From patchwork Tue Aug 18 14:25:28 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Philippe Blain via GitGitGadget X-Patchwork-Id: 11721107 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E22B6722 for ; Tue, 18 Aug 2020 14:26:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BDF9C20786 for ; Tue, 18 Aug 2020 14:26:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="lx6J6qdc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727031AbgHRO0H (ORCPT ); Tue, 18 Aug 2020 10:26:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51062 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726992AbgHROZn (ORCPT ); Tue, 18 Aug 2020 10:25:43 -0400 Received: from mail-wr1-x444.google.com (mail-wr1-x444.google.com [IPv6:2a00:1450:4864:20::444]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E0BDBC061389 for ; Tue, 18 Aug 2020 07:25:40 -0700 (PDT) Received: by mail-wr1-x444.google.com with SMTP id a15so18448557wrh.10 for ; Tue, 18 Aug 2020 07:25:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=message-id:in-reply-to:references:from:date:subject:fcc :content-transfer-encoding:mime-version:to:cc; bh=qizVdcDzIVOfB/xHbb8gJeYgB/xd90k8X14R8KwzFLo=; b=lx6J6qdcyKcvYhm7NtVULJsQNSQZx8P1dwA53lv9QbDQPnGjfE5+ehrIvuy2iUu8Ll cXEgXVbzH0MafsAWthJcqhrqxG2FIHKIygLSA3QUeoaIpBulogqlojtKLLpLtTSIx67X ZJHCJZoAb5S+If82f2s4K+MbrCxT8uz5FvhBbMwZd8BSc8edTdjaxoxa5ldAT06QVUfx rZKeJwQ2i+PIn+Bjre5a1DGPtzMz4mNBgh0+cRWDV5pwSU499RNUki33le7hnUStueEQ neJ6uzSDFQVd3TExBkcUKbJKgzTHSzODDybQ8DOlC8nADkWTkx2hAX9d/nrWCe/7/cjG 9/Kg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:message-id:in-reply-to:references:from:date :subject:fcc:content-transfer-encoding:mime-version:to:cc; bh=qizVdcDzIVOfB/xHbb8gJeYgB/xd90k8X14R8KwzFLo=; b=jV70xVP4N0+1Dyp+M7owBGTLGfmr+El+K2gifTSSosXJ//7vQRSdFJ2oKRApAoxQK9 ZduzGe2K/TeP15d3uRP32I/N5fuWHe75wICEyRbvULtJxawRE7LzMPl312ZMrGlrQe/W vxGKZEaf2okEbVG35j5QlBKdlZ/qEugXDK03mS0v0aB5EFabOoYkzW6+beLqzE1CwYkw S0fZRbAkDDQkG4tF+BE1G3ci/4XLgj5tjrlXbBDA8ZP+1cBfD9RSvUXXiROQ/Y0RQplG 4zCvirh1Fb1MdkwNpOWhZ5h65cLI6tx7OFhTU2HRevp65XkVEbh+YoucCNIX28A2A7bV O1Cw== X-Gm-Message-State: AOAM531TRY/EjZIXjT7weaYQlgk5kUZ04AenAi9ahzoty+zpy7jfcCvp kMXU32nrBNHp2oKaMJSRVp+1oPCoDC8= X-Google-Smtp-Source: ABdhPJzrMl3vbGbxNYT1LDGfNQgCGG3JPmZTKb5sug9jsXSn2rnd9EdWb9ku21PaplclD1vJ46Kt0g== X-Received: by 2002:a5d:4802:: with SMTP id l2mr19561319wrq.183.1597760739041; Tue, 18 Aug 2020 07:25:39 -0700 (PDT) Received: from [127.0.0.1] ([13.74.141.28]) by smtp.gmail.com with ESMTPSA id p6sm33363644wru.33.2020.08.18.07.25.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2020 07:25:38 -0700 (PDT) Message-Id: In-Reply-To: References: From: "Derrick Stolee via GitGitGadget" Date: Tue, 18 Aug 2020 14:25:28 +0000 Subject: [PATCH v2 7/9] maintenance: add incremental-repack task Fcc: Sent MIME-Version: 1.0 To: git@vger.kernel.org Cc: sandals@crustytoothpaste.net, steadmon@google.com, jrnieder@gmail.com, peff@peff.net, congdanhqx@gmail.com, phillip.wood123@gmail.com, emilyshaffer@google.com, sluongng@gmail.com, jonathantanmy@google.com, Derrick Stolee , Derrick Stolee Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org From: Derrick Stolee 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 'incremental-repack' task 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=' 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 approximates 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 incremental-repack task 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 af96fe3 (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 --- Documentation/git-maintenance.txt | 15 ++++ builtin/gc.c | 113 ++++++++++++++++++++++++++++++ midx.c | 2 +- midx.h | 1 + t/t5319-multi-pack-index.sh | 1 + t/t7900-maintenance.sh | 38 ++++++++++ 6 files changed, 169 insertions(+), 1 deletion(-) diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt index 85205b5bb9..b0b73b7185 100644 --- a/Documentation/git-maintenance.txt +++ b/Documentation/git-maintenance.txt @@ -88,6 +88,21 @@ loose-objects:: advisable to enable both the `loose-objects` and `gc` tasks at the same time. +incremental-repack:: + The `incremental-repack` job 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. + OPTIONS ------- --auto:: diff --git a/builtin/gc.c b/builtin/gc.c index 61d5752af5..9aabef44a8 100644 --- a/builtin/gc.c +++ b/builtin/gc.c @@ -30,6 +30,7 @@ #include "promisor-remote.h" #include "refs.h" #include "remote.h" +#include "midx.h" #define FAILED_RUN "failed to run %s" @@ -1028,6 +1029,113 @@ static int maintenance_task_loose_objects(struct maintenance_opts *opts) return prune_packed(opts) || pack_loose(opts); } +static int multi_pack_index_write(struct maintenance_opts *opts) +{ + struct child_process child = CHILD_PROCESS_INIT; + + child.git_cmd = 1; + strvec_pushl(&child.args, "multi-pack-index", "write", NULL); + + if (opts->quiet) + strvec_push(&child.args, "--no-progress"); + + if (run_command(&child)) + return error(_("failed to write multi-pack-index")); + + return 0; +} + +static int rewrite_multi_pack_index(struct maintenance_opts *opts) +{ + struct repository *r = the_repository; + char *midx_name = get_midx_filename(r->objects->odb->path); + + unlink(midx_name); + free(midx_name); + + return multi_pack_index_write(opts); +} + +static int multi_pack_index_verify(struct maintenance_opts *opts, + const char *message) +{ + struct child_process child = CHILD_PROCESS_INIT; + + child.git_cmd = 1; + strvec_pushl(&child.args, "multi-pack-index", "verify", NULL); + + if (opts->quiet) + strvec_push(&child.args, "--no-progress"); + + if (run_command(&child)) { + warning(_("'git multi-pack-index verify' failed %s"), message); + return 1; + } + + return 0; +} + +static int multi_pack_index_expire(struct maintenance_opts *opts) +{ + struct child_process child = CHILD_PROCESS_INIT; + + child.git_cmd = 1; + strvec_pushl(&child.args, "multi-pack-index", "expire", NULL); + + if (opts->quiet) + strvec_push(&child.args, "--no-progress"); + + close_object_store(the_repository->objects); + + if (run_command(&child)) + return error(_("'git multi-pack-index expire' failed")); + + return 0; +} + +static int multi_pack_index_repack(struct maintenance_opts *opts) +{ + struct child_process child = CHILD_PROCESS_INIT; + + child.git_cmd = 1; + strvec_pushl(&child.args, "multi-pack-index", "repack", NULL); + + if (opts->quiet) + strvec_push(&child.args, "--no-progress"); + + strvec_push(&child.args, "--batch-size=0"); + + close_object_store(the_repository->objects); + + if (run_command(&child)) + return error(_("'git multi-pack-index repack' failed")); + + return 0; +} + +static int maintenance_task_incremental_repack(struct maintenance_opts *opts) +{ + prepare_repo_settings(the_repository); + if (!the_repository->settings.core_multi_pack_index) { + warning(_("skipping incremental-repack task because core.multiPackIndex is disabled")); + return 0; + } + + if (multi_pack_index_write(opts)) + return 1; + if (multi_pack_index_verify(opts, "after initial write")) + return rewrite_multi_pack_index(opts); + if (multi_pack_index_expire(opts)) + return 1; + if (multi_pack_index_verify(opts, "after expire step")) + return !!rewrite_multi_pack_index(opts); + if (multi_pack_index_repack(opts)) + return 1; + if (multi_pack_index_verify(opts, "after repack step")) + return !!rewrite_multi_pack_index(opts); + return 0; +} + typedef int maintenance_task_fn(struct maintenance_opts *opts); /* @@ -1049,6 +1157,7 @@ struct maintenance_task { enum maintenance_task_label { TASK_PREFETCH, TASK_LOOSE_OBJECTS, + TASK_INCREMENTAL_REPACK, TASK_GC, TASK_COMMIT_GRAPH, @@ -1066,6 +1175,10 @@ static struct maintenance_task tasks[] = { maintenance_task_loose_objects, loose_object_auto_condition, }, + [TASK_INCREMENTAL_REPACK] = { + "incremental-repack", + maintenance_task_incremental_repack, + }, [TASK_GC] = { "gc", maintenance_task_gc, diff --git a/midx.c b/midx.c index aa37d5da86..66d7053d83 100644 --- a/midx.c +++ b/midx.c @@ -37,7 +37,7 @@ #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 b18cf53bc4..baeecc70c9 100644 --- a/midx.h +++ b/midx.h @@ -37,6 +37,7 @@ 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/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh index 12f41dfc18..26f224b0e3 100755 --- a/t/t5319-multi-pack-index.sh +++ b/t/t5319-multi-pack-index.sh @@ -3,6 +3,7 @@ test_description='multi-pack-indexes' . ./test-lib.sh +GIT_TEST_MULTI_PACK_INDEX=0 objdir=.git/objects midx_read_expect () { diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh index efda1cf69b..dde28cf837 100755 --- a/t/t7900-maintenance.sh +++ b/t/t7900-maintenance.sh @@ -5,6 +5,7 @@ test_description='git maintenance builtin' . ./test-lib.sh GIT_TEST_COMMIT_GRAPH=0 +GIT_TEST_MULTI_PACK_INDEX=0 test_expect_success 'help text' ' test_expect_code 129 git maintenance -h 2>err && @@ -150,4 +151,41 @@ test_expect_success 'maintenance.loose-objects.auto' ' done ' +test_expect_success 'incremental-repack task' ' + packDir=.git/objects/pack && + for i in $(test_seq 1 5) + do + test_commit $i || return 1 + done && + + # Create three disjoint pack-files with size BIG, small, small. + echo HEAD~2 | git pack-objects --revs $packDir/test-1 && + test_tick && + git pack-objects --revs $packDir/test-2 <<-\EOF && + HEAD~1 + ^HEAD~2 + EOF + test_tick && + git pack-objects --revs $packDir/test-3 <<-\EOF && + HEAD + ^HEAD~1 + EOF + rm -f $packDir/pack-* && + rm -f $packDir/loose-* && + ls $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 maintenance run --task=incremental-repack && + ls $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 maintenance run --task=incremental-repack && + ls .git/objects/pack/*.pack >packs-after && + test_line_count = 1 packs-after +' + test_done