Re: Session-ID proposal

Jim Seidman (
Mon, 14 Aug 95 09:40:35 -0500

At 05:48 PM 8/10/95 EDT, Dave Kristol writes:
>I have assumed (erroneously?) that a caching proxy must send
>conditional GETs to the origin server. If so, there's already the cost
>of a connection. The State-Info (previously "Session-ID") can ride the
>request almost for free.

This isn't necessarily true. If the server sends "Expires" headers, then
the proxy can pretty safely avoid sending if-modified-since requests, for

Even without "Expires" headers, some caching proxies just use simple
algorithms to avoid doing a GET on each request, e.g. only re-requesting
text/* files if they're at least an hour old. This applies not only to
proxies, but also to clients with persistent caches such, if I have a
document still cached on my hard-drive from an access yesterday.

Given these considerations, and the slowly increasing use of "Expires"
headers, State-Info could be expensive indeed.

Jim Seidman, Senior Software Engineer
Spyglass Inc., 1230 E. Diehl Road, Naperville IL 60563