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From: Jeff King <peff@peff.net>
To: "René Scharfe" <l.s.r@web.de>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Geert Jansen" <gerardu@amazon.com>,
	"Junio C Hamano" <gitster@pobox.com>,
	"git@vger.kernel.org" <git@vger.kernel.org>,
	"Takuto Ikuta" <tikuta@chromium.org>
Subject: Re: [PATCH 8/9] sha1-file: use loose object cache for quick existence check
Date: Mon, 3 Dec 2018 17:04:24 -0500	[thread overview]
Message-ID: <20181203220424.GA11883@sigill.intra.peff.net> (raw)
In-Reply-To: <221cb2e4-a024-e301-2b3f-e37dcd93795e@web.de>

On Sun, Dec 02, 2018 at 11:52:50AM +0100, René Scharfe wrote:

> > And for mu.git, a ~20k object repo:
> > 
> >     Test                                             origin/master     peff/jk/loose-cache       avar/check-collisions-config
> >     -------------------------------------------------------------------------------------------------------------------------
> >     0008.2: index-pack with 256*1 loose objects      0.59(0.91+0.06)   0.58(0.93+0.03) -1.7%     0.57(0.89+0.04) -3.4%
> >     0008.3: index-pack with 256*10 loose objects     0.59(0.91+0.07)   0.59(0.92+0.03) +0.0%     0.57(0.89+0.03) -3.4%
> >     0008.4: index-pack with 256*100 loose objects    0.59(0.91+0.05)   0.81(1.13+0.04) +37.3%    0.58(0.91+0.04) -1.7%
> >     0008.5: index-pack with 256*250 loose objects    0.59(0.91+0.05)   1.23(1.51+0.08) +108.5%   0.58(0.91+0.04) -1.7%
> >     0008.6: index-pack with 256*500 loose objects    0.59(0.90+0.06)   1.96(2.20+0.12) +232.2%   0.58(0.91+0.04) -1.7%
> >     0008.7: index-pack with 256*750 loose objects    0.59(0.92+0.05)   2.72(2.92+0.17) +361.0%   0.58(0.90+0.04) -1.7%
> >     0008.8: index-pack with 256*1000 loose objects   0.59(0.90+0.06)   3.50(3.67+0.21) +493.2%   0.57(0.90+0.04) -3.4%
> 
> OK, here's another theory: The cache scales badly with increasing
> numbers of loose objects because it sorts the array 256 times as it is
> filled.  Loading it fully and sorting once would help, as would using
> one array per subdirectory.

Yeah, that makes sense. This was actually how I had planned to do it
originally, but then I ended up just reusing the existing single-array
approach from the abbrev code.

I hadn't actually thought about the repeated sortings (but that
definitely makes sense that they would hurt in these pathological
cases), but more just that we get a 256x reduction in N for our binary
search (in fact we already do this first-byte lookup-table trick for
pack index lookups).

Your patch looks good to me. We may want to do one thing on top:

> diff --git a/object-store.h b/object-store.h
> index 8dceed0f31..ee67a50980 100644
> --- a/object-store.h
> +++ b/object-store.h
> @@ -20,7 +20,7 @@ struct object_directory {
>  	 * Be sure to call odb_load_loose_cache() before using.
>  	 */
>  	char loose_objects_subdir_seen[256];
> -	struct oid_array loose_objects_cache;
> +	struct oid_array loose_objects_cache[256];

The comment in the context there is warning callers to remember to load
the cache first. Now that we have individual caches, might it make sense
to change the interface a bit, and make these members private. I.e.,
something like:

  struct oid_array *odb_loose_cache(struct object_directory *odb,
                                    int subdir_nr) 
  {
	if (!loose_objects_subdir_seen[subdir_nr])
		odb_load_loose_cache(odb, subdir_nr); /* or just inline it here */

	return &odb->loose_objects_cache[subdir_nr];
  }

That's harder to get wrong, and this:

> diff --git a/sha1-file.c b/sha1-file.c
> index 05f63dfd4e..d2f5e65865 100644
> --- a/sha1-file.c
> +++ b/sha1-file.c
> @@ -933,7 +933,8 @@ static int quick_has_loose(struct repository *r,
>  	prepare_alt_odb(r);
>  	for (odb = r->objects->odb; odb; odb = odb->next) {
>  		odb_load_loose_cache(odb, subdir_nr);
> -		if (oid_array_lookup(&odb->loose_objects_cache, &oid) >= 0)
> +		if (oid_array_lookup(&odb->loose_objects_cache[subdir_nr],
> +				     &oid) >= 0)
>  			return 1;
>  	}

becomes:

  struct oid_array *cache = odb_loose_cache(odb, subdir_nr);
  if (oid_array_lookup(cache, &oid))
	return 1;

(An even simpler interface would be a single function that computes
subdir_nr and does the lookup itself, but that would not be enough for
find_short_object_filename()).

-Peff

  reply	other threads:[~2018-12-03 22:04 UTC|newest]

Thread overview: 99+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-25 18:38 [RFC PATCH] index-pack: improve performance on NFS Jansen, Geert
2018-10-26  0:21 ` Junio C Hamano
2018-10-26 20:38   ` Ævar Arnfjörð Bjarmason
2018-10-27  7:26     ` Junio C Hamano
2018-10-27  9:33       ` Jeff King
2018-10-27 11:22         ` Ævar Arnfjörð Bjarmason
2018-10-28 22:50           ` [PATCH 0/4] index-pack: optionally turn off SHA-1 collision checking Ævar Arnfjörð Bjarmason
2018-10-30  2:49             ` Geert Jansen
2018-10-30  9:04               ` Junio C Hamano
2018-10-30 18:43             ` [PATCH v2 0/3] index-pack: test updates Ævar Arnfjörð Bjarmason
2018-11-13 20:19               ` [PATCH v3] index-pack: add ability to disable SHA-1 collision check Ævar Arnfjörð Bjarmason
2018-11-14  7:09                 ` Junio C Hamano
2018-11-14 12:40                   ` Ævar Arnfjörð Bjarmason
2018-10-30 18:43             ` [PATCH v2 1/3] pack-objects test: modernize style Ævar Arnfjörð Bjarmason
2018-10-30 18:43             ` [PATCH v2 2/3] pack-objects tests: don't leave test .git corrupt at end Ævar Arnfjörð Bjarmason
2018-10-30 18:43             ` [PATCH v2 3/3] index-pack tests: don't leave test repo dirty " Ævar Arnfjörð Bjarmason
2018-10-28 22:50           ` [PATCH 1/4] pack-objects test: modernize style Ævar Arnfjörð Bjarmason
2018-10-28 22:50           ` [PATCH 2/4] pack-objects tests: don't leave test .git corrupt at end Ævar Arnfjörð Bjarmason
2018-10-28 22:50           ` [PATCH 3/4] index-pack tests: don't leave test repo dirty " Ævar Arnfjörð Bjarmason
2018-10-28 22:50           ` [PATCH 4/4] index-pack: add ability to disable SHA-1 collision check Ævar Arnfjörð Bjarmason
2018-10-29 15:04           ` [RFC PATCH] index-pack: improve performance on NFS Jeff King
2018-10-29 15:09             ` Jeff King
2018-10-29 19:36             ` Ævar Arnfjörð Bjarmason
2018-10-29 23:27               ` Jeff King
2018-11-07 22:55                 ` Geert Jansen
2018-11-08 12:02                   ` Jeff King
2018-11-08 20:58                     ` Geert Jansen
2018-11-08 21:18                       ` Jeff King
2018-11-08 21:55                         ` Geert Jansen
2018-11-08 22:20                     ` Ævar Arnfjörð Bjarmason
2018-11-09 10:11                       ` Ævar Arnfjörð Bjarmason
2018-11-12 14:31                       ` Jeff King
2018-11-12 14:46                     ` [PATCH 0/9] caching loose objects Jeff King
2018-11-12 14:46                       ` [PATCH 1/9] fsck: do not reuse child_process structs Jeff King
2018-11-12 15:26                         ` Derrick Stolee
2018-11-12 14:47                       ` [PATCH 2/9] submodule--helper: prefer strip_suffix() to ends_with() Jeff King
2018-11-12 18:23                         ` Stefan Beller
2018-11-12 14:48                       ` [PATCH 3/9] rename "alternate_object_database" to "object_directory" Jeff King
2018-11-12 15:30                         ` Derrick Stolee
2018-11-12 15:36                           ` Jeff King
2018-11-12 19:41                             ` Ramsay Jones
2018-11-12 14:48                       ` [PATCH 4/9] sha1_file_name(): overwrite buffer instead of appending Jeff King
2018-11-12 15:32                         ` Derrick Stolee
2018-11-12 14:49                       ` [PATCH 5/9] handle alternates paths the same as the main object dir Jeff King
2018-11-12 15:38                         ` Derrick Stolee
2018-11-12 15:46                           ` Jeff King
2018-11-12 15:50                             ` Derrick Stolee
2018-11-12 14:50                       ` [PATCH 6/9] sha1-file: use an object_directory for " Jeff King
2018-11-12 15:48                         ` Derrick Stolee
2018-11-12 16:09                           ` Jeff King
2018-11-12 19:04                             ` Stefan Beller
2018-11-22 17:42                               ` Jeff King
2018-11-12 18:48                           ` Stefan Beller
2018-11-12 14:50                       ` [PATCH 7/9] object-store: provide helpers for loose_objects_cache Jeff King
2018-11-12 19:24                         ` René Scharfe
2018-11-12 20:16                           ` Jeff King
2018-11-12 14:54                       ` [PATCH 8/9] sha1-file: use loose object cache for quick existence check Jeff King
2018-11-12 16:00                         ` Derrick Stolee
2018-11-12 16:01                         ` Ævar Arnfjörð Bjarmason
2018-11-12 16:21                           ` Jeff King
2018-11-12 22:18                             ` Ævar Arnfjörð Bjarmason
2018-11-12 22:30                               ` Ævar Arnfjörð Bjarmason
2018-11-13 10:02                                 ` Ævar Arnfjörð Bjarmason
2018-11-14 18:21                                   ` René Scharfe
2018-12-02 10:52                                   ` René Scharfe
2018-12-03 22:04                                     ` Jeff King [this message]
2018-12-04 21:45                                       ` René Scharfe
2018-12-05  4:46                                         ` Jeff King
2018-12-05  6:02                                           ` René Scharfe
2018-12-05  6:51                                             ` Jeff King
2018-12-05  8:15                                               ` Jeff King
2018-12-05 18:41                                                 ` René Scharfe
2018-12-05 20:17                                                   ` Jeff King
2018-11-12 22:44                             ` Geert Jansen
2018-11-27 20:48                         ` René Scharfe
2018-12-01 19:49                           ` Jeff King
2018-11-12 14:55                       ` [PATCH 9/9] fetch-pack: drop custom loose object cache Jeff King
2018-11-12 19:25                         ` René Scharfe
2018-11-12 19:32                           ` Ævar Arnfjörð Bjarmason
2018-11-12 20:07                             ` Jeff King
2018-11-12 20:13                             ` René Scharfe
2018-11-12 16:02                       ` [PATCH 0/9] caching loose objects Derrick Stolee
2018-11-12 19:10                         ` Stefan Beller
2018-11-09 13:43                   ` [RFC PATCH] index-pack: improve performance on NFS Ævar Arnfjörð Bjarmason
2018-11-09 16:08                     ` Duy Nguyen
2018-11-10 14:04                       ` Ævar Arnfjörð Bjarmason
2018-11-12 14:34                         ` Jeff King
2018-11-12 22:58                     ` Geert Jansen
2018-10-27 14:04         ` Duy Nguyen
2018-10-29 15:18           ` Jeff King
2018-10-29  0:48         ` Junio C Hamano
2018-10-29 15:20           ` Jeff King
2018-10-29 18:43             ` Ævar Arnfjörð Bjarmason
2018-10-29 21:34           ` Geert Jansen
2018-10-29 21:50             ` Jeff King
2018-10-29 22:21               ` Geert Jansen
2018-10-29 22:27             ` Jeff King
2018-10-29 22:35               ` Stefan Beller
2018-10-29 23:29                 ` Jeff King

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