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A simple distributed algorithm for small idempotent information

antirez.com

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Re: A simple distributed algorithm for small idempotent information

#11

Post by bch »

Knowing the Raft[0][1] protocol, I felt this post was disingenuous going on for its entire length, and only mentioning Raft basically as a footnote, w/ no other references.

I think Raft deserves a bit more prominence and credit here, Antirez.

  [0] (pdf) https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf
  [1] I kept reading thinking to myself repeatedly "This is just Raft".

Re: A simple distributed algorithm for small idempotent information

#12

Post by antirez »

bch wrote: post #11

Knowing the Raft[0][1] protocol, I felt this post was disingenuous going on for its entire length, and only mentioning Raft basically as a footnote, w/ no other references. I think Raft deserves a bit more prominence and credit here, Antirez. [0] (pdf) https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf [1] I kept reading thinking to myself repeatedly "This is just Raft".

In the very first part of the post: "The algorithm is mostly borrowed from Raft, however because of the premises it uses only a subset of Raft that is trivial to implement."

Maybe you only scanned the article.

Re: A simple distributed algorithm for small idempotent information

#13

Post by vishnugupta »

adolph wrote: post #2

Idempotence by example: Looking up some customer's name and address in a database are typically idempotent (in fact nullipotent), since this will not cause the database to change. Similarly, changing a customer's address is typically idempotent, because the final address will be the same no matter how many times it is submitted. However, placing an order for a car for the customer is typically not idempotent, since r…

While the wiki article seems to do a decent job of explaining mathematics behind idempotency it sheds no light on why it's so important in distributed systems. antirez talks about idempotency in sort of mathematical sense, though I could be wrong as I've just skimmed through the article.

Since failures are a norm in distributed systems one would want clients to retry a request without worrying about double updations (placing the order twice in the example above, debiting the money twice etc.,).

Just elaborate this further. Let's say the "place order" request didn't even reach the server. In this case client can just retry the request. However, if the request did reach the server but the response didn't reach the client then client can't safely retry without creating duplicate order. The problem here for the client is that there's no way for it to distinguish between a lost request vs lost response.

In such cases idempotency is achieved by requiring clients to send a unique identifier with each request. Server can now ensure that for a given request identifier the operation is performed just once.

Re: A simple distributed algorithm for small idempotent information

#14

Post by bch »

antirez wrote: post #12
bch wrote: post #11

Knowing the Raft[0][1] protocol, I felt this post was disingenuous going on for its entire length, and only mentioning Raft basically as a footnote, w/ no other references. I think Raft deserves a bit more prominence and credit here, Antirez. [0] (pdf) https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf [1] I kept reading thinking to myself repeatedly "This is just Raft".

In the very first part of the post: "The algorithm is mostly borrowed from Raft, however because of the premises it uses only a subset of Raft that is trivial to implement." Maybe you only scanned the article.

:) my apologies -- I started reading your introduction and then moved on to the meat of the article...

Re: A simple distributed algorithm for small idempotent information

#15

Post by antirez »

bch wrote: post #14
antirez wrote: post #12

Earlier quoted context omitted.

In the very first part of the post: "The algorithm is mostly borrowed from Raft, however because of the premises it uses only a subset of Raft that is trivial to implement." Maybe you only scanned the article.

:) my apologies -- I started reading your introduction and then moved on to the meat of the article...

np ;-) after all as an heavy HN reader I understand very well the impossibility to read whole posts...

Re: A simple distributed algorithm for small idempotent information

#16

Post by TempleOSV2 »

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