On 12/05/2013 19:33, John Keeping wrote:
On Sun, May 12, 2013 at 05:28:24PM +0100, John Keeping wrote:
You're right (and I was wrong in my reply to Junio's parallel message)
ancestry path does seem to be what I want:

     $ git rev-list --ancestry-path --left-right --count \
     2056    5

However, this doesn't seem to make a difference to the time taken when I
add in --cherry-mark (which is why I was partially correct in the
parallel thread - it doesn't have the effect on cherry-mark that I want
it to):

This seems to be caused by the code in revision.c::limit_list() which
does the cherry detection then limits to left/right and only then
applies the ancestry path.  I haven't looked further than that, but is
there any reason not to apply the ancestry path restriction before
looking for patch-identical commits?

That certainly sounds like it's doing it the wrong way round. At first sight, it seems obviously suboptimal.

No I didn't.  I forgot to update my $PATH when I built on master - those
results are from pu.  master says:

     fatal: --ancestry-path given but there are no bottom commits

Well, then it looks like we have a user for that particular syntax. Seemed a bit esoteric to me :) Although I realised after sending my mail you could also use

git log --ancestry-path --left-right E...F --not $(git merge-base --all E F)

which looks like we're having to repeat ourselves because it's not paying attention...

I hit it because one of my optimisations relies on knowing the bottom commits, and I made absolutely sure I was using the exactly same definition of "bottom" as --ancestry-path. And then I found that my optimisations didn't work properly with "..."

I suggest we pull my patch out from the more complex optimisation series so it can proceed to next faster. It shouldn't have to wait for all my new fancy stuff - it's fixing something that appears to be a clear bug.

Although Junio did have a comment about the implementation - I'll revisit it tomorrow and send a revised version separately, if everyone thinks that's sensible.

On this subject, is there any way to exclude a path from a log query? Is
there a "not" operator for paths? Might be another way of doing this -
disjoint histories probably have disjoint paths...
That relates to another idea I had about optimizing the detection of
patch-identical commits.  If the smaller side of a symmetric difference
is quite small (as it is likely to be if it's a topic branch), would it
be a good idea to calculate the set of paths touched by commits on that
side and then skip calculating the patch ID for any commits that touch
paths outside that set.  The tree comparison is a lot cheaper than doing
a diff on all of the files.

Sounds cute. Go for it :)


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