@matheusbsbs / matheus-bagliano / commits / 5f711504d9

repack: add --path-walk option

Since 'git pack-objects' supports a --path-walk option, allow passing it through in 'git repack'. This presents interesting testing opportunities for comparing the different repacking strategies against each other. Add the --path-walk option to the performance tests in p5313. For the microsoft/fluentui repo [1] checked out at a specific commit [2], the --path-walk tests in p5313 look like this: Test this tree ------------------------------------------------------------------------- 5313.18: thin pack with --path-walk 0.08(0.06+0.02) 5313.19: thin pack size with --path-walk 18.4K 5313.20: big pack with --path-walk 2.10(7.80+0.26) 5313.21: big pack size with --path-walk 19.8M 5313.22: shallow fetch pack with --path-walk 1.62(3.38+0.17) 5313.23: shallow pack size with --path-walk 33.6M 5313.24: repack with --path-walk 81.29(96.08+0.71) 5313.25: repack size with --path-walk 142.5M [1] https://github.com/microsoft/fluentui [2] e70848ebac1cd720875bccaa3026f4a9ed700e08 Along with the earlier tests in p5313, I'll instead reformat the comparison as follows: Repack Method Pack Size Time --------------------------------------- Hash v1 439.4M 87.24s Hash v2 161.7M 21.51s Path Walk 142.5M 81.29s There are a few things to notice here: 1. The benefits of --name-hash-version=2 over --name-hash-version=1 are significant, but --path-walk still compresses better than that option. 2. The --path-walk command is still using --name-hash-version=1 for the second pass of delta computation, using the increased name hash collisions as a potential method for opportunistic compression on top of the path-focused compression. 3. The --path-walk algorithm is currently sequential and does not use multiple threads for delta compression. Threading will be implemented in a future change so the computation time will improve to better compete in this metric. There are small benefits in size for my copy of the Git repository: Repack Method Pack Size Time --------------------------------------- Hash v1 248.8M 30.44s Hash v2 249.0M 30.15s Path Walk 213.2M 142.50s As well as in the nodejs/node repository [3]: Repack Method Pack Size Time --------------------------------------- Hash v1 739.9M 71.18s Hash v2 764.6M 67.82s Path Walk 698.1M 208.10s [3] https://github.com/nodejs/node This benefit also repeats in my copy of the Linux kernel repository: Repack Method Pack Size Time --------------------------------------- Hash v1 2.5G 554.41s Hash v2 2.5G 549.62s Path Walk 2.2G 1562.36s It is important to see that even when the repository shape does not have many name-hash collisions, there is a slight space boost to be found using this method. As this repacking strategy was released in Git for Windows 2.47.0, some users have reported cases where the --path-walk compression is slightly worse than the --name-hash-version=2 option. In those cases, it may be beneficial to combine the two options. However, there has not been a released version of Git that has both options and I don't have access to these repos for testing. Signed-off-by: Derrick Stolee <stolee@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Derrick Stolee committed May 16, 2025 at 18:11 UTC 5f711504d9540ef5c8ca4c9d43e6f5a1d0259d3c

3 files changed +18 -12

Documentation/git-repack.adoc

+4 -1

@@ -11,7 +11,7 @@ SYNOPSIS

11 [verse]

12 'git repack' [-a] [-A] [-d] [-f] [-F] [-l] [-n] [-q] [-b] [-m]

13 [--window=<n>] [--depth=<n>] [--threads=<n>] [--keep-pack=<pack-name>]

14 - [--write-midx] [--name-hash-version=<n>]

14 + [--write-midx] [--name-hash-version=<n>] [--path-walk]

16 DESCRIPTION

17 -----------

@@ -255,6 +255,9 @@ linkgit:git-multi-pack-index[1]).

255 Provide this argument to the underlying `git pack-objects` process.

256 See linkgit:git-pack-objects[1] for full details.

257

258 +--path-walk::

259 + Pass the `--path-walk` option to the underlying `git pack-objects`

260 + process. See linkgit:git-pack-objects[1] for full details.

261

262 CONFIGURATION

263 -------------

builtin/repack.c

+6 -1

@@ -43,7 +43,7 @@ static char *packdir, *packtmp_name, *packtmp;

43 static const char *const git_repack_usage[] = {

44 N_("git repack [-a] [-A] [-d] [-f] [-F] [-l] [-n] [-q] [-b] [-m]\n"

45 "[--window=<n>] [--depth=<n>] [--threads=<n>] [--keep-pack=<pack-name>]\n"

46 - "[--write-midx] [--name-hash-version=<n>]"),

46 + "[--write-midx] [--name-hash-version=<n>] [--path-walk]"),

47 NULL

48 };

@@ -63,6 +63,7 @@ struct pack_objects_args {

63 int quiet;

64 int local;

65 int name_hash_version;

66 + int path_walk;

67 struct list_objects_filter_options filter_options;

68 };

@@ -313,6 +314,8 @@ static void prepare_pack_objects(struct child_process *cmd,

314 strvec_pushf(&cmd->args, "--no-reuse-object");

315 if (args->name_hash_version)

316 strvec_pushf(&cmd->args, "--name-hash-version=%d", args->name_hash_version);

317 + if (args->path_walk)

318 + strvec_pushf(&cmd->args, "--path-walk");

319 if (args->local)

320 strvec_push(&cmd->args, "--local");

321 if (args->quiet)

@@ -1212,6 +1215,8 @@ int cmd_repack(int argc,

1215 N_("pass --no-reuse-object to git-pack-objects")),

1216 OPT_INTEGER(0, "name-hash-version", &po_args.name_hash_version,

1217 N_("specify the name hash version to use for grouping similar objects by path")),

1218 + OPT_BOOL(0, "path-walk", &po_args.path_walk,

1219 + N_("pass --path-walk to git-pack-objects")),

1220 OPT_NEGBIT('n', NULL, &run_update_server_info,

1221 N_("do not run git-update-server-info"), 1),

1222 OPT__QUIET(&po_args.quiet, N_("be quiet")),

t/perf/p5313-pack-objects.sh

+8 -10

@@ -55,23 +55,21 @@ test_all_with_args () {

55 test_size "shallow pack size with $parameter" '

56 test_file_size out

57 '

58 -}

59 -

60 -for version in 1 2

61 -do

62 - export version

63 -

64 - test_all_with_args --name-hash-version=$version

66 - test_perf "repack with --name-hash-version=$version" '

67 - git repack -adf --name-hash-version=$version

59 + test_perf "repack with $parameter" '

60 + git repack -adf $parameter

61 '

70 - test_size "repack size with --name-hash-version=$version" '

63 + test_size "repack size with $parameter" '

64 gitdir=$(git rev-parse --git-dir) &&

65 pack=$(ls $gitdir/objects/pack/pack-*.pack) &&

66 test_file_size "$pack"

67 '

68 +}

69 +

70 +for version in 1 2

71 +do

72 + test_all_with_args --name-hash-version=$version

73 done

75 test_all_with_args --path-walk