Paxos Agreement - Computerphile
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- Опубліковано 26 кві 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
This isn't an example. It's an abstraction in dire need of an example in order to ground it.
crystal clear until, bob came along with a higher id, then it became clear as mud
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!
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.
Great Videos Computerphile! Best chain of informative channels that you have got here with Brady and stuff!
Haven't you covered this before?
Nice explanation, very straight forward and easy to understand!
This is the simplest explanation of Paxos i've found yet. Great job!
Finally. I've been waiting for this video for a very long time. Thanks for the simple explanation, as always.
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
Looks like a fault-tolerant variant of 2-phase-commit protocol used to handle distributed transactions.
A very nice explanation, thank you!
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 ;-)
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 it's like a semaphore over a network with error correction? Neat.
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.
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.
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
"Is Alice stuffed"
What happens if there's an even number of nodes and half fail? Is that considered a majority?
It looked pretty much like 2PC(Phase Commit) protocol!
Why did the title change?
I have the lock!
What happens when all of the computers that were majority fail? Looks like then we have outdated data.
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?
Genuinely get confused 🤔...
no subtitles ??
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.
The changing numbers... and I think she's going a little all over the place. Interesting video though.
Hum, this reminds me of the Rust programming language...
Double digits! Also First.
You aren't first.
FIRST!!!!!!!111
Lmao no
next time a little bit brighter please
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!!!!
This reminds me very much of the bitcoin blockchain. Presumably one took inspiration from the other.
FIRST!