Flash crowds can cripple a web site's performance. Since they are infrequent and unpredictable, these floods do not justify the cost of traditional commercial solutions. We describe Backslash, a collaborative web mirroring system run by a collective of web sites that wish to protect themselves from flash crowds. Backslash is built on a distributed hash table overlay and uses the structure of the overlay to cache aggressively a resource that experiences an uncharacteristically high request load. By redirecting requests for that resource uniformly to the created caches, Backslash helps alleviate the effects of flash crosse. We explore cache diffusion techniques for use in such a system and find that probabilistic forwarding improves load distribution albeit not dramatically.
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