Unit II message ordering & snapshots message ordering and group communication: Message ordering paradigms

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MESSAGE ORDERING & SNAPSHOTS
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CS8603:Distributed Systems Department of CSE

6.14
(b) The main steps is as follows:
6. When A receives PROPOSED_TS(7) from C and PROPOSED_TS(10) from D, it
computes the final timestamp as max(7, 10) = 10, and sends FINAL_TS(10) to C and
D.
7.
When B receives PROPOSED_TS(9) from C and PROPOSED_TS(9) from D, it
computes the final timestamp as max(9, 9)= 9, and sends FINAL_TS(9) to C and D.
8.
C receives FINAL_TS(10) from A, updates the corresponding entry in temp_Q with the
timestamp, resorts the queue, and marks the message as deliverable. As the message is
not at the head of the queue, and some entry ahead of it is still undeliverable, the
message is not moved to delivery_Q.
9.
D receives FINAL_TS(9) from B, updates the corresponding entry in temp_Q by
marking the corresponding message as deliverable, and resorts the queue. As the
message is at the head of the queue, it is moved to delivery_Q.
10.
When C receives FINAL_TS(9) from B, it will update the corresponding entry in
temp_Q by marking the corresponding message as deliverable. As the message is at the
head of the queue, it is moved to the delivery_Q, and the next message (of A), which is
also deliverable, is also moved to the delivery_Q.

CS8603:Distributed Systems Department of CSE
2020 – 2021 2.
14
Jeppiaar Institute of Technology
11.
When D receives FINAL_TS(10) from A, it will update the corresponding entry in
temp_Q by marking the corresponding message as deliverable. As the message is at the
head of the queue, it is moved to the delivery_Q.
Figure An example to illustrate the three-phase total ordering algorithm. (a) A snapshot for PROPOSED_TS and
REVISE_TS messages. The dashed lines show the further execution after the snapshot. (b) The FINAL_TS
messages in the example.

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