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Politecnico di Milano Distributed Systems Questions a.a. 2018-2019 Author Tommaso Scarlatti Reviewer Emanuele Chioso December 26, 2018 Contents 1 Disclaimer 2 2 Modeling 3 3 Communication 5 4 Naming 8 5 Consistency and Replication 10 6 Synchronization 14 7 Peer to Peer 19 8 Fault tolerance 22 9 Big Data 26 10 Security 28 1 1 Disclaimer This is unofficial material. These are possible answers to the questions of the exams of the Distributed Systems course in Politecnico di Milano. The main idea is to use these questions as a support while studying the slides provided by the professor. Feel yourself free to use and enhance these questions. 2 2 Modeling (3) Describe the mobile code architectural style and the type of technologies that support them. Mobile code is an architectural style based on the ability of relocating components of an application at run-time. With components here we mean code or both code and state of the execution. There are different models depending on the original and final position of resources: • Remote evaluation: site A sends a request to site B and attach its code. Site B then process the data using the received code and send it back to site A. • Code on demand: site A has data and requests to site B the code and once received it executes it. A concrete example is JavaScript executed in the web browser. • Mobile agent: agent A migrates to site B bringing both the code and the compu- tational resources. Once arrived, it continues executing the code. CREST(Computational REST) joins together the concepts of REST with mobile code. We can differentiate between two types of mobility: strong mobility is the ability of a system to allow migration of both the code and the execution state of an executing unit to a different computational environment, weak…