Date: Fri, 4 Dec 2015 19:49:05 +0100 From: =?UTF-8?Q?Ulrich_Sp=C3=B6rlein?= <uqs@FreeBSD.org> To: freebsd-git@freebsd.org Cc: freebsd-current@freebsd.org, git-admin@freebsd.org Subject: Re: FYI: SVN to GIT converter currently broken, github is falling behind Message-ID: <CAJ9axoRV1gwpVsTpB_%2BPQX4ZrWpnJRtTJ77dsA0vC_BekR8=9g@mail.gmail.com> In-Reply-To: <CAJ9axoRcCUoLzyGN-JkJEn%2ByinWdVoSKUcBr7eas5638t6jBUg@mail.gmail.com> References: <CAJ9axoTuuBt4%2Bg4o1%2BLy9VmNfAa3pcMhcPr2ws8T1kCm=Om=tg@mail.gmail.com> <CAJ9axoRBcFD=-d=pzJJvYempEO-EyR_kAiK3EZQ_hp%2B7_J1iyQ@mail.gmail.com> <563EAAB8.5020702@freebsd.org> <CAJ9axoQmgT0B23UtmzGeMcvS%2BCHxC16FL53fPGObBZoxEC03aQ@mail.gmail.com> <CAJ9axoRcCUoLzyGN-JkJEn%2ByinWdVoSKUcBr7eas5638t6jBUg@mail.gmail.com>
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2015-11-08 12:06 GMT+01:00 Ulrich Sp=C3=B6rlein <uqs@freebsd.org>: > 2015-11-08 11:32 GMT+01:00 Ulrich Sp=C3=B6rlein <uqs@freebsd.org>: >> 2015-11-08 2:51 GMT+01:00 Alfred Perlstein <alfred@freebsd.org>: >>>> >>> Uli, >>> >>> One of the biggest concerns I've heard from folks using FreeBSD's git m= irror >>> is that the hashes can change. >>> >>> I have a question about this. Is it possible to keep track of what th= e >>> "official" git mirror (on github) is doing and keep that as a log. The= n >>> that log can be used to replay commits when there is a divergence probl= em. >>> >>> What I'm basically saying is that let's take this small example: >>> >>> importer is working fine @rev 10000 >>> imports 10000 >>> imports 10001 >>> imports 10002 >>> something happens to importer to give indeterminate shas. >>> imports 10003 - sha is "unstable" sha3 >>> imports 10004 - sha is "unstable" sha4 >>> imports 10005 - sha is "unstable" sha5 >>> imports 10006 - sha is "unstable" sha6 >>> importer is fixed >>> >>> >>> At this point normally we'd rewind the importer to 10002 and then force >>> update the affected branches. >>> >>> My question is... can the imports of 10003, 10004, 10005 and 10006 be p= ut >>> into the importer such that any "mirror site" that re-does the import u= sing >>> the most up to date importer will get the same shas. >>> >>> That would allow to proceed with 10007, etc without force pushing. >>> >>> This should be possible based on querying "git" for the meta data assoc= iated >>> with sha3..sha6 and then forcing those commits to have the same meta da= ta. >>> >>> This would eliminate the concern about shas in the mirror changing that= I've >>> heard. >> >> The goal of the conversion is that everyone can re-do the conversion >> in their basement and come up with the same history and checksums. >> This was not the case when I first started, as there was some >> non-deterministic hash structure being used in svn2git. This was fixed >> in the code and then all converter runs produced the very same >> results. >> >> The scenario that we have right now, is that one of the merge commits >> done about two weeks ago is being handled different by svn2git w/ svn >> v1.8 vs. svn v1.9 and I haven't investigated yet how the API's >> behavior changed to cause this. I'm afraid I also swapped out all my >> knowledge about svn2git internals and will have to redo this all from >> scratch :/ >> >> Your suggestion could only work, if we hard-code this svn revision >> special handling into svn2git, either in the code or by providing more >> mappings and rules to the process. svn2git should run hermetic and not >> poke at github's commits to see how things were handled in the past. >> It has to be self-sufficient and must not depend on github. >> >> This would also only work, if the "breakage" window was very small, >> but it is already about two weeks long and will surely increase till I >> find the proper fix. >> >> So, to take a stand here: this sort of kludge is unlikely to ever >> happen. Git commit hashes *might* change in the future. I really don't >> see how this is a big deal anyway. It happened once and I'm trying to >> have it never happen again. But why are people afraid of this >> happening? Every "official" git commit is tagged with a SVN revision >> and the contents of those revisions are obviously correct (just not >> the ancestry and the commit objects, possibly). So it would be easy to >> write a script that replays VendorA's git history and swaps out the >> new official commits for the old official commits. There would be no >> merge conflicts. >> >> I can see how this would be annoying if you have 100 developers and >> dozens of branches that are far from mainline FreeBSD. But I'm sure >> these companies that depend on git will come forward and donate some >> of their developer manpower to help me with keeping the converter >> stable/deterministic. Right? Right? :) :) >> >> Cheers, >> Uli > > Quick update: doc is so far unaffected by svn 1.9, but for ports, the > drift happened as of Jul 18, so you'd need to special case a lot of > commits. > > Here's the same commit, and the difference between 1.8 and 1.9: > > % git cat-file commit 803795d > tree 7fc83aba022834da5c218114b09ad4640735bcc0 > parent c96fb0418e545a569b5975b4d878a30a948c29d5 > author olgeni <olgeni@FreeBSD.org> 1437203525 +0000 > committer olgeni <olgeni@FreeBSD.org> 1437203525 +0000 > > Upgrade to version 0.4.1. > % git cat-file commit 61ca43b > tree 7fc83aba022834da5c218114b09ad4640735bcc0 > parent c96fb0418e545a569b5975b4d878a30a948c29d5 > author olgeni <olgeni@FreeBSD.org> 1437203529 +0000 > committer olgeni <olgeni@FreeBSD.org> 1437203529 +0000 > > Upgrade to version 0.4.1. > > > In case you don't see it, there's a 4s difference in the timestamps > for authoring and committing. Here's the original: > > % svn log -vc392405 svn://svn.freebsd.org/ports > ------------------------------------------------------------------------ > r392405 | olgeni | 2015-07-18 09:12:05 +0200 (Sat, 18 Jul 2015) | 2 lines > Changed paths: > M /head/www/elixir-maru/Makefile > M /head/www/elixir-maru/distinfo > > Upgrade to version 0.4.1. > > ------------------------------------------------------------------------ > > So yeah, svn 1.9 returned a timestamp that was off by 4s. WTF? > > For base it's actually even more complicated than I had thought so > far. But let's take this one step at time ... An update, which you won't like to hear: SVN v1.9 is totally innocent, the API changed a little and has been patched, this is not the source of the difference between the currently published repo and a clean run. The difference stems from the fact that the svnsync'ed copy on git.freebsd.org was poisoned and is *NOT* in sync with our main repo. People tell me this is due to a shortcoming of svnsync that can race and thus produce different metadata for a commit, depending on when it is run. This is a clusterfuck. Both freebsd-base and freebsd-ports are no longer reproducible by third-parties. It is only a matter of time when freebsd-doc is affected. clusteradm@ sadly has remained rather silent on this issue and unless we can move the mirroring to rsync or syncthing or whatever I don't see how the project can continue to provide a so-called git "mirror" Sad, Uli
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