Measuring cache freshness by additive age

Motivated by the work of cache freshness by Cho and Garcia-Molina [2], we present a new metric called <i>additive age</i> as an extension of existing freshness metrics. The <i>additive age</i>, being formulated somewhat differently, deviates from existing freshness metrics in its ability to better quantify the impact of frequently updated content on cache freshness. Mathematical result shows that the long-run average <i>additive age</i> is proportional to λT², where λ is the change rate of source content, and <i>T</i> the refresh interval. This short paper briefly reviews the key elements of Cho and Garcia-Molina's work and simplifies their derivation by using renewal reward theory, with a focus on formulation of the notion of <i>additive age</i>.