From: Derrick Stolee <stolee@gmail.com> To: Stefan Beller <sbeller@google.com> Cc: git <git@vger.kernel.org>, "Derrick Stolee" <dstolee@microsoft.com>, "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>, "Jonathan Nieder" <jrnieder@gmail.com>, "Jonathan Tan" <jonathantanmy@google.com>, "Martin Fick" <mfick@codeaurora.org> Subject: Re: [PATCH 02/23] midx: add midx format details to pack-format.txt Date: Mon, 18 Jun 2018 15:01:53 -0400 Message-ID: <a0dbd78c-507b-3005-c2eb-2fa82e7d29ec@gmail.com> (raw) In-Reply-To: <CAGZ79kaDiXnAuRym3HHQPEZh9z0-sPL5V4Yur5-_RojsyLJsYA@mail.gmail.com> On 6/11/2018 3:19 PM, Stefan Beller wrote: > Hi Derrick, > On Thu, Jun 7, 2018 at 7:03 AM Derrick Stolee <stolee@gmail.com> wrote: >> The multi-pack-index (MIDX) feature generalizes the existing pack- >> index (IDX) feature by indexing objects across multiple pack-files. >> >> Describe the basic file format, using a 12-byte header followed by >> a lookup table for a list of "chunks" which will be described later. >> The file ends with a footer containing a checksum using the hash >> algorithm. >> >> The header allows later versions to create breaking changes by >> advancing the version number. We can also change the hash algorithm >> using a different version value. >> >> We will add the individual chunk format information as we introduce >> the code that writes that information. >> >> Signed-off-by: Derrick Stolee <dstolee@microsoft.com> >> --- >> Documentation/technical/pack-format.txt | 49 +++++++++++++++++++++++++ >> 1 file changed, 49 insertions(+) >> >> diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt >> index 70a99fd142..17666b4bfc 100644 >> --- a/Documentation/technical/pack-format.txt >> +++ b/Documentation/technical/pack-format.txt >> @@ -252,3 +252,52 @@ Pack file entry: <+ >> corresponding packfile. >> >> 20-byte SHA-1-checksum of all of the above. >> + >> +== midx-*.midx files have the following format: >> + >> +The meta-index files refer to multiple pack-files and loose objects. > So is it meta or multi? Good catch. We were calling this the meta-index internally before changing to "multi-pack-index" (helps to not change the acronym). > >> +In order to allow extensions that add extra data to the MIDX, we organize >> +the body into "chunks" and provide a lookup table at the beginning of the >> +body. The header includes certain length values, such as the number of packs, >> +the number of base MIDX files, hash lengths and types. >> + >> +All 4-byte numbers are in network order. >> + >> +HEADER: >> + >> + 4-byte signature: >> + The signature is: {'M', 'I', 'D', 'X'} >> + >> + 1-byte version number: >> + Git only writes or recognizes version 1 >> + >> + 1-byte Object Id Version >> + Git only writes or recognizes verion 1 (SHA-1) > s/verion/version/ > >> + 1-byte number (C) of "chunks" >> + >> + 1-byte number (I) of base multi-pack-index files: >> + This value is currently always zero. > Oh? Are meta-index and multi-index files different things? Not intended to be different things, but this number is related to making the feature incremental. > >> + 4-byte number (P) of pack files >> + >> +CHUNK LOOKUP: >> + >> + (C + 1) * 12 bytes providing the chunk offsets: >> + First 4 bytes describe chunk id. Value 0 is a terminating label. >> + Other 8 bytes provide offset in current file for chunk to start. >> + (Chunks are provided in file-order, so you can infer the length >> + using the next chunk position if necessary.) > It is so nice to have the header also have 12 bytes, so it fits right into the > lookup table. So an alternative point of view: > > If a chunk needs to store more than 8 bytes, we'll have an offset after > the first 4 bytes that describe the chunk, otherwise you can store the 8 bytes > of information directly after the 4 bytes. > "MIDX" is a special chunk and must come first (does it?) and only once > as it contains the version number. This sounds feasible, but unnecessarily complicated. I don't think any other chunk will be this small. >> + The remaining data in the body is described one chunk at a time, and >> + these chunks may be given in any order. Chunks are required unless >> + otherwise specified. >> + >> +CHUNK DATA: >> + >> + (This section intentionally left incomplete.) >> + >> +TRAILER: >> + >> + H-byte HASH-checksum of all of the above. > This means we have to rehash the whole file for updating its contents. > okay.
next prev parent reply other threads:[~2018-06-18 19:02 UTC|newest] Thread overview: 192+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-06-07 14:03 [PATCH 00/23] Multi-pack-index (MIDX) Derrick Stolee 2018-06-07 14:03 ` [PATCH 01/23] midx: add design document Derrick Stolee 2018-06-11 19:04 ` Stefan Beller 2018-06-18 18:48 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 02/23] midx: add midx format details to pack-format.txt Derrick Stolee 2018-06-11 19:19 ` Stefan Beller 2018-06-18 19:01 ` Derrick Stolee [this message] 2018-06-18 19:41 ` Stefan Beller 2018-06-07 14:03 ` [PATCH 03/23] midx: add midx builtin Derrick Stolee 2018-06-07 17:20 ` Duy Nguyen 2018-06-18 19:23 ` Derrick Stolee 2018-06-11 21:02 ` Stefan Beller 2018-06-18 19:40 ` Derrick Stolee 2018-06-18 19:55 ` Stefan Beller 2018-06-18 19:58 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 04/23] midx: add 'write' subcommand and basic wiring Derrick Stolee 2018-06-07 17:27 ` Duy Nguyen 2018-06-07 14:03 ` [PATCH 05/23] midx: write header information to lockfile Derrick Stolee 2018-06-07 17:35 ` Duy Nguyen 2018-06-12 15:00 ` Duy Nguyen 2018-06-19 12:54 ` Derrick Stolee 2018-06-19 14:59 ` Duy Nguyen 2018-06-19 15:24 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 06/23] midx: struct midxed_git and 'read' subcommand Derrick Stolee 2018-06-07 17:54 ` Duy Nguyen 2018-06-20 13:13 ` Derrick Stolee 2018-06-07 18:31 ` Duy Nguyen 2018-06-20 13:33 ` Derrick Stolee 2018-06-20 15:07 ` Duy Nguyen 2018-06-20 16:39 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 07/23] midx: expand test data Derrick Stolee 2018-06-07 14:03 ` [PATCH 08/23] midx: read packfiles from pack directory Derrick Stolee 2018-06-07 18:03 ` Duy Nguyen 2018-06-20 16:33 ` [PATCH] packfile: generalize pack directory list Derrick Stolee 2018-06-07 14:03 ` [PATCH 09/23] midx: write pack names in chunk Derrick Stolee 2018-06-07 18:26 ` Duy Nguyen 2018-06-21 15:25 ` Derrick Stolee 2018-06-21 17:38 ` Junio C Hamano 2018-06-22 18:25 ` Derrick Stolee 2018-06-22 18:31 ` Junio C Hamano 2018-06-22 18:32 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 10/23] midx: write a lookup into the pack names chunk Derrick Stolee 2018-06-09 16:43 ` Duy Nguyen 2018-06-21 17:23 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 11/23] midx: sort and deduplicate objects from packfiles Derrick Stolee 2018-06-09 17:07 ` Duy Nguyen 2018-06-21 17:54 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 12/23] midx: write object ids in a chunk Derrick Stolee 2018-06-09 17:25 ` Duy Nguyen 2018-06-07 14:03 ` [PATCH 13/23] midx: write object id fanout chunk Derrick Stolee 2018-06-09 17:28 ` Duy Nguyen 2018-06-21 19:49 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 14/23] midx: write object offsets Derrick Stolee 2018-06-09 17:41 ` Duy Nguyen 2018-06-07 14:03 ` [PATCH 15/23] midx: create core.midx config setting Derrick Stolee 2018-06-07 14:03 ` [PATCH 16/23] midx: prepare midxed_git struct Derrick Stolee 2018-06-09 17:47 ` Duy Nguyen 2018-06-07 14:03 ` [PATCH 17/23] midx: read objects from multi-pack-index Derrick Stolee 2018-06-09 17:56 ` Duy Nguyen 2018-06-21 20:03 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 18/23] midx: use midx in abbreviation calculations Derrick Stolee 2018-06-09 18:01 ` Duy Nguyen 2018-06-22 18:38 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 19/23] midx: use existing midx when writing new one Derrick Stolee 2018-06-07 14:03 ` [PATCH 20/23] midx: use midx in approximate_object_count Derrick Stolee 2018-06-09 18:03 ` Duy Nguyen 2018-06-22 18:39 ` Derrick Stolee 2018-06-07 14:03 ` [PATCH 21/23] midx: prevent duplicate packfile loads Derrick Stolee 2018-06-09 18:05 ` Duy Nguyen 2018-06-07 14:03 ` [PATCH 22/23] midx: use midx to find ref-deltas Derrick Stolee 2018-06-07 14:03 ` [PATCH 23/23] midx: clear midx on repack Derrick Stolee 2018-06-09 18:13 ` Duy Nguyen 2018-06-22 18:44 ` Derrick Stolee 2018-06-07 14:06 ` [PATCH 00/23] Multi-pack-index (MIDX) Derrick Stolee 2018-06-07 14:45 ` Ævar Arnfjörð Bjarmason 2018-06-07 14:54 ` Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 00/24] " Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 01/24] multi-pack-index: add design document Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 02/24] multi-pack-index: add format details Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 03/24] multi-pack-index: add builtin Derrick Stolee 2018-06-25 19:15 ` Junio C Hamano 2018-06-25 14:34 ` [PATCH v2 04/24] multi-pack-index: add 'write' verb Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 05/24] midx: write header information to lockfile Derrick Stolee 2018-06-25 19:19 ` Junio C Hamano 2018-07-05 19:13 ` Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 06/24] multi-pack-index: load into memory Derrick Stolee 2018-06-25 19:38 ` Junio C Hamano 2018-07-05 14:19 ` Derrick Stolee 2018-07-05 18:58 ` Eric Sunshine 2018-07-06 19:20 ` Junio C Hamano 2018-06-25 14:34 ` [PATCH v2 07/24] multi-pack-index: expand test data Derrick Stolee 2018-06-25 19:45 ` Junio C Hamano 2018-06-25 14:34 ` [PATCH v2 08/24] packfile: generalize pack directory list Derrick Stolee 2018-06-25 19:57 ` Junio C Hamano 2018-06-25 14:34 ` [PATCH v2 09/24] multi-pack-index: read packfile list Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 10/24] multi-pack-index: write pack names in chunk Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 11/24] midx: read pack names into array Derrick Stolee 2018-06-25 23:52 ` Eric Sunshine 2018-06-25 14:34 ` [PATCH v2 12/24] midx: sort and deduplicate objects from packfiles Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 13/24] midx: write object ids in a chunk Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 14/24] midx: write object id fanout chunk Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 15/24] midx: write object offsets Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 16/24] config: create core.multiPackIndex setting Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 17/24] midx: prepare midxed_git struct Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 18/24] midx: read objects from multi-pack-index Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 19/24] midx: use midx in abbreviation calculations Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 20/24] midx: use existing midx when writing new one Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 21/24] midx: use midx in approximate_object_count Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 22/24] midx: prevent duplicate packfile loads Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 23/24] packfile: skip loading index if in multi-pack-index Derrick Stolee 2018-06-25 14:34 ` [PATCH v2 24/24] midx: clear midx on repack Derrick Stolee 2018-07-06 0:52 ` [PATCH v3 00/24] Multi-pack-index (MIDX) Derrick Stolee 2018-07-06 0:52 ` [PATCH v3 01/24] multi-pack-index: add design document Derrick Stolee 2018-07-06 0:52 ` [PATCH v3 02/24] multi-pack-index: add format details Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 03/24] multi-pack-index: add builtin Derrick Stolee 2018-07-06 3:54 ` Eric Sunshine 2018-07-06 0:53 ` [PATCH v3 04/24] multi-pack-index: add 'write' verb Derrick Stolee 2018-07-06 4:07 ` Eric Sunshine 2018-07-06 0:53 ` [PATCH v3 05/24] midx: write header information to lockfile Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 06/24] multi-pack-index: load into memory Derrick Stolee 2018-07-06 4:19 ` Eric Sunshine 2018-07-06 5:18 ` Eric Sunshine 2018-07-09 19:08 ` Junio C Hamano 2018-07-12 16:06 ` Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 07/24] multi-pack-index: expand test data Derrick Stolee 2018-07-06 4:36 ` Eric Sunshine 2018-07-06 5:20 ` Eric Sunshine 2018-07-12 14:10 ` Derrick Stolee 2018-07-12 18:02 ` Eric Sunshine 2018-07-12 18:06 ` Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 08/24] packfile: generalize pack directory list Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 09/24] multi-pack-index: read packfile list Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 10/24] multi-pack-index: write pack names in chunk Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 11/24] midx: read pack names into array Derrick Stolee 2018-07-06 4:58 ` Eric Sunshine 2018-07-06 0:53 ` [PATCH v3 12/24] midx: sort and deduplicate objects from packfiles Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 13/24] midx: write object ids in a chunk Derrick Stolee 2018-07-06 5:04 ` Eric Sunshine 2018-07-06 0:53 ` [PATCH v3 14/24] midx: write object id fanout chunk Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 15/24] midx: write object offsets Derrick Stolee 2018-07-06 5:27 ` Eric Sunshine 2018-07-12 16:33 ` Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 16/24] config: create core.multiPackIndex setting Derrick Stolee 2018-07-06 5:39 ` Eric Sunshine 2018-07-12 13:19 ` Derrick Stolee 2018-07-12 16:30 ` Derrick Stolee 2018-07-11 9:48 ` SZEDER Gábor 2018-07-12 13:01 ` Derrick Stolee 2018-07-12 13:31 ` SZEDER Gábor 2018-07-12 15:40 ` Derrick Stolee 2018-07-12 17:29 ` Junio C Hamano 2018-07-06 0:53 ` [PATCH v3 17/24] midx: prepare midxed_git struct Derrick Stolee 2018-07-06 5:41 ` Eric Sunshine 2018-07-06 0:53 ` [PATCH v3 18/24] midx: read objects from multi-pack-index Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 19/24] midx: use midx in abbreviation calculations Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 20/24] midx: use existing midx when writing new one Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 21/24] midx: use midx in approximate_object_count Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 22/24] midx: prevent duplicate packfile loads Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 23/24] packfile: skip loading index if in multi-pack-index Derrick Stolee 2018-07-06 0:53 ` [PATCH v3 24/24] midx: clear midx on repack Derrick Stolee 2018-07-06 5:52 ` Eric Sunshine 2018-07-12 19:39 ` [PATCH v4 00/23] Multi-pack-index (MIDX) Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 01/23] multi-pack-index: add design document Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 02/23] multi-pack-index: add format details Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 03/23] multi-pack-index: add builtin Derrick Stolee 2018-07-20 18:22 ` Junio C Hamano 2018-07-20 22:15 ` brian m. carlson 2018-07-20 22:28 ` Junio C Hamano 2018-07-12 19:39 ` [PATCH v4 04/23] multi-pack-index: add 'write' verb Derrick Stolee 2018-07-12 22:56 ` Eric Sunshine 2018-07-12 19:39 ` [PATCH v4 05/23] midx: write header information to lockfile Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 06/23] multi-pack-index: load into memory Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 07/23] t5319: expand test data Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 08/23] packfile: generalize pack directory list Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 09/23] multi-pack-index: read packfile list Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 10/23] multi-pack-index: write pack names in chunk Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 11/23] midx: read pack names into array Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 12/23] midx: sort and deduplicate objects from packfiles Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 13/23] midx: write object ids in a chunk Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 14/23] midx: write object id fanout chunk Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 15/23] midx: write object offsets Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 16/23] config: create core.multiPackIndex setting Derrick Stolee 2018-07-12 21:05 ` Junio C Hamano 2018-07-13 0:50 ` Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 17/23] midx: read objects from multi-pack-index Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 18/23] midx: use midx in abbreviation calculations Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 19/23] midx: use existing midx when writing new one Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 20/23] midx: use midx in approximate_object_count Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 21/23] midx: prevent duplicate packfile loads Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 22/23] packfile: skip loading index if in multi-pack-index Derrick Stolee 2018-07-12 19:39 ` [PATCH v4 23/23] midx: clear midx on repack Derrick Stolee 2018-07-12 21:11 ` [PATCH v4 00/23] Multi-pack-index (MIDX) Junio C Hamano
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style List information: http://vger.kernel.org/majordomo-info.html * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=a0dbd78c-507b-3005-c2eb-2fa82e7d29ec@gmail.com \ --to=stolee@gmail.com \ --cc=avarab@gmail.com \ --cc=dstolee@microsoft.com \ --cc=git@vger.kernel.org \ --cc=jonathantanmy@google.com \ --cc=jrnieder@gmail.com \ --cc=mfick@codeaurora.org \ --cc=sbeller@google.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
git@vger.kernel.org list mirror (unofficial, one of many) This inbox may be cloned and mirrored by anyone: git clone --mirror https://public-inbox.org/git git clone --mirror http://ou63pmih66umazou.onion/git git clone --mirror http://czquwvybam4bgbro.onion/git git clone --mirror http://hjrcffqmbrq6wope.onion/git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V1 git git/ https://public-inbox.org/git \ git@vger.kernel.org public-inbox-index git Example config snippet for mirrors. Newsgroups are available over NNTP: nntp://news.public-inbox.org/inbox.comp.version-control.git nntp://ou63pmih66umazou.onion/inbox.comp.version-control.git nntp://czquwvybam4bgbro.onion/inbox.comp.version-control.git nntp://hjrcffqmbrq6wope.onion/inbox.comp.version-control.git nntp://news.gmane.io/gmane.comp.version-control.git note: .onion URLs require Tor: https://www.torproject.org/ code repositories for the project(s) associated with this inbox: https://80x24.org/mirrors/git.git AGPL code for this site: git clone https://public-inbox.org/public-inbox.git