DS_10_tut_4_sol

# DS_10_tut_4_sol - with the Lamport’s clock e1,1(1,0,0 e...

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CS3283 Distributed Systems Tutorial 4 Time Synchronization II Some points for further considerations … - Differences between logical time and absolute time - The purposes, requirement and definition of maintaining logical time - Difference between partial ordering and total ordering - The rules for Lamport logical clock - Totally-ordered multicasting - The uses and limitation of Lamport logical clock - The rules for vector clock - The tradeoffs of using vector clock comparing with Lamport logical clock Question 1 What is the main limtation of the Lamport clock as comparing with the vector clock? Limitation: if time-stamp(e) > time-stamp(e’), we cannot tell which one are executed first. With the vector clock, we may be able to determine the precedence. Question 2 (i) Use the vector clock to assign time-stamps to the events of the three processes. Using the example events in the figure to explain the benefits and cost of using the vector clock comparing
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Unformatted text preview: with the Lamport’s clock. e1,1 (1,0,0); e 1,2 (2,1,0); e1,3 (3,1,0) e2,1 (0,1,0); e2,2 (0,2,2) e3,1 (0,0,1); e3,2 (0,0,2); e3,3 (3,1,3) Benefits: In Lamport logical clock, if time-stamp(e) > time-stamp(e’), we cannot tell which one are executed first. With the vector Lamport clock, we may be able to determine the precedence. For example, for events e1,1 with a clock reading of (1,0,0) and e3,1 with a clock reading of (0,0,1), we cannot tell their execution order. However, for events e3,2 and e2,2, based on their vector clock, we can determine that e3,2 is occurred before e2,2. The main cost of using vector clocks is higher costs in communication and management of the clocks. P1 P2 P3 e1,1 e1,2 e1,3 e2,1 e2,2 e3,1 e3,2 e3,3...
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