Content placement in networks of similarity caches

Similarity caching systems have recently attracted the attention of the scientific community, as they can be profitably used in many application contexts, like multimedia retrieval, advertising, object recognition, recommender systems and online content-match applications. In such systems, a user request for an object.., which is not in the cache, can be (partially) satisfied by a similar stored object o', at the cost of a loss of user utility. In this paper we make a first step into the novel area of similarity caching networks, where requests can be forwarded along a path of caches to get the best efficiency-accuracy tradeoff. The offline problem of content placement can be easily shown to be NP-hard, while different polynomial algorithms can be devised to approach the optimal solution in discrete cases. As the content space grows large, we propose a continuous problem formulation whose solution exhibits a simple structure in a class of tree topologies. We verify our findings using synthetic and realistic request traces.

Automated summary

Similarity caching systems are gaining attention for their various applications, but balancing efficiency and accuracy is a challenge. The offline content placement problem is proven to be NP-hard, but polynomial algorithms can be used to approach optimal solutions in discrete cases. Continuous problem formulation in tree topologies offers simple structure solutions as the content space grows.