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From "Petter Olofsson" <olofsson.pet...@gmail.com>
Subject Re: Problem closing database pool connections
Date Mon, 18 Feb 2008 19:48:06 GMT
Hi Len! Thanks for the reply.
The dconn was closed by simply calling the close function when I was
done with the connection.
This is something that has worked in the past so I'm a bit confused
when it stopped working now.

I have solved the problem now by just returning the connection from
the pool and close it later. The connection returned by calling
getInnermostDelegate() is not closed at all. Does anyone know if this
will cause problem later on? It seems to work correctly for now with a
connection pool consisting of only one connection.


2008/2/18, Len Popp <len.popp@gmail.com>:
> It looks to me like you're bypassing the connection pool and messing
> up the way it handles connections. You've only shown a snippet of
> code, so I have a couple of questions:
> 1. After dconn is returned from getConnection, how and when does it get closed?
> 2. Does the exception happen every time getConnection is called, or
> does it maybe succeed on the first call and fail during the second?
>
> When you get a connection from the connection pool, you're supposed to
> close it *after* you use it. At
> that time the underlying "real" connection is *not* closed, it's just
> returned to the pool. That's the point of the connection pool, it
> keeps a set of connections open to reduce overhead. Here you're
> closing the PoolableConnection immediately, before it's used, which is
> wrong.
>
> Here's what I think happens. (This is partly guesswork.)
>
> - DatabaseController.getConnection gets a PoolableConnection, extracts
> the underlying real connection (dconn), then returns the
> PoolableConnection to the pool.
>
> - The caller of DatabaseController.getConnection uses the real
> connection and then closes it.
>
> - Now the pool contains a PoolableConnection whose underlying
> connection is closed - This shouldn't happen!
>
> - DatabaseController.getConnection is called a second time, and
> returns the same PoolableConnection as before (because it's back in
> the pool).
>
> - conn.close() fails this time because the underlying connection was
> closed prematurely.
>
> Normally you'd never call getInnermostDelegate, you'd just use the
> PoolableConnection returned by DataSource.getConnection and close it
> when you're done. Is there a reason that you can't do that?
> --
> Len
>
>
> On Feb 18, 2008 11:05 AM, Petter Olofsson <olofsson.petter@gmail.com> wrote:
> > Hello tomcat users!
> >
> > I have a problem using the connection pool in Tomcat. The function
> > getConnection() throws the following error message:
> >
> > [Error message]
> > When trying to get a Connection an SQLExcpetion occurred:
> > java.sql.SQLException: Already closed.
> >        at org.apache.tomcat.dbcp.dbcp.PoolableConnection.close(PoolableConnection.java:84)
> >        at org.apache.tomcat.dbcp.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.close(PoolingDataSource.java:181)
> >        at org.metria.kiruna.profs.eniro.db.DatabaseController.getConnection(DatabaseController.java:136)
> >
> > [DatabaseController.java]
> >    protected Connection getConnection(){
> >        try{
> >            Context initContext = new InitialContext();
> >            Context envContext  = (Context)initContext.lookup("java:comp/env");
> >            DataSource ods = (DataSource) envContext.lookup("jdbc/yyy");
> >
> >            Connection conn = ods.getConnection();
> >
> >            Connection dconn = ((DelegatingConnection)
> > conn).getInnermostDelegate();
> >
> >            // if( conn != null && !conn.isClosed() ) // Line 135
> >                conn.close(); // Line 136
> >
> >            return dconn;
> >        }catch( SQLException sqle ){
> >            System.err.println("When trying to get a Connection an
> > SQLExcpetion occured.");
> >            sqle.printStackTrace();
> >        }catch( NamingException ne ){
> >            System.err.println("When trying to get a Connection an
> > NamingException occured.");
> >            System.err.println(ne);
> >        }
> >        return null;
> >    }
> >
> > [Context.xml]
> > <Resource accessToUnderlyingConnectionAllowed="true"
> >            auth="Container"
> >            driverClassName="oracle.jdbc.OracleDriver"
> >            maxActive="30"
> >            maxIdle="10"
> >            maxWait="1000"
> >            name="jdbc/yyy"
> >            username="xxx"
> >            password="xxx"
> >            type="javax.sql.DataSource"
> >            url="jdbc:oracle:thin:@drone:1521:top" />
> >
> > If the outer connection is left open ( line 135, 136 is deleted) then
> > all connections are used until "maxActive" connections are created.
> >
> > The program uses Tomcat 5.5.26 and Oracle 10.2.3.0.
> >
> > Does anybody have an idea of why I can't close the outer connection so
> > that the connections can be returned to the pool when I am done?
> >
> > / Petter
> >
> > ---------------------------------------------------------------------
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> >
> >
>
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>


-- 
Petter Olofsson

Student vid civilingenjörsprogrammet Interaktion och Design
på Umeå Universitet

Telefon: +46 (0)70 369 36 77
ICQ: 153888597
Msn: olofsson.petter@gmail.com

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