RE: GET, POST, and side-effects

On Thu, 4 Jan 1996, Paul Leach wrote:

> Note, finally, that it is not necessary for the same query to give the 
> same result _forever_ -- only that it give the same result for as long 
> as the Expires: and/or Cache-Control: headers say proxies are allowed 
> to believe it does.

It is not necessary even for a GET to return the same result, only that
the action of making the GET request won't change the result or have other
side-effects.

Any large constantly changing document repository can be expected to 
respond with a different result as document are added.  BUt the GET
doesn't cause this effect.

The cache-control mechanisms allow such a server to declare how long
the server finds it acceptable to provide the same response to the GET
no matter what the server would deliver itself. 'freshness' is a
judgement of the information provider which may choose to define
search results as static for 24 hours even though in fact they vary
by the second.

Other applications will use the same cache control mechanisms to forbid
caching because the risk associated with using inexact data is too 
great.

Dave Morris

Received on Friday, 5 January 1996 06:02:27 UTC