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Re: Caching and callbacks

From: Tai Jin <tai@nexus.hpl.hp.com>
Date: Tue, 3 Sep 1996 11:11:54 -0700
Message-Id: <199609031811.AA005864314@nexus.hpl.hp.com>
To: peterson@austin.ibm.com
Cc: fielding@avron.ICS.UCI.EDU, frystyk@w3.org, hallam@w3.org, jg@w3.org, mogul@pa.dec.com, timbl@hq.lcs.mit.edu, www-talk@w3.org
Another problem with callbacks is if the proxy is unreachable when the
server performs the callback.  And for scaling purposes, the server
would have to restrict the use of callbacks to proxies (no browsers)
or to some subset of proxies.

The overhead of maintaining all the callback state is probably not
worth the benefit of getting current content for most types of
content.  I would suggest a selective callback mechanism where only
certain types of content use callbacks.

Content which is updated on a regular schedule or have a known expiry
date do not require callbacks since the Expires: header will work just
fine for them.  And most other content is not so important that
serving a stale page is going to be a problem (e.g., my personal
page).

So callbacks should only be used for content which is updated in an
adhoc manner and which cannot afford to be served stale without
causing an inconvenience or worse (e.g., bus schedule information).
The question is whether the amount of content in this category is
small enough that a callback scheme could be feasible from a
scalability perspective.  And you still have to deal with the issues
that were mentioned before.

...tai
Received on Tuesday, 3 September 1996 14:12:26 GMT

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