Re: Closed connections in pool

[Armin Waibel]

Hi Ilkka,
Ilkka Priha wrote:
Hello
We noticed that under heavy load (lack of memory) OJB returns closed 
Connections into the pool. This happens when the finalizer activates the 
finalize method of PersistenceBroker instances. At least MySQL 
Connections are already closed at this point (their finalize called as 
well?). Closed Connections cause a lot of trouble later on when borrowed 
back to use from the pool.

isn't it possible to avoid these problems when you enable property 
'testOnReturn' in connection-pool setting?

<connection-pool
            maxActive="30"
            validationQuery=""
            testOnBorrow="true"
            testOnReturn="true"
            whenExhaustedAction="0"
            maxWait="10000"
        />
If 'testOnReturn' is true the ObjectPool validate the connection before 
it was returned to pool.
http://jakarta.apache.org/commons/pool/apidocs/index.html


System Thread [Finalizer] (Suspended (breakpoint at line 61 in
    ConnectionFactoryPooledImpl))
ConnectionFactoryPooledImpl.returnConnectionToPool(JdbcConnectionDescriptor, 

    Connection) line: 61
ConnectionFactoryPooledImpl(ConnectionFactoryAbstractImpl).releaseConnection( 

    JdbcConnectionDescriptor, Connection) line: 90
ConnectionManagerImpl.releaseConnection() line: 314
PersistenceBrokerImpl.close() line: 336
PersistenceBrokerImpl.finalize() line: 1946
Finalizer.invokeFinalizeMethod(Object) line: not available [native method]
Finalizer.runFinalizer() line: 83
Finalizer.access$100(Finalizer) line: 14
Finalizer$FinalizerThread.run() line: 160
We added a simple check to an extended version of the 
ConnectionFactoryPooledImpl, which fixes the problem and could be 
applied to the original version, too.

thanks, I will add the con.close check to all pooling ConnectionFactory 
implementations. This will help to avoid problems with closed connection 
independent from connection-pool settings (think con.close() isn't 
costly to perform, so it doesn't matter if it was performed twice on 
return of the connection - testOnReturn enabled).

regards,
Armin
-- Ilkka
    public void returnConnectionToPool(JdbcConnectionDescriptor jcd,
        Connection con) throws LookupException
    {
        try
        {
            if (!con.isClosed())
            {
                super.returnConnectionToPool(jcd, con);
            }
        }
        catch (LookupException x)
        {
            throw x;
        }
        catch (Exception x)
        {
            throw new LookupException(x);
        }
    }
    public Connection getConnectionFromPool(JdbcConnectionDescriptor jcd)
        throws LookupException
    {
        try
        {
            Connection con;
            do
            {
                con = super.getConnectionFromPool(jcd);
            } while (con.isClosed());
            return con;
        }
        catch (LookupException x)
        {
            throw x;
        }
        catch (Exception x)
        {
            throw new LookupException(x);
        }
    }

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