Hidden Challenges on Teaching Web Software Engineering

8/6/2019 Hidden Challenges on Teaching Web Software Engineering

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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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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

Hidden Challenges on Teaching Web Software Engineering

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