Proceedings of the Sixth International Workshop on Web Caching and Content Distribution

OVERVIEW The International Web Content Caching and Distribution Workshop (WCW) is a premiere technical meeting for researchers and practitioners interested in all aspects of content caching, distribution and delivery on the Internet. The 2001 WCW meeting was held on the Boston University Campus. Building on the successes of the five previous WCW meetings, WCW01 featured a strong technical program and record participation from leading researchers and practitioners in the field. This report includes all the technical papers presented at WCW'01. Note: Proceedings of WCW'01 are published by Elsevier. Hardcopies of these proceedings can be purchased through the workshop organizers. As a service to the community, electronic copies of all WCW'01 papers are accessible through Technical Report BUCS‐TR‐2001‐017, available from the Boston University Computer Science Technical Report Archives at http://www.cs.bu.edu/techreps. [Ed.note: URL outdated. Use http://www.bu.edu/cs/research/technical-reports/ or http://hdl.handle.net/2144/1455 in this repository to access the reports.]Cisco Systems; InfoLibria; Measurement Factory Inc; Voler

Safe Speculative Replication

This article argues that commonly-studied techniques for speculative replication—such as prefetching or prepushing content to a location before it is requested there—are inherently unsafe: they pose unacceptable risks of catastrophic overload and they may introduce bugs into systems by weakening consistency guarantees. To address these problems, the article introduces SSR, a new, general architecture for Safe Speculative Replication. SSR specifies the mechanisms that control how data flows through the system and leaves as a policy choice the question of what data to replicate to what nodes. SSR’s mechanisms (1) separate invalidations, demand updates, and speculative updates into three logical flows, (2) use per-resource schedulers that prioritize invalidations and demand updates over speculative updates, and (3) use a novel scheduler at the receiver to integrate these three flows in a way that maximizes performance and availability while meeting specified consistency constraints. We demonstrate the SSR architecture via two extensive case studies and show that SSR makes speculative replication practical for widespread adoption by (1) enabling self-tuning speculative replication, (2) cleanly integratin

High throughput Byzantine fault tolerance

We argue for a simple change to Byzantine Fault Tolerant state machine replication libraries in order to provide high throughput. Traditional state machine replication based Byzantine fault tolerant (BFT) techniques provide high availability and security but fail to provide high throughput. This limitation stems from the fundamental assumption of generalized state machine replication techniques that all replicas execute requests sequentially in the same total order to ensure consistency across replicas. We propose a high throughput Byzantine fault tolerant architecture that uses application-specific information to identify and concurrently execute independent requests. Our architecture thus provides a general way to exploit application parallelism in order to provide high throughput without compromising correctness. Although this approach is extremely simple, it yields dramatic practical benefits. When sufficient application concurrency and hardware resources exist, CBASE, our system prototype, provides orders of magnitude improvements in throughput over BASE, a traditional BFT architecture. CBASE-FS, a Byzantine fault tolerant file system that uses CBASE, achieves twice the throughput of BASE-FS for the IOZone micro-benchmarks even in a configuration with modest available hardware parallelism.

Shruti: A Self-Tuning Hierarchical Aggregation System

Current aggregation systems either have a single inbuilt aggregation mechanism or require applications to specify an aggregation policy a priori. It is hard to predict the read and write access patterns in large systems and hence applications built on such systems suffer from inefficient network usage. We present Shruti, a system that demonstrates a general approach for self-tuning the aggregation aggressiveness to the measured workload in the system, thus optimizing the overall communication costs (e.g., the number of messages exchanged on read and write operations)