Re: Scrolling through cursors - Mailing list pgsql-jdbc

Peter,


I use a connection pool to deal with startup penalties, which I think
are significant.

It is a process on the backend.

Not sure what you mean by serialized on the backend?

Dave

> -----Original Message-----
> From: Peter V Cooper [mailto:pvcooper@adelphia.net]
> Sent: Monday, March 18, 2002 10:52 AM
> To: Dave@micro-automation.net; 'Fredrik Wendt';
> pgsql-jdbc@postgresql.org
> Subject: Re: [JDBC] Scrolling through cursors
>
>
> For my information; this means I probably need a
> new connection object for each cursor due to the fact
> that it is within a transaction and those are serial in
> nature by default on a connection even though this
> is a pure select statement. This begs the question
> of how expensive is a new connection. Is it a new
> thread or process on the backend? I think the answer
> is process. Again FMI, why is a cursor necessarily
> within a transaction? Also I think any connection
> object is serialized at the backend anyway true/false?
>
> TIA for any responses.
>
> BTW, this is not a complaint by me as most modern UNIX'es
> are reasonably efficient at process creation and destruction
> especially when the initial data and stack segments are
> reasonable in size since the Text segment is irrelevant.
> Might be more of a problem for other OS'es.
>
> At 10:48 PM 3/17/2002 -0500, Dave Cramer wrote:
> >Fredik
> >
> >Here is some code which uses cursors
> >
> >Dave
> >
> >   public void testCursor()
> >   {
> >     Connection con = null;
> >     try {
> >       con = getConnection();
> >
> >       // cursors work inside a transaction
> >       con.setAutoCommit(false);
> >
> >       Statement stmt = con.createStatement();
> >
> >       // sufficiently long select as to get us something we
> can scroll
> >through
> >       stmt.execute("declare cursorname cursor for select * from
> >pg_class");
> >
> >       ResultSet rs = stmt.executeQuery("fetch 10 from cursorname");
> >
> >       while (rs.next()){
> >         System.out.println(rs.getString(1));
> >       }
> >       rs.close();
> >
> >       // close the cursor
> >       con.commit();
> >
> >     }
> >     catch (Exception ex)
> >     {
> >       ex.printStackTrace();
> >     }
> >     finally
> >     {
> >       try {
> >         if ( con != null )
> >           con.close();
> >       }catch ( SQLException ex ) {}
> >     }
> >
> >   }
> >
> >
> >
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