Re: [tcpm] draft-minshall-nagle

[Joe Touch <[e-mail]>]

On 6/3/2014 8:20 PM, Wesley Eddy wrote:
> On 6/3/2014 1:07 PM, Joe Touch wrote:
...
>> My point is that even by the time of this paper, it was well-understood
>> that Nagle should not be used in these environments. The paper cites
>> 1999 personal communication with Jim Gettys for this, but it was
>> well-known long before it was recited as an issue in this 1996 paper:
>> http://ccr.sigcomm.org/archive/1997/apr97/ccr-9704-heidemann.pdf
>
> Even before that!  RFC 1122 (from 1989) says:
>
>     Some applications (e.g., real-time display window
>     updates) require that the Nagle algorithm be turned
>     off, so small data segments can be streamed out at the
>     maximum rate.

I saw that, but it's more than for displays; it's actually anything 
*interactive* where the data unit is longer than one byte (e.g., Unicode 
telnet!).

>> The use case cited is quite dated - network news has been largely
>> abandoned. Is there a currently relevant use case for this approach, and
>> given that interactive apps already should be disabling Nagle, how much
>> will it help?
>
>
> I agree that disabling Nagle for "interactive" flows should be a
> recognized best current practice.  (assuming they're aiming for
> a packets/segments per second rate that isn't absurd)
>
> I think this would be a part of the "TCP Usage Guidelines"
> analogue to RFC 5405 (for UDP) that Lars once thought about.
>
> Since Nagle is on by default in many OSes, and deciding to turn
> it off means a developer has to know what it is, and that it's
> even there to be turned off,

I didn't think O_NODELAY was all that cryptic...


> the Minshall tweak to Nagle does
> seem to make it "more friendly" default to a diversity of
> application behaviors (small writes, or odd patterns of writes),
> while retaining the benefit of conserving packet count.
>
> I've noticed some people seem to have a tendency to disable Nagle
> automatically, whether or not that's really necessary, since
> maybe it bit them once in the distant past, and was difficult to
> debug or understand.  The Minshall flavor stands a better chance
> of not indoctrinating people against Nagle this way.

Nagle is useful in a very small use case that no longer exists - it's 
rare that we have interactive traffic that we know can be split at a 
byte boundary.

> That said, this is not a burning problem.

Agreed.

Joe