Architecture of proxy partial caching using HTTP for supporting interactive video and cache consistency

Abstract

Proxy partial caching, e.g. segment-based proxy caching or proxy prefix caching, partitions the object into nonoverlapping pieces. The proxy cache then treats each piece as an individual file when performing caching and replacing. Upon receipt of request to the object, the proxy cache delivers the cached portion to the client immediately to mask the start-up delay. However, two architectural challenges are confronted when implementing this technique in the web proxy software, e.g., Squid cache. The first challenge is related to caching video streams. Although not until recently, HTTP is recognized as an efficient method to support interactive video. Many fundamental issues are still required to be solved. To this end, we propose an approach of segment-based video streams retrieval and caching via HTTP byte-range requests to further mask the possible startup delay, enhance the interactive function "pause", and simplify the web proxy cache design. Proxy partial caching introduces the second architectural challenge called dirty-initial-segments problem, i.e. cached portion in the proxy cache is inconsistent with the original in the server. If this happens, the cached portion already delivered to the client cannot be concatenated with the latter portion from the server. To relieve this problem, we propose a novel algorithm called validating upon partial replacement, which synchronizes the operations of proactive consistency validation, partition and replacement performed upon an object. We show that our proposed algorithm bears the merit of controllable chance to disturb users, easily embedding into the existing web proxy cache software with minimum modification, and improving the cache performance.