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6.8.4 Cache consistency

 

The Cache employs TTL-based cache consistency, patterned after the Internet's Domain Naming System [19]. Because of this, the Cache can return stale data. Unfortunately, HTTP, Gopher, and FTP provide neither a means for owners to specify TTLs, nor a protocol to pass TTLs from servers to caches and clients gif. Hence, when the Harvest cache fetches an object from the object's home, it is forced to assign a default TTL. When the TTL expires, the cache discards the object. When a cache fetches an object from a parent or neighbor, it inherits the parent's remaining TTL. In a future release of Harvest we will implement a heuristic mechanism to set TTLs based on objects' last modification dates.

For measurements about the Cache's consistency mechanism (and other mechanisms with which we have experimented), see [9].



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Next: 6.8.5 Negative caching and Up: 6.8 Details of Cache Previous: 6.8.3 Unique object naming



Darren Hardy
Mon Apr 3 15:22:37 MDT 1995