Web Caching Research Articles

A protocol-independent technique for eliminating redundant network traffic

We present a technique for identifying repetitive information transfers and use it to analyze the redundancy of network traffic. Our insight is that dynamic content, streaming media and other traffic that is not caught by today's Web caches is nonetheless likely to derive from similar information. We have therefore adapted similarity detection techniques to the problem of designing a system to eliminate redundant transfers. We identify repeated byte ranges between packets to avoid retransmitting the redundant data. We find a high level of redundancy and are able to detect repetition that Web proxy caches are not. In our traces, after Web proxy caching has been applied, an additional 39% of the original volume of Web traffic is found to be redundant. Moreover, because our technique makes no assumptions about HTTP protocol syntax or caching semantics, it provides immediate benefits for other types of content, such as streaming media, FTP traffic, news and mail.

A stochastic model of TCP/IP with stationary random losses

We present a technique for identifying repetitive information transfers and use it to analyze the redundancy of network traffic. Our insight is that dynamic content, streaming media and other traffic that is not caught by today's Web caches is nonetheless likely to derive from similar information. We have therefore adapted similarity detection techniques to the problem of designing a system to eliminate redundant transfers. We identify repeated byte ranges between packets to avoid retransmitting the redundant data.

Herding cats: modelling Quality of Service for Internet applications

The art and science of tele–traffic modelling is quite mature. On the other hand, Internet traffic seems to defy all attempts to capture its essence in simple models. This is not so surprising when we consider that the Internet consists of a large number of self–organizing systems, each evolved almost independently, which is quite a different way to construct a network than the ground-up design associated with telecommunications. IP routing, TCP congestion control, Relative Transport Protocol playout and loss adaption, Web caching and load balancing, and user behaviour are all involved in a system of massive complexity. In this paper, we survey some of these mechanisms and some of the attempts to bring this unruly bunch of schemes into a more coherent whole. We argue that these attempts are misguided, and that the strength of the Internet design is in the loose organization of these components. As the commercial investors turn their eyes on the Internet with a view to pricing, we argue that they should take extreme care not to propose mechanisms that kill the goose that lays the golden egg. See http://www-mash.cs.berkeley.edu/ns/ for details about the network simulator. National Laboratory for Applied Network Research at http://www.nlanr.net. VBNS Network Topology at http://www.vbns.net/logical.html.

A scalable and efficient cooperative system for Web caches

The authors propose two novel algorithms that exploit the latest reports about Web usage. From the standpoint of cooperating caches, they propose a cooperation protocol that minimizes the associated network bandwidth, processing load, and storage consumption among caches.

Collaborative Web caching based on proxy affinities

With the exponential growth of hosts and traffic workloads on the Internet, collaborative web caching has been recognized as an efficient solution to alleviate web page server bottlenecks and reduce traffic. However, cache discovery, i.e., locating where a page is cached, is a challenging problem, especially in the fast growing World Wide Web environment, where the number of participating proxies can be very large. In this paper, we propose a new scheme which employs proxy affinities to maintain a dynamic distributed collaborative caching infrastructure. Web pages are partitioned into clusters according to proxy reference patterns. All proxies which frequently access some page(s) in the same web page cluster form an “information group”. When web pages belonging to a web page cluster are deleted from or added into a proxy's cache, only proxies in the associated information group are notified. This scheme can be shown to greatly reduce the number of messages and other overhead on individual proxies while maintaining a high cache hit rate. Finally, we employ trace driven simulation to evaluate our web caching scheme using three web access trace logs to verify that our caching structure can provide significant benefits on real workloads.

Proactive Web caching with cumulative prefetching for large multimedia data

Web proxy caching provides an effective way to reduce access latency and bandwidth consumption, and thus improve performance of the World Wide Web. Due to the simplicity of incorporating various types of data into the Web, non-negligible access for large multimedia data is observed. Large multimedia data transfer, requiring a long-lived connection with consecutive data transmissions, often fails over wide area networks. Repetitive attempts to fetch large objects through proxy caches would waste network resources with no success guaranteed. In this paper, we propose on-demand cumulative prefetching to enhance proxy caches for better data availability of large multimedia files. Our analysis shows that on-demand cumulative prefetching can be performed within a few trials with minimal additional bandwidth requirement. The experimental results demonstrate that the proposed scheme substantially reduces error rate and increases byte hit rate for large multimedia data.

Latency-sensitive hashing for collaborative Web caching

Many geographically distributed proxies are increasingly used for collaborative Web caching to improve performance. In hashing-based collaborative Web caching, the response times can be negatively impacted for those URL requests hashed into geographically distant or overloaded proxies. In this paper, we present and evaluate a latency-sensitive hashing scheme for collaborative Web caching. It takes into account latency delays due to both geographical distances and dynamic load conditions. Each URL request is first hashed into an anchor hash bucket, with each bucket mapping to one of the proxies. Secondly, a number of nearby hash buckets are examined to select the proxy with the smallest latency delay to the browser. Trace-driven simulations are conducted to evaluate the performance of this new latency-sensitive hashing. The results show that (1) with the presence of load imbalance due to skew in request origination or hot-spot references, latency-sensitive hashing effectively balances the load by hashing into geographically distributed proxies for collaborative Web caching, and (2) when the overall system is lightly loaded, latency-sensitive hashing effectively reduces latency delays by directing requests to geographically closer proxies.

World Wide Web caching: trends and techniques

Academic and corporate communities have been dedicating considerable effort to World Wide Web caching. When correctly deployed, Web caching systems can lead to significant bandwidth savings, server load balancing, perceived network latency reduction, and higher content availability. We survey the state of the art in caching designs, presenting a taxonomy of architectures and describing a variety of specific trends and techniques.

Optimal Broadcasting of Two Files over an Asymmetric Channel

We study the problem of scheduling files over a broadcast channel in an asymmetric environment. The goal is to minimize the mean response time for clients who access the broadcast channel. Asymmetric channels have gained a lot of attention because they are used to model wireless ccxnmunication, teletext systems, and web caching in satellite systems. This paper addresses the two-files case. We design a simple algorithm that defines the optimal schedule given the demand probability for each file. Our solution is extended to include other important factors, such as dependencies between files, variable-length files, and other extensions, such as different priorities for the clients. For all the above extensions, we prove the surprising result that there exists a simple optimal schedule. Such a schedule is composed of a repeated pattern of AA…AB, where A is the more “popular” file and B is the less “popular” file.

Adaptive-level memory caches on World Wide Web servers

Owing to the fast growth of World Wide Web (WWW), web traffic has become a major component of Internet traffics. Consequently, the reduction of document retrieval latency on WWW becomes more and more important. The latency can be reduced in two ways: reduction of network delay and improvement of web servers’ throughput. Our research aims at improving a web server’s throughput by keeping a memory cache in a web server’s address space. In this paper, we focus on the design and implementation of a memory cache scheme. We propose a novel web cache management policy named the adaptive-level policy that either caches the whole file content or only a portion of it, according to the file size. The experimental results show three things. First, our memory cache is beneficial since, under our experimental workloads, the throughput improvement can achieve 32.7%. Second, our cache management policy is suitable for current web traffic. Third, with the increasing popularity of multimedia files, our policy will outperform others currently used in WWW.

File popularity characterisation

A key determinant of the effectiveness of a web cache is the locality of the files requested. In the past this has been difficult to model, as locality appears to be cache specific. We show that locality can be characterised with a single parameter, which primarily varies with the topological position of the cache, and is largely independent of the culture of the cache users. Accurate cache models can therefore be built without any need to consider cultural effects that are hard to predict.

A workload characterization study of the 1998 World Cup Web site

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.

A survey of web caching schemes for the Internet

The World Wide Web can be considered as a large distributed information system that provides access to shared data objects. As one of the most popular applications currently running on the Internet, the World Wide Web is of an exponential growth in size, which results in network congestion and server overloading. Web caching has been recognized as one of the effective schemes to alleviate the service bottleneck and reduce the network traffic, thereby minimize the user access latency. In this paper, we first describe the elements of a Web caching system and its desirable properties. Then, we survey the state-of-art techniques which have been used in Web caching systems. Finally, we discuss the research frontier in Web caching.

The effect of Web caching on network planning

In this paper, the effect of Web caching on network planning, in the sense of bandwidth computation for the access link interconnecting the ISP's subnet with the Internet, is studied by means of simulations. The latency of a browser retrieving files is studied for given traffic characteristics, number of users, bandwidth of access link, and cache hit rate. From our analysis, we find that using a well-designed Web cache with a 50% hit rate is more effective than doubling the bandwidth for an ISP's access link to the Internet, with respect to decreasing retrieval latency. In other words, we can reduce half of the bandwidth of the access link by using Web caching without compromising retrieval latency. The results are very encouraging and useful to the ISPs, enterprises and universities that are planning to interconnect their Intranets with the Internet.

A scalable Web cache consistency architecture

The rapid increase in web usage has led to dramatically increased loads on the network infrastructure and on individual web servers. To ameliorate these mounting burdens, there has been much recent interest in web caching architectures and algorithms. Web caching reduces network load, server load, and the latency of responses. However, web caching has the disadvantage that the pages returned to clients by caches may be stale , in that they may not be consistent with the version currently on the server. In this paper we describe a scalable web cache consistency architecture that provides fairly tight bounds on the staleness of pages. Our architecture borrows heavily from the literature, and can best be described as an invalidation approach made scalable by using a caching hierarchy and application-level multicast routing to convey the invalidations. We evaluate this design with calculations and simulations, and compare it to several other approaches.

Web caching with consistent hashing

A key performance measure for the World Wide Web is the speed with which content is served to users. As traffic on the Web increases, users are faced with increasing delays and failures in data delivery. Web caching is one of the key strategies that has been explored to improve performance. An important issue in many caching systems is how to decide what is cached where at any given time. Solutions have included multicast queries and directory schemes. In this paper, we offer a new Web caching strategy based on consistent hashing. Consistent hashing provides an alternative to multicast and directory schemes, and has several other advantages in load balancing and fault tolerance. Its performance was analyzed theoretically in previous work; in this paper we describe the implementation of a consistent-hashing-based system and experiments that support our thesis that it can provide performance improvements.

A user-access model-driven approach to proxy cache performance analysis

World-Wide Web usage has experienced tremendous growth in recent years. This growth has resulted in a significant increase in network and server loads that have adversely affected user response times. Among many viable and available approaches to reducing user response time, Web caching has received considerable attention. The purpose of this paper is to present an empirically derived model of Internet user-access activity, and to demonstrate its usefulness for conducting model-driven discrete simulation studies of cache performance analysis. The user-access model is shown to be a reasonable representation of Internet activity, and the user-access approach to cache performance analysis is shown to be a favorable alternative to trace-driven simulation. A report on the accuracy of the model and a summary of the findings are presented.

Towards a better understanding of Web resources and server responses for improved caching

This work focuses on characterizing information about Web resources and server responses that is relevant to Web caching. The approach is to study a set of URLs at a variety of sites and gather statistics about the rate and nature of changes compared with the resource type. In addition, we gather response header information reported by the servers with each retrieved resource. Results from the work indicate that there is potential to reuse more cached resources than is currently being realized due to inaccurate and nonexistent cache directives. In terms of implications for caching, the relationships between resources used to compose a page must be considered. Embedded images are often reused, even in pages that change frequently. This result both points to the need to cache such images and to discard them when they are no longer included as part of any page. Finally, while the results show that HTML resources frequently change, these changes can be in a predictable and localized manner. Separating out the dynamic portions of a page into their own resources allows relatively static portions to be cached, while retrieval of the dynamic resources can trigger retrieval of new resources along with any invalidation of already cached resources.

Variable Qos from Shared Web Caches: User-Centered Design and Value-Sensitive Replacement

Due to differences in server capacity, external bandwidth, and client demand, some Web servers value cache hits more than others. Assuming that a shared cache knows the extent to which different servers value hits, it may employ a value-sensitive replacement policy in order to generate higher aggregate value for servers. We consider both the predictionand value aspects of this problem and introduce a novel value-sensitive LFU/LRU hybrid that biases the allocation of cache space toward documents whose origin servers value caching most highly. We compare our algorithm with others from the Web caching literature and discuss from an economic standpoint the problems associated with obtaining servers’ private valuation information.

H [formula omitted] N [formula omitted]: Network support for scaling of large-scale services

With the explosive growth of demand for services on the Internet, the networking infrastructure (routers, protocols, servers) is under considerable stress. Mechanisms are needed for current and future IP services to scale in a client-transparent way. We present H YDRA N ET, an infrastructure that allows to dynamically distribute IP services by placing service agents (caching agents, mirrors, replicas) that are under the server's control at strategic points in the internetwork. H YDRA N ET is based on replicating transport-level service access points (TCP or UDP ports in the case of IP) for transparent distribution or replication of IP services. Measurements on a local testbed show that the overhead of our scheme is small. This form of service access point replication is widely applicable. We use H YDRA NET to implement H YDRA W EB, a system for Web server replication to realize intelligent, client-transparent, Web caching. Similarly, H YDRA N ET can be used to implement highly fault-tolerant servers or application-level gateways.