Re: jk/tag-contains (Re: What's cooking in git.git (Jul 2010, #05; Wed, 28))

Jeff King [off-list ref] writes:

On Sat, Jul 31, 2010 at 01:07:03AM -0500, Jonathan Nieder wrote:

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The third one is where we start defaulting things to "assume no more
than 1 day of clock skew by default", which can cause incorrect answers
in the face of skew.

I think the default should be something that (just barely) works
correctly for linux-2.6.git.

I am tempted by that (and it is why I made the fourth patch to actually
calculate the worst skew). But my concern is that there are projects
with even worse skew. Maybe that is unfounded.

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The fourth is just an illustrative patch for per-repo skew detection.

I have been hoping for a chance to look these over, time hasn’t come my
way yet.

Sorry, but I am right in the middle of phisically moving, so my weekend
and evening git time has been nil recently.

It just a git-skew program to calculate the skew, but doesn't do
anything fancy like detect-on-gc. However, it would be nice to have
somebody sanity check the algorithm. Looking at it again, I think it
might actually miss some skew if the skewed commit can be reached in
multiple ways.

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Additional things to do (this is mostly a note to myself):

 - refuse to commit with a timestamp long before any parent

Agreed.

You need to be careful here, though.  What if you pulled from somebody
whose clock is set grossly in the future?

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 - check slop and warn about it in fsck (maybe your patch does this
   already)

No, it doesn't, but it is something we should probably do.

I wonder if we can make fsck to notice a commit with a wrong timestamp
(i.e. older than some of its parents) and make a note of it (hopefully
they are miniscule minority)---then during the revision traversal when we
hit such a commit, we perhaps ignore its timestamp (pretending as if its
timestamp is one of its children or parent---I haven't thought about the
details, but the note fsck leaves can record what adjusted timestamp
should be used) to fix the issue?