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Comment by weitendorf | Hacker News Reader

Well, you have to either capture/eliminate/persist side effects and control the environment tightly, or it's limited in what it can do.

In a distributed or concurrent system, for full granularity, that can require specialized timing or virtualization techniques up to ensuring fully atomic snapshots and deterministic execution environments (and whether or not that properly models the SUT in real environments, or introduces bias/breaks the reproducibility in a way you care about)

Otherwise if you're only running against fixed checkpoints you have something closer to traces that maybe you could re-run or test against, in some cases, if you put in the work to set it up. In distributed systems that can be a lot of work so it's a bit vague if left unspecified. Because it's not enough to merely replay something if things can drift or don't accurately model the real system

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> Well, you have to either capture/eliminate/persist side effects and control the environment tightly, or it's limited in what it can do.

You really need to read up on durable executions before commenting. Your comment reads as if you are completely oblivious to them. Their whole point is benefiting from an execution model where your workflow is comprised of idempotent pure functions whose inputs and outputs are tracked by the durable task persistence.

It's a problem I've spent a lot of time on, just not through the products marketed like temporal. I commented on the article because it's about program replay with checkpointing which is similar to what I worked with/mentioned.

I didn't see the article mention idempotency anywhere, and you didn't in the original response to the guy who said it just sounded like a buzzword; atomic snapshotting with deterministic execution is literally how you make a program continuation an idempotent function!

And the article is about solving the problem at the language runtime level so it doesn't even do that. So it would be reasonable to assume it is a buzzword if it does not have the essential property you mentioned and I was referring to. I was not even intending to disagree with you but just add what would make it less of a buzzword in this kind of case.

For the sort of architecture described in the blog post, you're persisting the program rather than a log, so you only need idempotency between any two checkpoints. For a lot of apps that's easy to achieve if write the snapshot into the same transaction the user is using for application data, and if you create/propagate idempotency tokens to other services.

You don't need specialized timing or virtualization techniques.

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