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> The three hard problems in computer science: naming things, cache invalidation, and off-by-one errors

No, just two.

> EDIT: Doh, I can't believe I messed up the joke

Well, it is a hard problem..

And the three hard problems in distributed queues are:

2. In-order delivery

1. Once-only delivery

If someone notes that's only two problems, you can add that reliable delivery is the third.

That's a nice variation :)

I only saw one problem.

Actually, you didn't mess up the joke, you proved the point in a way that not much else could. This is exactly why it is a hard problem.

There are only two hard problems in computer science:

Cache invalidation

ParaOff-by-one

llelism errors