From patchwork Fri Sep 4 15:42:06 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: 11757855 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 52EC6618 for ; Fri, 4 Sep 2020 15:42:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3AC9C20770 for ; Fri, 4 Sep 2020 15:42:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="CNPEmgeK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726714AbgIDPmv (ORCPT ); Fri, 4 Sep 2020 11:42:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43262 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726555AbgIDPmX (ORCPT ); Fri, 4 Sep 2020 11:42:23 -0400 Received: from mail-wm1-x342.google.com (mail-wm1-x342.google.com [IPv6:2a00:1450:4864:20::342]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A7FCDC061258 for ; Fri, 4 Sep 2020 08:42:15 -0700 (PDT) Received: by mail-wm1-x342.google.com with SMTP id a65so6460981wme.5 for ; Fri, 04 Sep 2020 08:42:15 -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=Cf/9rLerrKy0dWPIT/MDxkaFTJmcOoY5Q1E+Hba6jjY=; b=CNPEmgeKMdEXyKBJbBWfsQ/h4T9nW8dF6tx5JuTZ95P6DhKJqOlzCcunyNbdKpDqtM O67pBPnCi0Nv7U9Nq0RzWutnxqhOn8j8VYO/uSgOYCUlon7YjjtebwUkxghGcuSrgZiH 5z0rLyBCDNespLZWdKsBx56po9lxjFNY/3AStQz67loMKMPFSpOOxv11kUjZCcnfy5go AnW4J7ro8cQH3+KBZ+0/3Nqm7ALmp6ncMJ3q4eXB4pPTFUn6oguvUvqhZ4sZLAscV5nb uVtLZsikYFDEB5GDsWzLZxU3J0BFcM2Voh4WEJyY0MSw8ulVbYNC9NzYh/isRAuZFjzF Ru9A== 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=Cf/9rLerrKy0dWPIT/MDxkaFTJmcOoY5Q1E+Hba6jjY=; b=SQU3kF7jCmMGMkxSO+b+aMYqkr/objQ37Qzo6JFdlR936ZZU/YHoh9L8jIrYpvrQsV AbCMJztzAKmuMH3KC0Kzcy9p0jC3FVGoKrMbOigqN99ELzdq6GAe1yX94cOB1znUzQlm uDCnebTLRFgSMx1L5bvFxHZVfLZVJgBLIzhOMGENPlh31MBZlbv179WZf5TKaAqJOB40 RQmZsCzlYvQOJKM0ym5P7IFeZ5sNpC0pTYj88It+XqRd/vVAf+YjGO11D3IAFYxRL4IA CV+rvoVg6ip5+LaO3pgp4r/RCDzh9RgNYcRxDokKgPK/TBq4XPQ6hJsoNMYRXhzdcOXA cjvw== X-Gm-Message-State: AOAM531IXEqGEgiXTXAYxhMKd2lG+SjVTwZDjUFukKBh1Ul8s5uCRbxh CP3Gh2xCGofe15fkTvJkY/w7IykkndI= X-Google-Smtp-Source: ABdhPJwZWPn5ClbLh875ywzAknf0tczTpWCCnPuUIC7KxLDxfpknnshuxs7RdeDMjBD7WBk559r6kQ== X-Received: by 2002:a1c:e108:: with SMTP id y8mr8276899wmg.178.1599234134105; Fri, 04 Sep 2020 08:42:14 -0700 (PDT) Received: from [127.0.0.1] ([13.74.141.28]) by smtp.gmail.com with ESMTPSA id m185sm13085658wmf.5.2020.09.04.08.42.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Sep 2020 08:42:13 -0700 (PDT) Message-Id: In-Reply-To: References: From: "Derrick Stolee via GitGitGadget" Date: Fri, 04 Sep 2020 15:42:06 +0000 Subject: [PATCH 7/7] maintenance: add troubleshooting guide to docs Fcc: Sent MIME-Version: 1.0 To: git@vger.kernel.org Cc: jrnieder@gmail.com, jonathantanmy@google.com, sluongng@gmail.com, congdanhqx@gmail.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 'git maintenance run' subcommand takes a lock on the object database to prevent concurrent processes from competing for resources. This is an important safety measure to prevent possible repository corruption and data loss. This feature can lead to confusing behavior if a user is not aware of it. Add a TROUBLESHOOTING section to the 'git maintenance' builtin documentation that discusses these tradeoffs. The short version of this section is that Git will not corrupt your repository, but if the list of scheduled tasks takes longer than an hour then some scheduled tasks may be dropped due to this object database collision. For example, a long-running "daily" task at midnight might prevent an "hourly" task from running at 1AM. The opposite is also possible, but less likely as long as the "hourly" tasks are much faster than the "daily" and "weekly" tasks. Helped-by: Junio C Hamano Signed-off-by: Derrick Stolee --- Documentation/git-maintenance.txt | 44 +++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+) diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt index 364b3e32bf..f58dd60e40 100644 --- a/Documentation/git-maintenance.txt +++ b/Documentation/git-maintenance.txt @@ -161,6 +161,50 @@ OPTIONS `maintenance..enabled` configured as `true` are considered. See the 'TASKS' section for the list of accepted `` values. + +TROUBLESHOOTING +--------------- +The `git maintenance` command is designed to simplify the repository +maintenance patterns while minimizing user wait time during Git commands. +A variety of configuration options are available to allow customizing this +process. The default maintenance options focus on operations that complete +quickly, even on large repositories. + +Users may find some cases where scheduled maintenance tasks do not run as +frequently as intended. Each `git maintenance run` command takes a lock on +the repository's object database, and this prevents other concurrent +`git maintenance run` commands from running on the same repository. Without +this safeguard, competing processes could leave the repository in an +unpredictable state. + +The background maintenance schedule runs `git maintenance run` processes +on an hourly basis. Each run executes the "hourly" tasks. At midnight, +that process also executes the "daily" tasks. At midnight on the first day +of the week, that process also executes the "weekly" tasks. A single +process iterates over each registered repository, performing the scheduled +tasks for that frequency. Depending on the number of registered +repositories and their sizes, this process may take longer than an hour. +In this case, multiple `git maintenance run` commands may run on the same +repository at the same time, colliding on the object database lock. This +results in one of the two tasks not running. + +If you find that some maintenance windows are taking longer than one hour +to complete, then consider reducing the complexity of your maintenance +tasks. For example, the `gc` task is much slower than the +`incremental-repack` task. However, this comes at a cost of a slightly +larger object database. Consider moving more expensive tasks to be run +less frequently. + +Expert users may consider scheduling their own maintenance tasks using a +different schedule than is available through `git maintenance start` and +Git configuration options. These users should be aware of the object +database lock and how concurrent `git maintenance run` commands behave. +Further, the `git gc` command should not be combined with +`git maintenance run` commands. `git gc` modifies the object database +but does not take the lock in the same way as `git maintenance run`. If +possible, use `git maintenance run --task=gc` instead of `git gc`. + + GIT --- Part of the linkgit:git[1] suite