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INTRODUCTIONWith the increase of the internet traffic it badly
effected to users response time. As solution for that
web caching is use. Web caching has also advantagesand disadvantages.
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Why we need web cachingy Number of unique pages: 800M < X < 2.2B
y Number of unique web sites: 8,500,000
y static pages: %30 - %40
y pages revisited: %80
y expected hit-rate: %24-32%
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y Bandwidth
y
Latencyy Performance = Response Time
y Server Load
y Failure Redundancy
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What is web caching?Intermediary systems are used to temporarily
store information that maybe retrieved by multiple
users or by a same user multiple times
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Reverser xy
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Reverser xy
Intranet
Where
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Data CenterIS
cdn
cache
cache
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Reverser xy
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cache
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cdn
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Advantages of web cachingDocuments can be cached on the clients, the proxies, and the
servers. The effects of Web caching are two-fold. First, it has beenshown that caching documents can improve Web performance
significantly. There are several advantages of using Web caching.
y Web caching reduces bandwidth consumption, therebydecreases network traffic and lessens network congestion.
y
Web caching reduces access latency due to two reasons:y Frequently accessed documents are fetched from nearby proxy
caches instead of remote data servers, the transmission delay isminimized.
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y Web caching reduces the workload of the remote Web server bydisseminating data among the proxy caches over the wide areanetwork.
y If the remote server is not available due to the remote server's crash ornetwork partitioning, the client can obtain a cached copy at the proxy.Thus, the robustness of the Web service is enhanced.
y A side effect of Web caching is that it provides us a chance to analyzean organization's usage patterns.
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Disadvantages of web cachingy of clients a proxy can serve. An efficiency lower bound (i.e. the proxy
system is ought to be at least as efficient as using direct contact withthe remote The main disadvantage is that a client might be looking at
stale data due to the lack of proper proxy updating.y The access latency may increase in the case of a cache miss due to the
extra proxy processing. Hence, cache hit rate should be maximized andthe cost of a cache miss should be minimized when designing a cachingsystem.
y
A single proxy cache is always a bottleneck. A limit has to be set for thenumber servers)
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y should also be enforced.
y A single proxy is a single point of failure.
y Using a proxy cache will reduce the hits on the original remote server
which might disappoint a lot of information providers, since theycannot maintain a true log of the hits to their pages. Hence, they mightdecide not to allow their documents to be cacheable