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From: Jeff King <>
To: "Ævar Arnfjörð Bjarmason" <>
Cc:, Git Mailing List <>,
	Lars Schneider <>
Subject: Re: [ANNOUNCE] git-sizer: compute various size-related metrics for your Git repository
Date: Fri, 16 Mar 2018 17:29:21 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Fri, Mar 16, 2018 at 09:01:42PM +0100, Ævar Arnfjörð Bjarmason wrote:

> Suggestion for a thing to add to it, I don't have the time on the Go
> tuits:
> One thing that can make repositories very pathological is if the ratio
> of trees to commits is too low.
> I was dealing with a repo the other day that had several thousand files
> all in the same root directory, and no subdirectories.

We've definitely run into this problem before (CocoaPods/Specs, for
example). The metric that would hopefully show this off is "what is the
tree object with the most entries". Or possibly "what is the average
number of entries in a tree object".

That's not the _whole_ story, because the really pathological case is
when you then touch that giant tree a lot. But if you assume the paths
touched by commits are reasonably distributed over the tree, then having
a huge number of entries in one tree will also mean that more commits
will touch that tree. Sort of a vaguely quadratic problem.

Doing it at the root is obviously the worst case, but the same thing can
happen if you have "foo/bar" as a huge tree, and every single commit
needs to touch some variant of "foo/bar/baz".

That's why I suspect some "average per tree object" may show this type
of problem, because you'd have a lot of near-identical copies of that
giant tree if it's being modified a lot.

> But it's not something where you can just say having more trees is
> better, because on the other end of the spectrume we can imagine a repo
> like linux.git where each file like COPYING instead exists at
> C/O/P/Y/I/N/G, that would also be pathological.
> It would be very interesting to do some tests to see what the optimal
> value would be.

I suspect there's some math that could give us the solution. You want
approximately equal-sized trees, so maybe log(N) levels?


  reply	other threads:[~2018-03-16 21:29 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-16 15:28 [ANNOUNCE] git-sizer: compute various size-related metrics for your Git repository Michael Haggerty
2018-03-16 20:01 ` Ævar Arnfjörð Bjarmason
2018-03-16 21:29   ` Jeff King [this message]
2018-03-18 19:06     ` Michael Haggerty
2018-03-21 16:02 ` Johannes Schindelin

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