From patchwork Thu Aug 6 15:48:35 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: 11703539 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 A3F8B13B1 for ; Thu, 6 Aug 2020 16:48:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F026B2311A for ; Thu, 6 Aug 2020 16:48:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="oE9uO0Mt" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729459AbgHFQrm (ORCPT ); Thu, 6 Aug 2020 12:47:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42448 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728720AbgHFQpH (ORCPT ); Thu, 6 Aug 2020 12:45:07 -0400 Received: from mail-wm1-x343.google.com (mail-wm1-x343.google.com [IPv6:2a00:1450:4864:20::343]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8F7AAC002142 for ; Thu, 6 Aug 2020 08:48:49 -0700 (PDT) Received: by mail-wm1-x343.google.com with SMTP id t14so10151477wmi.3 for ; Thu, 06 Aug 2020 08:48:49 -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=303SZoeGqCA0672IdnCKWTl2RMdleMaL49S3kRHa8CY=; b=oE9uO0Mt0t5TloYkjvoOMiKFdp9jk5j4TwOhbYZ1EOhrJyuSACQiJzq0pDOChhrxC6 vhOmlo9A18qla20Ru3Tlo19sG3sIDTvBTGvawu0i83/3HQLm39FU0BOryEDeV4YovuX8 7VyQsgIqQDdMBG2EJlfWCSh1j+xN3crlNWG+HhcXdB42IW+ps+N2THSli2vfT+oHhLwq x7PRWkpNrE7QzCEzfgPAMyJIvVbXHNwsqGUQaIFnalBamnFGZhk8xCrROAA6KX5tDtff UahxFMVhB9KKmF/zjdk9lWuJCoy7k+rgtdkscwoU0E40dXgrwMYfLw5hiyTKw17ceSdM ysDQ== 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=303SZoeGqCA0672IdnCKWTl2RMdleMaL49S3kRHa8CY=; b=nJF4T4xgt9ilwS1bTgpnJyo13lih5c8zuKx7R0XFkktgDLHSNUdjZ3H6DC0yaD1wwA yh6Z6hNbeYk7Gq1A2mpoXfpmE/wwINcxN3yHmXOCJRKTqdYb0Sh+X6OI4LfRwXkbTxit j4ETjs1DyHUiPktxOaLIN9S2ysHJtXqL54Ws66JVnQjhfegYux+8q9NNPGsEGomBLY2I osjbLjbSxKB7MpPvy1RZF9fYLh0GP3RwJHsDFq+Yf7dASi2MPr5bocnrQ/nT+LNXdeYJ +rgNXe5LtSFmBOOGqDR4WzZkf4hbO5lx8lP40HhBD5+zO69o5V77V7JynMIcsH+DOz2G vQUw== X-Gm-Message-State: AOAM531edXdwubnln1K64T1U+kcfRbEChbmmy1nd+pCh3hKizhTCDUYi I/C+ufGiRUk5rVdNx6ECN5bfXrkn X-Google-Smtp-Source: ABdhPJxzWm4GGCV8rrDC4OHeKMRI8H4AXXwSAuel2TMtc2Uj31/0Ii7ns3Zgh8kYLQYp81DzVSxN0g== X-Received: by 2002:a1c:2d95:: with SMTP id t143mr8276889wmt.44.1596728928031; Thu, 06 Aug 2020 08:48:48 -0700 (PDT) Received: from [127.0.0.1] ([13.74.141.28]) by smtp.gmail.com with ESMTPSA id 31sm6880784wrj.94.2020.08.06.08.48.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Aug 2020 08:48:47 -0700 (PDT) Message-Id: <902b742032ae19087392538936cc81768a59e0e1.1596728921.git.gitgitgadget@gmail.com> In-Reply-To: References: From: "Derrick Stolee via GitGitGadget" Date: Thu, 06 Aug 2020 15:48:35 +0000 Subject: [PATCH 05/11] maintenance: add commit-graph 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 first new task in the 'git maintenance' builtin is the 'commit-graph' job. It is based on the sequence of events in the 'commit-graph' job in Scalar [1]. This sequence is as follows: 1. git commit-graph write --reachable --split 2. git commit-graph verify --shallow 3. If the verify succeeds, stop. 4. Delete the commit-graph-chain file. 5. git commit-graph write --reachable --split By writing an incremental commit-graph file using the "--split" option we minimize the disruption from this operation. The default behavior is to merge layers until the new "top" layer is less than half the size of the layer below. This provides quick writes most of the time, with the longer writes following a power law distribution. Most importantly, concurrent Git processes only look at the commit-graph-chain file for a very short amount of time, so they will verly likely not be holding a handle to the file when we try to replace it. (This only matters on Windows.) If a concurrent process reads the old commit-graph-chain file, but our job expires some of the .graph files before they can be read, then those processes will see a warning message (but not fail). This could be avoided by a future update to use the --expire-time argument when writing the commit-graph. By using 'git commit-graph verify --shallow' we can ensure that the file we just wrote is valid. This is an extra safety precaution that is faster than our 'write' subcommand. In the rare situation that the newest layer of the commit-graph is corrupt, we can "fix" the corruption by deleting the commit-graph-chain file and rewrite the full commit-graph as a new one-layer commit graph. This does not completely prevent _that_ file from being corrupt, but it does recompute the commit-graph by parsing commits from the object database. In our use of this step in Scalar and VFS for Git, we have only seen this issue arise because our microsoft/git fork reverted 43d3561 ("commit-graph write: don't die if the existing graph is corrupt" 2019-03-25) for a while to keep commit-graph writes very fast. We dropped the revert when updating to v2.23.0. The verify still has potential for catching corrupt data across the layer boundary: if the new file has commit X with parent Y in an old file but the commit ID for Y in the old file had a bitswap, then we will notice that in the 'verify' command. [1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/CommitGraphStep.cs Signed-off-by: Derrick Stolee --- Documentation/git-maintenance.txt | 18 +++++++++ builtin/gc.c | 63 +++++++++++++++++++++++++++++++ commit-graph.c | 8 ++-- commit-graph.h | 1 + t/t7900-maintenance.sh | 2 + 5 files changed, 88 insertions(+), 4 deletions(-) diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt index 089fa4cedc..35b0be7d40 100644 --- a/Documentation/git-maintenance.txt +++ b/Documentation/git-maintenance.txt @@ -35,6 +35,24 @@ run:: TASKS ----- +commit-graph:: + The `commit-graph` job updates the `commit-graph` files incrementally, + then verifies that the written data is correct. If the new layer has an + issue, then the chain file is removed and the `commit-graph` is + rewritten from scratch. ++ +The verification only checks the top layer of the `commit-graph` chain. +If the incremental write merged the new commits with at least one +existing layer, then there is potential for on-disk corruption being +carried forward into the new file. This will be noticed and the new +commit-graph file will be clean as Git reparses the commit data from +the object database. ++ +The incremental write is safe to run alongside concurrent Git processes +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. + 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 150dce4301..3b7b914d60 100644 --- a/builtin/gc.c +++ b/builtin/gc.c @@ -710,6 +710,64 @@ struct maintenance_opts { int quiet; }; +static int run_write_commit_graph(struct maintenance_opts *opts) +{ + struct child_process child = CHILD_PROCESS_INIT; + + child.git_cmd = 1; + strvec_pushl(&child.args, "commit-graph", "write", + "--split", "--reachable", NULL); + + if (opts->quiet) + strvec_push(&child.args, "--no-progress"); + + return !!run_command(&child); +} + +static int run_verify_commit_graph(struct maintenance_opts *opts) +{ + struct child_process child = CHILD_PROCESS_INIT; + + child.git_cmd = 1; + strvec_pushl(&child.args, "commit-graph", "verify", + "--shallow", NULL); + + if (opts->quiet) + strvec_push(&child.args, "--no-progress"); + + return !!run_command(&child); +} + +static int maintenance_task_commit_graph(struct maintenance_opts *opts) +{ + struct repository *r = the_repository; + char *chain_path; + + close_object_store(r->objects); + if (run_write_commit_graph(opts)) { + error(_("failed to write commit-graph")); + return 1; + } + + if (!run_verify_commit_graph(opts)) + return 0; + + warning(_("commit-graph verify caught error, rewriting")); + + chain_path = get_commit_graph_chain_filename(r->objects->odb); + if (unlink(chain_path)) { + UNLEAK(chain_path); + die(_("failed to remove commit-graph at %s"), chain_path); + } + free(chain_path); + + if (!run_write_commit_graph(opts)) + return 0; + + error(_("failed to rewrite commit-graph")); + return 1; +} + static int maintenance_task_gc(struct maintenance_opts *opts) { struct child_process child = CHILD_PROCESS_INIT; @@ -738,6 +796,7 @@ struct maintenance_task { enum maintenance_task_label { TASK_GC, + TASK_COMMIT_GRAPH, /* Leave as final value */ TASK__COUNT @@ -749,6 +808,10 @@ static struct maintenance_task tasks[] = { maintenance_task_gc, 1, }, + [TASK_COMMIT_GRAPH] = { + "commit-graph", + maintenance_task_commit_graph, + }, }; static int maintenance_run(struct maintenance_opts *opts) diff --git a/commit-graph.c b/commit-graph.c index 1af68c297d..9705d237e4 100644 --- a/commit-graph.c +++ b/commit-graph.c @@ -172,7 +172,7 @@ static char *get_split_graph_filename(struct object_directory *odb, oid_hex); } -static char *get_chain_filename(struct object_directory *odb) +char *get_commit_graph_chain_filename(struct object_directory *odb) { return xstrfmt("%s/info/commit-graphs/commit-graph-chain", odb->path); } @@ -521,7 +521,7 @@ static struct commit_graph *load_commit_graph_chain(struct repository *r, struct stat st; struct object_id *oids; int i = 0, valid = 1, count; - char *chain_name = get_chain_filename(odb); + char *chain_name = get_commit_graph_chain_filename(odb); FILE *fp; int stat_res; @@ -1619,7 +1619,7 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx) } if (ctx->split) { - char *lock_name = get_chain_filename(ctx->odb); + char *lock_name = get_commit_graph_chain_filename(ctx->odb); hold_lock_file_for_update_mode(&lk, lock_name, LOCK_DIE_ON_ERROR, 0444); @@ -1996,7 +1996,7 @@ static void expire_commit_graphs(struct write_commit_graph_context *ctx) if (ctx->split_opts && ctx->split_opts->expire_time) expire_time = ctx->split_opts->expire_time; if (!ctx->split) { - char *chain_file_name = get_chain_filename(ctx->odb); + char *chain_file_name = get_commit_graph_chain_filename(ctx->odb); unlink(chain_file_name); free(chain_file_name); ctx->num_commit_graphs_after = 0; diff --git a/commit-graph.h b/commit-graph.h index 28f89cdf3e..3c202748c3 100644 --- a/commit-graph.h +++ b/commit-graph.h @@ -25,6 +25,7 @@ struct commit; struct bloom_filter_settings; char *get_commit_graph_filename(struct object_directory *odb); +char *get_commit_graph_chain_filename(struct object_directory *odb); int open_commit_graph(const char *graph_file, int *fd, struct stat *st); /* diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh index 7b63b4ec0c..384294d111 100755 --- a/t/t7900-maintenance.sh +++ b/t/t7900-maintenance.sh @@ -4,6 +4,8 @@ test_description='git maintenance builtin' . ./test-lib.sh +GIT_TEST_COMMIT_GRAPH=0 + test_expect_success 'help text' ' test_expect_code 129 git maintenance -h 2>err && test_i18ngrep "usage: git maintenance run" err