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Interesting idea. Along those lines, I thought about returning a "redirect"
which points right back to the object that was sought in the first place.
I junked it when I realized that it violates the most basic principals of
congestion control!
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I see a potential problem with your suggestion which relates to relative
URLs. Unless the mirror site mirrors the entire original site, relative
URLs could break.
Another issue is synchronization. Suppose the primary site makes a change
to the document "web" resulting in link changes. Now let's say you're
reading around in the primary site's web, it gets busy, you get redirected
to the secondary site, and the link is invalid because the mirror site
hasn't been sync'ed since the changes at the primary.
-- Bob