Please Help! problem with C3P0

mnrz · **Joined:** Sat Oct 08, 2005 2:13 am **Posts:** 47

Hi all,

I have a problem with connection pooling using C3P0, the problem is, after opening a hibernate session and some transaction the following exception will be thrown, it seems something wrong with c3p0.

if anyone had such experience please enlighten me on this issue.

Hibernate version: 3.2

Mapping documents: HBM files

Code in which I acquire the current session:

Code:

public static Session currentSession () {

        Session s = (Session)session.get();

        if (s == null) {

            try {

                s= sessionFactory.openSession();

                s.connection().setAutoCommit(true);

                session.set(s);

            } catch (SQLException e) {

                s.close() ;

                return null ;

}

        }

        return s ;

    }

Full stack trace of any exception that occurs:

Code:

 WARN BasicResourcePool com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask:1841 run - com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@ae525c -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 

java.sql.SQLException: Data source rejected establishment of connection,  message from server: "Too many connections"

            at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:990)

            at com.mysql.jdbc.Connection.createNewIO(Connection.java:2544)

            at com.mysql.jdbc.Connection.<init>(Connection.java:1474)

            at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:264)

            at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134)

            at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)

            at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)

            at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)

            at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)

            at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)

            at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)

            at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)

!

!

Name and version of the database you are using:Mysql 4

Hibernate & c3p0 settings: (in hibernate.cfg.xml)

Code:

<hibernate-configuration>

            <session-factory>

                        <property name="hibernate.dialect">org.hibernate.dialect.MySQLInnoDBDialect</property>

                        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>

                        <property name="connection.url">jdbc:mysql://localhost/otpwithebTracker?characterEncoding=utf8</property>

                        <property name="connection.username">root</property>

                        <property name="connection.password"></property>

                        <property name="show_sql">true</property>

        <property name="hibernate.c3p0.min_size">5</property>

        <property name="hibernate.c3p0.max_size">20</property>

        <property name="hibernate.c3p0.acquire_increment">1</property>

        <property name="hibernate.c3p0.timeout">60</property>

Any help would be appreciated.

farzad · **Posted:** Mon Jan 21, 2008 11:22 am

Open your MySQL admin console and see how many connections you have. It seems more like MySQL is rejecting the request for a new connection.

Farzad-

mnrz · **Joined:** Sat Oct 08, 2005 2:13 am **Posts:** 47

farzad wrote:

Open your MySQL admin console and see how many connections you have. It seems more like MySQL is rejecting the request for a new connection.

Farzad-

thanks, yes in fact, the number of connection exceeds the value specified in Hibernate config file and the problem is that, because Hibernate or rather c3p0 should release connections that no longer is used but it doesn't function properly

as you can see I set the maximum size to 20 but even is a small scale test case in which we have only one user session, this value is exceeding!!!

mnrz · **Joined:** Sat Oct 08, 2005 2:13 am **Posts:** 47

any idea? :(

mnrz · **Joined:** Sat Oct 08, 2005 2:13 am **Posts:** 47

my project stopped progressing by this problem, please give me your advice.

thanks

farzad · **Posted:** Mon Jan 28, 2008 12:27 pm

mnrz wrote:

my project stopped progressing by this problem, please give me your advice.

thanks

I don't know why I didn't get any notification for your reply but here I am now :)

Well, I don't have a good feeling about the acquire_increment parameter as also it appears to be depreciated in c3p0 API too. However, you could have problems returning connections to connection pool. Also you might want to try to switch to another connection that is more sensitive and gives more messages. JBoss connection pool is a good one and tells you when your application is not returning the connections. DBCP might be also good.

Farzad-