From patchwork Thu Aug 6 16:30:17 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: 11703773 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 AA8BC138C for ; Thu, 6 Aug 2020 17:53:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0EB55221E2 for ; Thu, 6 Aug 2020 17:53:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="eepivPes" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729567AbgHFRxa (ORCPT ); Thu, 6 Aug 2020 13:53:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40182 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728363AbgHFQbD (ORCPT ); Thu, 6 Aug 2020 12:31:03 -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 D3E86C00217B for ; Thu, 6 Aug 2020 09:30:29 -0700 (PDT) Received: by mail-wr1-x444.google.com with SMTP id a14so44636764wra.5 for ; Thu, 06 Aug 2020 09:30:29 -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=0hSCVk2CC7v2IqEhzQdyOPS8QhjoXAQ0BoaG6W/wtMY=; b=eepivPes3oOz/LB0xy1KKD/d8F/a/91PPopIbU1xnl4oLBZkRkI8oOS7w/bCOJ/Nlo 3hvTpqmyxTfCmcfnE223eUBogWXv9s3TZuHaWihNpD9PMQV3iR3jVj5Lq3QybIrLQSO7 PnSk0CeALFwvkRw2cYzINccrXj0QZ4ZvVuwiXfmttpCLpnxBwfiHNd0/dtgPAiMcvsbu c+Kbj0CPWwyzMYMU6EB9u4Ii79zyMUANgt1GyeDsvinfVDcvE224mDgH7/MUjDXEq1ym fEM9tSxA2suYpwFC+PNvkux8B6010Ywa9ptKvQ+JeYKCkQxMZ4pnVuZC2/l+8f4jHVGI iRQw== 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=0hSCVk2CC7v2IqEhzQdyOPS8QhjoXAQ0BoaG6W/wtMY=; b=jdIlB/AvFp1pcxMcyHyyHkvSAA/BIHn0ai1PoJvrjpaB7GGj+4WuoH/jx9MJNMFWw3 uD/jOH9xsFpeA9Z3BMPCxq3GUnpVYiMDenx0dImjc6AOmWrn7bPFDMSIuDY3mL6n+CPV GM55jAr4hETZgFk3rpvjwXRWD99wJ8nlV0ORbxZpYT4w9+boTnuJX6KmFeyklZA1oS64 4a0E2eNh+TJM0h6GYM0ULKl8qeFZoO9vFyVSbbfDdV1mVfouLkBHx7K27f+dUkogYYZ8 nFfpH0ecvC3U4unKc589Jhye/OEXH5UpTt1WJiWoxo28qTKI35n4noSo3UHz3yl/9gM/ JVSg== X-Gm-Message-State: AOAM531aNGgUo6S11E1zI3HbFgJ7egXYxwNRRU6wUxrdmlNAyV2c1God Sjh8+WyO824Q7jF3eJ0HXCVX0dm9 X-Google-Smtp-Source: ABdhPJxOxGFWYgK6BxRJ2PLNRlekUOW+3fGG+pgfVtlo/Il+bR7eay/4c1tKSFwGxUz0ClvwkqmFbA== X-Received: by 2002:adf:ec8b:: with SMTP id z11mr7932916wrn.51.1596731428012; Thu, 06 Aug 2020 09:30:28 -0700 (PDT) Received: from [127.0.0.1] ([13.74.141.28]) by smtp.gmail.com with ESMTPSA id c24sm7213967wrb.11.2020.08.06.09.30.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Aug 2020 09:30:27 -0700 (PDT) Message-Id: <85118ed5f19468d5051dd1579e35cae3c3114d24.1596731425.git.gitgitgadget@gmail.com> In-Reply-To: References: From: "Derrick Stolee via GitGitGadget" Date: Thu, 06 Aug 2020 16:30:17 +0000 Subject: [PATCH 2/9] maintenance: add prefetch 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 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 foregroudn '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 | 52 +++++++++++++++++++++++++++++++ t/t7900-maintenance.sh | 25 +++++++++++++++ 3 files changed, 92 insertions(+) diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt index e1a2a8902c..bb0d5eded4 100644 --- a/Documentation/git-maintenance.txt +++ b/Documentation/git-maintenance.txt @@ -57,6 +57,21 @@ since it will not expire `.graph` files that were in the previous `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:: Cleanup 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 8162bca974..942b7ea535 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" @@ -843,6 +844,52 @@ static int maintenance_task_commit_graph(struct maintenance_opts *opts) return 1; } +static int fetch_remote(const char *remote, struct maintenance_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", "--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 fill_each_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_opts *opts) +{ + int result = 0; + struct string_list_item *item; + struct string_list remotes = STRING_LIST_INIT_DUP; + + if (for_each_remote(fill_each_remote, &remotes)) { + error(_("failed to fill remotes")); + result = 1; + goto cleanup; + } + + for (item = remotes.items; + item && item < remotes.items + remotes.nr; + item++) + result |= fetch_remote(item->string, opts); + +cleanup: + string_list_clear(&remotes, 0); + return result; +} + static int maintenance_task_gc(struct maintenance_opts *opts) { struct child_process child = CHILD_PROCESS_INIT; @@ -880,6 +927,7 @@ struct maintenance_task { }; enum maintenance_task_label { + TASK_PREFETCH, TASK_GC, TASK_COMMIT_GRAPH, @@ -888,6 +936,10 @@ 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 406dc7c303..3dd99ef660 100755 --- a/t/t7900-maintenance.sh +++ b/t/t7900-maintenance.sh @@ -58,4 +58,29 @@ 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 --refmap= --quiet" && + test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\*