Re: [PATCH 8/6] commit: use generation numbers for in_merge_bases()

From: Jeff King <peff@peff.net>
Date: Apr 4, 2018, 18:59 UTC
Message-ID: <20180404185950.GF9055@sigill.intra.peff.net>
In-Reply-To: <aa28c3e5-7645-ffe0-78a3-e3cbd2ea8cec@gmail.com>

On Wed, Apr 04, 2018 at 02:53:45PM -0400, Derrick Stolee wrote:

Show 8 quoted lines

> > I'd have to do some timings, but I suspect we may want to switch to the
> > "tag --contains" algorithm anyway. This still does N independent
> > merge-base operations, one per ref. So with enough refs, you're still
> > better off throwing it all into one big traversal.
> 
> ...and I suppose your timings are to find out if there are data shapes where
> the branch algorithm is faster. Perhaps that is impossible now that we have
> the generation number cutoff for the tag algorithm.

Well, I wanted to show the opposite: that the branch algorithm can still perform quite poorly. :)

I think with generation numbers that the tag algorithm should always perform better, since you can't walk past a merge base when using a cutoff. But it could definitely perform worse in a case where you don't have generation numbers.

> Patches 7 and 8 seem to me like simple changes with no downside UNLESS we
> are deciding instead to delete the code I'm changing.

Yeah, I think they are strict improvements modulo the inverted UNDEF logic I mentioned.

-Peff