Paxos Agreement - Computerphile
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- čas přidán 26. 04. 2016
- The Democracy of computer collaboration, PAXOS is a method for ensuring networked computers reach agreement. Heidi Howard of the University of Cambridge Computer Laboratory explains.
/ computerphile
/ computer_phile
This video was filmed and edited by Sean Riley.
Computer Science at the University of Nottingham: bit.ly/nottscomputer
Computerphile is a sister project to Brady Haran's Numberphile. More at www.bradyharan.com
crystal clear until, bob came along with a higher id, then it became clear as mud
This isn't an example. It's an abstraction in dire need of an example in order to ground it.
the thing that bothers me here is that she doesn't explain anything about the IDs. are they randomly generated at joining times, built upon ranking or time bound?
+luciusandco Depends. The algorithm must produce a potentially infinite sequence of values and have a means to compare them. So for example you could start with "a" as the first key, then "aa", then "aaa" and so on measuring the length of the key as comparator. Or you just start at zero and count upwards.
This was the hardest assignment I ever did in school. AI was easier than paxos
Great video!
PAXOS: The official operating system of the Penny Arcade eXpo. 😸
PAXOS, & Vecotor Clocks some of the hardest concepts in Distributed Systems! Both by Leslie Lamport. You guys should snag and interview with HIM!
Great Videos Computerphile! Best chain of informative channels that you have got here with Brady and stuff!
Haven't you covered this before?
can this be used for Angel-only encryption? Where several systems have pieces of the key, but a majority need to agree before the thing can be decrypted
When I had distributed systems class my professor said paxos is so complex that nobody's able to implement it the way Lamport described
Nice explanation, very straight forward and easy to understand!
This is the simplest explanation of Paxos i've found yet. Great job!
Looks like a fault-tolerant variant of 2-phase-commit protocol used to handle distributed transactions.
Which node generates the system-wide id's, such that they are guaranteed to be unique? And if any node can generate the new id, how is the lock for that authority negotiated, so that no two nodes attempt to generate the same id?
So what if node 3 commits Alice, but fails after committing just to node 4. Then node 4 fails, and then Bob comes along and commits with a lower id to node 5 while node 3 and4 are still down. Bob presumably gets the key using nodes 5, 6 and 1. But if nodes 3 and 4 then come back online and nodes 1 and 6 go offline, then alice asks for the lock again... The majority of nodes think that she has the lock and she has the highest id... So presumably she gets the lock.
Example of locking: When in the office you want to change an excel file that is on the shared drive but you can't open it because someone else has it open. You're welcome.
A very nice explanation, thank you!
So it's like a semaphore over a network with error correction? Neat.
Finally. I've been waiting for this video for a very long time. Thanks for the simple explanation, as always.
Raft is a more straight-forward solution and I think it's more widely used.
I can't say if raft is more widely used, but i've encountered it on more systems than paxos. Most universities (I can only speak for the US) tend to focus on paxos as a part of distributed/parallel systems education. Raft was mentioned in the course I took, but paxos was the "teaching algorithm" so to speak.
+Matthew Mitchell Yes. Paxos was known as notoriously hard to understand and implement right, but of course Lamport through that was so much nonsense he had to write his "Paxos Made Simple", thereby proving himself wrong ;-)
"Is Alice stuffed"
The Paxos algorithm was actually developed from the tiny Greek island of Paxos' voting system I believe. I've been on holiday there many times :D
What happens if there's an even number of nodes and half fail? Is that considered a majority?
What happens when all of the computers that were majority fail? Looks like then we have outdated data.
Why did the title change?
It looked pretty much like 2PC(Phase Commit) protocol!
I have the lock!
Sounds like something VMSclusters have been doing since the 1980s.
42th comment. This is the ultimate number as a comment
How is this 'protocol' (paxos) logic realized? SSL/TLS? Or is this a 'special' protocol?
you guys need to buy an ipad to draw these diagrams and stream it to a mac or PC over airplay to record them, instead of re-drawing.
Genuinely get confused 🤔...
no subtitles ??
Double digits! Also First.
no kudos to the editor. I tried to focus on her drawing and the editor switched all the time between her, her drawings and a digital version of it. Pick one thing!!!!
The changing numbers... and I think she's going a little all over the place. Interesting video though.
You aren't first.
Lmao no
Hum, this reminds me of the Rust programming language...
next time a little bit brighter please
FIRST!!!!!!!111
This reminds me very much of the bitcoin blockchain. Presumably one took inspiration from the other.
FIRST!