# Intro Last year, John Cai sent 2 versions of a patch series to implement `git repack --filter=<filter-spec>` and later I sent 4 versions of a patch series trying to do it a bit differently: - https://lore.kernel.org/git/pull.1206.git.git.1643248180.gitgitgadget@xxxxxxxxx/ - https://lore.kernel.org/git/20221012135114.294680-1-christian.couder@xxxxxxxxx/ In these patch series, the `--filter=<filter-spec>` removed the filtered out objects altogether which was considered very dangerous even though we implemented different safety checks in some of the latter series. In some discussions, it was mentioned that such a feature, or a similar feature in `git gc`, or in a new standalone command (perhaps called `git prune-filtered`), should put the filtered out objects into a new packfile instead of deleting them. Recently there were internal discussions at GitLab about either moving blobs from inactive repos onto cheaper storage, or moving large blobs onto cheaper storage. This lead us to rethink at repacking using a filter, but moving the filtered out objects into a separate packfile instead of deleting them. So here is a new patch series doing that while implementing the `--filter=<filter-spec>` option in `git repack`. # Use cases for the new feature This could be useful for example for the following purposes: 1) As a way for servers to save storage costs by for example moving large blobs, or all the blobs, or all the blobs in inactive repos, to separate storage (while still making them accessible using for example the alternates mechanism). 2) As a way to use partial clone on a Git server to offload large blobs to, for example, an http server, while using multiple promisor remotes (to be able to access everything) on the client side. (In this case the packfile that contains the filtered out object can be manualy removed after checking that all the objects it contains are available through the promisor remote.) 3) As a way for clients to reclaim some space when they cloned with a filter to save disk space but then fetched a lot of unwanted objects (for example when checking out old branches) and now want to remove these unwanted objects. (In this case they can first move the packfile that contains filtered out objects to a separate directory or storage, then check that everything works well, and then manually remove the packfile after some time.) As the features and the code are quite different from those in the previous series, I decided to start a new series instead of continuing a previous one. Also since version 2 of this new series, commit messages, don't mention uses cases like 2) or 3) above, as people have different opinions on how it should be done. How it should be done could depend a lot on the way promisor remotes are used, the software and hardware setups used, etc, so it seems more difficult to "sell" this series by talking about such use cases. As use case 1) seems simpler and more appealing, it makes more sense to only talk about it in the commit messages. # Changes since version 3 Thanks to Junio who reviewed both version 1, 2 and 3, and to Taylor who reviewed version 1 and 3! The changes are the following: - In patch 2/8, which introduces `test-tool find-pack`, a new `--check-count <n>` option has been added to check the number of packfiles an object is in. To keep things simple and extendable, the parse-options API is now used to parse arguments and options. - Also in patch 2/8, a test script 't0080-find-pack.sh' has been introduced to test `test-tool find-pack`, as suggested by Taylor. - In patch 4/8, which refactors code into a find_pack_prefix() function, this function has been changed to accept a `packdir` and a `packtmp` argument, instead of using the global variables with the same names, as suggested by Taylor. - In patch 5/8, which introduces `--filter=<filter-spec>` option, a `struct list_objects_filter_option` and some related functions and macros are now used to handle these options, instead of a character string. This allows more than one `--filter=<filter-spec>` option to be passed, and a new test has been added to check that this works, as suggested by Taylor. - In patch 5/8, some changes have been made to better handle kept packfiles and related tests have been added to check that this works well, as suggested by Taylor. - In patch 5/8, a comment about the 'names' variable has been shortened a lot and improved a bit with additional useful information, as suggested by Taylor. - Also in patch 5/8, tests have been improved and shortened by using the new `--check-count <n>` option of `test-tool find-pack`. - Also in patch 5/8, the test that checks that `--filter=...` fails with `--write-bitmap-index` has been changed to use GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP=0 which should fix a CI test that sets this variable to 1. This test has also been simplified by removing a useless call to `repack --filter=...` as suggested by Taylor. - Also in patch 5/8, the commit message has been improved a bit and now only talks about the use case of moving some blobs that take up precious space to a cheaper storage, as suggested by Junio. - In patch 6/8, which implements the `gc.repackFilter` config option, a line in the tests that was too long has been split over 2 lines, as suggested by Taylor. - In patch 7/8, which implements the `--filter-to=<dir>` option, the documentation of that option talking about possible corruption has been clarified a bit, as suggested by Junio. - Also in patch 7/8, tests have been improved and shortened by using the new `--check-count <n>` option of `test-tool find-pack`. # Commit overview * 1/8 pack-objects: allow `--filter` without `--stdout` This patch is the same as in v1, v2 and v3. To be able to later repack with a filter we need `git pack-objects` to write packfiles when it's filtering instead of just writing the pack without the filtered out objects to stdout. * 2/8 t/helper: add 'find-pack' test-tool For testing `git repack --filter=...` that we are going to implement, it's useful to have a test helper that can tell which packfiles contain a specific object. Since v3 the new `--check-count <n>` option has been added, and tests have been added in a new 't0080-find-pack.sh' test script. * 3/8 repack: refactor finishing pack-objects command No change in this patch compared to v2 and v3. This is a small refactoring creating a new useful function, so that `git repack --filter=...` will be able to reuse it. * 4/8 repack: refactor finding pack prefix This is another small refactoring creating a small function that will be reused in the next patch. Since v3 the new function introduced in this patch has been changed to accept a `packdir` and a `packtmp` argument, instead of using the global variables with the same names. * 5/8 repack: add `--filter=<filter-spec>` option This actually adds the `--filter=<filter-spec>` option. It uses one `git pack-objects` process with the `--filter` option. And then another `git pack-objects` process with the `--stdin-packs` option. A lot of changes have been made since v3: - The `list_objects_filter_option` struct and some related functions and macros are used to handle the new `--filter=<filter-spec>` option. A new test has been added to check that using multiple such options works. - Handling of kept packfiles has been improved and related tests have been added. - A comment about the 'names' variable has been shortened a lot and improved a bit. - Tests have been improved and shortened by using the new `--check-count <n>` option of `test-tool find-pack`. - The test that checks that `--filter=...` fails with `--write-bitmap-index` has been improved to pass a CI test and shortened. - The commit message has been improved a bit. * 6/8 gc: add `gc.repackFilter` config option This is a gc config option so that `git gc` can also repack using a filter and put the filtered out objects into a separate packfile. Since v3, a line in the tests that was too long has been split over 2 lines. * 7/8 repack: implement `--filter-to` for storing filtered out objects For some use cases, it's interesting to create the packfile that contains the filtered out objects into a separate location. This is similar to the `--expire-to` option for cruft packfiles. Since v3, documentation of that option talking about possible corruption has been clarified a bit, and tests have been improved and shortened by using the new `--check-count <n>` option of `test-tool find-pack`. * 8/8 gc: add `gc.repackFilterTo` config option No change in this patch compared to v3. This allows specifying the location of the packfile that contains the filtered out objects when using `gc.repackFilter`. # Range-diff since v3 (Sorry, but the range-diff doesn't show changes in patches 2/8 and 5/8 as there has been a lot of changes in them. Instead it shows that the old commit has been removed and a new one added.) 1: 4d75a1d7c3 = 1: 4d75a1d7c3 pack-objects: allow `--filter` without `--stdout` 2: fdf9b6e8cc < -: ---------- t/helper: add 'find-pack' test-tool -: ---------- > 2: 0bf9f53158 t/helper: add 'find-pack' test-tool 3: e7cfdebc78 = 3: 54060d775e repack: refactor finishing pack-objects command 4: 9c51063795 ! 4: 948ea541ae repack: refactor finding pack prefix @@ builtin/repack.c: static int write_cruft_pack(const struct pack_objects_args *ar return finish_pack_objects_cmd(&cmd, names, local); } -+static const char *find_pack_prefix(void) ++static const char *find_pack_prefix(char *packdir, char *packtmp) +{ + const char *pack_prefix; + if (!skip_prefix(packtmp, packdir, &pack_prefix)) @@ builtin/repack.c: int cmd_repack(int argc, const char **argv, const char *prefix - packtmp, packdir); - if (*pack_prefix == '/') - pack_prefix++; -+ const char *pack_prefix = find_pack_prefix(); ++ const char *pack_prefix = find_pack_prefix(packdir, packtmp); if (!cruft_po_args.window) cruft_po_args.window = po_args.window; 5: a90e8045c3 < -: ---------- repack: add `--filter=<filter-spec>` option -: ---------- > 5: 0635425289 repack: add `--filter=<filter-spec>` option 6: 335b7f614d ! 6: bf8be2c812 gc: add `gc.repackFilter` config option @@ t/t6500-gc.sh: test_expect_success 'one of gc.reflogExpire{Unreachable,}=never d + git -C bare.git -c gc.cruftPacks=false gc && + test_stdout_line_count = 1 ls bare.git/objects/pack/*.pack && + -+ GIT_TRACE=$(pwd)/trace.out git -C bare.git -c gc.repackFilter=blob:none -c repack.writeBitmaps=false -c gc.cruftPacks=false gc && ++ GIT_TRACE=$(pwd)/trace.out git -C bare.git -c gc.repackFilter=blob:none \ ++ -c repack.writeBitmaps=false -c gc.cruftPacks=false gc && + test_stdout_line_count = 2 ls bare.git/objects/pack/*.pack && + grep -E "^trace: (built-in|exec|run_command): git repack .* --filter=blob:none ?.*" trace.out +' 7: b1be7f60b7 ! 7: abe7526222 repack: implement `--filter-to` for storing filtered out objects @@ Commit message Signed-off-by: Christian Couder <chriscool@xxxxxxxxxxxxx> - repack: add test with --max-pack-size - ## Documentation/git-repack.txt ## @@ Documentation/git-repack.txt: depth is 4095. a single packfile containing all the objects. See @@ Documentation/git-repack.txt: depth is 4095. + used for putting the pack on a separate object directory that + is accessed through the Git alternates mechanism. **WARNING:** + If the packfile containing the filtered out objects is not -+ accessible, the repo could be considered corrupt by Git as it -+ migh not be able to access the objects in that packfile. See -+ the `objects` and `objects/info/alternates` sections of ++ accessible, the repo can become corrupt as it might not be ++ possible to access the objects in that packfile. See the ++ `objects` and `objects/info/alternates` sections of + linkgit:gitrepository-layout[5]. + -b:: @@ builtin/repack.c: int cmd_repack(int argc, const char **argv, const char *prefix }; @@ builtin/repack.c: int cmd_repack(int argc, const char **argv, const char *prefix) - strvec_push(&cmd.args, "--incremental"); - } - -+ if (filter_to && !po_args.filter) + if (po_args.filter_options.choice) + strvec_pushf(&cmd.args, "--filter=%s", + expand_list_objects_filter_spec(&po_args.filter_options)); ++ else if (filter_to) + die(_("option '%s' can only be used along with '%s'"), "--filter-to", "--filter"); -+ + if (geometry) cmd.in = -1; - else @@ builtin/repack.c: int cmd_repack(int argc, const char **argv, const char *prefix) } - if (po_args.filter) { + if (po_args.filter_options.choice) { + if (!filter_to) + filter_to = packtmp; + ret = write_filtered_pack(&po_args, - packtmp, + filter_to, - find_pack_prefix(), + find_pack_prefix(packdir, packtmp), + &keep_pack_list, &names, - &existing_nonkept_packs, ## t/t7700-repack.sh ## -@@ t/t7700-repack.sh: test_expect_success '--filter fails with --write-bitmap-index' ' - --filter=blob:none +@@ t/t7700-repack.sh: test_expect_success '--filter works with --pack-kept-objects and .keep packs' ' + ) ' +test_expect_success '--filter-to stores filtered out objects' ' @@ t/t7700-repack.sh: test_expect_success '--filter fails with --write-bitmap-index + test_stdout_line_count = 1 ls bare.git/objects/pack/pack-*.pack && + test_stdout_line_count = 1 ls filtered.git/objects/pack/pack-*.pack && + -+ commit_pack=$(test-tool -C bare.git find-pack HEAD) && -+ test -n "$commit_pack" && -+ blob_pack=$(test-tool -C bare.git find-pack HEAD:file1) && -+ test -z "$blob_pack" && ++ commit_pack=$(test-tool -C bare.git find-pack -c 1 HEAD) && ++ blob_pack=$(test-tool -C bare.git find-pack -c 0 HEAD:file1) && + blob_hash=$(git -C bare.git rev-parse HEAD:file1) && + test -n "$blob_hash" && -+ blob_pack=$(test-tool -C filtered.git find-pack $blob_hash) && -+ test -n "$blob_pack" && ++ blob_pack=$(test-tool -C filtered.git find-pack -c 1 $blob_hash) && + + echo $(pwd)/filtered.git/objects >bare.git/objects/info/alternates && -+ blob_pack=$(test-tool -C bare.git find-pack HEAD:file1) && -+ test -n "$blob_pack" && ++ blob_pack=$(test-tool -C bare.git find-pack -c 1 HEAD:file1) && + blob_content=$(git -C bare.git show $blob_hash) && + test "$blob_content" = "content1" +' @@ t/t7700-repack.sh: test_expect_success '--filter fails with --write-bitmap-index + # Check that the 3 blobs are in different packfiles in filtered.git + test_stdout_line_count = 3 ls ../filtered.git/objects/pack/pack-*.pack && + test_stdout_line_count = 1 ls objects/pack/pack-*.pack && -+ foo_pack=$(test-tool find-pack HEAD:foo) && -+ bar_pack=$(test-tool find-pack HEAD:bar) && -+ base_pack=$(test-tool find-pack HEAD:base.t) && ++ foo_pack=$(test-tool find-pack -c 1 HEAD:foo) && ++ bar_pack=$(test-tool find-pack -c 1 HEAD:bar) && ++ base_pack=$(test-tool find-pack -c 1 HEAD:base.t) && + test "$foo_pack" != "$bar_pack" && + test "$foo_pack" != "$base_pack" && + test "$bar_pack" != "$base_pack" && 8: ed66511823 = 8: ccdc858f73 gc: add `gc.repackFilterTo` config option Christian Couder (8): pack-objects: allow `--filter` without `--stdout` t/helper: add 'find-pack' test-tool repack: refactor finishing pack-objects command repack: refactor finding pack prefix repack: add `--filter=<filter-spec>` option gc: add `gc.repackFilter` config option repack: implement `--filter-to` for storing filtered out objects gc: add `gc.repackFilterTo` config option Documentation/config/gc.txt | 16 ++ Documentation/git-pack-objects.txt | 4 +- Documentation/git-repack.txt | 23 +++ Makefile | 1 + builtin/gc.c | 10 ++ builtin/pack-objects.c | 8 +- builtin/repack.c | 169 +++++++++++++++------ t/helper/test-find-pack.c | 50 +++++++ t/helper/test-tool.c | 1 + t/helper/test-tool.h | 1 + t/t0080-find-pack.sh | 82 +++++++++++ t/t5317-pack-objects-filter-objects.sh | 8 + t/t6500-gc.sh | 24 +++ t/t7700-repack.sh | 196 +++++++++++++++++++++++++ 14 files changed, 543 insertions(+), 50 deletions(-) create mode 100644 t/helper/test-find-pack.c create mode 100755 t/t0080-find-pack.sh -- 2.42.0.rc0.8.g76fac86b0e
