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RE: Interest in standardizing Batch methods?

From: Geoffrey M Clemm <geoffrey.clemm@us.ibm.com>
Date: Thu, 17 Jul 2003 18:03:28 -0400
To: "WebDAV" <w3c-dist-auth@w3.org>
Message-ID: <OFB98EEFD3.57770D02-ON85256D66.0078D50C-85256D66.00792B22@us.ibm.com>

I agree.  Note that my statement "it probably is
worthwhile trying to define generic transactioning support for
WebDAV" explicitly did not suggest that such an attempt would
succeed (:-).  In particular, I believe it is likely that such
an attempt would fail for the reasons Julian describes.

Cheers,
Geoff

"Julian Reschke" <julian.reschke@gmx.de> wrote on 07/17/2003 05:20:46 PM:

> True, but...
> 
> ...speaking from personal experience working on a document management
> system, the temptation "give up" and just state "transactions are going 
to
> solve this problem in general" is big. However, transactions can be very
> expensive to implement, in particular in a HTTP server scenario. How 
many
> concurrent transactions are you going to support? What are you going to 
do
> if a client starts a transaction but doesn't finish it within a few 
minutes?
> 
> IMHO it makes a lot of sense to try to *avoid* them by
> 
> a) defining methods with the "right" level of transactionality (for
> instance, see PROPPATCH or ORDERPATCH) or
> 
> b) try to do things using the existing locking and/or versioning 
machinery.
> 
> 
> So at a minimum, I'd expect a working group activity on transactions to
> start with a list of use cases. Then we can take a look at the use cases 
and
> decide whether they require a generic transaction mechanism, or whether
> something simpler can do that as well (and please don't say: I want to 
do
> JDBC over HTTP).
> 
> 
> Julian
> 
> --
> <green/>bytes GmbH -- http://www.greenbytes.de -- tel:+492512807760
> 
> > -----Original Message-----
> > From: w3c-dist-auth-request@w3.org
> > [mailto:w3c-dist-auth-request@w3.org]On Behalf Of Geoffrey M Clemm
> > Sent: Thursday, July 17, 2003 11:02 PM
> > To: WebDAV
> > Subject: Re: Interest in standardizing Batch methods?
> >
> >
> >
> > If you are interested in defining a transactioning model, then
> > it would be best to make that explicit, because the term "batch"
> > is used to encompass many things.  To date, the WebDAV approach has
> > been to define specific transacted operations (e.g. PROPPATCH),
> > because that is something that can be implemented on a wide range
> > of repositories, while generic transactioning support is likely to
> > only be feasible on repositories that are actually databases.
> >
> > But enough repositories really are databases that it probably is
> > worthwhile trying to define generic transactioning support for
> > WebDAV.
> >
> > Cheers,
> > Geoff
> >
> > >
> > > I am sure that you guys, who don't agree with standardising Batch
> > > method, have good reasons for that. But shall we be more clear about
> > > those reasons which might not quite clear for all. Of course I know
> > > some of those reasons by chasing the thread with the same subject in
> > > the WebDAV mailing list. But I think the WebDAV protocol is almost
> > > enough mature to interest many organisations and Web users. So that
> > > they would like to apply this protocol rather HTTP protocol, and use
> > > the WebDAV advantages such as metadata, access control,... to author
> > > Web resources.
> > >
> > > Now the question is: if the WebDAV is going to be a substitute for 
HTTP
> > > protocol, can it handle authoring all kind of Web resources as it
> > > claims, or still we need other conventions based on the HTTP 
protocol
> > > in order to support authoring Web resources except file systems.
> > >
> > > So if you believe the WebDAV as a protocol for authoring all Web
> > > resources (and not only the file systems), then how we can handle 
Web
> > > resources such as emails and databases. In order to implement some
> > > operations on those resources, you might use a sequence of WebDAV
> > > methods which need to be considered as one transaction. In those 
cases
> > > lock method cannot help. So what is your suggestion to handle those
> > > operations?
> > >
> > > I think a mechanism for supporting transactions is a strong point 
that
> > > WebDAV needs.
> > >
> > > >
> > > > I agree with Chris.  The easy things aren't worth doing (you get
> > > > virtually
> > > > all of the benefit by streaming your requests and not blocking
> > > > waiting for
> > > > the response to each request), and the hard things are very 
complex
> > > > and
> > > > any given approach is unlikely to be a good basis for
> > > > interoperation.
> > > >
> > > > Cheers,
> > > > Geoff
> > > >
> > > > Chris wrote on 07/17/2003 02:27:27 PM:
> > > >
> > > > > And boy, the semantics of batch requests are pretty hairy. At 
the
> > > > end of
> > > >
> > > > > the day is there much benefit? Is each request in a batch atomic
> > > > and/or
> > > > > is the entire batch? (Do you have multiple levels of 
transactions?)
> > > > How
> > > > > do you cache a batch? (Boy, there's a long topic...)
> > > > >
> > > > > The HTTP overhead for multiple requests (made over the same TCP
> > > > > connection, mind you) is small (arguably, couldn't be much 
smaller)
> > > > and
> > > > > if you want atomic batches, locks do an ok job of it.
> > > > >
> > > > > I've certainly considered something like a PUT/PROPPATCH
> > > > combination
> > > > > (for example if you had "required dead properties") but it's
> > > > probably
> > > > > just easier to do a null lock and the two requests separately.
> > > > >
> > > >
> > >
> >
> 
Received on Thursday, 17 July 2003 18:03:27 GMT

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