Whoops!: a clustered Web cache for DSM systems using memory mapped networks

Abstract

We present Whoops!, a clustered Web cache prototype based on SciFS, a distributed shared memory (DSM) that benefits from the high performances and the remote addressing capabilities of memory mapped networks like Scalable Coherent Interface (SCI). Whoops! uses the DSM for all Web cache management and cache storage. Using a memory mapped network and a DSM programming model allows us to investigate a new algorithm to distribute and handle requests. We present a new implementation of TCP handoff that directly maps remote TCP/IP stacks through the network. This technique reduces processor overhead and forwards TCP acknowledgements in few microseconds. We have also designed parallel pull-based LRU (PPBL), an efficient request distribution algorithm for use with DSM systems. The decision is distributed over all nodes thus providing better scalability. PPBL supports multi-frontend environments letting the DSM handle data distribution. Finally, Whoops! implements on the fly compression when fetching documents from the Web and on the fly decompression when sending documents to clients. We show how this technique can reduce paging activity in the DSM and improve overall cache performance.