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0 pointsdelusional2y ago0 comments

> where the code doesn't have to be idempotent

Is that true? I don't think that makes any theoretical sense, since I'm pretty sure the whole thing relies on transparent retries for external calls.

If I complete some action that can't be retried and then die before writing it to the log (completing an action unatomically) there would seem to be no way for this to recover without idempotency.

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p10jkle2y ago

Absolutely, individual atomic side effects need to be idempotent. We can't solve the fundamental distributed system problem there (eg an HTTP 500 - did it actually get executed) However, the string of operations doesn't need to be idempotent - lets say your handler does 3 tasks A B C, and the machine dies at C. Only C will be re-executed. A and B need to be atomically idempotent, but once we move on, we don't start again

Critical point - its much easier to think about and test for the re-execution of C in a vacuum, than to test for A B C all re-executing in sequence, with a variable number of those having already executed before

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