_generator_mappings" value="false"/>
            <property name="hibernate.hbm2ddl.auto" value="validate" />
            <property name="hibernate.connection.isolation" value="2"/>

            <property name="hibernate.c3p0.min_size" value="2"/>
            <property name="hibernate.c3p0.timeout" value="61"/>
            <property name="hibernate.c3p0.acquire_increment" value="2"/>
            <property name="hibernate.c3p0.max_size" value="20"/>
            <property name="hibernate.c3p0.idle_test_period" value="30"/>
            <property name="hibernate.c3p0.unreturnedConnectionTimeout" value="300"/>
            <property name="hibernate.c3p0.preferredTestQuery" value="SELECT 1"/>
            <property name="hibernate.c3p0.testConnectionOnCheckin" value="true"/>
            <property name="hibernate.c3p0.testConnectionOnCheckout" value="true"/>

My understanding of how this should work is that testConnectionOnCheckin/testConnectionOnCheckOut together with idle_test_period should test these connections regularly and if one is closed or not working it would recover it.

But something here seems to not be working as I think it does. I have not been able to figure out exactly when connections get retained in a closed state or whats going on there, but when a connection like this does occur it will continue to fail requests for a period. Sometimes it recovers on its own and sometimes not (possibly depending on the frequency of the requests?). Redeploying the service always fixes this issue though (until it happens again that it keeps a closed connection.)

I’ve not had this happen locally and not sure how to reliably replicate it on our test server. Also somewhat lost in terms of how to verify if the testing of connections is working as intended with c3p0 when it’s deployed? I see the idle test queries are running locally.