# 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 5 Thanks to Junio who reviewed or commented on versions 1, 2, 3, 4 and 5, and to Taylor who reviewed or commented on version 1, 3, 4 and 5! Thanks also to Robert Coup who participated in the discussions related to version 2 and Peff who participated in the discussions related to version 4. There is only the following code change since version 5: - Patch 5/9 (pack-bitmap-write: rebuild using new bitmap when remapping) is new. It fixes a bitmap rebuilding issue that wasn't triggered previously but got triggered by this series and caused CI tests to fail. The patch is taken from a suggestion by Taylor in: https://lore.kernel.org/git/ZNwFlcS3SOS9h77N@nand.local/ I checked that CI tests now passes in: https://github.com/chriscool/git/actions/runs/6122146278 (There is a failure on 'win test (5)' with "failed: t7527.17 directory changes to a file", but it looks like it's not related to the previous issue and also not related to to this series at all.) Another change is that this series has been rebased on top of 94e83dcf5b (The seventh batch, 2023-09-07) to fix a few conflicts related to changes in the geometry code, as can be seen in the short range-diff below. # Commit overview (No changes in any of the patches compared to version 5, except that patch 5/9 is new.) * 1/9 pack-objects: allow `--filter` without `--stdout` 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. * 2/9 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. * 3/9 repack: refactor finishing pack-objects command This is a small refactoring creating a new useful function, so that `git repack --filter=...` will be able to reuse it. * 4/9 repack: refactor finding pack prefix This is another small refactoring creating a small function that will be reused in the next patch. * 5/9 pack-bitmap-write: rebuild using new bitmap when remapping This patch is new in version 6. It fixes an issue when bitmaps are rebuilt that was revealed by this series, and caused a CI test to fail. * 6/9 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. * 7/9 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. * 8/9 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. * 9/9 gc: add `gc.repackFilterTo` config option This allows specifying the location of the packfile that contains the filtered out objects when using `gc.repackFilter`. # Range-diff since v5 1: bbcc368876 = 1: da931b5082 pack-objects: allow `--filter` without `--stdout` 2: f1b80e5728 = 2: 10504b3699 t/helper: add 'find-pack' test-tool 3: ffecc73960 ! 3: ee12eb8ad7 repack: refactor finishing pack-objects command @@ builtin/repack.c: static int write_cruft_pack(const struct pack_objects_args *ar @@ builtin/repack.c: int cmd_repack(int argc, const char **argv, const char *prefix) struct string_list existing_nonkept_packs = STRING_LIST_INIT_DUP; struct string_list existing_kept_packs = STRING_LIST_INIT_DUP; - struct pack_geometry *geometry = NULL; + struct pack_geometry geometry = { 0 }; - struct strbuf line = STRBUF_INIT; struct tempfile *refs_snapshot = NULL; int i, ext, ret; 4: 6c2f381a88 = 4: d197e0c370 repack: refactor finding pack prefix -: ---------- > 5: abeef5fbad pack-bitmap-write: rebuild using new bitmap when remapping 5: 134700c2ce ! 6: 31ca2579d3 repack: add `--filter=<filter-spec>` option @@ builtin/repack.c: int cmd_repack(int argc, const char **argv, const char *prefix + strvec_pushf(&cmd.args, "--filter=%s", + expand_list_objects_filter_spec(&po_args.filter_options)); + - if (geometry) + if (geometry.split_factor) cmd.in = -1; else @@ 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 @@ builtin/repack.c: int cmd_repack(int argc, const char **argv, const char *prefix) string_list_clear(&existing_nonkept_packs, 0); string_list_clear(&existing_kept_packs, 0); - clear_pack_geometry(geometry); + free_pack_geometry(&geometry); + list_objects_filter_release(&po_args.filter_options); return ret; 6: d3365c7b48 = 7: fa70ae85f2 gc: add `gc.repackFilter` config option 7: 9a09382cd1 ! 8: e01ea3dd70 repack: implement `--filter-to` for storing filtered out objects @@ builtin/repack.c: int cmd_repack(int argc, const char **argv, const char *prefix + else if (filter_to) + die(_("option '%s' can only be used along with '%s'"), "--filter-to", "--filter"); - if (geometry) + if (geometry.split_factor) cmd.in = -1; @@ builtin/repack.c: int cmd_repack(int argc, const char **argv, const char *prefix) } 8: a52e3a71db = 9: d6ff314189 gc: add `gc.repackFilterTo` config option Christian Couder (9): pack-objects: allow `--filter` without `--stdout` t/helper: add 'find-pack' test-tool repack: refactor finishing pack-objects command repack: refactor finding pack prefix pack-bitmap-write: rebuild using new bitmap when remapping 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 | 167 +++++++++++++++------ pack-bitmap-write.c | 6 +- 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 | 197 +++++++++++++++++++++++++ 15 files changed, 547 insertions(+), 51 deletions(-) create mode 100644 t/helper/test-find-pack.c create mode 100755 t/t0080-find-pack.sh -- 2.42.0.167.gd6ff314189
