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From: Christian Couder <christian.couder@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, John Cai <johncai86@gmail.com>,
	Jonathan Tan <jonathantanmy@google.com>,
	Jonathan Nieder <jrnieder@gmail.com>,
	Taylor Blau <me@ttaylorr.com>, Derrick Stolee <stolee@gmail.com>,
	Patrick Steinhardt <ps@pks.im>,
	Christian Couder <chriscool@tuxfamily.org>
Subject: Re: [PATCH v2 5/8] repack: add `--filter=<filter-spec>` option
Date: Tue, 25 Jul 2023 17:22:46 +0200	[thread overview]
Message-ID: <CAP8UFD3b6gCog5P7WKzTuPQV2Lhf51=xO7ys+W7o0pGewJMcFg@mail.gmail.com> (raw)
In-Reply-To: <xmqqila9p3j8.fsf@gitster.g>

On Mon, Jul 24, 2023 at 8:28 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Christian Couder <christian.couder@gmail.com> writes:
>
> >> Minor nit.  Aren't the above two the same use case?
> >
> > In the first case only some large blobs are moved to slower storage
> > and in the other case all the blobs are moved to slower storage. So
> > yeah the use cases are very similar. Not sure if and how I can improve
> > the above wording though.
>
> Just by removing one or the other, it would be quite improved, no?
> Moving away some blobs could move away all or just a selected
> subset.

Ok, I have done that in my current version.

> > I think it can work if the call to write_filtered_pack() is either
> > before the call to close_object_store() or after it. It would just use
> > the tempfiles with their temporary name in the first case and with
> > their final name in the second case.
> >
> > write_filtered_pack() is very similar to write_cruft_pack() which is
> > called before the call to close_object_store(), so I prefer to keep it
> > before that call too, if possible, for consistency.
>
> As long as the set-up is not racy, either would be OK, as the names
> are not recorded in the end result.
>
> If the upstream tells the downstream the temporary's name and then
> finializes the temporary to the final name before the downstream
> reacts to the input,

It doesn't seem to me that it's what happens.

We have the following order:

  - finish_pack_objects_cmd() is called for the first pack-objects
process. It populates the 'names' string_list with the temporary name
of the packfile it generated (which doesn't contain the filtered out
objects) and calls finish_command() to finish the first pack-objects
process. So as far as I understand nothing can be written anymore to
the packfile when finish_pack_objects_cmd() returns.

  - write_filtered_pack() is called. It starts the second pack-objects
process and passes it the temporary name of the packfile that was just
written, taking it from the 'names' string_list. It then calls
finish_pack_objects_cmd() for the second process which populates the
'names' string_list with the temporary name of the packfile created by
the second process and finishes the second process. So nothing can
then be written in the second packfile anymore.

  - close_object_store() is called which renames the packfiles from
the 'names' string_list giving them their final name.

So the final names are given only once both processes are finished and
both packfiles have been fully written.

> however, then by the time downstream starts
> working on the file, the file may not exist under its original,
> temporary name, and that kind of race was what I was worried about.
>
> > Perhaps this could be dealt with separately though, as I think we
> > might want to fix write_cruft_pack() first then.
>
> Sorry, I am not understanding this quite well.  Do you mean we
> should add one more known-to-be-racy-and-incorrect codepath because
> there is already a codepath that needs to be fixed anyway?

No.

> If write_cruft_pack() has a similar issue, then yeah, let's fix that
> first (testing might be tricky for any racy bugs).  And let's use
> the same technique as used to fix it in this series, too, so that we
> do not reintroduce a similar bug due to racy setup.

Yeah, that's what I mean.

I am not sure the race actually exists though. I have tried to explain
why it seems to me that things look correct, but from previous
experience I know that you are very often right, and I might have
missed something.

Thanks.

  reply	other threads:[~2023-07-25 15:23 UTC|newest]

Thread overview: 161+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-06-14 19:25 [PATCH 0/9] Repack objects into separate packfiles based on a filter Christian Couder
2023-06-14 19:25 ` [PATCH 1/9] pack-objects: allow `--filter` without `--stdout` Christian Couder
2023-06-21 10:49   ` Taylor Blau
2023-07-05  6:16     ` Christian Couder
2023-06-14 19:25 ` [PATCH 2/9] pack-objects: add `--print-filtered` to print omitted objects Christian Couder
2023-06-15 22:50   ` Junio C Hamano
2023-06-21 10:52     ` Taylor Blau
2023-06-21 11:11       ` Christian Couder
2023-06-21 11:54         ` Taylor Blau
2023-06-14 19:25 ` [PATCH 3/9] t/helper: add 'find-pack' test-tool Christian Couder
2023-06-15 23:32   ` Junio C Hamano
2023-06-21 10:40     ` Christian Couder
2023-06-21 10:54     ` Taylor Blau
2023-06-14 19:25 ` [PATCH 4/9] repack: refactor piping an oid to a command Christian Couder
2023-06-15 23:46   ` Junio C Hamano
2023-06-21 10:55     ` Taylor Blau
2023-06-21 10:56     ` Christian Couder
2023-06-14 19:25 ` [PATCH 5/9] repack: refactor finishing pack-objects command Christian Couder
2023-06-16  0:13   ` Junio C Hamano
2023-06-21 11:06     ` Taylor Blau
2023-06-21 11:19       ` Christian Couder
2023-06-21 11:05   ` Taylor Blau
2023-06-14 19:25 ` [PATCH 6/9] repack: add `--filter=<filter-spec>` option Christian Couder
2023-06-16  0:43   ` Junio C Hamano
2023-06-21 11:20     ` Taylor Blau
2023-06-21 15:04       ` Christian Couder
2023-06-22 11:05         ` Taylor Blau
2023-06-21 14:40     ` Christian Couder
2023-06-21 16:53       ` Junio C Hamano
2023-06-22  8:39         ` Christian Couder
2023-06-22 18:32           ` Junio C Hamano
2023-06-21 11:17   ` Taylor Blau
2023-07-05  7:18     ` Christian Couder
2023-06-14 19:25 ` [PATCH 7/9] gc: add `gc.repackFilter` config option Christian Couder
2023-06-14 19:25 ` [PATCH 8/9] repack: implement `--filter-to` for storing filtered out objects Christian Couder
2023-06-16  2:21   ` Junio C Hamano
2023-06-21 11:49   ` Taylor Blau
2023-06-21 12:08     ` Christian Couder
2023-06-21 12:25       ` Taylor Blau
2023-06-21 16:44         ` Junio C Hamano
2023-07-05  6:19     ` Christian Couder
2023-06-14 19:25 ` [PATCH 9/9] gc: add `gc.repackFilterTo` config option Christian Couder
2023-06-16  2:54   ` Junio C Hamano
2023-06-14 21:36 ` [PATCH 0/9] Repack objects into separate packfiles based on a filter Junio C Hamano
2023-06-16  3:08   ` Junio C Hamano
2023-07-05  6:08 ` [PATCH v2 0/8] " Christian Couder
2023-07-05  6:08   ` [PATCH v2 1/8] pack-objects: allow `--filter` without `--stdout` Christian Couder
2023-07-05  6:08   ` [PATCH v2 2/8] t/helper: add 'find-pack' test-tool Christian Couder
2023-07-05  6:08   ` [PATCH v2 3/8] repack: refactor finishing pack-objects command Christian Couder
2023-07-05  6:08   ` [PATCH v2 4/8] repack: refactor finding pack prefix Christian Couder
2023-07-05  6:08   ` [PATCH v2 5/8] repack: add `--filter=<filter-spec>` option Christian Couder
2023-07-05 17:53     ` Junio C Hamano
2023-07-24  9:01       ` Christian Couder
2023-07-24 18:28         ` Junio C Hamano
2023-07-25 15:22           ` Christian Couder [this message]
2023-07-25 17:25             ` Junio C Hamano
2023-07-25 23:08               ` Junio C Hamano
2023-08-08  8:45                 ` Christian Couder
2023-08-09 20:38                   ` Taylor Blau
2023-08-09 22:50                   ` Junio C Hamano
2023-08-09 23:38                     ` Junio C Hamano
2023-08-10  0:10                       ` Jeff King
2023-07-05 18:12     ` Junio C Hamano
2023-07-24  9:02       ` Christian Couder
2023-07-05  6:08   ` [PATCH v2 6/8] gc: add `gc.repackFilter` config option Christian Couder
2023-07-05  6:08   ` [PATCH v2 7/8] repack: implement `--filter-to` for storing filtered out objects Christian Couder
2023-07-05 18:26     ` Junio C Hamano
2023-07-24  9:00       ` Christian Couder
2023-07-24 18:18         ` Junio C Hamano
2023-07-25 13:41           ` Robert Coup
2023-07-25 16:50             ` Junio C Hamano
2023-07-25 15:45           ` Christian Couder
2023-07-05  6:08   ` [PATCH v2 8/8] gc: add `gc.repackFilterTo` config option Christian Couder
2023-07-24  8:59   ` [PATCH v3 0/8] Repack objects into separate packfiles based on a filter Christian Couder
2023-07-24  8:59     ` [PATCH v3 1/8] pack-objects: allow `--filter` without `--stdout` Christian Couder
2023-07-25 22:38       ` Taylor Blau
2023-07-25 23:51         ` Junio C Hamano
2023-07-24  8:59     ` [PATCH v3 2/8] t/helper: add 'find-pack' test-tool Christian Couder
2023-07-25 22:44       ` Taylor Blau
2023-08-08  8:28         ` Christian Couder
2023-07-24  8:59     ` [PATCH v3 3/8] repack: refactor finishing pack-objects command Christian Couder
2023-07-25 22:45       ` Taylor Blau
2023-07-24  8:59     ` [PATCH v3 4/8] repack: refactor finding pack prefix Christian Couder
2023-07-25 22:47       ` Taylor Blau
2023-08-08  8:29         ` Christian Couder
2023-07-24  8:59     ` [PATCH v3 5/8] repack: add `--filter=<filter-spec>` option Christian Couder
2023-07-25 23:04       ` Taylor Blau
2023-08-08  8:34         ` Christian Couder
2023-08-09 21:12           ` Taylor Blau
2023-07-24  8:59     ` [PATCH v3 6/8] gc: add `gc.repackFilter` config option Christian Couder
2023-07-25 23:07       ` Taylor Blau
2023-08-08  8:38         ` Christian Couder
2023-08-09 21:15           ` Taylor Blau
2023-07-24  8:59     ` [PATCH v3 7/8] repack: implement `--filter-to` for storing filtered out objects Christian Couder
2023-07-24  8:59     ` [PATCH v3 8/8] gc: add `gc.repackFilterTo` config option Christian Couder
2023-07-25 23:10     ` [PATCH v3 0/8] Repack objects into separate packfiles based on a filter Taylor Blau
2023-08-08  8:26     ` [PATCH v4 " Christian Couder
2023-08-08  8:26       ` [PATCH v4 1/8] pack-objects: allow `--filter` without `--stdout` Christian Couder
2023-08-08  8:26       ` [PATCH v4 2/8] t/helper: add 'find-pack' test-tool Christian Couder
2023-08-09 21:18         ` Taylor Blau
2023-08-08  8:26       ` [PATCH v4 3/8] repack: refactor finishing pack-objects command Christian Couder
2023-08-08  8:26       ` [PATCH v4 4/8] repack: refactor finding pack prefix Christian Couder
2023-08-09 21:20         ` Taylor Blau
2023-08-08  8:26       ` [PATCH v4 5/8] repack: add `--filter=<filter-spec>` option Christian Couder
2023-08-09 21:40         ` Taylor Blau
2023-08-08  8:26       ` [PATCH v4 6/8] gc: add `gc.repackFilter` config option Christian Couder
2023-08-08  8:26       ` [PATCH v4 7/8] repack: implement `--filter-to` for storing filtered out objects Christian Couder
2023-08-08  8:26       ` [PATCH v4 8/8] gc: add `gc.repackFilterTo` config option Christian Couder
2023-08-09 21:45       ` [PATCH v4 0/8] Repack objects into separate packfiles based on a filter Taylor Blau
2023-08-09 21:57         ` Junio C Hamano
2023-08-12  0:12         ` Christian Couder
2023-08-12  0:00       ` [PATCH v5 " Christian Couder
2023-08-12  0:00         ` [PATCH v5 1/8] pack-objects: allow `--filter` without `--stdout` Christian Couder
2023-08-12  0:00         ` [PATCH v5 2/8] t/helper: add 'find-pack' test-tool Christian Couder
2023-08-12  0:00         ` [PATCH v5 3/8] repack: refactor finishing pack-objects command Christian Couder
2023-08-12  0:00         ` [PATCH v5 4/8] repack: refactor finding pack prefix Christian Couder
2023-08-12  0:00         ` [PATCH v5 5/8] repack: add `--filter=<filter-spec>` option Christian Couder
2023-08-12  0:00         ` [PATCH v5 6/8] gc: add `gc.repackFilter` config option Christian Couder
2023-08-12  0:00         ` [PATCH v5 7/8] repack: implement `--filter-to` for storing filtered out objects Christian Couder
2023-08-12  0:00         ` [PATCH v5 8/8] gc: add `gc.repackFilterTo` config option Christian Couder
2023-08-15  0:51         ` [PATCH v5 0/8] Repack objects into separate packfiles based on a filter Junio C Hamano
2023-08-15 21:43           ` Taylor Blau
2023-08-15 22:32             ` Junio C Hamano
2023-08-15 23:09               ` Taylor Blau
2023-08-15 23:18                 ` Junio C Hamano
2023-08-16  0:38                   ` Taylor Blau
2023-08-16 17:16                     ` Junio C Hamano
2023-09-11 15:20                 ` Christian Couder
2023-09-11 15:06         ` [PATCH v6 0/9] " Christian Couder
2023-09-11 15:06           ` [PATCH v6 1/9] pack-objects: allow `--filter` without `--stdout` Christian Couder
2023-09-11 15:06           ` [PATCH v6 2/9] t/helper: add 'find-pack' test-tool Christian Couder
2023-09-11 15:06           ` [PATCH v6 3/9] repack: refactor finishing pack-objects command Christian Couder
2023-09-11 15:06           ` [PATCH v6 4/9] repack: refactor finding pack prefix Christian Couder
2023-09-11 15:06           ` [PATCH v6 5/9] pack-bitmap-write: rebuild using new bitmap when remapping Christian Couder
2023-09-11 15:06           ` [PATCH v6 6/9] repack: add `--filter=<filter-spec>` option Christian Couder
2023-09-11 15:06           ` [PATCH v6 7/9] gc: add `gc.repackFilter` config option Christian Couder
2023-09-11 15:06           ` [PATCH v6 8/9] repack: implement `--filter-to` for storing filtered out objects Christian Couder
2023-09-11 15:06           ` [PATCH v6 9/9] gc: add `gc.repackFilterTo` config option Christian Couder
2023-09-25 15:25           ` [PATCH v7 0/9] Repack objects into separate packfiles based on a filter Christian Couder
2023-09-25 15:25             ` [PATCH v7 1/9] pack-objects: allow `--filter` without `--stdout` Christian Couder
2023-09-25 15:25             ` [PATCH v7 2/9] t/helper: add 'find-pack' test-tool Christian Couder
2023-09-25 15:25             ` [PATCH v7 3/9] repack: refactor finishing pack-objects command Christian Couder
2023-09-25 15:25             ` [PATCH v7 4/9] repack: refactor finding pack prefix Christian Couder
2023-09-25 15:25             ` [PATCH v7 5/9] pack-bitmap-write: rebuild using new bitmap when remapping Christian Couder
2023-09-25 15:25             ` [PATCH v7 6/9] repack: add `--filter=<filter-spec>` option Christian Couder
2023-09-25 15:25             ` [PATCH v7 7/9] gc: add `gc.repackFilter` config option Christian Couder
2023-09-25 15:25             ` [PATCH v7 8/9] repack: implement `--filter-to` for storing filtered out objects Christian Couder
2023-09-25 15:25             ` [PATCH v7 9/9] gc: add `gc.repackFilterTo` config option Christian Couder
2023-09-25 19:14             ` [PATCH v7 0/9] Repack objects into separate packfiles based on a filter Junio C Hamano
2023-09-25 22:41               ` Taylor Blau
2023-10-02 16:54             ` [PATCH v8 " Christian Couder
2023-10-02 16:54               ` [PATCH v8 1/9] pack-objects: allow `--filter` without `--stdout` Christian Couder
2023-10-02 16:54               ` [PATCH v8 2/9] t/helper: add 'find-pack' test-tool Christian Couder
2023-10-02 16:54               ` [PATCH v8 3/9] repack: refactor finishing pack-objects command Christian Couder
2023-10-02 16:54               ` [PATCH v8 4/9] repack: refactor finding pack prefix Christian Couder
2023-10-02 16:55               ` [PATCH v8 5/9] pack-bitmap-write: rebuild using new bitmap when remapping Christian Couder
2023-10-02 16:55               ` [PATCH v8 6/9] repack: add `--filter=<filter-spec>` option Christian Couder
2023-10-02 16:55               ` [PATCH v8 7/9] gc: add `gc.repackFilter` config option Christian Couder
2023-10-02 16:55               ` [PATCH v8 8/9] repack: implement `--filter-to` for storing filtered out objects Christian Couder
2023-10-02 16:55               ` [PATCH v8 9/9] gc: add `gc.repackFilterTo` config option Christian Couder
2023-10-02 20:14               ` [PATCH v8 0/9] Repack objects into separate packfiles based on a filter Taylor Blau

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