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Introduction to Distributed Algorithms

Gerard Tel

Chapter 10

Snapshots - all with Video Answers

Educators

Chapter Questions

02:39

Problem 1

Consider the registration of the local snapshot of $p$ as an additional internal event $a_p$. Prove that
$$
S^* \text { is meaningful } \Longleftrightarrow \forall p, q: a_p \| a_q .
$$

Lourence Gonhovi
Lourence Gonhovi
Numerade Educator

Problem 2

Give a full description of the Lan-Yang algorithm, including mechanisms to enforce completion of the snapshot and construction of the channel states.

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Problem 3

Professor Prlwytszkowsky writes:
"Reading Chapter 10 improved my understanding of the algorithms of Chapter 8. In Safra's algorithm (Algorithm 8.7), for example, the handling of the token by $p$ should be seen as defining $p$ 's snapshot state. In the constructed snapshot all processes are passive, because the token is only handled by passive processes. So the computation of Pholds only requires a check of whether all channels are empty, to which end the token collects the sum of the message counts.
I do not understand, however, the role of the colors white and black, and how the meaningfulness of the snapshot is guaranteed."
Can you help the professor?

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