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From "Vadim Gritsenko" <vgritse...@hns.com>
Subject RE: [C2] SQLTransformer
Date Wed, 08 Aug 2001 14:14:35 GMT
> -----Original Message-----
> From: tom.klaasen@the-ecorp.com [mailto:tom.klaasen@the-ecorp.com]
> Sent: Wednesday, August 08, 2001 9:38 AM
> To: cocoon-dev@xml.apache.org
> Subject: RE: [C2] SQLTransformer
> 
> 
> You seem to be absolutely right.
> 
> We're using a slightly different version of SQLTransformer (the one Sven
> Beauprez was working on), and he assured me that he had followed the
> evolutions SQLTransformer in C2 and made all relevant patches on our
> version. Now Sven is on a holiday (which is the reason I got involved in
> it), so I'll have to wait a few weeks more before I can strangle him ;)
> 
> There's still one problem though: if the pool of connections is empty when
> you arrive at line 827, the thing just explodes (you'll only notice this
> under load). 
> 
> I've tried to loop there until I get a connection, but this of course leads
> to a deadlock (almost all our queries are nested 2 deep, so if 20 requests
> arrive at the same time for a pool of 10 connections, all nested queries are
> deadlocked)
> 
> I'm now trying to get a hold on all necessary connections before trying to
> execute the queries. Wish me luck, because it looks like a bee's nest to
> me...

It seems possible to obtain all required connections before executing queries...
Try to get required number of connections (queries.size()) in endExecuteQueryElement
method, before executeQuery(0). If you are unable to get connections, you need to
release all of them and try to get them again in loop. I would recommend to add small
random delay (as in ethernet collision resolution protocol) before obtaining 
connections again - to avoid repetitive deadlocks.

Good luck!

> 
> Thanks for your reaction, and my excuses for the misunderstanding

No problem, you are welcome

Vadim

> tomK
> 
> 
> -----Original Message-----
> From: Vadim Gritsenko [mailto:vgritsenko@hns.com]
> Sent: woensdag 8 augustus 2001 15:14
> To: cocoon-dev@xml.apache.org
> Subject: RE: [C2] SQLTransformer
> 
> 
> Hi,
> 
> I don't know what version of SQLTransformer you are talking about,
> IIRC this was fixed in CVS a weeks ago. If not, please show these 
> lines of code.
> 
> Right now ($Revision: 1.5.2.6 from cocoon_20_branch), query is executed
> in method "executeQuery(int index)", and it also extracts all results in
> "while (query.next())" loop, and then connection is closed in "finally"
> statement.
> 
> Regards,
> Vadim
> 
> > -----Original Message-----
> > From: tom.klaasen@the-ecorp.com [mailto:tom.klaasen@the-ecorp.com]
> > Sent: Tuesday, August 07, 2001 2:41 PM
> > To: cocoon-dev@xml.apache.org
> > Subject: [C2] SQLTransformer
> > 
> > 
> > Hi all,
> > 
> > There's a serious bug in the SQLTransformer: a query gets executed, and
> > after that the results are sucked out of it. Now, the moment the query is
> > executed, its Connection is given back to the Pool it belongs is (which is
> > good). But, if this Connection is reused before the results are sucked out
> > of it, serious problems arise (genre NullPointerException).
> > 
> > The problem does not arise ATM with the Excalibur that is in C2 now,
> because
> > that also has a serious bug in it (which I will report and patch tomorrow
> to
> > the Avalon people).
> > 
> > I'm working on a solution for the SQLTransformer, but I need one piece of
> > information: can I trust C2 to execute recycle() or dispose() as soon as
> the
> > pipeline has ended executing? This would allow me to allocate a Connection
> > in the setup(), and throw it back in the Pool in the recycle() resp.
> > dispose().
> > 
> > Once this is solved, I will of course send the patch to the list, but I
> need
> > this information to be able to patch it.
> > 
> > Thanks a lot,
> > tomK
> > 
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