Re: [PATCH v2] add test to demonstrate that shallow recursive clones fail

[Jeff King <peff@peff.net>]

On Wed, Nov 18, 2015 at 01:32:36PM +0100, Duy Nguyen wrote:

> Yeah I think that was the 10k commits in Shawn's mail: the number of
> commits we may have to walk until we hit a reachability bitmap. It
> looks like C Git will create a bitmap every 5k commits, not 10k,
> though, if I read the code correctly. The point is reachability test
> with the presence of pack bitmaps is not O(n) anymore. Which is
> probably good enough for now.

There are some pathological cases, though. I hit one recently that still
took 40s to do "rev-list --objects --all --use-bitmap-index" (it's 80s
without bitmaps).  The problem is that it has over 20,000 refs. We try
to put a bitmap at the tip of each ref, but it's tough when there are
that many.

I suspect there's room for improvement in the commit selection in such
cases. That code hasn't really been tweaked since it was originally
written, and repositories like that are extreme outliers.

-Peff