The sharing of caches among Web proxies is an important technique to reduce Web traffic and alleviate network bottlenecks. Nevertheless it is not widely deployed due to the overhead of existing protocols. In this paper we demonstrate the benefits of cache sharing, measure the overhead of the existing protocols, and propose a new protocol called "summary cache". In this new protocol, each proxy keeps a summary of the cache directory of each participating proxy, and checks these summaries for potential hits before sending any queries. Two factors contribute to our protocol's low overhead: the summaries are updated only periodically, and the directory representations are very economical, as low as 8 bits per entry. Using trace-driven simulations and a prototype implementation, we show that, compared to existing protocols such as the Internet cache protocol (ICP), summary cache reduces the number of intercache protocol messages by a factor of 25 to 60, reduces the bandwidth consumption by over 50%, eliminates 30% to 95% of the protocol CPU overhead, all while maintaining almost the same cache hit ratios as ICP. Hence summary cache scales to a large number of proxies. (This paper is a revision of Fan et al. 1998; we add more data and analysis in this version.).

Summary cache: a scalable wide-area web cache sharing protocol

We estimated the world’s technological capacity to store, communicate, and compute information, tracking 60 analog and digital technologies during the period from 1986 to 2007. In 2007, humankind was able to store 2.9 × 10 20 optimally compressed bytes, communicate almost 2 × 10 21 bytes, and carry out 6.4 × 10 18 instructions per second on general-purpose computers. General-purpose computing capacity grew at an annual rate of 58%. The world’s capacity for bidirectional telecommunication grew at 28% per year, closely followed by the increase in globally stored information (23%). Humankind’s capacity for unidirectional information diffusion through broadcasting channels has experienced comparatively modest annual growth (6%). Telecommunication has been dominated by digital technologies since 1990 (99.9% in digital format in 2007), and the majority of our technological memory has been in digital format since the early 2000s (94% digital in 2007).

/pdf/the-world-s-technological-capacity-to-store-communicate-and-39dybc0mey.pdf

The World’s Technological Capacity to Store, Communicate, and Compute Information

Key-value stores are a vital component in many scale-out enterprises, including social networks, online retail, and risk analysis. Accordingly, they are receiving increased attention from the research community in an effort to improve their performance, scalability, reliability, cost, and power consumption. To be effective, such efforts require a detailed understanding of realistic key-value workloads. And yet little is known about these workloads outside of the companies that operate them. This paper aims to address this gap.To this end, we have collected detailed traces from Facebook's Memcached deployment, arguably the world's largest. The traces capture over 284 billion requests from five different Memcached use cases over several days. We analyze the workloads from multiple angles, including: request composition, size, and rate; cache efficacy; temporal patterns; and application use cases. We also propose a simple model of the most representative trace to enable the generation of more realistic synthetic workloads by the community.Our analysis details many characteristics of the caching workload. It also reveals a number of surprises: a GET/SET ratio of 30:1 that is higher than assumed in the literature; some applications of Memcached behave more like persistent storage than a cache; strong locality metrics, such as keys accessed many millions of times a day, do not always suffice for a high hit rate; and there is still room for efficiency and hit rate improvements in Memcached's implementation. Toward the last point, we make several suggestions that address the exposed deficiencies.

/pdf/workload-analysis-of-a-large-scale-key-value-store-26qh7uqcca.pdf

Workload analysis of a large-scale key-value store

Web caching is an important technique to scale the Internet. One important performance factor of Web caches is the replacement strategy. Due to specific characteristics of the World Wide Web, there exist a huge number of proposals for cache replacement. This article proposes a classification for these proposals that subsumes prior classifications. Using this classification, different proposals and their advantages and disadvantages are described. Furthermore, the article discusses the importance of cache replacement strategies in modern proxy caches and outlines potential future research topics.

/pdf/a-survey-of-web-cache-replacement-strategies-1h4qa1pui3.pdf

A survey of Web cache replacement strategies

This article presents a detailed workload characterization study of the 1998 World Cup Web site. Measurements from this site were collected over a three-month period. During this time the site received 1.35 billion requests, making this the largest Web workload analyzed to date. By examining this extremely busy site and through comparison with existing characterization studies, we are able to determine how Web server workloads are evolving. We find that improvements in the caching architecture of the World Wide Web are changing the workloads of Web servers, but major improvements to that architecture are still necessary. In particular, we uncover evidence that a better consistency mechanism is required for World Wide Web caches.

/pdf/a-workload-characterization-study-of-the-1998-world-cup-web-38km64wyjd.pdf

A workload characterization study of the 1998 World Cup Web site

The continued growth of the World-Wide Web and the emergence of new end-user technologies such as cable modems necessitate the use of proxy caches to reduce latency, network traffic and Web server loads. Current Web proxy caches utilize simple replacement policies to determine which files to retain in the cache. We utilize a trace of client requests to a busy Web proxy in an ISP environment to evaluate the performance of several existing replacement policies and of two new, parameterless replacement policies that we introduce in this paper. Finally, we introduce Virtual Caches, an approach for improving the performance of the cache for multiple metrics simultaneously.

https://www.hpl.hp.com/techreports/98/HPL-98-173.pdf

Evaluating content management techniques for Web proxy caches

Performance evaluation of Web proxy cache replacement policies

This paper presents a detailed workload characterization study of a World-Wide Web proxy. Measurements from a proxy within an Internet Service Provider (ISP) environment were collected. This ISP allows clients to access the Web using high-speed cable modems rather than traditional dialup modems. By examining this site we are able to evaluate the effects that cable modems have on proxy workloads.This paper focuses on workload characteristics such as file type distribution, file size distribution, file referencing behaviour and turnover in the active set of files. We find that when presented with faster access speeds users are willing to download extremely large files. A widespread increase in the transfer of these large files would have a significant impact on the Web. This behaviour increases the importance of caching for ensuring the scalability of the Web.

http://www.hpl.hp.com/techreports/1999/HPL-1999-48.pdf

Workload characterization of a Web proxy in a cable modem environment

An energy management system for one or more computer data centers (101-301), including a plurality of racks (110) containing electronic packages (112). The electronic packages (112) may be one or a combination of components such as, processors, microcontrollers, high-speed video cards, memories, semi-conductor devices, computer and the like. The energy management system includes a system controller (130) for distributing workload among the electronic packages (112). The system controller (130) is also configured to manipulate cooling systems (115) within the one or more data centers (101-301).

Rich Friedrich

Papers

Evaluating content management techniques for Web proxy caches

Performance evaluation of Web proxy cache replacement policies

Workload characterization of a Web proxy in a cable modem environment

Data center energy management system

Web server performance measurement and modeling techniques