Tracing the Origins of the First Idempotency Key in Distributed Systems
I explored the history of idempotency keys to find their true origin, moving past popular assumptions about Stripe and AWS. While ancient systems like the Inca quipu offered similar guarantees, I discovered the first electronic implementation in a 1984 paper by Birrell and Nelson on Remote Procedure Calls at Xerox PARC. This journey reveals how fundamental distributed system concepts evolved from early research to modern API standards.
The call identifier serves two purposes. It allows the caller to determine that the result packet is
- saltcured
Some might call this pedantic, but I think physical reality provided us the earliest idempotency keys, which were natural keys in specific systems. Some effects are idempotent because they address physical reality in a way that converges or provides mutual exclusion.
The pigeon-hole principle isn't an instruction guide for birds, it just describes the reality of occupancy. An egg-tooth keeps pecking, escaping at most one egg. A dog may circle, but occupies at most one bed.
The real value of idempotence is being truly end-to-end. It is about the final effect being controlled, rather than about some message hop in the middle. In my opinion, the impulse to isolate it to a messaging layer is often misguided. It presupposes that the other layers don't also have similar failure modes.
It makes for a more robust system when you can elicit the desired idempotence from natural keys and occupancy rules. For example, the way REST can make creation idempotent when the name can be established ahead of the creation request, or deletion is idempotent when names are not reused.
- reactordev
The biggest misconception here is that the client or requester is responsible for the keys. They aren’t. They can be but ideally a signed response from the service with a key is ideal. Still, a client header key is better than no key.
In situations where it’s fire and forget, like payments, it’s fine to generate a deterministic key from the requesters side. In situations where transactions or escrow is in play, it’s best to request from the service so the service can orchestrate.
But I’m not a CTO, just an engineer. I can’t spin bad decisions into “features” like they can. Or small novel fixes as profound advances to the industry.
- jonhohle
Spoiler: the best free restaurant bread in America is cranberry walnut bread served at Le Diplomate in Washington, D.C., and Parc in Philadelphia. Second place, surprisingly, is Cheddar Bay biscuits at Red Lobster, and third is the dark wheat at Cheesecake Factory (which I usually like but, coincidentally, earlier this week I found lacking).
I don’t have access to the Atlantic, but I’d probably throw Cracker Barrel’s biscuits and cornbread in there, but I suppose those aren’t free.