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RE: Interest in standardizing Batch methods?

From: Clemm, Geoff <gclemm@rational.com>
Date: Mon, 7 Jan 2002 22:57:45 -0500
Message-ID: <3906C56A7BD1F54593344C05BD1374B105577350@SUS-MA1IT01>
To: WebDAV <w3c-dist-auth@w3.org>
Like Greg, I'd like to see some evidence that this is not
a problem that is more generally solved by pipelining requests.

Cheers,
Geoff

-----Original Message-----
From: Greg Stein [mailto:gstein@lyra.org]
Sent: Monday, January 07, 2002 9:33 PM
To: Jim Whitehead
Cc: WebDAV
Subject: Re: Interest in standardizing Batch methods?


On Fri, Jan 04, 2002 at 01:11:03PM -0800, Jim Whitehead wrote:
>...
> To address these performance issues, several "Batch" methods were
developed
> as relatively simple extensions to existing WebDAV methods. Switching
> Outlook Web Access to use these methods resulted in approximately an order
> of magnitude performance increase (obviously, the performance benefit of
> going from N round-trips to 1 round trip depends on N). From the user
> perspective, the observed elapsed time for executing an operation went
from
> multiple seconds down to close to a second (depending on latency, of
> course). It was a signficant performance improvement. The batch methods
are:

I wonder whether the performance suffered because the requests were
performed in a request/response fashion, rather than as a series of
pipelined requests. If you can pipeline requests, not waiting for an answer,
then a series of DELETE operations is simply a "larger request" and then you
handle a "larger response". Yes, each request/response has more overhead
than a batched operation.

Personally, I'm going to guess they didn't pipeline requests, so a batch
mechanism was a must to get around deficiencies in their protocol stack.


That said, it is important to recognize the overhead in a sequence of, say,
DELETE requests and their responses, relative to a potential batch
operation. Specifically, you're going to have a lot of duplicate headers on
the requests and responses (there are no bodies in this case). How much does
this pose over a batch delete with a list of URLs? Maybe 3x or 4x in the
number of bytes? Maybe 10x? When you're talking over a modem (which is
typically the case for MSFT's Hotmail servers), then that 10x can be rather
significant.

Ah, it's all a numbers game. Personally, I'm not interested in batch
operations. I would guess that most of their benefit is obviating by
pipelining requests.

Cheers,
-g

ps. yes, this is mostly supposition; I'm not about to sit down and start
measuring byte counts and network traffic; I don't know whether they were or
were not pipelining; but my intuition tells me "no" and that pipelining is
the answer...

-- 
Greg Stein, http://www.lyra.org/
Received on Monday, 7 January 2002 23:38:39 GMT

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