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From: Taylor Blau <me@ttaylorr.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Taylor Blau <me@ttaylorr.com>,
	Jonathan Nieder <jrnieder@gmail.com>,
	git@vger.kernel.org, tytso@mit.edu, derrickstolee@github.com,
	larsxschneider@gmail.com
Subject: Re: [PATCH v3 01/17] Documentation/technical: add cruft-packs.txt
Date: Tue, 29 Mar 2022 22:23:59 -0400	[thread overview]
Message-ID: <YkO/P3xgGYmhAz2O@nand.local> (raw)
In-Reply-To: <xmqqa6d8yckj.fsf@gitster.g>

On Tue, Mar 29, 2022 at 08:59:24AM -0700, Junio C Hamano wrote:
> Taylor Blau <me@ttaylorr.com> writes:
>
> > I'm not sure... if we did:
> >
> > --- 8< ---
> >
> > diff --git a/setup.c b/setup.c
> > index 04ce33cdcd..fa54c9baa4 100644
> > --- a/setup.c
> > +++ b/setup.c
> > @@ -565,2 +565,4 @@ static enum extension_result handle_extension(const char *var,
> >  		return EXTENSION_OK;
> > +	} else if (!strcmp(ext, "cruftpacks")) {
> > +		return EXTENSION_OK;
> >  	}
> >
> > --- >8 ---
> >
> > but nothing more, then a hypothetical `extensions.cruftPacks` could be
> > used to prevent older writers in a mixed version environment. But if you
> > don't have or care about older versions of Git, you can avoid setting it
> > altogether.
>
> Smells like "unsafe by default, but you can opt into safety", which
> is backwards, isn't it?

I see it a little differently. The default (not writing cruft packs at
all) is safe, even in a mixed-version environment. If a user (a) wants
to use cruft packs, and (b) has older versions of Git also gc'ing the
repository, and (c) can't get rid of them, _then_ an opt-in extension
would make it impossible for those older versions to interact with the
repository.

I still can't shake the feeling that this is a pretty fringe and
timing-dependent scenario, which at worst keeps too many unreachable
objects around.

But I think this in conjunction with the already opt-in nature of cruft
packs would be a nice way to create safeguards for the situation
Jonathan described. There may be a simpler way, but I'm not sure I see
it (i.e., if you control whether or not `--cruft` is passed when
doing maintenance with newer versions of Git, but not whether older
versions are running around doing their own maintenance, then an
extension would be necessary to lock the old versions out).

> > But cruft packs are already guarded in two places:
> >
> >   - `git repack` won't write a cruft pack unless given the `--cruft`
> >     flag (i.e., `git repack -A` doesn't suddenly start generating cruft
> >     packs upon upgrade).
> >
> >   - `git gc` won't write cruft packs unless the `gc.cruftPacks`
> >     configuration is set, or `--cruft` is given as a flag.
>
> Hmph, OK.  So individuals can sort-of protect from hurting
> themselves by refraining from running these with --cruft or writing
> --cruft in their maintenance scripts.  An organization that wants to
> let the more adventurous types to early opt-in can prepare two
> versions of the maintenance scripts they distribute to their users,
> one with and the other without --cruft, and use the mechanism they
> use for gradual rollouts to control the population.  Perhaps that
> would make sufficient protection?  I dunno.
>
> Jonathan, what do you think?

I'm confused: if newer versions of Git are writing cruft packs, then
having the older versions gc'ing in the same repository runs into the
same scenario Jonathan originally describes.

The thing I think Jonathan seeks to prevent is older versions of Git
gc'ing a repo that has cruft packs. I think I may need you to clarify a
little, sorry :-(.

> > I'd be curious what Jonathan and others think of that approach (which,
> > to be clear, is what this series already implements). We could make it
> > clear to say:
> >
> >     If you have mixed versions of Git which both repack a repository
> >     (either manually or by auto-GC / background maintenance), consider
> >     leaving `gc.cruftPacks` unset and avoiding passing `--cruft` as a
> >     command-line argument to `git repack` and `git gc`, since doing so
> >     can lead to [...]
>
> That message is (depending on what comes in [...]) much more helpful
> than just throwing a word "mtime" out and letting the reader figure
> out the rest ;-)

Yes, totally agreed.

Thanks,
Taylor

  reply	other threads:[~2022-03-30  2:24 UTC|newest]

Thread overview: 201+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-29 22:25 [PATCH 00/17] cruft packs Taylor Blau
2021-11-29 22:25 ` [PATCH 01/17] Documentation/technical: add cruft-packs.txt Taylor Blau
2021-12-02 14:33   ` Derrick Stolee
2021-12-03 21:53     ` Taylor Blau
2021-12-04 22:20   ` Elijah Newren
2021-12-04 23:32     ` Taylor Blau
2021-11-29 22:25 ` [PATCH 02/17] pack-mtimes: support reading .mtimes files Taylor Blau
2021-12-02 15:06   ` Derrick Stolee
2021-12-02 22:32     ` brian m. carlson
2021-12-03 22:24     ` Taylor Blau
2022-01-07 19:41       ` Taylor Blau
2021-11-29 22:25 ` [PATCH 03/17] pack-write: pass 'struct packing_data' to 'stage_tmp_packfiles' Taylor Blau
2021-11-29 22:25 ` [PATCH 04/17] chunk-format.h: extract oid_version() Taylor Blau
2021-12-02 15:22   ` Derrick Stolee
2021-12-03 22:40     ` Taylor Blau
2021-12-06 17:33       ` Derrick Stolee
2021-11-29 22:25 ` [PATCH 05/17] pack-mtimes: support writing pack .mtimes files Taylor Blau
2021-12-02 15:36   ` Derrick Stolee
2021-12-03 23:04     ` Taylor Blau
2021-11-29 22:25 ` [PATCH 06/17] t/helper: add 'pack-mtimes' test-tool Taylor Blau
2021-12-06 21:16   ` Derrick Stolee
2022-02-23 22:24     ` Taylor Blau
2021-11-29 22:25 ` [PATCH 07/17] builtin/pack-objects.c: return from create_object_entry() Taylor Blau
2021-11-29 22:25 ` [PATCH 08/17] builtin/pack-objects.c: --cruft without expiration Taylor Blau
2021-12-06 21:44   ` Derrick Stolee
2022-03-01  2:48     ` Taylor Blau
2021-12-07 15:17   ` Derrick Stolee
2022-02-23 23:34     ` Taylor Blau
2021-11-29 22:25 ` [PATCH 09/17] reachable: add options to add_unseen_recent_objects_to_traversal Taylor Blau
2021-11-29 22:25 ` [PATCH 10/17] reachable: report precise timestamps from objects in cruft packs Taylor Blau
2021-11-29 22:25 ` [PATCH 11/17] builtin/pack-objects.c: --cruft with expiration Taylor Blau
2021-12-07 15:30   ` Derrick Stolee
2022-02-23 23:35     ` Taylor Blau
2021-11-29 22:25 ` [PATCH 12/17] builtin/repack.c: support generating a cruft pack Taylor Blau
2021-12-05 20:46   ` Junio C Hamano
2022-03-01  2:00     ` Taylor Blau
2021-12-07 15:38   ` Derrick Stolee
2022-02-23 23:37     ` Taylor Blau
2021-11-29 22:25 ` [PATCH 13/17] builtin/repack.c: allow configuring cruft pack generation Taylor Blau
2021-11-29 22:25 ` [PATCH 14/17] builtin/repack.c: use named flags for existing_packs Taylor Blau
2021-11-29 22:25 ` [PATCH 15/17] builtin/repack.c: add cruft packs to MIDX during geometric repack Taylor Blau
2021-11-29 22:25 ` [PATCH 16/17] builtin/gc.c: conditionally avoid pruning objects via loose Taylor Blau
2021-11-29 22:25 ` [PATCH 17/17] sha1-file.c: don't freshen cruft packs Taylor Blau
2021-12-03 19:51 ` [PATCH 00/17] " Junio C Hamano
2021-12-03 20:08   ` Taylor Blau
2021-12-03 20:47     ` Taylor Blau
2022-03-02  0:57 ` [PATCH v2 " Taylor Blau
2022-03-02  0:58   ` [PATCH v2 01/17] Documentation/technical: add cruft-packs.txt Taylor Blau
2022-03-02  0:58   ` [PATCH v2 02/17] pack-mtimes: support reading .mtimes files Taylor Blau
2022-03-02 20:22     ` Derrick Stolee
2022-03-02 21:33       ` Taylor Blau
2022-03-02  0:58   ` [PATCH v2 03/17] pack-write: pass 'struct packing_data' to 'stage_tmp_packfiles' Taylor Blau
2022-03-02  0:58   ` [PATCH v2 04/17] chunk-format.h: extract oid_version() Taylor Blau
2022-03-02  0:58   ` [PATCH v2 05/17] pack-mtimes: support writing pack .mtimes files Taylor Blau
2022-03-02  0:58   ` [PATCH v2 06/17] t/helper: add 'pack-mtimes' test-tool Taylor Blau
2022-03-02  0:58   ` [PATCH v2 07/17] builtin/pack-objects.c: return from create_object_entry() Taylor Blau
2022-03-02  0:58   ` [PATCH v2 08/17] builtin/pack-objects.c: --cruft without expiration Taylor Blau
2022-03-02  0:58   ` [PATCH v2 09/17] reachable: add options to add_unseen_recent_objects_to_traversal Taylor Blau
2022-03-02 20:19     ` Derrick Stolee
2022-03-02 21:28       ` Taylor Blau
2022-03-02  0:58   ` [PATCH v2 10/17] reachable: report precise timestamps from objects in cruft packs Taylor Blau
2022-03-02  0:58   ` [PATCH v2 11/17] builtin/pack-objects.c: --cruft with expiration Taylor Blau
2022-03-02  7:42     ` Junio C Hamano
2022-03-02 15:54       ` Taylor Blau
2022-03-02 19:57         ` Derrick Stolee
2022-03-02  0:58   ` [PATCH v2 12/17] builtin/repack.c: support generating a cruft pack Taylor Blau
2022-03-02  0:58   ` [PATCH v2 13/17] builtin/repack.c: allow configuring cruft pack generation Taylor Blau
2022-03-02  0:58   ` [PATCH v2 14/17] builtin/repack.c: use named flags for existing_packs Taylor Blau
2022-03-02  0:58   ` [PATCH v2 15/17] builtin/repack.c: add cruft packs to MIDX during geometric repack Taylor Blau
2022-03-02  0:58   ` [PATCH v2 16/17] builtin/gc.c: conditionally avoid pruning objects via loose Taylor Blau
2022-03-02  0:58   ` [PATCH v2 17/17] sha1-file.c: don't freshen cruft packs Taylor Blau
2022-03-02 20:23   ` [PATCH v2 00/17] " Derrick Stolee
2022-03-02 21:36     ` Taylor Blau
2022-03-03  0:20 ` [PATCH v3 " Taylor Blau
2022-03-03  0:20   ` [PATCH v3 01/17] Documentation/technical: add cruft-packs.txt Taylor Blau
2022-03-07 18:03     ` Jonathan Nieder
2022-03-22  1:16       ` Taylor Blau
2022-03-22 21:45         ` Jonathan Nieder
2022-03-22 22:02           ` Taylor Blau
2022-03-22 23:04             ` Jonathan Nieder
2022-03-23  1:01               ` Taylor Blau
2022-03-28 18:46                 ` Taylor Blau
2022-03-28 20:55                   ` Junio C Hamano
2022-03-28 21:21                     ` Taylor Blau
2022-03-29 15:59                       ` Junio C Hamano
2022-03-30  2:23                         ` Taylor Blau [this message]
2022-03-30 13:37                           ` Junio C Hamano
2022-03-30 17:30                             ` Taylor Blau
2022-03-03  0:20   ` [PATCH v3 02/17] pack-mtimes: support reading .mtimes files Taylor Blau
2022-03-03  0:20   ` [PATCH v3 03/17] pack-write: pass 'struct packing_data' to 'stage_tmp_packfiles' Taylor Blau
2022-03-03  0:20   ` [PATCH v3 04/17] chunk-format.h: extract oid_version() Taylor Blau
2022-03-03 16:30     ` Ævar Arnfjörð Bjarmason
2022-03-03 23:32       ` Taylor Blau
2022-03-04  0:16         ` Junio C Hamano
2022-03-03  0:20   ` [PATCH v3 05/17] pack-mtimes: support writing pack .mtimes files Taylor Blau
2022-03-03 16:45     ` Ævar Arnfjörð Bjarmason
2022-03-03 23:35       ` Taylor Blau
2022-03-04 10:40         ` Ævar Arnfjörð Bjarmason
2022-03-03  0:20   ` [PATCH v3 06/17] t/helper: add 'pack-mtimes' test-tool Taylor Blau
2022-03-03  0:21   ` [PATCH v3 07/17] builtin/pack-objects.c: return from create_object_entry() Taylor Blau
2022-03-03  0:21   ` [PATCH v3 08/17] builtin/pack-objects.c: --cruft without expiration Taylor Blau
2022-03-03  0:21   ` [PATCH v3 09/17] reachable: add options to add_unseen_recent_objects_to_traversal Taylor Blau
2022-03-03  0:21   ` [PATCH v3 10/17] reachable: report precise timestamps from objects in cruft packs Taylor Blau
2022-03-03  0:21   ` [PATCH v3 11/17] builtin/pack-objects.c: --cruft with expiration Taylor Blau
2022-03-03  0:21   ` [PATCH v3 12/17] builtin/repack.c: support generating a cruft pack Taylor Blau
2022-03-03  0:21   ` [PATCH v3 13/17] builtin/repack.c: allow configuring cruft pack generation Taylor Blau
2022-03-03  0:21   ` [PATCH v3 14/17] builtin/repack.c: use named flags for existing_packs Taylor Blau
2022-03-03  0:21   ` [PATCH v3 15/17] builtin/repack.c: add cruft packs to MIDX during geometric repack Taylor Blau
2022-03-03  0:21   ` [PATCH v3 16/17] builtin/gc.c: conditionally avoid pruning objects via loose Taylor Blau
2022-03-03  0:21   ` [PATCH v3 17/17] sha1-file.c: don't freshen cruft packs Taylor Blau
2022-03-03  1:29   ` [PATCH v3 00/17] " Derrick Stolee
2022-05-18 23:10 ` [PATCH v4 " Taylor Blau
2022-05-18 23:10   ` [PATCH v4 01/17] Documentation/technical: add cruft-packs.txt Taylor Blau
2022-05-19 14:04     ` Junio C Hamano
2022-05-18 23:10   ` [PATCH v4 02/17] pack-mtimes: support reading .mtimes files Taylor Blau
2022-05-19 10:40     ` Ævar Arnfjörð Bjarmason
2022-05-19 15:21       ` Junio C Hamano
2022-05-20  7:32         ` Ævar Arnfjörð Bjarmason
2022-05-20 22:37           ` Taylor Blau
2022-05-18 23:10   ` [PATCH v4 03/17] pack-write: pass 'struct packing_data' to 'stage_tmp_packfiles' Taylor Blau
2022-05-18 23:11   ` [PATCH v4 04/17] chunk-format.h: extract oid_version() Taylor Blau
2022-05-19 11:44     ` Ævar Arnfjörð Bjarmason
2022-05-18 23:11   ` [PATCH v4 05/17] pack-mtimes: support writing pack .mtimes files Taylor Blau
2022-05-18 23:11   ` [PATCH v4 06/17] t/helper: add 'pack-mtimes' test-tool Taylor Blau
2022-05-18 23:11   ` [PATCH v4 07/17] builtin/pack-objects.c: return from create_object_entry() Taylor Blau
2022-05-18 23:11   ` [PATCH v4 08/17] builtin/pack-objects.c: --cruft without expiration Taylor Blau
2022-05-19 10:04     ` Junio C Hamano
2022-05-19 15:16       ` Junio C Hamano
2022-05-20 22:52         ` Taylor Blau
2022-05-18 23:11   ` [PATCH v4 09/17] reachable: add options to add_unseen_recent_objects_to_traversal Taylor Blau
2022-05-18 23:11   ` [PATCH v4 10/17] reachable: report precise timestamps from objects in cruft packs Taylor Blau
2022-05-18 23:11   ` [PATCH v4 11/17] builtin/pack-objects.c: --cruft with expiration Taylor Blau
2022-05-18 23:11   ` [PATCH v4 12/17] builtin/repack.c: support generating a cruft pack Taylor Blau
2022-05-19 11:29     ` Ævar Arnfjörð Bjarmason
2022-05-20 22:39       ` Taylor Blau
2022-05-18 23:11   ` [PATCH v4 13/17] builtin/repack.c: allow configuring cruft pack generation Taylor Blau
2022-05-18 23:11   ` [PATCH v4 14/17] builtin/repack.c: use named flags for existing_packs Taylor Blau
2022-05-18 23:11   ` [PATCH v4 15/17] builtin/repack.c: add cruft packs to MIDX during geometric repack Taylor Blau
2022-05-19 11:32     ` Ævar Arnfjörð Bjarmason
2022-05-20 22:42       ` Taylor Blau
2022-05-18 23:11   ` [PATCH v4 16/17] builtin/gc.c: conditionally avoid pruning objects via loose Taylor Blau
2022-05-18 23:11   ` [PATCH v4 17/17] sha1-file.c: don't freshen cruft packs Taylor Blau
2022-05-18 23:48   ` [PATCH v4 00/17] " Derrick Stolee
2022-05-20 23:19     ` Junio C Hamano
2022-05-20 23:30       ` Taylor Blau
2022-05-19 11:42   ` [RFC PATCH 0/2] Utility functions for duplicated pack(write) code Ævar Arnfjörð Bjarmason
2022-05-19 11:42     ` [RFC PATCH 1/2] packfile API: add and use a pack_name_to_ext() utility function Ævar Arnfjörð Bjarmason
2022-05-19 15:40       ` Junio C Hamano
2022-05-19 11:42     ` [RFC PATCH 2/2] hash API: add and use a hash_short_id_by_algo() function Ævar Arnfjörð Bjarmason
2022-05-19 15:50       ` Junio C Hamano
2022-05-19 19:07         ` Ævar Arnfjörð Bjarmason
2022-05-19 15:31     ` [RFC PATCH 0/2] Utility functions for duplicated pack(write) code Junio C Hamano
2022-05-19 11:54   ` [PATCH v4 00/17] cruft packs Ævar Arnfjörð Bjarmason
2022-05-20 23:17 ` [PATCH v5 " Taylor Blau
2022-05-20 23:17   ` [PATCH v5 01/17] Documentation/technical: add cruft-packs.txt Taylor Blau
2022-05-20 23:17   ` [PATCH v5 02/17] pack-mtimes: support reading .mtimes files Taylor Blau
2022-05-24 19:32     ` Jonathan Nieder
2022-05-24 19:44       ` rsbecker
2022-05-24 22:25         ` Taylor Blau
2022-05-24 23:24           ` rsbecker
2022-05-25  0:07             ` Taylor Blau
2022-05-25  0:20               ` rsbecker
2022-05-25  9:11               ` adding new 32-bit on-disk (unsigned) timestamp formats (was: [PATCH v5 02/17] pack-mtimes: support reading .mtimes files) Ævar Arnfjörð Bjarmason
2022-05-25 13:30                 ` Derrick Stolee
2022-05-25 21:13                   ` Taylor Blau
2022-05-26  0:02                     ` Ævar Arnfjörð Bjarmason
2022-05-26  0:12                       ` Taylor Blau
2022-05-24 22:21       ` [PATCH v5 02/17] pack-mtimes: support reading .mtimes files Taylor Blau
2022-05-25  7:48         ` Jonathan Nieder
2022-05-25 21:36           ` Taylor Blau
2022-05-25 21:58             ` rsbecker
2022-05-25 22:59               ` Taylor Blau
2022-05-25 23:02     ` Taylor Blau
2022-05-26  0:30       ` Junio C Hamano
2023-06-01 13:01     ` Andreas Schwab
2022-05-20 23:17   ` [PATCH v5 03/17] pack-write: pass 'struct packing_data' to 'stage_tmp_packfiles' Taylor Blau
2022-05-20 23:17   ` [PATCH v5 04/17] chunk-format.h: extract oid_version() Taylor Blau
2022-05-20 23:17   ` [PATCH v5 05/17] pack-mtimes: support writing pack .mtimes files Taylor Blau
2022-05-20 23:17   ` [PATCH v5 06/17] t/helper: add 'pack-mtimes' test-tool Taylor Blau
2022-05-20 23:17   ` [PATCH v5 07/17] builtin/pack-objects.c: return from create_object_entry() Taylor Blau
2022-05-20 23:17   ` [PATCH v5 08/17] builtin/pack-objects.c: --cruft without expiration Taylor Blau
2022-05-20 23:17   ` [PATCH v5 09/17] reachable: add options to add_unseen_recent_objects_to_traversal Taylor Blau
2022-05-20 23:17   ` [PATCH v5 10/17] reachable: report precise timestamps from objects in cruft packs Taylor Blau
2022-05-20 23:18   ` [PATCH v5 11/17] builtin/pack-objects.c: --cruft with expiration Taylor Blau
2022-05-20 23:18   ` [PATCH v5 12/17] builtin/repack.c: support generating a cruft pack Taylor Blau
2022-05-20 23:18   ` [PATCH v5 13/17] builtin/repack.c: allow configuring cruft pack generation Taylor Blau
2022-05-20 23:18   ` [PATCH v5 14/17] builtin/repack.c: use named flags for existing_packs Taylor Blau
2022-05-20 23:18   ` [PATCH v5 15/17] builtin/repack.c: add cruft packs to MIDX during geometric repack Taylor Blau
2022-05-20 23:18   ` [PATCH v5 16/17] builtin/gc.c: conditionally avoid pruning objects via loose Taylor Blau
2022-06-19  5:38     ` René Scharfe
2022-06-21 15:58       ` Junio C Hamano
2022-05-20 23:18   ` [PATCH v5 17/17] sha1-file.c: don't freshen cruft packs Taylor Blau
2022-05-21 11:17   ` [PATCH v5 00/17] " Ævar Arnfjörð Bjarmason
2022-05-24 19:39     ` Jonathan Nieder
2022-05-24 21:50       ` Taylor Blau
2022-05-24 21:55         ` Ævar Arnfjörð Bjarmason
2022-05-24 22:12           ` Taylor Blau
2022-05-25  7:53             ` Jonathan Nieder
2022-05-25 19:59               ` Derrick Stolee
2022-05-25 21:09                 ` Taylor Blau
2022-05-26  0:06                   ` Ævar Arnfjörð Bjarmason

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