MySQLNonTransientConnectionException: Too many connections

Question

My Spring-MVC application sometimes crashes when navigating around the site, the error message I've gotten from the logs are found below. I have absolutely no idea of what is causing this and would be very thankful for any tips that'll lead me in the right direction.

    SEVERE: Servlet.service() for servlet HS threw exception
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Data source rejected establishment of connection,  message from server: "Too many connections"
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:407)
    at com.mysql.jdbc.Util.getInstance(Util.java:382)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1013)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:987)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:982)
    at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1116)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2338)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2371)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2163)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:794)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
    at sun.reflect.GeneratedConstructorAccessor56.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:407)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:378)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:305)
    at org.apache.commons.dbcp.DriverConnectionFactory.createConnection(DriverConnectionFactory.java:38)
    at org.apache.commons.dbcp.PoolableConnectionFactory.makeObject(PoolableConnectionFactory.java:582)
    at org.apache.commons.dbcp.BasicDataSource.validateConnectionFactory(BasicDataSource.java:1556)
    at org.apache.commons.dbcp.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:1545)
    at org.apache.commons.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1388)
    at org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
    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.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:161)
    at org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1577)
    at org.hibernate.loader.Loader.doQuery(Loader.java:696)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:259)
    at org.hibernate.loader.Loader.doList(Loader.java:2232)
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2129)
    at org.hibernate.loader.Loader.list(Loader.java:2124)
    at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:401)
    at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:363)
    at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)
    at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1149)
    at org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
    at org.springframework.orm.hibernate3.HibernateTemplate$30.doInHibernate(HibernateTemplate.java:921)
    at org.springframework.orm.hibernate3.HibernateTemplate$30.doInHibernate(HibernateTemplate.java:1)
    at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:406)
    at org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:374)
    at org.springframework.orm.hibernate3.HibernateTemplate.find(HibernateTemplate.java:912)
    at org.springframework.orm.hibernate3.HibernateTemplate.find(HibernateTemplate.java:904)
    at se.hs.daos.UserDAOImpl.findByName(UserDAOImpl.java:42)
    at se.hs.controllers.LoginController.checkPassword(LoginController.java:20)
    at se.hs.pagecontrollers.LoginPageController.submitForm(LoginPageController.java:26)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:616)
    at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:560)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    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.Http11Processor.process(Http11Processor.java:859)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:636)

What my UserDaoImpl looks like:

package se.hs.daos;

import java.util.List;

import org.hibernate.SessionFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.orm.hibernate3.HibernateTemplate;
import org.springframework.orm.hibernate3.support.HibernateDaoSupport;

import se.hs.models.User;

public class UserDAOImpl extends HibernateDaoSupport implements UserDAO {

    private ApplicationContext context = new ClassPathXmlApplicationContext(
            "classpath*:applicationContext.xml");
    private SessionFactory sessionFactory = (SessionFactory) context
            .getBean("mySessionFactory");
    private HibernateTemplate hibernateTemplate = new HibernateTemplate(
            sessionFactory, true);

    public void saveUser(User user) {
        hibernateTemplate.save(user);
    }

    public User getUserById(Integer id) {

        User userFromDB = hibernateTemplate.get(User.class, id);
        return userFromDB;
    }

    public void removeUser(User user) {
        hibernateTemplate.delete(user);
    }

    public User findByName(String name) {

        String query = "SELECT u.userId FROM User u WHERE u.userName='" + name
                + "'";

        @SuppressWarnings("unchecked")
        List<Integer> list = hibernateTemplate.find(query);

        User userFromDB = null;

        if (list.size() > 0) {
            userFromDB = getUserById(list.get(0));
        }

        return userFromDB;
    }

}

UPDATE:

    exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.jdbc.UncategorizedSQLException: Hibernate operation: Cannot release connection; uncategorized SQLException for SQL [???]; SQL state [null]; error code [0]; Already closed.; nested exception is java.sql.SQLException: Already closed.
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:656)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:560)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause

org.springframework.jdbc.UncategorizedSQLException: Hibernate operation: Cannot release connection; uncategorized SQLException for SQL [???]; SQL state [null]; error code [0]; Already closed.; nested exception is java.sql.SQLException: Already closed.
    org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:83)
    org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:80)
    org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:80)
    org.springframework.orm.hibernate3.HibernateAccessor.convertJdbcAccessException(HibernateAccessor.java:424)
    org.springframework.orm.hibernate3.HibernateAccessor.convertHibernateAccessException(HibernateAccessor.java:410)
    org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:411)
    org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:374)
    org.springframework.orm.hibernate3.HibernateTemplate.save(HibernateTemplate.java:683)
    se.hsr.daos.InfoTextDAOImpl.saveInfoText(InfoTextDAOImpl.java:26)
    se.hsr.controllers.InfoTextController.saveInfoText(InfoTextController.java:31)
    se.hsr.pagecontrollers.InfoTextPageController.submitForm(InfoTextPageController.java:35)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:616)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:560)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause

java.sql.SQLException: Already closed.
    org.apache.commons.dbcp.PoolableConnection.close(PoolableConnection.java:114)
    org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.close(PoolingDataSource.java:191)
    org.springframework.orm.hibernate3.LocalDataSourceConnectionProvider.closeConnection(LocalDataSourceConnectionProvider.java:95)
    org.hibernate.jdbc.ConnectionManager.closeConnection(ConnectionManager.java:474)
    org.hibernate.jdbc.ConnectionManager.aggressiveRelease(ConnectionManager.java:429)
    org.hibernate.jdbc.ConnectionManager.afterStatement(ConnectionManager.java:304)
    org.hibernate.jdbc.AbstractBatcher.closePreparedStatement(AbstractBatcher.java:572)
    org.hibernate.jdbc.AbstractBatcher.closeStatement(AbstractBatcher.java:291)
    org.hibernate.id.insert.AbstractReturningDelegate.releaseStatement(AbstractReturningDelegate.java:82)
    org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:60)
    org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2176)
    org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2656)
    org.hibernate.action.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:71)
    org.hibernate.engine.ActionQueue.execute(ActionQueue.java:279)
    org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:321)
    org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:204)
    org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:130)
    org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)
    org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:56)
    org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)
    org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:50)
    org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
    org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:563)
    org.hibernate.impl.SessionImpl.save(SessionImpl.java:551)
    org.hibernate.impl.SessionImpl.save(SessionImpl.java:547)
    org.springframework.orm.hibernate3.HibernateTemplate$12.doInHibernate(HibernateTemplate.java:686)
    org.springframework.orm.hibernate3.HibernateTemplate$12.doInHibernate(HibernateTemplate.java:1)
    org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:406)
    org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:374)
    org.springframework.orm.hibernate3.HibernateTemplate.save(HibernateTemplate.java:683)
    se.hsr.daos.InfoTextDAOImpl.saveInfoText(InfoTextDAOImpl.java:26)
    se.hsr.controllers.InfoTextController.saveInfoText(InfoTextController.java:31)
    se.hsr.pagecontrollers.InfoTextPageController.submitForm(InfoTextPageController.java:35)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:616)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:560)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

Answer 1

It means DB SQL server is running out of connections. Server has a configuration parameter that specifies how maximum allowed connections.

This usually indicates that connections are not being closed. Are you requesting Connection objects from Hibernate in your code?

In short term, you can just increase maximum connections till this problem is fixed.

Answer 2

If you increase the number of connections may fix it but there is still possibility to happen this same exception in future.

Make sure that you have defined <property name="maxIdle" value="1" /> in your database configuration xml file. Also I had this same problem when I defined <property name="maxIdle" value="1" /> it fixed my problem.

<bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost/crm" />
        <property name="username" value="root" />
        <property name="password" value="root" />
        <property name="initialSize" value="10" />
        <property name="maxActive" value="15" />
        <property name="maxWait" value="5000" />
        <property name="maxIdle" value="1" />

    </bean>

Answer 3

In the above Tag this line is important

 <property name="maxIdle" value="1" />

will work, as it will allow only one connection for the AJAX or the DB request

Answer 4

In MySql, check maximum no of concurrent connection using

SHOW VARIABLES LIKE "max_connections";

By default it will be 151 ( 0 - 150). Then change max concurrent connection by

SET GLOBAL max_connections = 250;

This resolved my issue.