Pipeline hinting revisited

[Brian Pane <[e-mail]>]

I've been thinking some more about request pipelining recently,
triggered by several observations:

- A significant number of real-world websites could be made faster via
widespread adoption of request pipelining (based on my study of
~15,000 sites in the httparchive.org corpus).
- A nontrivial fraction of mobile browsers are using pipelining
already, albeit not as aggressively as they could (based on Blaze's
study: http://www.blaze.io/mobile/http-pipelining-big-in-mobile/ )
- Client implementations that currently pipeline their requests are
using heuristics of varying complexity to try to decide when
pipelining is safe.  The list of conditions documented here is at the
complex end of the spectrum, and it's perhaps still incomplete:
https://bugzilla.mozilla.org/show_bug.cgi?id=599164

The key question, I think, is whether heuristics implemented on the
client side will end up being sufficient to detect safe opportunities
for pipelining.  If not, a server-driven hinting mechanism of the sort
proposed in Mark's "making pipelining usable" draft (
http://tools.ietf.org/html/draft-nottingham-http-pipeline-01 ) seems
necessary.

Anybody have additional experimental data on pipelining (including the
effectiveness of heuristics for turning pipelining on or off) that
they can share?

Thanks,
-Brian