A case for delay-conscious caching of Web documents
01 Sep 1997-Vol. 29, pp 997-1005
TL;DR: This paper presents a new, delay-conscious cache replacement algorithm LNC-R-W3 which maximizes a performance metric called delay-savings-ratio and compares it with other existing cache replacement algorithms, namely LRU and LRU-MIN.
Abstract: Caching at proxy servers plays an important role in reducing the latency of the user response, the network delays and the load on Web servers. The cache performance depends critically on the design of the cache replacement algorithm. Unfortunately, most cache replacement algorithms ignore the Web's scale. In this paper we argue for the design of delay-conscious cache replacement algorithms which explicitly consider the Web's scale by preferentially caching documents which require a long time to fetch to the cache. We present a new, delay-conscious cache replacement algorithm LNC-R-W3 which maximizes a performance metric called delay-savings-ratio. Subsequently, we test the performance of LNC-R-W3 experimentally and compare it with the performance of other existing cache replacement algorithms, namely LRU and LRU-MIN.
Citations
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TL;DR: This article proposes a classification for proposals for cache replacement that subsumes prior classifications and discusses the importance of cache replacement strategies in modern proxy caches and outlines potential future research topics.
Abstract: 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.
767 citations
Additional excerpts
...LNC-R-W3 [Scheuermann et al. 1997]....
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05 Oct 1999
TL;DR: This paper first describes the elements of a Web caching system and its desirable properties, then the state-of-art techniques which have been used in Web caching systems are surveyed, and the research frontier in Web cache is discussed.
Abstract: 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.
759 citations
Cites background from "A case for delay-conscious caching ..."
...LeastNormalized CostReplacement (LCN-R) [70] em- ploys a rational function of the access frequency, the transfer time cost and the size....
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...Least Normalized Cost Replacement (LCN-R) [70] employs a rational function of the access frequency, the transfer time cost and the size....
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21 Mar 1999
TL;DR: It is argued that the placement of web proxy is critical to the performance and the optimal placement policy of web proxies for a target web server in the Internet is investigated and this can be modeled a dynamic programming problem.
Abstract: Web caching or web proxy has been considered as the prime vehicle of coping with the ever-increasing demand for information retrieval over the Internet, the WWW being a typical example. Existing work on web proxy has primarily focused on content based caching; relatively less attention has been given to the development of proper placement strategies for the potential web proxies in the Internet. In this paper, we argue that the placement of web proxies is critical to the performance and further investigates the optimal placement policy of web proxies for a target web server in the Internet. The objective is to optimize a given performance measure for the target web server subject to system resources and traffic pattern. Specifically, we are interested in finding the optimal placement of multiple web proxies (M) among potential sites (N) under a given traffic pattern. We show this can be modeled a dynamic programming problem. We further obtain the optimal solution for the tree topology using O(N/sup 3/M/sup 2/) time.
471 citations
Cites background from "A case for delay-conscious caching ..."
...Unfortunately, both do little towards improving overall network performance [ 13 ]....
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IBM1
TL;DR: This paper gives an overview of caching policies designed specifically for Web objects and provides a new algorithm of their own, regarded as a generalization of the standard LRU algorithm.
Abstract: With the recent explosion in usage of the World Wide Web, the problem of caching Web objects has gained considerable importance. Caching on the Web differs from traditional caching in several ways. The nonhomogeneity of the object sizes is probably the most important such difference. In this paper, we give an overview of caching policies designed specifically for Web objects and provide a new algorithm of our own. This new algorithm can be regarded as a generalization of the standard LRU algorithm. We examine the performance of this and other Web caching algorithms via event- and trace-driven simulation.
377 citations
TL;DR: A unified cache maintenance algorithm, LNC-R-WS-U, is described, which integrates both cache replacement and consistency algorithms and considers in the eviction consideration the validation rate of each document, as provided by the cache consistency component of LNC.R-W3-U.
Abstract: Caching at proxy servers is one of the ways to reduce the response time perceived by World Wide Web users. Cache replacement algorithms play a central role in the response time reduction by selecting a subset of documents for caching, so that a given performance metric is maximized. At the same time, the cache must take extra steps to guarantee some form of consistency of the cached documents. Cache consistency algorithms enforce appropriate guarantees about the staleness of the cached documents. We describe a unified cache maintenance algorithm, LNC-R-WS-U, which integrates both cache replacement and consistency algorithms. The LNC-R-WS-U algorithm evicts documents from the cache based on the delay to fetch each document into the cache. Consequently, the documents that took a long time to fetch are preferentially kept in the cache. The LNC-R-W3-U algorithm also considers in the eviction consideration the validation rate of each document, as provided by the cache consistency component of LNC-R-WS-U. Consequently, documents that are infrequently updated and thus seldom require validations are preferentially retained in the cache. We describe the implementation of LNC-R-W3-U and its integration with the Apache 1.2.6 code base. Finally, we present a trace-driven experimental study of LNC-R-W3-U performance and its comparison with other previously published algorithms for cache maintenance.
211 citations
Cites background or methods from "A case for delay-conscious caching ..."
...Several cache replacement algorithms tailored to the proxy cache environment have been published [1], [4], [5], [26], including our own work [ 24 ]....
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...Two very similar cost-based algorithms for delay sensitive cache replacement have been independently published in [ 24 ], [26]....
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...We compared the performance of LNC-R-W3-U against plain LRU, LRU-MIN [1], and LNC-R-W3 [ 24 ]....
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...3.1 Optimal Cache Replacement Although it has been frequently pointed out that cache replacement algorithms for proxy servers should somehow reflect document sizes and the delays to fetch documents into the cache [1], [4], [5], [ 24 ], [26], it is not a priori clear how to combine these metrics into a single cost function....
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...The published work on the topic usually considers the two algorithms as two separate mechanisms and studies one of the two in isolation [1], [4], [7], [11], [17], [5], [18], [ 24 ], [26], [16]....
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References
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Proceedings Article•
03 Sep 1996TL;DR: The design of an intelligent cache manager for sets retrieved by queries called WATCHMAN, which is particularly well suited for data warehousing environment, and achieves a substantial performance improvement in a decision support environment when compared to a traditional LRU replacement algorithm.
Abstract: Data warehouses store large volumes of data which are used frequently by decision support applications. Such applications involve complex queries. Query performance in such an environment is critical because decision support applications often require interactive query response time. Because data warehouses are updated infrequently, it becomes possible to improve query performance by caching sets retrieved by queries in addition to query execution plans. In this paper we report on the design of an intelligent cache manager for sets retrieved by queries called WATCHMAN, which is particularly well suited for data warehousing environment. Our cache manager employs two novel, complementary algorithms for cache replacement and for cache admission. WATCHMAN aims at minimizing query response time and its cache replacement policy swaps out entire retrieved sets of queries instead of individual pages. The cache replacement and admission algorithms make use of a profit metric, which considers for each retrieved set its average rate of reference, its size, and execution cost of the associated query. We report on a performance evaluation based on the TPC-D and Set Query benchmarks. These experiments show that WATCHMAN achieves a substantial performance improvement in a decision support environment when compared to a traditional LRU replacement algorithm.
165 citations
"A case for delay-conscious caching ..." refers background in this paper
...The high response time perceived by Web clients is caused primarily by the long communication delays, although other factors (such as slow service times) also contribute....
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...…Di si - size of document Di di - delay to fetch document Di to cache In order to maximize the delay-savings ratio, the above statistics are combined into one performance metric, called profit, defined as (2) profit(Di) = (li * di) / si LNC-R selects for replacement the least profitable documents....
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01 May 1996
TL;DR: This paper considers performance issues related to dimensioning and caching, and advocates the use of novel cache replacement algorithms that explicitly take document size and network load into account so as to minimize the retrieval time perceived by clients.
Abstract: The quality of the service provided by the World Wide Web, namely convenient access to a tremendous amount of information in remote locations, depends in an important way on the time required to retrieve this information. This time in turn depends on a number of parameters, in particular the load at the server and in the network. Overloads are avoided by carefully dimensioning the server (so that it has enough resources such as CPU power and disk space to handle expected requests) and the network (so that it has enough resources such as bandwidth and buffers to transport requests and replies), and by using mechanisms such as caching that minimize the resource requirements of user requests. In this paper, we consider performance issues related to dimensioning and caching. Our contribution is twofold. Regarding dimensioning, we advocate the use of time series analysis techniques for Web traffic modeling and forecasting. We show using experimental data that quantities of interest such as the number of Web requests handled by a server, or the amount of data retrieved per hour by a server, can be accurately modeled with time series such as seasonal ARIMA models. We then use these models to make medium-term predictions of client requests characteristics (number of such requests and size of document retrieved), which in turn can be used as a basis for dimensioning decisions. Regarding caching, we advocate the use of novel cache replacement algorithms that explicitly take document size and network load into account so as to minimize the retrieval time perceived by clients.
110 citations
01 May 1996
TL;DR: It is shown that even a small amount of main memory that is used as a document cache, is enough to hold more than 60% of the documents requested, and that traditional file system cache management methods are inappropriate for managing Main Memory Web caches.
Abstract: An increasing amount of information is currently becoming available through World Wide Web servers. Document requests to popular Web servers arrive every few tens of milliseconds at peak rate. To reduce the overhead imposed by frequent document requests, we propose the notion of caching a World Wide Web server's documents in its main memory (which we call Main Memory Web Caching). We show that even a small amount of main memory (512 Kbytes) that is used as a document cache, is enough to hold more than 60% of the documents requested. We also show that traditional file system cache management methods are inappropriate for managing Main Memory Web caches, and may result in poor performance. Based on trace-driven simulations of several server traces we quantify our claims, and propose a new cache management that dynamically adjusts itself to the clients' request pattern and cache size. We show that our policy is robust over a variety of parameters and results is better overall performance.
100 citations
"A case for delay-conscious caching ..." refers background or methods in this paper
...Several studies of Web reference patterns show that Web clients exhibit a strong preference for accessing small documents [6, 7, 9, 11]....
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...Subsequently, we test the performance of LNC-R-W3 experimentally and compare it with the performance of other existing cache replacement algorithms, namely LRU and LRU-MIN....
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