Mobility.- Mobility Aware Server Selection for Mobile Streaming Multimedia Content Distribution Networks.- Performance of PEPs in Cellular Wireless Networks.- Applications.- Edge Caching for Directory Based Web Applications.- Computing on the Edge: A Platform for Replicating Internet Applications.- Scalable Consistency Maintenance for Edge Query Caches.- Architectures.- Proxy+: Simple Proxy Augmentation for Dynamic Content Processing.- Multicast Cloud with Integrated Multicast and Unicast Content Distribution Routing.- A Large Enterprise Content Distribution Network: Design, Implementation and Operation.- Architectural Choices for Video-On-Demand Systems.- Multimedia.- Dynamic Cache Reconfiguration Strategies for a Cluster-Based Streaming Proxy.- Stream Engine: A New Kernel Interface for High-Performance Internet Streaming Servers.- Streaming Flow Analyses for Prefetching in Segment-Based Proxy Caching to Improve Delivery Quality.- Customization.- Subscription-Enhanced Content Delivery.- Cooperative Architectures and Algorithms for Discovery and Transcoding of Multi-Version Content.- User Specific Request Redirection in a Content Delivery Network.- Peer-to-Peer.- Friendships that Last: Peer Lifespan and its Role in P2P Protocols.- A Fine-Grained Peer Sharing Technique for Delivering Large Media Files Over the Internet.- Performance and Measurement.- Proxy-Cache Aware Object Bundling for Web Access Acceleration.- A Case for Dynamic Selection of Replication and Caching Strategies.- Link Prefetching in Mozilla: A Server-Driven Approach.- A Generalized Model for Characterizing Content Modification Dynamics of Web Objects.- Delta Encoding.- Server-Friendly Delta Compression for Efficient Web Access.- Evaluation of ESI and Class-Based Delta Encoding.
SERVER-FRIENDLY DELTA COMPRESSION FOR EFFICIENT WEB ACCESS (p. 303-304)
Anubhav Savant and Torsten Suel
CIS Department, Polytechnic University
Abstract
A number of researchers have studied delta compression techniques for improving the efficiency of web page accesses over slow communication links. Most of these schemes exploit the fact that updated web pages often change only very slightly, thus resulting in very small sizes for the transmitted deltas. However, these schemes are only applicable to a minority of page accesses, and require web or proxy servers to retain potentially many different outdated versions of pages for use as reference files in the encoding. Another approach, studied by Chan and Woo [4], encodes a page with respect to similar files located on the same web server that are already in the client's browser cache. Based on the latter approach, we study different delta compression policies for web access. Our emphasis is on web and proxy server-friendly policies that do not require the maintenance of multiple older versions of a page, but only use reference files accessed by the client within the last few minutes. We compare several policies for identifying appropriate reference files and evaluate their performance on a set of traces. We show that there are very simple policies that achieve significant benefits over gzip compression on most web accesses, and that can be efficiently implemented at web or proxy servers. We also study the potential of file synchronization techniques such as rsync [28] for web access.
1. Introduction
Delta compression (delta encoding) is the process of encoding a target file with respect to one or several, usually similar, referenceles. This encoding, called a delta, describes the target file in terms of the reference files, and a recipient that receives the encoding and already knows the reference files can thus efficiently reconstruct the target. Delta compression has numerous applications in scenarios where there are several versions of a file or many similar files, such as software revision control systems, distribution of software updates, content distribution networks, or efficient storage of related files. Several tools for delta compression, such as bdiff, vcdiff [10, 13], Xdelta [14], and zdelta [25], are freely available. We refer to [23] for an overview of delta compression techniques and applications.
1.1 Delta compression for Web access
A number of authors have proposed the use of delta compression techniques to improve the ef.ciency of web access [1, 4, 7, 9, 16, 17, 21, 27, 29]. In particular, when web pages are updated, they typically do not change by much, and thus delta compression can be used to very succinctly encode the difference between a new version of a web page and an outdated version already in the client's browser cache. Most proposals focus on encodings between different versions located at the same URL, which results in small sizes for the deltas but is restricted to pages that have been previously visited by the client. One exception is the work by Chan andWoo [4], which proposes to use as reference files other pages on the same site recently visited by the client, which tend to have a significant degree of similarity due to common layout features and HTML structure. In general, delta compression schemes for web access can be distinguished along the following axes.
