Re: problem with LargeObject and commit - Mailing list pgsql-jdbc

Hi,

Did you give it a look ?

Regards

Marc

On Sunday 06 October 2013 19:14:41 Marc Cousin wrote:
> Hi,
>
> Attached is an attempt to do this (git diff on head).
>
> The code seems to work. It has been tested on the program we are migrating
> from SQL Server, we can now stream LOBs directly to web browsers...
>
> Please note that I am not usually a Java developper. I did my best to do
> this correctly, and the Java way (as far as I know :) ). If some things are
> not done the right way, or there is a smarter solution, tell me, I'll
> improve this.
>
> Regards,
>
> Marc
>
> On Tuesday 01 October 2013 08:11:21 Dave Cramer wrote:
> > Well I don't see any reason not to open up the LOM class to allow you to
> > extend it.
> >
> > Can you send a git pull?
> >
> > Dave Cramer
> >
> > dave.cramer(at)credativ(dot)ca
> > http://www.credativ.ca
> >
> > On Tue, Oct 1, 2013 at 3:52 AM, Marc Cousin <cousinmarc@gmail.com> wrote:
> > > Sorry, I don't think I get it, so please correct me below if I didn't.
> > >
> > > I currently use getInputStream() on my large object. How could I provide
> > > a
> > > connection to the extended InputStream ? I am calling a LargeObject
> > > method.
> > >
> > > Or maybe extend LargeObject to have a new getInputStream method with a
> > > connection provided, and then provide this connection to the extended
> > > InputStream ?
> > >
> > > My initial idea was to not have to provide the connection as a
> > > parameter,
> > > so I
> > > wanted to use the Lob Manager.
> > >
> > > Anyway, shouldn't streaming a large object in this special case be
> > > easier
> > > to
> > > do ? The original code (from SQL Server) didn't have to do all these
> > > workarounds, and I'll get this objection from people that will have to
> > > use
> > > this code :)
> > >
> > > Just having conn as protected instead of private in the
> > > LargeObjectManager
> > > would have made it possible to me to do it simply: I could have provided
> > > the
> > > connection to my extended LargeObject, and from there end the
> > > transaction
> > > on
> > > close().
> > >
> > > Regards.
> > >
> > > On Monday 30 September 2013 17:08:18 Dave Cramer wrote:
> > > > Marc,
> > > >
> > > > You required the connection to create the LargeObjectManager, so why
> > > > not
> > > > just extend the InputStream and add the connection to that object.
> > > > When you close the input stream, close the connection ????
> > > >
> > > > Dave Cramer
> > > >
> > > > dave.cramer(at)credativ(dot)ca
> > > > http://www.credativ.ca
> > > >
> > > > On Mon, Sep 30, 2013 at 11:18 AM, Marc Cousin <cousinmarc@gmail.com>
> > >
> > > wrote:
> > > > > Hi,
> > > > >
> > > > > I'm having the following problem: I need to stream a LOB to a web
> > >
> > > client,
> > >
> > > > > without consuming
> > > > > a lot of memory. So I am returning getInputStream() to the caller.
> > > > >
> > > > > This works perfectly, except that I have to keep a transaction open
> > > > > to
> > > > > return the large object
> > > > > stream, and I have (or found) no way of closing the transaction when
> > >
> > > the
> > >
> > > > > filestream is closed.
> > > > >
> > > > > So of course, if I did that, I would get a lot of IDLE in
> > > > > transaction
> > > > > sessions...
> > > > >
> > > > > So the logical way seemed to me to extend LargeObjectManager and
> > > > > LargeObject to have a
> > > > > close method on my LargeObject that closes the transaction, meaning
> > >
> > > that
> > >
> > > > > my LargeObject
> > > > > should have a connection attribute. So I wanted to do something like
> > >
> > > this
> > >
> > > > > (not working,
> > > > > it's just for the sake of explanation):
> > > > >
> > > > >
> > > > > public class StreamLargeObjectManager extends LargeObjectManager{
> > > > >
> > > > >            public StreamLargeObject openStreamLargeObject(long oid,
> > > > >            int
> > > > >
> > > > > mode)
> > > > >
> > > > >              throws SQLException
> > > > >
> > > > >            {
> > > > >
> > > > >              LargeObject lo = super.open(oid, mode);
> > > > >              StreamLargeObject so = new StreamLargeObject(lo,
> > > > >
> > > > > super.getConn()); //cannot be done because no access to connection
> > > > >
> > > > >              return so;
> > > > >
> > > > >            }
> > > > >
> > > > > }
> > > > >
> > > > >
> > > > > and
> > > > >
> > > > > public class StreamLargeObject extends
> > > > > org.postgresql.largeobject.LargeObject{
> > > > >
> > > > >         Connection conn;
> > > > >
> > > > >         LargeObject lobj;
> > > > >
> > > > >
> > > > >         public StreamLargeObject(LargeObject lg, BaseConnection
> > > > >         conn)
> > > > >
> > > > > throws SQLException {
> > > > >
> > > > >                 this.lobj = lg;
> > > > >                 this.conn = conn;
> > > > >
> > > > >         }
> > > > >
> > > > >
> > > > >         @Override
> > > > >         public void close() throws SQLException {
> > > > >
> > > > >                 lobj.close();
> > > > >                 this.conn.commit();
> > > > >
> > > > >         }
> > > > >
> > > > >        public getInputStream() throws SQLException
> > > > >
> > > > >     {
> > > > >
> > > > >         return lobj.getInputStream();
> > > > >
> > > > >     }
> > > > >
> > > > > }
> > > > >
> > > > >
> > > > > As the comment says it all, I cannot do this: conn is private in
> > > > > LargeObjectManager. For now, the problem has been
> > > > > worked around by duplicating all the LargeObjectManager code, but
> > > > > this
> > >
> > > is
> > >
> > > > > obviously ugly and not
> > > > > maintainable. So my question is: have I missed some obvious solution
> > > > > ?
> > > > > Could a getter be added to
> > > > > the LargeObjectManager's connection ?
> > > > >
> > > > > Regards,
> > > > >
> > > > > Marc
> > > > >
> > > > >
> > > > > --
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