war story: parallel(1) command

[D. Hugh Redelmeier]

| From: Christopher Browne <cbbrowne-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org>

| On Wed, Jul 31, 2013 at 9:24 AM, D. Hugh Redelmeier <hugh-pmF8o41NoarQT0dZR+AlfA at public.gmane.org> wrote:

| > The hashes we're talking about (long cryptographic hashes) make
| > accidental collisions practically impossible.  Git, for example,
| > assumes that.
| 
| I hope that comes with an "expect, but verify."

Nope.

Here's a relevant message in a thread on the subject:
  <http://marc.info/?l=git&m=115678778717621&w=2>
Context: a paper had just reported weaknesses in SHA-1.

| If it's a hard dependency, and there's no test, then your repository
| might get destroyed if a (highly improbable) collision did took place.

Right.

But then a creative memory (RAM or disk) error is way way more likely.

| It's tempting to say "no need to bother, [heat death of universe]...",
| but depending on how bad it is to have a collision, it may be somewhat
| important to check.

Well, that argument applies to the heat death of the universe.  Just
what are we doing about that?  Speeding it up by doing unnecessary
file compares?
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