Subject: Re: [PATCH 8/7] cat-file: sort and de-dup output of --batch-all-objects

From: Jeff King <[email-masked]>
Date: Mon, 22 Jun 2015 19:46:25 -0400

On Mon, Jun 22, 2015 at 11:03:50PM +0100, Charles Bailey wrote:

> > The patch below does the sort/de-dup. I'd probably just squash it into
> > patch 7, though.
> 
> Woah, 8 out of 7! Did you get a chance to measure the performance hit of
> the sort? If not, I may test it out when I next get the chance.

No, that last patch was my "eh, one more thing before bed" patch. ;)

It's easy enough to time, though. Running:

  git cat-file --batch-all-objects \
               --batch-check='%(objectsize) %(objectname)' \
	       --buffer >/dev/null

on linux.git, my best-of-five goes from (no sorting):

  real    0m3.604s
  user    0m3.556s
  sys     0m0.048s

to (with sorting):

  real    0m4.053s
  user    0m4.004s
  sys     0m0.052s

So it does matter, but not too much. We could de-dup with a hash table,
which might be a little faster, but I doubt it would make much
difference.  It's also mostly in sorted order already; it's possible
that a merge sort would behave a little better. I'm not sure how deep
it's worth going into that rabbit hole.

-Peff