Re: patch: add a finalizer to AbstractJdbc1Statement

On 18/08/2003 12:11 Oliver Jowett wrote:
> On Mon, Aug 18, 2003 at 11:38:22AM +0100, Paul Thomas wrote:
> >
> > On 17/08/2003 15:00 Oliver Jowett wrote:
> > >This patch adds a finalizer to AbstractJdbc1Statement that closes the
> > >statement. Without this, when server-side preparation is in use
> > >statements
> > >that are executed then discarded without an explicit close() will leak
> > >resources on the backend while that connection remains open, as a
> > >DEALLOCATE
> > >never gets executed.
> >
> > Not a good solution IMHO. Relying on GC to clean up resource leaks is a
> > poor solution.
>
> I'm not suggesting that relying on GC for cleanup is a good idea.
> However,
> without this patch, the driver will *always* leak backend resources with
> longlived connections and leaky client code (which is possibly not under
> the
> control of the eventual owner of the connection -- e.g. the appserver
> case).
>
> > And it you simply System.exit() the JVM, GC is not called
> > at all.
>
> When the JVM exits, the physical connections go down so the backend will
> do
> resource cleanup on its own.

This is the area where my knowledge of the back-end processing could be
better (and I've not yet had sufficient time to "nail it" by grepping the
back-end sources). Are server-side prepares tied to a connection? If yes,
then I can easily see back-end resource clean-up happening. And this might
provide us with another strategy for handling orphaned statements:

I would envisage a scenario where the prepare-string/statement-name pair
are cached in the connection. When a connection.prepareStatement(..) call
is made, if there is already an entry in the cache, then use that
otherwise prepare a new BE statement and add details to cache. This way,
we would never need to worry about statement leaks as we wouldn't get
duplicates in the BE connection. What we _would_ need to do is make
PreparedStatement.close() a NOP when using server-side prepares as some
connection pool implementations (I've been looking at Apache DBCP
specifically as thats what I use ;-) call close on the underlying
statement when close is called on their wrapper class
(DelegatingPreparedStatement for DBCP). The actual DEALLOACTE would then
be done on connection.close() (assuming we don't just let the BE take of
it).

Sorry if I've gone a bit OT

regards

--
Paul Thomas
+------------------------------+---------------------------------------------+
| Thomas Micro Systems Limited | Software Solutions for the Smaller 
Business |
| Computer Consultants         | 
http://www.thomas-micro-systems-ltd.co.uk   |
+------------------------------+---------------------------------------------+


---------------------------(end of broadcast)---------------------------
TIP 5: Have you checked our extensive FAQ?

              http://www.postgresql.org/docs/faqs/FAQ.html