Distributed System Seminar 1

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fregoton
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225285
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Distributed System Seminar 1
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2013-06-28 10:23:43
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  1. What is the role of middleware in a distributed system?
    To enhance the distribution transparency that is missing in network operating systems. In other words, middleware aims at improving the single-system view that a distributed system should have
  2. Explain what is meant by (distribution) transparency and give examples of different types of transparency?
    Distribution transparency is the phenomenon by which distribution aspects in a system are hidden from users and applications. Examples include access transperency, location transparency, migration transparency, relocation transparency, replication transparency, concurrency transparency, failure transparency, and persistence transparency
  3. Why is it sometimes so hard to hide the occurrence and recovery from failures in a distributed system?
    It is generally impossible to detect whether a server is actually down, or that it is simply slow in responding. Consequently, a system may have to report that a service is not available, although, in fact, the server is just slow
  4. Why is it not always a good idea to aim at implementing the highest degree of transparency possible?
    Aiming at the highest degree of transparency may lead to a considerable loss of performance that users are not willing to accept
  5. Describe precisely what is meant by a scalable system. Scalability can be achieved by applying different techniques. What are these techniques?
    A system is scalable with respect to either its number of componenets, geographical size, or number and size of administrative domains, if it can grow in one or more of these dimensions without an unacceptable loss of performance. Scaling can be acheived through distribution, replication, and caching
  6. When a transaction is aborted, we have said that the world is restored to its previous state, as though the transaction had never happened. We lied. Give an example where resetting the world is impossible
    Any situation in which physical I/O has occurred cannot be reset. For example, if the process has printed some output, the ink cannot be removed from the paper. Also in a system that controls any kind of industrial process, it is usually impossible to undo work that has been done
  7. We argued that distribution transparency may not be in place for pervasive systems. This statement is not true for all types of transparencies. Give an example
    Think of migration transparency. In many pervasive systems, components are mobile and will need to re-establish connections when moving from one access point to another. Preferably, such handovers should be completely transparent. Likewise, it can be argued that many other types of transparencies should be supported as well. However, what should not be hidden is a user is possibly accessing resources that are directly coupled to the user's current environement

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