Collaborative caching of a requested object by a lower level node as a function of the caching status of the object at a higher level node

Abstract

A method and system of collaboratively caching information to allow improved caching decisions by a lower level or sibling node. In a caching hierarchy, the client and/or servers may factor in the caching status at the higher level in deciding whether to cache an object and which objects are to be replaced. The PICS protocol may be used to pass the caching information of some or all the upper hierarchy down the hierarchy. Furthermore, the caching status information can also be used to direct the object request to the closest higher level proxy which has potentially cached the object, instead of blindly requesting it from the next immediate higher level proxy. A selection policy used to select objects for replacement in the cache may be prioritized not only on the size and the frequency of access of the object, but also on the access time required to get the object if it is not cached. The selection policy may also include a selection weight factor wherein each object is assigned a selection weight based on its replacement cost, the object size and how frequently it is modified. Non-uniform size objects may be classified in ranges of selection weights having geometrically increasing intervals. Multiple LRU stacks may be independently maintained wherein each stack contains objects in a certain range of selection weights. In order to choose candidates for replacement, only the least recently used objects in each group need be considered.

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