A3Q1

[Ravi]

Hello,

I'm a little confused about question 1. The question implies that we
should be able to prove that the lamport timestamp on event e is smaller
than the lamport timestamp on event e' even if zero messages occur. How
is this possible? Say event e occurs on computer X, and event e' occurs
on computer Y. Furthermore, say absolutely no messages have passed
between X and Y. Say 10 events took place before event e happened on X
(there L(e) = 11) and say 5 events took place before event e' happened on
Y (so L(e') = 6). Since no messages pass between the two computers, isn't
such a case possible? Thanks in advance for your help,

Ravi

[Khuzaima Daudjee]

You have given a scenario where the events belong to different
processes. The question, however, does not specify which event belongs
to which process.

Khuzaima

[Khuzaima Daudjee]

Please see my post dated Mar 19 at around 12 noon.

Khuzaima

Kang Chu wrote:

> So what does the question mean? Are the events from the same process
> or different process?
>
> kang

[Asem Rustum]

Hello,

Shouldn't Question 1 say:
e --> e' => C(e) < C(e')

instead of:
e --> e' => C(e) --> C(e').

In other words, use the less-than sign <, instead of an arrow -->,
following the convention used in the textbook p. 254 for Lamport's logical
clocks.

Thanks,
Asem

[Zaid Masud]

I agree that the question seems to be using totally incorrect notation for
comparing C(e) and C(e'). But they have clarified in another post that for
the clock, "->" is the same as "<".

[Jin Xiao]

Yes, my earlier post have cleared that "-->" for the logical clock means
"<".

cheers,
Jin

[Filip Lazar]

So which notation should I use in my final answer? I think i've figured it
out, (hopefully), but I would like to ensure that whatever notation i use
is considered correct. Are they interchangeable? Also, for the purpose
of the final exam, should
there by questions where we would need to make use of this notation, which
should we use?

Thanks,

Filip

[Jin Xiao]

Hi Filip,

You may use either notation, they are both acceptable for this assignment.
In final exam, both notations are acceptable too.

Cheers,
Jin

[Ravi]

Can we assume e and e' are the events in which messages were actually
sent/received?

Thanks,
Ravi

[zaid....@gmail.com]

If e and e' are in the same processes then messages don't have to be
sent/received.

[Jin Xiao]

Hi Ravi,

You do not need to assume e and e' as the send and receive event to make a
valid induction. They could be any events.

cheers,
Jin