From: Derrick Stolee <stolee@gmail.com> To: git@vger.kernel.org Cc: sbeller@google.com, pclouds@gmail.com, avarab@gmail.com, Derrick Stolee <dstolee@microsoft.com> Subject: [PATCH v2 02/24] multi-pack-index: add format details Date: Mon, 25 Jun 2018 10:34:12 -0400 Message-ID: <20180625143434.89044-3-dstolee@microsoft.com> (raw) In-Reply-To: <20180625143434.89044-1-dstolee@microsoft.com> The multi-pack-index feature generalizes the existing pack-index 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..e060e693f4 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. + +== multi-pack-index (MIDX) files have the following format: + +The multi-pack-index files refer to multiple pack-files and loose objects. + +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 version 1 (SHA1). + + 1-byte number of "chunks" + + 1-byte number of base multi-pack-index files: + This value is currently always zero. + + 4-byte number 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.) + + 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: + + 20-byte SHA1-checksum of the above contents. -- 2.18.0.24.g1b579a2ee9
next prev parent reply other threads:[~2018-06-25 14:34 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 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 ` Derrick Stolee [this message] 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
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