Re: [PATCH v6 00/11] nd/pack-objects-pack-struct updates

From: Ramsay Jones <ramsay@ramsayjones.plus.com>
Date: Mar 23, 2018, 16:01 UTC
Message-ID: <4395a668-845e-a66f-2a14-f6a4474c3d4b@ramsayjones.plus.com>
In-Reply-To: <20180323055027.GA30227@sigill.intra.peff.net>

On 23/03/18 05:50, Jeff King wrote:

> On Thu, Mar 22, 2018 at 10:46:09PM -0400, Jeff King wrote:

[snip]

Show 5 quoted lines

> I was curious whether my hand-waving there was true. It turns out that
> it is: the radix sort has stayed about the same speed but the comparison
> sort has gotten even slower. Here are best-of-five timings for "git
> cat-file --batch-check='%(objectsize:disk)'", which does very little
> besides generate the rev-index:

Not that it matters, but I assume this was something like:

  $ time (echo HEAD | git cat-file --batch-check="%(objectsize:disk)")

... and I suspect it was on the linux.git repo, yes?

I used to have a copy of the linux repo on disk, but I had to delete it a while ago to recover some disk space (no matter how big disks get, they never seem big enough)!

If I do this on my biggest repo (ffmpeg), I get:

  $ cd ../ffmpeg/

  $ time (echo HEAD | git cat-file --batch-check="%(objectsize:disk)")
  227

  real	0m0.037s
  user	0m0.020s
  sys	0m0.004s

  $ time (echo HEAD | ../git/git-cat-file --batch-check="%(objectsize:disk)")
  227

  real	0m0.146s
  user	0m0.112s
  sys	0m0.012s

Where I'm using a version with my patch applied, rather than reverting commit 8b8dfd5132. A 395% slowdown is bad enough, but not as bad as a factor of 11! I bet you have a much more modern system (with a fast SSD) than my old laptop. :-D

Show 11 quoted lines

>   [current master, using radix sort]
>   real	0m0.104s
>   user	0m0.088s
>   sys	0m0.016s
> 
>   [reverting 8b8dfd5132, going back to qsort]
>   real	0m1.193s
>   user	0m1.176s
>   sys	0m0.016s
> 
> So it's now a factor of 11. Yikes.

Thanks for looking into this, even if it was a wild goose chase. :)

ATB, Ramsay Jones