Hibernate - org.hibernate.exception.GenericJDBCException: Cannot open connection

Question

In order to solve the issue of too many connections to DB and idle connections, we made the following changes to the Configuration file-

c3p0.min_size=1
c3p0.max_size=20
c3p0.timeout=1800
c3p0.max_statements=50
connection.release_mode=on_close

After that, while trying to run the application, we are getting the following exception. Please advice why this is happening & how this can be corrected -

---

HTTP Status 500 - org.hibernate.exception.GenericJDBCException: Cannot open connection

type Exception report

message org.hibernate.exception.GenericJDBCException: Cannot open connection

description The server encountered an internal error that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: org.hibernate.exception.GenericJDBCException: Cannot open connection
    org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:286)
    org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
    org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    com.alci.filters.ParamFilter.doFilter(ParamFilter.java:27)
root cause

org.hibernate.exception.GenericJDBCException: Cannot open connection
    org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:126)
    org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:114)
    org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
    org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:52)
    org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:449)
    org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
    org.hibernate.jdbc.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:161)
    org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1577)
    org.hibernate.loader.Loader.doQuery(Loader.java:696)
    org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:259)
    org.hibernate.loader.Loader.doList(Loader.java:2232)
    org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2129)
    org.hibernate.loader.Loader.list(Loader.java:2124)
    org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:401)
    org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:363)
    org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)
    org.hibernate.impl.SessionImpl.list(SessionImpl.java:1149)
    org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
    com.alci.common.LoginAction.login(LoginAction.java:127)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    java.lang.reflect.Method.invoke(Method.java:597)
    org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:269)
    org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:170)
    org.apache.struts.chain.commands.servlet.ExecuteAction.execute(ExecuteAction.java:58)
    org.apache.struts.chain.commands.AbstractExecuteAction.execute(AbstractExecuteAction.java:67)
    org.apache.struts.chain.commands.ActionCommandBase.execute(ActionCommandBase.java:51)
    org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
    org.apache.commons.chain.generic.LookupCommand.execute(LookupCommand.java:304)
    org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
    org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:283)
    org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
    org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    com.alci.filters.ParamFilter.doFilter(ParamFilter.java:27)
root cause

java.sql.SQLException: Connections could not be acquired from the underlying database!
    com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:106)
    com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:529)
    com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
    org.hibernate.connection.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:78)
    org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)
    org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
    org.hibernate.jdbc.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:161)
    org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1577)
    org.hibernate.loader.Loader.doQuery(Loader.java:696)
    org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:259)
    org.hibernate.loader.Loader.doList(Loader.java:2232)
    org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2129)
    org.hibernate.loader.Loader.list(Loader.java:2124)
    org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:401)
    org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:363)
    org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)
    org.hibernate.impl.SessionImpl.list(SessionImpl.java:1149)
    org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
    com.alci.common.LoginAction.login(LoginAction.java:127)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    java.lang.reflect.Method.invoke(Method.java:597)
    org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:269)
    org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:170)
    org.apache.struts.chain.commands.servlet.ExecuteAction.execute(ExecuteAction.java:58)
    org.apache.struts.chain.commands.AbstractExecuteAction.execute(AbstractExecuteAction.java:67)
    org.apache.struts.chain.commands.ActionCommandBase.execute(ActionCommandBase.java:51)
    org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
    org.apache.commons.chain.generic.LookupCommand.execute(LookupCommand.java:304)
    org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
    org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:283)
    org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
    org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    com.alci.filters.ParamFilter.doFilter(ParamFilter.java:27)
root cause

com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.
    com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1319)
    com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:557)
    com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:477)
    com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525)
    com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
    org.hibernate.connection.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:78)
    org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)
    org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
    org.hibernate.jdbc.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:161)
    org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1577)
    org.hibernate.loader.Loader.doQuery(Loader.java:696)
    org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:259)
    org.hibernate.loader.Loader.doList(Loader.java:2232)
    org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2129)
    org.hibernate.loader.Loader.list(Loader.java:2124)
    org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:401)
    org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:363)
    org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)
    org.hibernate.impl.SessionImpl.list(SessionImpl.java:1149)
    org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
    com.alci.common.LoginAction.login(LoginAction.java:127)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    java.lang.reflect.Method.invoke(Method.java:597)
    org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:269)
    org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:170)
    org.apache.struts.chain.commands.servlet.ExecuteAction.execute(ExecuteAction.java:58)
    org.apache.struts.chain.commands.AbstractExecuteAction.execute(AbstractExecuteAction.java:67)
    org.apache.struts.chain.commands.ActionCommandBase.execute(ActionCommandBase.java:51)
    org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
    org.apache.commons.chain.generic.LookupCommand.execute(LookupCommand.java:304)
    org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
    org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:283)
    org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
    org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    com.alci.filters.ParamFilter.doFilter(ParamFilter.java:27)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.36 logs.

Answer 1

This sometimes arises due to timeout. Increase the timeout and it will hopefully resolve the issue.

c3p0.timeout=6000

Answer 2

You ran out of database connections.

This means two things:

1. Your transaction take too much time because of slow queries so a connection is being held for way too much time
2. You have very high traffic demands which can't fit into a 20 connections pool size.

I recommend you read the following read my answer of this SO question.

I don't think this settings is recommended:

connection.release_mode=on_close

ON_CLOSE - is essentially the legacy behavior described above. The Hibernate session obtains a connection when it first needs to perform some JDBC access and holds unto that connection until the session is closed.

on_close - says to use ConnectionReleaseMode.ON_CLOSE. This setting is left for backwards compatibility, but its use is highly discouraged.

Try using "auto" instead.