Why might the number of messages exchanged in a protocol be more significant to

Question

Why might the number of messages exchanged in a protocol be more significant to performance than the total amount of data sent? A voting algorithm for distributed mutual exclusion has each process VOTE for which process can hold the mutual exclusion. Each process can VOTE once at any given time; a given process will have access to the mutual exclusion if it has a majority of the votes. To enter a critical section at process i: Broadcast REQUEST, collect VOTEs Can enter critical section if collecting a majority of votes To leave a critical section, broadcast a RELEASE-VOTE to all processes who VOTEd for you. On receipt of REQUEST from process j, if you have not voted, VOTE for j; otherwise, add request to your queue. On receipt of RELEASE-VOTE, if your queue is not empty, vote for the process at the top of the queue. Answer the following questions for the voting protocol: What are the advantages of the protocol? What are the disadvantages of the protocol? How would you solve some of the disadvantages? What is the minimum number of messages exchanged? A client attempts to synchronize with a time server. It records the round-trip times and timestamps returned by the server in the table below. Which of these times should it use to set its clock? To what time should it set it? Estimate the accuracy of the setting with respect to the server' s clock. If it is known that the message transfer time in the system concerned is at least 8 ms, do your answers change? Deferred synchronous requests, such as Futures and Promises, return control to the Client as soon as the middleware has accepted the request. A deferred synchronous request returns some kind of Future rather than the result of the request. In this model, when a Client needs the result of a request it makes an explicit claim call on the Future that blocks until that result is available. How would you implement a Futures-based system with explicit claims above a synchronous RMI system? The first stage of answering this question is to think about how a synchronous method invocation works, and then to think about how, using synchronous methods, you would design a deferred synchronous implementation. You will want to think about the following concepts:

Explanation / Answer

Algorithm has an average performance in relation to the number of voters used – i.e., the algorithm scales extremely well to systems with large numbers of voters. This result is especially important given that the security and fault-tolerance (as opposed to performance) of a system using this algorithm rises linearly with the number of voters in the system.

Possibility of a Deadlock
Consider a situation when each candidate wins one-third of votes…..

One of the possible solutions would be :
Any process retrieves its REPLY message by sending an INQUIRY if the requestor is not currently executing in the critical section. The Requestor has to return the vote through a RELINQUISH message.

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