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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01 Jan 2007
TL;DR: A space of proxy evaluation methodologies based on source of workload used and form of algorithm implementation is defined and their locations are surveyed.
Abstract: Proxy caches are increasingly used around the world to reduce bandwidth requirements and alleviate delays associated with the World-Wide Web In order to compare proxy cache performances, objective measurements must be made In this paper, we define a space of proxy evaluation methodologies based on source of workload used and form of algorithm implementation We then survey recent publications and show their locations within this space
28 citations
Cites background from "A case for delay-conscious caching ..."
...Nain [NLN98], Kurcewicz, Sylwestrzak and Wierzbicki [KSW98] and Scheuermann, Shim and Vingralek [ SSV97 , SSV98, SSV99] all utilize trace-based simulation to evaluate difierent cache management algorithms....
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TL;DR: This article proposes an optimal solution using dynamic programming to compute the optimal locations for caching multiple versions of the same multimedia object in transcoding proxies for tree networks, and significantly outperforms existing models that consider Web caching in transcoded proxies either on a single path or at individual nodes.
Abstract: Transcoding is a promising technology that allows systems to effect a quality-versus-size tradeoff on multimedia objects. As audio and video applications have proliferated on the Internet, caching in transcoding proxies has become an important technique for improving network performance, especially in mobile networks. This article addresses the problem of coordinated enroute multimedia object caching in transcoding proxies for tree networks. We formulate this problem as an optimization problem based on our proposed model, in which multimedia object caching decisions are made on all enroute caches along the routing path by integrating both object placement and replacement policies and cache status information along the routing path of a request is used to determine the optimal locations for caching multiple versions of the same multimedia object. We propose an optimal solution using dynamic programming to compute the optimal locations. We also extend this solution to solve the same problem for several constrained cases, including constraints on the cost gain per node and on the number of versions to be placed. Our model is evaluated on different performance metrics through extensive simulation experiments. The implementation results show that our model significantly outperforms existing models that consider Web caching in transcoding proxies either on a single path or at individual nodes.
28 citations
01 Jun 2000
TL;DR: This paper shows that the commonly-used distribution of reference interarrival times is predominantly determined by the power law governing the popularity of documents in a request stream, and proposes a new and robust metric that enables accurate delineation between locality due to popularity and that due to temporal correlation.
Abstract: Temporal locality of reference in Web request streams emerges from two distinct phenomena: the popularity of Web objects and the temporal correlation of requests. Capturing these two elements of temporal locality is important because it enables cache replacement policies to adjust how they capitalize on temporal locality based on the relative prevalence of these phenomena. In this paper, we show that temporal locality metrics proposed in the literature are unable to delineate between these two sources of temporal locality. In particular, we show that the commonly-used distribution of reference interarrival times is predominantly determined by the power law governing the popularity of documents in a request stream. To capture (and more importantly quantify) both sources of temporal locality in a request stream, we propose a new and robust metric that enables accurate delineation between locality due to popularity and that due to temporal correlation. Using this metric, we characterize the locality of reference in a number of representative proxy cache traces. Our ndings show that there are measurable di erences between the degrees (and sources) of temporal locality across these traces, and that these di erences are e ectively captured using our proposed metric. We illustrate the signi cance of our ndings by proposing and evaluating a novel Web cache replacement policy|called GreedyDual*|which exploits both long-term popularity and short-term temporal correlation in an adaptive fashion. Our trace-driven simulation experiments show the superior performance of GreedyDual* when compared to other Web cache replacement policies.
26 citations
Cites background or methods from "A case for delay-conscious caching ..."
...The LNC-W3 algorithm [35, 36] is a generalization of LRU-K....
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...Generalizations for variable cost=size include LNC-W3 [35, 36], GDSF [3], GD-LFU in [26], GDSP [25], and LRV [28]....
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Patent•
IBM1
TL;DR: Disclose as mentioned in this paper is a system, method, and program for accessing files maintained in a server that is capable of being accessed over a network, where a request is received for a file maintained in the server and a determination is then made as to whether a copy of the requested file is stored in a storage system.
Abstract: Disclose is a system, method, and program for accessing files maintained in a server that is capable of being accessed over a network. A request is received for a file maintained in the server. A determination is then made as to whether a copy of the requested file is stored in a storage system. The system then determines a delay time associated with retrieving the copy of the requested file from the storage system after determining that the storage system includes the copy of the requested file. A determination is then made as to whether the delay time exceeds a maximum delay time. The system retrieves the requested file from the storage system to return to the request after determining that the delay time does not exceed the maximum delay time. Alternatively, the system retrieves the requested file from the server over the network to return to the request after determining that the delay time exceeds the maximum delay time.
25 citations
IBM1
TL;DR: This paper shows how to achieve a generalization of the LRU policy for the case of caching web documents in such a way that the disk placement and fragmentation issue is handled efficiently.
Abstract: With the increasing popularity of the world wide web, it may be desirable to store copies of popular documents in proxy caches and thus diminish the delay times for URL requests. Web documents have to be treated as indivisible objects for the purpose of caching. In this paper we study the problem of caching web documents on disks. In web apphcations, the objects are of non-homogeneous size, and this leads to a problem in physical placement in any scheme which tries to emulate LRU. One solution is to use the FIFO scheme which simplifies the disk placement issue, because the order of physical placement can be completely dictated by the order of entry of an object into the cache. In this paper, we show how to achieve a generalization of the LRU policy for the case of caching web documents in such a way that the disk placement and fragmentation issue is handled efficiently.
25 citations
References
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01 Jun 1993
TL;DR: The LRU-K algorithm surpasses conventional buffering algorithms in discriminating between frequently and infrequently referenced pages, and adapts in real time to changing patterns of access.
Abstract: This paper introduces a new approach to database disk buffering, called the LRU-K method The basic idea of LRU-K is to keep track of the times of the last K references to popular database pages, using this information to statistically estimate the interarrival times of references on a page by page basis Although the LRU-K approach performs optimal statistical inference under relatively standard assumptions, it is fairly simple and incurs little bookkeeping overhead As we demonstrate with simulation experiments, the LRU-K algorithm surpasses conventional buffering algorithms in discriminating between frequently and infrequently referenced pages In fact, LRU-K can approach the behavior of buffering algorithms in which page sets with known access frequencies are manually assigned to different buffer pools of specifically tuned sizes Unlike such customized buffering algorithms however, the LRU-K method is self-tuning, and does not rely on external hints about workload characteristics Furthermore, the LRU-K algorithm adapts in real time to changing patterns of access
1,033 citations
"A case for delay-conscious caching ..." refers methods in this paper
...We call the resulting cache replacement algorithm for proxy caching on the Web LNC-R-W3....
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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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22 Jan 1996
TL;DR: The design and performance of a hierarchical proxy-cache designed to make Internet information systems scale better are discussed, and performance measurements indicate that hierarchy does not measurably increase access latency.
Abstract: This paper discusses the design and performance of a hierarchical proxy-cache designed to make Internet information systems scale better. The design was motivated by our earlier trace-driven simulation study of Internet traffic. We challenge the conventional wisdom that the benefits of hierarchical file caching do not merit the costs, and believe the issue merits reconsideration in the Internet environment.
The cache implementation supports a highly concurrent stream of requests. We present performance measurements that show that our cache outperforms other popular Internet cache implementations by an order of magnitude under concurrent load. These measurements indicate that hierarchy does not measurably increase access latency. Our software can also be configured as a Web-server accelerator; we present data that our httpd-accelerator is ten times faster than Netscape's Netsite and NCSA 1.4 servers.
Finally, we relate our experience fitting the cache into the increasingly complex and operational world of Internet information systems, including issues related to security, transparency to cache-unaware clients, and the role of file systems in support of ubiquitous wide-area information systems.
853 citations
"A case for delay-conscious caching ..." refers methods in this paper
...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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Book•
01 Oct 1973
TL;DR: As one of the part of book categories, operating systems theory always becomes the most wanted book.
Abstract: If you really want to be smarter, reading can be one of the lots ways to evoke and realize. Many people who like reading will have more knowledge and experiences. Reading can be a way to gain information from economics, politics, science, fiction, literature, religion, and many others. As one of the part of book categories, operating systems theory always becomes the most wanted book. Many people are absolutely searching for this book. It means that many love to read this kind of book.
670 citations
"A case for delay-conscious caching ..." refers methods in this paper
...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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01 Apr 1995
TL;DR: This paper presents a descriptive statistical summary of the traces of actual executions of NCSA Mosaic, and shows that many characteristics of WWW use can be modelled using power-law distributions, including the distribution of document sizes, the popularity of documents as a function of size, and the Distribution of user requests for documents.
Abstract: The explosion of WWW traffic necessitates an accurate picture of WWW use, and in particular requires a good understanding of client requests for WWW documents. To address this need, we have collected traces of actual executions of NCSA Mosaic, reflecting over half a million user requests for WWW documents. In this paper we present a descriptive statistical summary of the traces we collected, which identifies a number of trends and reference patterns in WWW use. In particular, we show that many characteristics of WWW use can be modelled using power-law distributions, including the distribution of document sizes, the popularity of documents as a function of size, the distribution of user requests for documents, and the number of references to documents as a function of their overall rank in popularity (Zipf''s law). In addition, we show how the power-law distributions derived from our traces can be used to guide system designers interested in caching WWW documents. --- Our client-based traces are available via FTP from http://www.cs.bu.edu/techreports/1995-010-www-client-traces.tar.gz http://www.cs.bu.edu/techreports/1995-010-www-client-traces.a.tar.gz
624 citations
"A case for delay-conscious caching ..." refers background or methods in this paper
...The browsers were temporarily adjusted so that all requests were re-directed to a proxy where for each referenced URL, we recorded the size the of requested document and the difference between the time when the request for document Di arrives at the proxy and the time when Di is actually fetched to…...
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...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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18 Jul 1995
TL;DR: This work assesses the potential of proxy servers to cache documents retrieved with the HTTP protocol, and finds that a proxy server really functions as a second level cache, and its hit rate may tend to decline with time after initial loading given a more or less constant set of users.
Abstract: As the number of World-Wide Web users grow, so does the number of connections made to servers. This increases both network load and server load. Caching can reduce both loads by migrating copies of server files closer to the clients that use those files. Caching can either be done at a client or in the network (by a proxy server or gateway). We assess the potential of proxy servers to cache documents retrieved with the HTTP protocol. We monitored traffic corresponding to three types of educational workloads over a one semester period, and used this as input to a cache simulation. Our main findings are (1) that with our workloads a proxy has a 30-50% maximum possible hit rate no matter how it is designed; (2) that when the cache is full and a document is replaced, least recently used (LRU) is a poor policy, but simple variations can dramatically improve hit rate and reduce cache size; (3) that a proxy server really functions as a second level cache, and its hit rate may tend to decline with time after initial loading given a more or less constant set of users; and (4) that certain tuning configuration parameters for a cache may have little benefit.
495 citations
"A case for delay-conscious caching ..." refers methods in this paper
...The trace contains about 20K requests....
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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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