From: Derrick Stolee <dstolee@xxxxxxxxxxxxx> The previous change cleaned up loose objects using the 'loose-objects' that can be run safely in the background. Add a similar job that performs similar cleanups for pack-files. One issue with running 'git repack' is that it is designed to repack all pack-files into a single pack-file. While this is the most space-efficient way to store object data, it is not time or memory efficient. This becomes extremely important if the repo is so large that a user struggles to store two copies of the pack on their disk. Instead, perform an "incremental" repack by collecting a few small pack-files into a new pack-file. The multi-pack-index facilitates this process ever since 'git multi-pack-index expire' was added in 19575c7 (multi-pack-index: implement 'expire' subcommand, 2019-06-10) and 'git multi-pack-index repack' was added in ce1e4a1 (midx: implement midx_repack(), 2019-06-10). The 'pack-files' job runs the following steps: 1. 'git multi-pack-index write' creates a multi-pack-index file if one did not exist, and otherwise will update the multi-pack-index with any new pack-files that appeared since the last write. This is particularly relevant with the background fetch job. When the multi-pack-index sees two copies of the same object, it stores the offset data into the newer pack-file. This means that some old pack-files could become "unreferenced" which I will use to mean "a pack-file that is in the pack-file list of the multi-pack-index but none of the objects in the multi-pack-index reference a location inside that pack-file." 2. 'git multi-pack-index expire' deletes any unreferenced pack-files and updaes the multi-pack-index to drop those pack-files from the list. This is safe to do as concurrent Git processes will see the multi-pack-index and not open those packs when looking for object contents. (Similar to the 'loose-objects' job, there are some Git commands that open pack-files regardless of the multi-pack-index, but they are rarely used. Further, a user that self-selects to use background operations would likely refrain from using those commands.) 3. 'git multi-pack-index repack --bacth-size=<size>' collects a set of pack-files that are listed in the multi-pack-index and creates a new pack-file containing the objects whose offsets are listed by the multi-pack-index to be in those objects. The set of pack- files is selected greedily by sorting the pack-files by modified time and adding a pack-file to the set if its "expected size" is smaller than the batch size until the total expected size of the selected pack-files is at least the batch size. The "expected size" is calculated by taking the size of the pack-file divided by the number of objects in the pack-file and multiplied by the number of objects from the multi-pack-index with offset in that pack-file. The expected size approximats how much data from that pack-file will contribute to the resulting pack-file size. The intention is that the resulting pack-file will be close in size to the provided batch size. The next run of the pack-files job will delete these repacked pack-files during the 'expire' step. In this version, the batch size is set to "0" which ignores the size restrictions when selecting the pack-files. It instead selects all pack-files and repacks all packed objects into a single pack-file. This will be updated in the next change, but it requires doing some calculations that are better isolated to a separate change. Each of the above steps update the multi-pack-index file. After each step, we verify the new multi-pack-index. If the new multi-pack-index is corrupt, then delete the multi-pack-index, rewrite it from scratch, and stop doing the later steps of the job. This is intended to be an extra-safe check without leaving a repo with many pack-files without a multi-pack-index. These steps are based on a similar background maintenance step in Scalar (and VFS for Git) [1]. This was incredibly effective for users of the Windows OS repository. After using the same VFS for Git repository for over a year, some users had _thousands_ of pack-files that combined to up to 250 GB of data. We noticed a few users were running into the open file descriptor limits (due in part to a bug in the multi-pack-index fixed by af96fe3392 (midx: add packs to packed_git linked list, 2019-04-29). These pack-files were mostly small since they contained the commits and trees that were pushed to the origin in a given hour. The GVFS protocol includes a "prefetch" step that asks for pre-computed pack- files containing commits and trees by timestamp. These pack-files were grouped into "daily" pack-files once a day for up to 30 days. If a user did not request prefetch packs for over 30 days, then they would get the entire history of commits and trees in a new, large pack-file. This led to a large number of pack-files that had poor delta compression. By running this pack-file maintenance step once per day, these repos with thousands of packs spanning 200+ GB dropped to dozens of pack- files spanning 30-50 GB. This was done all without removing objects from the system and using a constant batch size of two gigabytes. Once the work was done to reduce the pack-files to small sizes, the batch size of two gigabytes means that not every run triggers a repack operation, so the following run will not expire a pack-file. This has kept these repos in a "clean" state. [1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/PackfileMaintenanceStep.cs Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx> --- Documentation/git-run-job.txt | 18 ++++++- builtin/run-job.c | 90 ++++++++++++++++++++++++++++++++++- midx.c | 2 +- midx.h | 1 + t/t7900-run-job.sh | 39 +++++++++++++++ 5 files changed, 147 insertions(+), 3 deletions(-) diff --git a/Documentation/git-run-job.txt b/Documentation/git-run-job.txt index 43ca1160b5a..108ed25b8bd 100644 --- a/Documentation/git-run-job.txt +++ b/Documentation/git-run-job.txt @@ -9,7 +9,7 @@ git-run-job - Run a maintenance job. Intended for background operation. SYNOPSIS -------- [verse] -'git run-job (commit-graph|fetch|loose-objects)' +'git run-job (commit-graph|fetch|loose-objects|pack-files)' DESCRIPTION @@ -71,6 +71,22 @@ a batch of loose objects. The batch size is limited to 50 thousand objects to prevent the job from taking too long on a repository with many loose objects. +'pack-files':: + +The `pack-files` job incrementally repacks the object directory using +the `multi-pack-index` feature. In order to prevent race conditions with +concurrent Git commands, it follows a two-step process. First, it +deletes any pack-files included in the `multi-pack-index` where none of +the objects in the `multi-pack-index` reference those pack-files; this +only happens if all objects in the pack-file are also stored in a newer +pack-file. Second, it selects a group of pack-files whose "expected +size" is below the batch size until the group has total expected size at +least the batch size; see the `--batch-size` option for the `repack` +subcommand in linkgit:git-multi-pack-index[1]. The default batch-size is +zero, which is a special case that attempts to repack all pack-files +into a single pack-file. + + GIT --- Part of the linkgit:git[1] suite diff --git a/builtin/run-job.c b/builtin/run-job.c index cecf9058c51..d3543f7ccb9 100644 --- a/builtin/run-job.c +++ b/builtin/run-job.c @@ -1,13 +1,14 @@ #include "builtin.h" #include "config.h" #include "commit-graph.h" +#include "midx.h" #include "object-store.h" #include "parse-options.h" #include "repository.h" #include "run-command.h" static char const * const builtin_run_job_usage[] = { - N_("git run-job (commit-graph|fetch|loose-objects)"), + N_("git run-job (commit-graph|fetch|loose-objects|pack-files)"), NULL }; @@ -238,6 +239,91 @@ static int run_loose_objects_job(void) return prune_packed() || pack_loose(); } +static int multi_pack_index_write(void) +{ + struct argv_array cmd = ARGV_ARRAY_INIT; + argv_array_pushl(&cmd, "multi-pack-index", "write", + "--no-progress", NULL); + return run_command_v_opt(cmd.argv, RUN_GIT_CMD); +} + +static int rewrite_multi_pack_index(void) +{ + char *midx_name = get_midx_filename(the_repository->objects->odb->path); + + unlink(midx_name); + free(midx_name); + + if (multi_pack_index_write()) { + error(_("failed to rewrite multi-pack-index")); + return 1; + } + + return 0; +} + +static int multi_pack_index_verify(void) +{ + struct argv_array cmd = ARGV_ARRAY_INIT; + argv_array_pushl(&cmd, "multi-pack-index", "verify", + "--no-progress", NULL); + return run_command_v_opt(cmd.argv, RUN_GIT_CMD); +} + +static int multi_pack_index_expire(void) +{ + struct argv_array cmd = ARGV_ARRAY_INIT; + argv_array_pushl(&cmd, "multi-pack-index", "expire", + "--no-progress", NULL); + return run_command_v_opt(cmd.argv, RUN_GIT_CMD); +} + +static int multi_pack_index_repack(void) +{ + int result; + struct argv_array cmd = ARGV_ARRAY_INIT; + argv_array_pushl(&cmd, "multi-pack-index", "repack", + "--no-progress", "--batch-size=0", NULL); + result = run_command_v_opt(cmd.argv, RUN_GIT_CMD); + + if (result && multi_pack_index_verify()) { + warning(_("multi-pack-index verify failed after repack")); + result = rewrite_multi_pack_index(); + } + + return result; +} + +static int run_pack_files_job(void) +{ + if (multi_pack_index_write()) { + error(_("failed to write multi-pack-index")); + return 1; + } + + if (multi_pack_index_verify()) { + warning(_("multi-pack-index verify failed after initial write")); + return rewrite_multi_pack_index(); + } + + if (multi_pack_index_expire()) { + error(_("multi-pack-index expire failed")); + return 1; + } + + if (multi_pack_index_verify()) { + warning(_("multi-pack-index verify failed after expire")); + return rewrite_multi_pack_index(); + } + + if (multi_pack_index_repack()) { + error(_("multi-pack-index repack failed")); + return 1; + } + + return 0; +} + int cmd_run_job(int argc, const char **argv, const char *prefix) { static struct option builtin_run_job_options[] = { @@ -261,6 +347,8 @@ int cmd_run_job(int argc, const char **argv, const char *prefix) return run_fetch_job(); if (!strcmp(argv[0], "loose-objects")) return run_loose_objects_job(); + if (!strcmp(argv[0], "pack-files")) + return run_pack_files_job(); } usage_with_options(builtin_run_job_usage, diff --git a/midx.c b/midx.c index 1527e464a7b..0f0d0a38812 100644 --- a/midx.c +++ b/midx.c @@ -36,7 +36,7 @@ #define PACK_EXPIRED UINT_MAX -static char *get_midx_filename(const char *object_dir) +char *get_midx_filename(const char *object_dir) { return xstrfmt("%s/pack/multi-pack-index", object_dir); } diff --git a/midx.h b/midx.h index e6fa356b5ca..cf2c09dffc2 100644 --- a/midx.h +++ b/midx.h @@ -39,6 +39,7 @@ struct multi_pack_index { #define MIDX_PROGRESS (1 << 0) +char *get_midx_filename(const char *object_dir); struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local); int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id); int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result); diff --git a/t/t7900-run-job.sh b/t/t7900-run-job.sh index 41da083257b..416ba04989d 100755 --- a/t/t7900-run-job.sh +++ b/t/t7900-run-job.sh @@ -6,6 +6,7 @@ Testing the background jobs, in the foreground ' GIT_TEST_COMMIT_GRAPH=0 +GIT_TEST_MULTI_PACK_INDEX=0 . ./test-lib.sh @@ -93,4 +94,42 @@ test_expect_success 'loose-objects job' ' test_cmp packs-between packs-after ' +test_expect_success 'pack-files job' ' + packDir=.git/objects/pack && + + # Create three disjoint pack-files with size BIG, small, small. + + echo HEAD~2 | git -C client pack-objects --revs $packDir/test-1 && + + test_tick && + git -C client pack-objects --revs $packDir/test-2 <<-\EOF && + HEAD~1 + ^HEAD~2 + EOF + + test_tick && + git -C client pack-objects --revs $packDir/test-3 <<-\EOF && + HEAD + ^HEAD~1 + EOF + + rm -f client/$packDir/pack-* && + rm -f client/$packDir/loose-* && + + ls client/$packDir/*.pack >packs-before && + test_line_count = 3 packs-before && + + # the job repacks the two into a new pack, but does not + # delete the old ones. + git -C client run-job pack-files && + ls client/$packDir/*.pack >packs-between && + test_line_count = 4 packs-between && + + # the job deletes the two old packs, and does not write + # a new one because only one pack remains. + git -C client run-job pack-files && + ls client/.git/objects/pack/*.pack >packs-after && + test_line_count = 1 packs-after +' + test_done -- gitgitgadget
