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-ASN: AS3215 2.6.0.0/16 X-Spam-Status: No, score=-3.8 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE,URIBL_CSS, URIBL_CSS_A shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from out1.vger.email (out1.vger.email [IPv6:2620:137:e000::1:20]) by dcvr.yhbt.net (Postfix) with ESMTP id 44D781F403 for ; Sat, 25 Jun 2022 02:27:19 +0000 (UTC) Authentication-Results: dcvr.yhbt.net; dkim=pass (2048-bit key; unprotected) header.d=bytedance-com.20210112.gappssmtp.com header.i=@bytedance-com.20210112.gappssmtp.com header.b="aHRgzYSQ"; dkim-atps=neutral Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231235AbiFYCZr (ORCPT ); Fri, 24 Jun 2022 22:25:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48386 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229912AbiFYCZq (ORCPT ); Fri, 24 Jun 2022 22:25:46 -0400 Received: from mail-yw1-x1129.google.com (mail-yw1-x1129.google.com [IPv6:2607:f8b0:4864:20::1129]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EF773B875 for ; Fri, 24 Jun 2022 19:25:44 -0700 (PDT) Received: by mail-yw1-x1129.google.com with SMTP id 00721157ae682-3177e60d980so40017077b3.12 for ; Fri, 24 Jun 2022 19:25:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=4Gml/2GH4DJjzM4dvGvKs/vUf92sEyIUETKVoiN4AGc=; b=aHRgzYSQiNxYjfLn0TzjubB/m1PiNBKXEtg+EZ/PP7VvCmFvHWRH5aaLbNE6k3u9ZB BmGpX3Q3Jp2lT6hBEtsVYUPtn793gR4I8SfuWUu9dFjBka68KVLxr6SofIElN90mRx2k 2sKAHDBhkLKqsi5X+3zquK9xC4ZL/JfY+2FukZZt70ar20mKhtZELjyILyXloCgirxUo 1J9OR8D9080NjYCDl8DMRNan2ZouJpHOgsSeUgGiSv+3Wm5SCrjecfjwhG07JNiwwu+p fWGb5SfSCQAKvnGX3ClUIOi+SyQNJWI/Vn/XWWPvW82fTT3eTrdhQUjOdB1oQFM0Pblh b7ow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=4Gml/2GH4DJjzM4dvGvKs/vUf92sEyIUETKVoiN4AGc=; b=46FqqCAC827C817Ygvspds09y5d5/TMaKoy1ULdp5Yj7hz6W+2k6kcwSLB9R7MkpAy ihs4+67ETnd4rCp0BbiNXYR0GqMgVCCfwIAAQ5wFgHweJIOlgWf/OR+P7z1jmkFvFjsz 1BoNMnL3l1VVa+yd7aFCmBxruU2/1uXxWQcHG8Sti/Ha682IvfoCLjDSuTN0Fcr0y1io m8gaEVgXnXqrTIweRHsh9cbGGpAJnDm87n/rBWuRJptQ+3T86zYaSWbfRvg0TuOKrdpF tyFhTiyuIaoTtjAG2LNWtWhKEkNoo4yIBmNzJeoiLlTAewkJqb0dSQRYdUjN7KBNc0KK +DDA== X-Gm-Message-State: AJIora9UMgeU4Kj6di6vua3RN276ejsSWj6OaFNj4LOKkVG8L4fQH5nD c9KXA4ROd3KSL/ByzMRPAoZM8pHmMy7+a9QTnJESdw== X-Google-Smtp-Source: AGRyM1vXomWGYDh0vKiSe9yT40A0NhrzkfEOnn3QfvYD9VDHuB8hQ0dGSI0RRUigtl4fxeYYOMShzZXTxCKZ17lBeoI= X-Received: by 2002:a81:1cc:0:b0:317:a0fa:7a61 with SMTP id 195-20020a8101cc000000b00317a0fa7a61mr2199354ywb.10.1656123944183; Fri, 24 Jun 2022 19:25:44 -0700 (PDT) MIME-Version: 1.0 References: <20220618030130.36419-1-hanxin.hx@bytedance.com> In-Reply-To: From: Han Xin Date: Sat, 25 Jun 2022 10:25:33 +0800 Message-ID: Subject: Re: Re: [PATCH v2 2/2] commit-graph.c: no lazy fetch in lookup_commit_in_graph() To: Junio C Hamano Cc: chiyutianyi@gmail.com, derrickstolee@github.com, git@vger.kernel.org, haiyangtand@gmail.com, Jonathan Tan , Taylor Blau , Patrick Steinhardt Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Sat, Jun 25, 2022 at 12:56 AM Junio C Hamano wrote: > > Han Xin writes: > > > If a commit is in the commit graph, we would expect the commit to also > > be present. > > > When we found the commit in the graph in lookup_commit_in_graph(), > > but the commit is missing from the repository, we will try > > promisor_remote_get_direct() and then enter another loop. While > > sometimes it will finally succeed because it cannot fork > > subprocess, > > Is that a mode of "succeed"-ing? Or merely a way to exit an endless > loop that does not make any progress with a failure? For the user, "fetch-pack" does succeed, because in deref_without_lazy_fetch(), even if lookup_commit_in_graph() fails to lazy fetch the lost commit, the following oid_object_info_extended() will help us complete the previous work. In a sense, this infinite loop is based on the fact that infinite processes can be created. However, your attempt to express the reasoning bellow is clearer. > > > it has exhausted the local process resources and can be harmful to the > > remote service. > > > > Signed-off-by: Han Xin > > --- > > I think the single-liner change in the patch is a good one, but I am > having a hard time to agree with the reasoning above that explains > why it is a good change. > > Here is an attempt to express a reasoning I can understand, can > agree with, and (I think) better describes why the change is a good > one. Does my understanding of the problem and the solution totally > misses the mark? > > The commit-graph is used to opportunistically optimize > accesses to certain pieces of information on commit objects, > and lookup_commit_in_graph() tries to say "no" when the > requested commit does not locally exist by returning NULL, > in which case the caller can ask for (which may result in > on-demand fetching from a promisor remote) and parse the > commit object itself. > > However, it uses a wrong helper, repo_has_object_file(), to > do so. This helper not only checks if an object is > immediately available in the local object store, but also > tries to fetch from a promisor remote. But the fetch > machinery calls lookup_commit_in_graph(), thus causing an > infinite loop. > > We should make lookup_commit_in_graph() expect that a commit > given to it can be legitimately missing from the local > object store, by using the has_object_file() helper instead. > > > diff --git a/t/t5329-no-lazy-fetch-with-commit-graph.sh b/t/t5329-no-lazy-fetch-with-commit-graph.sh > > new file mode 100755 > > index 0000000000..4d25d2c950 > > --- /dev/null > > +++ b/t/t5329-no-lazy-fetch-with-commit-graph.sh > > Hmph, does this short-test need a completely new file? > > > @@ -0,0 +1,47 @@ > > +#!/bin/sh > > + > > +test_description='test for no lazy fetch with the commit-graph' > > + > > +. ./test-lib.sh > > + > > +test_expect_success 'setup: prepare a repository with a commit' ' > > + git init with-commit && > > + test_commit -C with-commit the-commit && > > + oid=$(git -C with-commit rev-parse HEAD) > > +' > > + > > +test_expect_success 'setup: prepare a repository with commit-graph contains the commit' ' > > + git init with-commit-graph && > > + echo "$(pwd)/with-commit/.git/objects" \ > > + >with-commit-graph/.git/objects/info/alternates && > > + # create a ref that points to the commit in alternates > > + git -C with-commit-graph update-ref refs/ref_to_the_commit "$oid" && > > + # prepare some other objects to commit-graph > > + test_commit -C with-commit-graph somthing && > > somthing? something? Nod. > > > + git -c gc.writeCommitGraph=true -C with-commit-graph gc && > > + test_path_is_file with-commit-graph/.git/objects/info/commit-graph > > +' > > + > > +test_expect_success 'setup: change the alternates to what without the commit' ' > > + git init --bare without-commit && > > + echo "$(pwd)/without-commit/objects" \ > > + >with-commit-graph/.git/objects/info/alternates && > > Doesn't this deliberately _corrupt_ the with-commit-graph repository > that depended on the object whose name is $oid in with-commit > repository? Do we require a corrupt repository to trigger the "bug"? > The "bug" depends on the commit exist in the commit-graph but missing in the repository. I didn't find a better way to make this kind of scene. This bug was first found when alternates and commit-graph were both used. Since the promise did not maintain all the references, I suspect that the "auto gc" during the update process of the promise caused the loss of the unreachable commits in the promise. > > + test_must_fail git -C with-commit-graph cat-file -e $oid > > +' > > + > > +test_expect_success 'setup: prepare another commit to fetch' ' > > + test_commit -C with-commit another-commit && > > + anycommit=$(git -C with-commit rev-parse HEAD) > > anycommit? another_commit? Be consistent in naming. > Nod. > > +' > > + > > +test_expect_success ULIMIT_PROCESSES 'fetch any commit from promisor with the usage of the commit graph' ' > > So we did all of the above set-up sequences only to skip the most > interesting test, if we were testing with "dash"? I suspect that it > may be cleaner to put the prerequisite to the whole file with the > "early test_done" trick like t0051 and t3008. > It make sense to me. Thanks. -Han Xin