From: Duy Nguyen <pclouds@gmail.com>
To: Jeff King <peff@peff.net>
Cc: "Junio C Hamano" <gitster@pobox.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
gerardu@amazon.com, "Git Mailing List" <git@vger.kernel.org>,
"Christian Couder" <christian.couder@gmail.com>
Subject: Re: [RFC PATCH] index-pack: improve performance on NFS
Date: Sat, 27 Oct 2018 16:04:32 +0200 [thread overview]
Message-ID: <CACsJy8A2MFbZQ-y5ufw-D6zzc-ye_gJmLVbDbgA+=2mhFiTusQ@mail.gmail.com> (raw)
In-Reply-To: <20181027093300.GA23974@sigill.intra.peff.net>
On Sat, Oct 27, 2018 at 11:34 AM Jeff King <peff@peff.net> wrote:
> Taking one step back, the root problem in this thread is that stat() on
> non-existing files is slow (which makes has_sha1_file slow).
>
> One solution there is to cache the results of looking in .git/objects
> (or any alternate object store) for loose files. And indeed, this whole
> scheme is just a specialized form of that: it's a flag to say "hey, we
> do not have any objects yet, so do not bother looking".
>
> Could we implement that in a more direct and central way? And could we
> implement it in a way that catches more cases? E.g., if I have _one_
> object, that defeats this specialized optimization, but it is probably
> still beneficial to cache that knowledge (and the reasonable cutoff is
> probably not 1, but some value of N loose objects).
And we do hit this on normal git-fetch. The larger the received pack
is (e.g. if you don't fetch often), the more stat() we do, so your
approach is definitely better.
> Of course any cache raises questions of cache invalidation, but I think
> we've already dealt with that for this case. When we use
> OBJECT_INFO_QUICK, that is a sign that we want to make this kind of
> accuracy/speed tradeoff (which does a similar caching thing with
> packfiles).
We don't care about a separate process adding more loose objects while
index-pack is running, do we? I'm guessing we don't but just to double
check...
> So putting that all together, could we have something like:
>
> diff --git a/object-store.h b/object-store.h
> index 63b7605a3e..28cde568a0 100644
> --- a/object-store.h
> +++ b/object-store.h
> @@ -135,6 +135,18 @@ struct raw_object_store {
> */
> struct packed_git *all_packs;
>
> + /*
> + * A set of all loose objects we have. This probably ought to be split
> + * into a set of 256 caches so that we can fault in one directory at a
> + * time.
> + */
> + struct oid_array loose_cache;
> + enum {
> + LOOSE_CACHE_UNFILLED = 0,
> + LOOSE_CACHE_INVALID,
> + LOOSE_CACHE_VALID
> + } loose_cache_status;
> +
> /*
> * A fast, rough count of the number of objects in the repository.
> * These two fields are not meant for direct access. Use
> diff --git a/packfile.c b/packfile.c
> index 86074a76e9..68ca4fff0e 100644
> --- a/packfile.c
> +++ b/packfile.c
> @@ -990,6 +990,8 @@ void reprepare_packed_git(struct repository *r)
> r->objects->approximate_object_count_valid = 0;
> r->objects->packed_git_initialized = 0;
> prepare_packed_git(r);
> + oid_array_clear(&r->objects->loose_cache);
> + r->objects->loose_cache_status = LOOSE_CACHE_UNFILLED;
> }
>
> struct packed_git *get_packed_git(struct repository *r)
> diff --git a/sha1-file.c b/sha1-file.c
> index dd0b6aa873..edbe037eaa 100644
> --- a/sha1-file.c
> +++ b/sha1-file.c
> @@ -1172,6 +1172,40 @@ int parse_sha1_header(const char *hdr, unsigned long *sizep)
> return parse_sha1_header_extended(hdr, &oi, 0);
> }
>
> +/* probably should be configurable? */
Yes, perhaps with gc.auto config value (multiplied by 256) as the cut
point. If it's too big maybe just go with a bloom filter. For this
particular case we expect like 99% of calls to miss.
> +#define LOOSE_OBJECT_CACHE_MAX 65536
> +
> +static int fill_loose_cache(const struct object_id *oid,
> + const char *path,
> + void *data)
> +{
> + struct oid_array *cache = data;
> +
> + if (cache->nr == LOOSE_OBJECT_CACHE_MAX)
> + return -1;
> +
> + oid_array_append(data, oid);
> + return 0;
> +}
> +
> +static int quick_has_loose(struct raw_object_store *r,
> + struct object_id *oid)
> +{
> + struct oid_array *cache = &r->loose_cache;
> +
> + if (r->loose_cache_status == LOOSE_CACHE_UNFILLED) {
> + if (for_each_loose_object(fill_loose_cache, cache, 0) < 0)
> + r->loose_cache_status = LOOSE_CACHE_INVALID;
> + else
> + r->loose_cache_status = LOOSE_CACHE_VALID;
> + }
> +
> + if (r->loose_cache_status == LOOSE_CACHE_INVALID)
> + return -1;
> +
> + return oid_array_lookup(cache, oid) >= 0;
> +}
> +
> static int sha1_loose_object_info(struct repository *r,
> const unsigned char *sha1,
> struct object_info *oi, int flags)
> @@ -1198,6 +1232,19 @@ static int sha1_loose_object_info(struct repository *r,
> if (!oi->typep && !oi->type_name && !oi->sizep && !oi->contentp) {
> const char *path;
> struct stat st;
> + if (!oi->disk_sizep && (flags & OBJECT_INFO_QUICK)) {
> + struct object_id oid;
> + hashcpy(oid.hash, sha1);
> + switch (quick_has_loose(r->objects, &oid)) {
> + case 0:
> + return -1; /* missing: error */
> + case 1:
> + return 0; /* have: 0 == success */
> + default:
> + /* unknown; fall back to stat */
> + break;
> + }
> + }
> if (stat_sha1_file(r, sha1, &st, &path) < 0)
> return -1;
> if (oi->disk_sizep)
>
> That's mostly untested, but it might be enough to run some timing tests
> with. I think if we want to pursue this, we'd want to address the bits I
> mentioned in the comments, and look at unifying this with the loose
> cache from cc817ca3ef (which if I had remembered we added, probably
> would have saved some time writing the above ;) ).
>
> -Peff
--
Duy
next prev parent reply other threads:[~2018-10-27 14:08 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
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 [this message]
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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