Performance Modeling of Proxy Cache Servers

Jelen disszertáció keretében a Proxy Cache szerverek hatékonyságát vizsgáltam meg. A disszertációban bemutattam az általunk általánosított Proxy Cache szerver modellt majd megvizsgáltam, hogy milyen paraméterek mellett éri meg Proxy Cache szervert üzemeltetni. További általánosításként megvizsgáltam azt az esetet is, amikor a Proxy Cache szerver valamint a Web szerver nem megbízható. A dolgozatban tanulmányoztam azt az esetet is, amikor az érkezési folyamatok nem Poisson folyamat, hanem úgynevezett GI - General interarrival" folyamat, melyet az érkezési időközök várható értékével és a relatív szórásnégyzetével jellemzünk, valamint a kiszolgálási idő bármilyen általános eloszlású lehet. Az így kapott modellben a rendszerparaméterek kiszámításához a GI/G/1 approximációt használtam. Végül megvizsgáltam hogyan milyen hatással van a heterogén forgalom a Proxy Cache szerverek hatékonyságára. In this dissertation I described the mathematical model of Proxy Cache servers and I studied the conditions under which installing a Proxy Cache server becomes beneficial. I also analyze how various factors affect the performance of a Proxy Cache server. Than, I generalize the performance model of the Proxy Cache server using a more realistic case when the Proxy Cache server and the remote Web server are unreliable. Later I analyse the case when the arrival process is a general (GI) arrival process characterised by a mean arrival rate and a squared coeficient of variation (SQV) of the inter-arrival time and the service time may have any general distribution. To obtain the response times I used the GI/G/1 approximation. Than I examine the performance behavior of a Proxy Cache server when we use heterogeneous trafic. In this thesis we describe the modified multi-class queuing network model of the Proxy Cache server

On the Intrinsic Locality Properties of Web Reference Streams

There has been considerable work done in the study of Web reference streams: sequences of requests for Web objects. In particular, many studies have looked at the locality properties of such streams, because of the impact of locality on the design and performance of caching and prefetching systems. However, a general framework for understanding why reference streams exhibit given locality properties has not yet emerged. In this work we take a first step in this direction, based on viewing the Web as a set of reference streams that are transformed by Web components (clients, servers, and intermediaries). We propose a graph-based framework for describing this collection of streams and components. We identify three basic stream transformations that occur at nodes of the graph: aggregation, disaggregation and filtering, and we show how these transformations can be used to abstract the effects of different Web components on their associated reference streams. This view allows a structured approach to the analysis of why reference streams show given properties at different points in the Web. Applying this approach to the study of locality requires good metrics for locality. These metrics must meet three criteria: 1) they must accurately capture temporal locality; 2) they must be independent of trace artifacts such as trace length; and 3) they must not involve manual procedures or model-based assumptions. We describe two metrics meeting these criteria that each capture a different kind of temporal locality in reference streams. The popularity component of temporal locality is captured by entropy, while the correlation component is captured by interreference coefficient of variation. We argue that these metrics are more natural and more useful than previously proposed metrics for temporal locality. We use this framework to analyze a diverse set of Web reference traces. We find that this framework can shed light on how and why locality properties vary across different locations in the Web topology. For example, we find that filtering and aggregation have opposing effects on the popularity component of the temporal locality, which helps to explain why multilevel caching can be effective in the Web. Furthermore, we find that all transformations tend to diminish the correlation component of temporal locality, which has implications for the utility of different cache replacement policies at different points in the Web.National Science Foundation (ANI-9986397, ANI-0095988); CNPq-Brazi

A Literature Survey of Cooperative Caching in Content Distribution Networks

Content distribution networks (CDNs) which serve to deliver web objects (e.g., documents, applications, music and video, etc.) have seen tremendous growth since its emergence. To minimize the retrieving delay experienced by a user with a request for a web object, caching strategies are often applied - contents are replicated at edges of the network which is closer to the user such that the network distance between the user and the object is reduced. In this literature survey, evolution of caching is studied. A recent research paper [15] in the field of large-scale caching for CDN was chosen to be the anchor paper which serves as a guide to the topic. Research studies after and relevant to the anchor paper are also analyzed to better evaluate the statements and results of the anchor paper and more importantly, to obtain an unbiased view of the large scale collaborate caching systems as a whole.Comment: 5 pages, 5 figure

Basis Token Consistency: A Practical Mechanism for Strong Web Cache Consistency

With web caching and cache-related services like CDNs and edge services playing an increasingly significant role in the modern internet, the problem of the weak consistency and coherence provisions in current web protocols is becoming increasingly significant and drawing the attention of the standards community [LCD01]. Toward this end, we present definitions of consistency and coherence for web-like environments, that is, distributed client-server information systems where the semantics of interactions with resource are more general than the read/write operations found in memory hierarchies and distributed file systems. We then present a brief review of proposed mechanisms which strengthen the consistency of caches in the web, focusing upon their conceptual contributions and their weaknesses in real-world practice. These insights motivate a new mechanism, which we call "Basis Token Consistency" or BTC; when implemented at the server, this mechanism allows any client (independent of the presence and conformity of any intermediaries) to maintain a self-consistent view of the server's state. This is accomplished by annotating responses with additional per-resource application information which allows client caches to recognize the obsolescence of currently cached entities and identify responses from other caches which are already stale in light of what has already been seen. The mechanism requires no deviation from the existing client-server communication model, and does not require servers to maintain any additional per-client state. We discuss how our mechanism could be integrated into a fragment-assembling Content Management System (CMS), and present a simulation-driven performance comparison between the BTC algorithm and the use of the Time-To-Live (TTL) heuristic.National Science Foundation (ANI-9986397, ANI-0095988