17-Comp-B10 Distributed Systems — National Examinations, December 2019. 3 hours, closed book, Casio/Sharp approved calculator only. Candidates were instructed to answer any five of the six questions, all carrying equal weight (20 marks each) and mostly requiring essay-format answers, with only the first five as they appear in the answer book marked; all six are answered below as a complete study resource.
Reference texts: Coulouris, Dollimore, Kindberg & Blair, Distributed Systems: Concepts and Design (5th ed.) — system models, client-server architecture and mobile/ubiquitous computing (ch. 1–2, 19), interprocess communication and remote invocation, RPC (ch. 4–5), operating system support and middleware (ch. 6–8), security (ch. 11), distributed file systems (ch. 12), transactions and concurrency control, distributed transactions and two-phase commit (ch. 13–14).
Check — Question 5(a) as printed. The paper prints transaction U as “U: x = write(i,55); write(j,66);” — assigning the result of a write to a variable is not meaningful pseudocode. Since the assigned name x is never subsequently read by U, this does not change the analysis below; U is treated as the two-operation transaction write(i,55); write(j,66), and T as x = read(i); write(j,44), exactly as printed.
