Distributed Systems 5.2: Quorums

[elvis]

absolutely gold, got to understand the whole quorum thing in less than 10 minutes ! thanks Martin!

[andrewsouthpaw]

7:18 that diagram is so simple yet helped me understand the r + w > n formula *way* better. 👏

[zhouyuan]

Probability of faults
Read-after-write consistency [2:06]
Quorum (2 out of 3) [3:58]
Read and write quorums [5:41]
r + w > n
Read repair [8:19]

[dwyanewan]

This is the author of the famous book Designing Data-Intensive Applications (DDIA)!

[RKelly]

Your are such a legend, thank you so much for this video. I went through my lecture notes continuously, but none of it even remotely came close to how well you explained it. Honestly, couldn't thank you enough and that example was brilliant.

[debasishmallick]

Absolutely pleasure watching it. Nice way of presenting it. Thank you Martin !!

[Endredos]

Pleasantly clear and simple explanation. Thank you!

[mrmaker]

very good and well defined explanation. Thanks!

[omar_m_othman]

Beautiful explanation, thank you so much!

[Lller]

Thank you so much for the video, I found it very helpful in understanding the Sloppy Quorum!

[welltv]

Vielen Dank fuer die tolle Erklaerung!

[sarkersunzidmahmud]

thanks a lot, Martin for the clear explanation.

[SJM]

Good job Martin, thanks for shedding light on this topic!

[abcdef-fotf]

at 4:30 what if one of the acknowledgement also fails. We could have another node read the responses and use it, but the initial write doesn't know it's successful, would it write again? it could potentially overwrite the other nodes' work if it does that

[xxbighotshotxx]

Much appreciated. Thank you! You made this incredibly simple to understand

[adityadeo]

How following problems are solved in replication?

Question 1. Suppose there are 3 nodes.
Variable 'x' has initial value of 0 on all the nodes.
Client triggers operation 'x = 1'.
The operation is successfull on node 1 but fails on nodes 2 and 3 (due to unrelated issue e.g. broken network).
Hence the update operation as a whole has failed but the data on node 1 has changed.
This will lead to inconsist reads - If the quorum includes node 1 then the read(x) will return 1, otherwise read(x) will return 0.


Question 2. In case of multiple variables that form an invariant, one variable might be updated successfully while the other one encounters an issue.

[nealdi]

Question: what if when the quorum write 1 out of 3 succeeded, but 2 failed to write, how can we rollback the one that write ok? Because we already return the client that write if failed.

[ronakjacob]

dude i died, but thnx for explaining i might pass my exams now

[good-vibes-inc]

Are there any real world examples of such data replication exist? It multiplies number of your datastores that you should pay for :c

[iyadelwy]

Thank you.
- 10 egyptian procrastinators the night before the exam