some HLL comments
Jecel Mattos de Assumpcao Jr.
Tue, 7 Mar 1995 18:32:06 -0300
On Mon, 6 Mar 95 13:19 EST Raul Miller wrote:
> Francois-Rene Rideau
> On netscape, the "reload" icon should flush this cache; but I'd
> recommend you have a local copy of the whole Tunes distribution,
> and then use the GNU patch utility to update it. Patch 0.0.0.9 is
> just out !
> Nope. This is one of the issues you have to deal with in a
> distributed system: computational integrity with distributed data.
> [And my "favorite" hobby horse: many people with computer science
> training are used to thinking in terms of "atomic" operations which
> maintain computational integrity, but distributed systems need some
> form of instancing instead.]
This is what I spent most of 1993 and half of 94 think of in the Merlin
project. I still can't handle replication very well, but I am working
> The problem here is that Jecel does not have direct access to external
> HTTP servers. Instead, an http query is handled by a local server
> which caches query results for some period of time. During that time
> period, the locally cached copy is used. This saves communications
> bandwidth when compared to fetching the same text from remote sites
> every time someone looks at it.
The problem is that the local server has lots of space for the cache
and tries to be smart ( but fails ) at guessing when a page might have
been changed or not. I can bypass the local server if I use Mosaic
rather than Netscape, but it isn't a very good solution at 1200 bps.
> There's several ways around this caching mechanism. The "right way"
> is to issue a unique id to web pages when they change. Typically,
> this means incrementing a version counter (or generating some sort of
> hash code).
The problem goes beyond caching. The browser shows links you have read
in a different color from those you haven't seen yet. If a page changes,
the browser still tells you that you have already looked at it. Ted
Nelson's Xanadu didn't have this problem, I think.
> Another workaround is to fetch enough data from the web to flush the
> cache of the server. However, this isn't necessarily easy (or even a
> good idea). For instance, think about fetching several gigabytes of
> information (for a server with a big local disk) across a 14.4 slip
14400! You're lucky...