[e2e] Number of persistent connections per HTTP server?

Venkat Padmanabhan padmanab at microsoft.com
Thu Oct 10 11:29:45 PDT 2002

I believe the reason the recommended number of persistent connections
per client was set to 2 rather than 1 was to prevent head-of-line
blocking. With a single connection (and in the absence of byte-range
requests), the transfer of a large object could block subsequent
requests for a significant length of time. With two connections, one can
confine the large transfers to one connection, keeping the other one
clear for short transfers. This is analogous to why a two-lane road is
far better than a single-lane one.


Venkat Padmanabhan
Microsoft Research
padmanab at microsoft.com

> -----Original Message-----
> From: Greg Minshall [mailto:minshall at acm.org]
> Sent: Wednesday, October 09, 2002 5:03 PM
> To: Spencer Dawkins
> Cc: end2end-interest at postel.org
> Subject: Re: [e2e] Number of persistent connections per HTTP server?
> Spencer,
> in 1996 or so there was a feeling that opening 4, say, parallel
> connections
> was evil.  possibly the http spec says "2" to mute the brickbats that
> might
> otherwise have been tossed its way because of the then prevailing
> i
> think 4 has always been the number most browsers use.  (i.e., i
> Netscape used 4 and others followed suit.)
> cheers, Greg Minshall

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