From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by dcvr.yhbt.net (Postfix) with ESMTP id 7577D1F4B4 for ; Fri, 25 Sep 2020 12:33:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728339AbgIYMdp (ORCPT ); Fri, 25 Sep 2020 08:33:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35888 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726368AbgIYMdn (ORCPT ); Fri, 25 Sep 2020 08:33:43 -0400 Received: from mail-wr1-x443.google.com (mail-wr1-x443.google.com [IPv6:2a00:1450:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1B4B6C0613CE for ; Fri, 25 Sep 2020 05:33:43 -0700 (PDT) Received: by mail-wr1-x443.google.com with SMTP id g4so3424158wrs.5 for ; Fri, 25 Sep 2020 05:33:43 -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=4M7aBuZa+23SPS0EXGE8b/xKhtx/rwIrAZGhG9usDN8=; b=grby7MkVvdZvFVGH39zuPUSrH0k43lxKMGPv25fwWh1pdVnh3agr/TKB6mczX4MU7L huqWx6ZSU9VBR71qE5PkVbIUGS+o8qAiizKkTAi+bj0oIHr7Hn+lmTt1irIbVpozQQ0A 8Yq1g+mLZuxXZiUiqaOZL958yCf8H0ekapDrKNUt91SXGhqQduvXSGXdOekdVh9Hm194 XgLFJruj4sj7yKurd4UXI/IAWhJn/93XwGLnRn3jzZxnL5LqLVzRp2MBcqs54w37jDD5 XR+szB4GlT3mXe17DFvBCcTQOF0s+fnE1K4T7inGzwe+d2/spMf0KT/uwgCUBMUf00pM JNSA== 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=4M7aBuZa+23SPS0EXGE8b/xKhtx/rwIrAZGhG9usDN8=; b=Og0JDDs1z78OXl5+rnSUAByrXhU74VaIkU8HDy7yWkxx50rY/CYP4GZDX6WCpODGNx T0TUvg7LpvGwiax2aVRWTwar/9+2hqdve+341NaE8Nf6EZgDUmRROHEnlFti0IRxB7CS vSuewAkpTSjqGQtqx5DjZVkuWntC5VC/aGlbKtVc87HvFWNthmZtfja9+pVgwo4tMgt1 AVPVjlKguro89ETzK8VXGJhSAE75sQKPXonk4U3D4DRB/mHuQCAlAIIGwgloSzq0GIx8 c9EZO1x9d38sIwHD+PGOdN/baZ2f6Vo2dF4onUJunfdig7MTV3IxvXffs+NdjyGsUgVx cPeA== X-Gm-Message-State: AOAM533PkVSDQb/+e3yjumEeb3wn6b6QZalL5PX4TRe8mDv2WmouLzac q7uDAXlHXi1Sqx/C2LJsL0lemFn4lA0= X-Google-Smtp-Source: ABdhPJzBknkPK+UGUXh+BrOXQeufBpDeu9llDhinnrECLK9D1JuKWi1qBVfv7t2vqrn23JnlZlDExw== X-Received: by 2002:adf:ef48:: with SMTP id c8mr4360990wrp.370.1601037221155; Fri, 25 Sep 2020 05:33:41 -0700 (PDT) Received: from [127.0.0.1] ([13.74.141.28]) by smtp.gmail.com with ESMTPSA id q20sm2731519wmj.5.2020.09.25.05.33.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Sep 2020 05:33:40 -0700 (PDT) Message-Id: <7a62e224cfa4e353572d90ad2bdef0b9e348def4.1601037218.git.gitgitgadget@gmail.com> In-Reply-To: References: From: "Derrick Stolee via GitGitGadget" Date: Fri, 25 Sep 2020 12:33:31 +0000 Subject: [PATCH v4 1/8] maintenance: add prefetch task Fcc: Sent Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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, Jonathan Tan , Derrick Stolee , Derrick Stolee , Derrick Stolee Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org From: Derrick Stolee When working with very large repositories, an incremental 'git fetch' command can download a large amount of data. If there are many other users pushing to a common repo, then this data can rival the initial pack-file size of a 'git clone' of a medium-size repo. Users may want to keep the data on their local repos as close as possible to the data on the remote repos by fetching periodically in the background. This can break up a large daily fetch into several smaller hourly fetches. The task is called "prefetch" because it is work done in advance of a foreground fetch to make that 'git fetch' command much faster. However, if we simply ran 'git fetch ' in the background, then the user running a foreground 'git fetch ' would lose some important feedback when a new branch appears or an existing branch updates. This is especially true if a remote branch is force-updated and this isn't noticed by the user because it occurred in the background. Further, the functionality of 'git push --force-with-lease' becomes suspect. When running 'git fetch ' in the background, use the following options for careful updating: 1. --no-tags prevents getting a new tag when a user wants to see the new tags appear in their foreground fetches. 2. --refmap= removes the configured refspec which usually updates refs/remotes//* with the refs advertised by the remote. While this looks confusing, this was documented and tested by b40a50264ac (fetch: document and test --refmap="", 2020-01-21), including this sentence in the documentation: Providing an empty `` to the `--refmap` option causes Git to ignore the configured refspecs and rely entirely on the refspecs supplied as command-line arguments. 3. By adding a new refspec "+refs/heads/*:refs/prefetch//*" we can ensure that we actually load the new values somewhere in our refspace while not updating refs/heads or refs/remotes. By storing these refs here, the commit-graph job will update the commit-graph with the commits from these hidden refs. 4. --prune will delete the refs/prefetch/ refs that no longer appear on the remote. 5. --no-write-fetch-head prevents updating FETCH_HEAD. We've been using this step as a critical background job in Scalar [1] (and VFS for Git). This solved a pain point that was showing up in user reports: fetching was a pain! Users do not like waiting to download the data that was created while they were away from their machines. After implementing background fetch, the foreground fetch commands sped up significantly because they mostly just update refs and download a small amount of new data. The effect is especially dramatic when paried with --no-show-forced-udpates (through fetch.showForcedUpdates=false). [1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/FetchStep.cs Signed-off-by: Derrick Stolee --- Documentation/git-maintenance.txt | 15 +++++++++ builtin/gc.c | 51 +++++++++++++++++++++++++++++++ t/t7900-maintenance.sh | 26 ++++++++++++++++ 3 files changed, 92 insertions(+) diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt index 6abcb8255a..12668fccf7 100644 --- a/Documentation/git-maintenance.txt +++ b/Documentation/git-maintenance.txt @@ -47,6 +47,21 @@ commit-graph:: `commit-graph-chain` file. They will be deleted by a later run based on the expiration delay. +prefetch:: + The `prefetch` task updates the object directory with the latest + objects from all registered remotes. For each remote, a `git fetch` + command is run. The refmap is custom to avoid updating local or remote + branches (those in `refs/heads` or `refs/remotes`). Instead, the + remote refs are stored in `refs/prefetch//`. Also, tags are + not updated. ++ +This is done to avoid disrupting the remote-tracking branches. The end users +expect these refs to stay unmoved unless they initiate a fetch. With prefetch +task, however, the objects necessary to complete a later real fetch would +already be obtained, so the real fetch would go faster. In the ideal case, +it will just become an update to bunch of remote-tracking branches without +any object transfer. + gc:: Clean up unnecessary files and optimize the local repository. "GC" stands for "garbage collection," but this task performs many diff --git a/builtin/gc.c b/builtin/gc.c index 090959350e..5e469488f4 100644 --- a/builtin/gc.c +++ b/builtin/gc.c @@ -29,6 +29,7 @@ #include "tree.h" #include "promisor-remote.h" #include "refs.h" +#include "remote.h" #define FAILED_RUN "failed to run %s" @@ -816,6 +817,51 @@ static int maintenance_task_commit_graph(struct maintenance_run_opts *opts) return 0; } +static int fetch_remote(const char *remote, struct maintenance_run_opts *opts) +{ + struct child_process child = CHILD_PROCESS_INIT; + + child.git_cmd = 1; + strvec_pushl(&child.args, "fetch", remote, "--prune", "--no-tags", + "--no-write-fetch-head", "--recurse-submodules=no", + "--refmap=", NULL); + + if (opts->quiet) + strvec_push(&child.args, "--quiet"); + + strvec_pushf(&child.args, "+refs/heads/*:refs/prefetch/%s/*", remote); + + return !!run_command(&child); +} + +static int append_remote(struct remote *remote, void *cbdata) +{ + struct string_list *remotes = (struct string_list *)cbdata; + + string_list_append(remotes, remote->name); + return 0; +} + +static int maintenance_task_prefetch(struct maintenance_run_opts *opts) +{ + int result = 0; + struct string_list_item *item; + struct string_list remotes = STRING_LIST_INIT_DUP; + + if (for_each_remote(append_remote, &remotes)) { + error(_("failed to fill remotes")); + result = 1; + goto cleanup; + } + + for_each_string_list_item(item, &remotes) + result |= fetch_remote(item->string, opts); + +cleanup: + string_list_clear(&remotes, 0); + return result; +} + static int maintenance_task_gc(struct maintenance_run_opts *opts) { struct child_process child = CHILD_PROCESS_INIT; @@ -854,6 +900,7 @@ struct maintenance_task { }; enum maintenance_task_label { + TASK_PREFETCH, TASK_GC, TASK_COMMIT_GRAPH, @@ -862,6 +909,10 @@ enum maintenance_task_label { }; static struct maintenance_task tasks[] = { + [TASK_PREFETCH] = { + "prefetch", + maintenance_task_prefetch, + }, [TASK_GC] = { "gc", maintenance_task_gc, diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh index 53c883531e..045524e6ad 100755 --- a/t/t7900-maintenance.sh +++ b/t/t7900-maintenance.sh @@ -62,4 +62,30 @@ test_expect_success 'run --task duplicate' ' test_i18ngrep "cannot be selected multiple times" err ' +test_expect_success 'run --task=prefetch with no remotes' ' + git maintenance run --task=prefetch 2>err && + test_must_be_empty err +' + +test_expect_success 'prefetch multiple remotes' ' + git clone . clone1 && + git clone . clone2 && + git remote add remote1 "file://$(pwd)/clone1" && + git remote add remote2 "file://$(pwd)/clone2" && + git -C clone1 switch -c one && + git -C clone2 switch -c two && + test_commit -C clone1 one && + test_commit -C clone2 two && + GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch 2>/dev/null && + fetchargs="--prune --no-tags --no-write-fetch-head --recurse-submodules=no --refmap= --quiet" && + test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\*