[Zope-dev] Question about _v_ attributes and database connections

[Marco Bizzarri]

On Fri, Mar 05, 2004 at 11:16:37AM +0000, Chris Withers wrote:
> Hi Marco,

Hi.
 
> Marco Bizzarri wrote:
> 
> >We're trying to tackle a problem in hanging connections in ZPsycopg.
> 
> Hehe, I fixed this for ZOracleDA a couple of months ago. You may want to 
> look at the thread pool code in there to see how I did it, gimme a nod if 
> you need a URL (it's on a CVS branch in cvs.zope.org)

I took a look at that, the connections.CTM, and the other. The simple
question is if this is a known problem with *ALL* db adapters, and, in
this case, it could be possible to devise a general solution, or if this
has something to do with psycopg.

I've a scenario where I can produce hanging connections in ZPsycopg:

1) use page with sql methods
2) refresh a product
3) repeat 1)
4) refresh a product

if you have 4 threads, you should have now 5 connections. Obviously here
there is something wrong with the management of _v_ attributes, in
particular the _v_database_connection in the DA.py. The psycopg code is
quite similar to the basic DA.py code, so I was looking for other ways
of approaching the problem.

> >However, I would like to have some information about the functioning of
> >the _v_ attributes, and the cache management. In particular:
> >
> >1) where is the code which handles the _v_ attributes (I like to look at
> >the source code, you know ;))
> 
> Never bothered finding it, the sematics are pretty well documented.

Yes, actually.

> >2) where is the code which handles the caching of the objects?
> 
> The ZODB cache. It's big and complicated, trust me, you DON'T need to go 
> there...

:(

> >3) is it possible to disable caching of some object?
> 
> No. The fact that you want to means you're mis-using _v_ attributes ;-)

My feeling was that the hanging connection problem was related to the
cache... so the question (I'm not using _v_ attributes in any particular
way)

> >4) when an _v_ attribute is removed, what code of the object/attribute
> >itself is called?
> 
> None. I believe it gets lost at the object is ghosted.
> 
> >If possible, please answer also directly to me (I'm not on this list).
> 
> Are you maintaining ZPsychopg? If not, the maintainers might be able to 
> help...

No, actually we've a db application which makes a lot of use of zpsycopg
for insert/updates, not only for select, and we stumbled on this
problem. We're working with Federico Di Gregorio (psycopg mantainer) in
order to solve the problem.

> cheers,
> 
> Chris - who learnt a whole lot more about ZODB and ZODB caching when 
> solving this kind of problem in ZOracleDA ;-)

I suspect I will have to learn something in the hard way too :)

> -- 
> Simplistix - Content Management, Zope & Python Consulting
>            - http://www.simplistix.co.uk

Thanks for your help

Regards
Marco

-- 
Marco Bizzarri - Amministratore Delegato - Icube S.r.l.
Sede:   Via Ridolfi 15 - 56124 Pisa (PI), Italia 
E-mail: m.bizzarri at icube.it		WWW: www.icube.it	
Tel: 	(+39) 050 97 02 07		Fax: (+39) 050 31 36 588	
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: not available
Url : http://mail.zope.org/pipermail/zope-dev/attachments/20040305/33a3f3d0/attachment.bin