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From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: Taylor Blau <me@ttaylorr.com>,
	git@vger.kernel.org, dstolee@microsoft.com
Subject: Re: [PATCH v4 3/8] builtin/pack-objects.c: add '--stdin-packs' option
Date: Tue, 23 Feb 2021 13:51:39 -0500	[thread overview]
Message-ID: <YDVOuwMTBoQ57Omk@coredump.intra.peff.net> (raw)
In-Reply-To: <xmqqsg5n436v.fsf@gitster.g>

On Tue, Feb 23, 2021 at 12:07:52AM -0800, Junio C Hamano wrote:

> Taylor Blau <me@ttaylorr.com> writes:
> 
> > (I found it convenient while developing this patch to have 'git
> > pack-objects' report the number of objects which were visited and got
> > their namehash fields filled in during traversal. This is also included
> > in the below patch via trace2 data lines).
> 
> It does sound like a well thought out strategy to give name-hash to
> entries that we may have to find good delta bases afresh, while
> stopping upon hitting parts of the history we won't have to (either
> because they are in "excluded" packs, which you did here, or because
> they can take advantage of the "reuse existing delta base" logic [*],
> which we may want to look further into in future follow-on topics).
> 
> [Footnote]
> 
> * I presume that such a logic may, instead of stopping at an object
>   that is in an excluded pack, stop at an object that is stored in
>   the current pack as a delta and its base is also going to be
>   packed (and the latter by definition is always true, I presume, as
>   everything in the included pack would be packed)

I'm not sure if using deltas as a heuristic for stopping traversal makes
sense. They don't necessarily correspond to the history graph, or to
what was pushed. E.g., if I see that tree X is a delta against tree Y,
then we might say: if Y is not excluded by being in one of the base
packs, then we will reuse the delta. We do not need the namehash of X,
since we already know its delta.

But that does not tell us anything about the subtrees and blobs
contained in X. We still want to traverse X in order to find out _their_
name hashes, because it is likely that we will need to delta some of
those.

Of course if you see a blob that is a delta that you plan to reuse, you
know you can stop there. But by the time you get to it, you already know
its namehash, and there is nothing left to traverse. :)

-Peff

  reply	other threads:[~2021-02-23 18:52 UTC|newest]

Thread overview: 120+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-19 23:23 [PATCH 00/10] repack: support repacking into a geometric sequence Taylor Blau
2021-01-19 23:24 ` [PATCH 01/10] packfile: introduce 'find_kept_pack_entry()' Taylor Blau
2021-01-20 13:40   ` Derrick Stolee
2021-01-20 14:38     ` Taylor Blau
2021-01-29  2:33   ` Junio C Hamano
2021-01-29 18:38     ` Taylor Blau
2021-01-29 19:31     ` Jeff King
2021-01-29 20:20       ` Junio C Hamano
2021-01-19 23:24 ` [PATCH 02/10] revision: learn '--no-kept-objects' Taylor Blau
2021-01-29  3:10   ` Junio C Hamano
2021-01-29 19:13     ` Taylor Blau
2021-01-19 23:24 ` [PATCH 03/10] builtin/pack-objects.c: learn '--assume-kept-packs-closed' Taylor Blau
2021-01-29  3:21   ` Junio C Hamano
2021-01-29 19:19     ` Jeff King
2021-01-29 20:01       ` Taylor Blau
2021-01-29 20:25         ` Jeff King
2021-01-29 22:10           ` Taylor Blau
2021-01-29 22:57             ` Jeff King
2021-01-29 23:03             ` Junio C Hamano
2021-01-29 23:28               ` Taylor Blau
2021-02-02  3:04                 ` Taylor Blau
2021-01-29 23:31               ` Jeff King
2021-01-29 22:13           ` Junio C Hamano
2021-01-29 20:30       ` Junio C Hamano
2021-01-29 22:43         ` Jeff King
2021-01-29 22:53           ` Taylor Blau
2021-01-29 23:00             ` Jeff King
2021-01-29 23:10             ` Junio C Hamano
2021-01-19 23:24 ` [PATCH 04/10] p5303: add missing &&-chains Taylor Blau
2021-01-19 23:24 ` [PATCH 05/10] p5303: measure time to repack with keep Taylor Blau
2021-01-29  3:40   ` Junio C Hamano
2021-01-29 19:32     ` Jeff King
2021-01-29 20:04       ` [PATCH] p5303: avoid sed GNU-ism Jeff King
2021-01-29 20:19         ` Eric Sunshine
2021-01-29 20:27           ` Jeff King
2021-01-29 20:36             ` Eric Sunshine
2021-01-29 22:11               ` Taylor Blau
2021-01-29 20:38       ` [PATCH 05/10] p5303: measure time to repack with keep Junio C Hamano
2021-01-29 22:10         ` Jeff King
2021-01-29 23:12           ` Junio C Hamano
2021-01-19 23:24 ` [PATCH 06/10] pack-objects: rewrite honor-pack-keep logic Taylor Blau
2021-01-19 23:24 ` [PATCH 07/10] packfile: add kept-pack cache for find_kept_pack_entry() Taylor Blau
2021-01-19 23:24 ` [PATCH 08/10] builtin/pack-objects.c: teach '--keep-pack-stdin' Taylor Blau
2021-01-19 23:24 ` [PATCH 09/10] builtin/repack.c: extract loose object handling Taylor Blau
2021-01-20 13:59   ` Derrick Stolee
2021-01-20 14:34     ` Taylor Blau
2021-01-20 15:51       ` Derrick Stolee
2021-01-21  3:45     ` Junio C Hamano
2021-01-19 23:24 ` [PATCH 10/10] builtin/repack.c: add '--geometric' option Taylor Blau
2021-01-20 14:05 ` [PATCH 00/10] repack: support repacking into a geometric sequence Derrick Stolee
2021-02-04  3:58 ` [PATCH v2 0/8] " Taylor Blau
2021-02-04  3:58   ` [PATCH v2 1/8] packfile: introduce 'find_kept_pack_entry()' Taylor Blau
2021-02-16 21:42     ` Jeff King
2021-02-16 21:48       ` Taylor Blau
2021-02-04  3:58   ` [PATCH v2 2/8] revision: learn '--no-kept-objects' Taylor Blau
2021-02-16 23:17     ` Jeff King
2021-02-17 18:35       ` Taylor Blau
2021-02-04  3:59   ` [PATCH v2 3/8] builtin/pack-objects.c: add '--stdin-packs' option Taylor Blau
2021-02-16 23:46     ` Jeff King
2021-02-17 18:59       ` Taylor Blau
2021-02-17 19:21         ` Jeff King
2021-02-04  3:59   ` [PATCH v2 4/8] p5303: add missing &&-chains Taylor Blau
2021-02-04  3:59   ` [PATCH v2 5/8] p5303: measure time to repack with keep Taylor Blau
2021-02-16 23:58     ` Jeff King
2021-02-17  0:02       ` Jeff King
2021-02-17 19:13       ` Taylor Blau
2021-02-17 19:25         ` Jeff King
2021-02-04  3:59   ` [PATCH v2 6/8] builtin/pack-objects.c: rewrite honor-pack-keep logic Taylor Blau
2021-02-17 16:05     ` Jeff King
2021-02-17 19:23       ` Taylor Blau
2021-02-17 19:29         ` Jeff King
2021-02-04  3:59   ` [PATCH v2 7/8] packfile: add kept-pack cache for find_kept_pack_entry() Taylor Blau
2021-02-17 17:11     ` Jeff King
2021-02-17 19:54       ` Taylor Blau
2021-02-17 20:25         ` Jeff King
2021-02-17 20:29           ` Taylor Blau
2021-02-17 21:43             ` Jeff King
2021-02-04  3:59   ` [PATCH v2 8/8] builtin/repack.c: add '--geometric' option Taylor Blau
2021-02-17 18:17     ` Jeff King
2021-02-17 20:01       ` Taylor Blau
2021-02-17  0:01   ` [PATCH v2 0/8] repack: support repacking into a geometric sequence Jeff King
2021-02-17 18:18     ` Jeff King
2021-02-18  3:14 ` [PATCH v3 " Taylor Blau
2021-02-18  3:14   ` [PATCH v3 1/8] packfile: introduce 'find_kept_pack_entry()' Taylor Blau
2021-02-18  3:14   ` [PATCH v3 2/8] revision: learn '--no-kept-objects' Taylor Blau
2021-02-18  3:14   ` [PATCH v3 3/8] builtin/pack-objects.c: add '--stdin-packs' option Taylor Blau
2021-02-18  3:14   ` [PATCH v3 4/8] p5303: add missing &&-chains Taylor Blau
2021-02-18  3:14   ` [PATCH v3 5/8] p5303: measure time to repack with keep Taylor Blau
2021-02-18  3:14   ` [PATCH v3 6/8] builtin/pack-objects.c: rewrite honor-pack-keep logic Taylor Blau
2021-02-18  3:14   ` [PATCH v3 7/8] packfile: add kept-pack cache for find_kept_pack_entry() Taylor Blau
2021-02-18  3:14   ` [PATCH v3 8/8] builtin/repack.c: add '--geometric' option Taylor Blau
2021-02-23  0:31   ` [PATCH v3 0/8] repack: support repacking into a geometric sequence Jeff King
2021-02-23  1:06     ` Taylor Blau
2021-02-23  1:42       ` Jeff King
2021-02-23  2:24 ` [PATCH v4 " Taylor Blau
2021-02-23  2:25   ` [PATCH v4 1/8] packfile: introduce 'find_kept_pack_entry()' Taylor Blau
2021-02-23  2:25   ` [PATCH v4 2/8] revision: learn '--no-kept-objects' Taylor Blau
2021-02-23  2:25   ` [PATCH v4 3/8] builtin/pack-objects.c: add '--stdin-packs' option Taylor Blau
2021-02-23  8:07     ` Junio C Hamano
2021-02-23 18:51       ` Jeff King [this message]
2021-02-23  2:25   ` [PATCH v4 4/8] p5303: add missing &&-chains Taylor Blau
2021-02-23  2:25   ` [PATCH v4 5/8] p5303: measure time to repack with keep Taylor Blau
2021-02-23  2:25   ` [PATCH v4 6/8] builtin/pack-objects.c: rewrite honor-pack-keep logic Taylor Blau
2021-02-23  2:25   ` [PATCH v4 7/8] packfile: add kept-pack cache for find_kept_pack_entry() Taylor Blau
2021-02-23  2:25   ` [PATCH v4 8/8] builtin/repack.c: add '--geometric' option Taylor Blau
2021-02-24 23:19     ` Junio C Hamano
2021-02-24 23:43       ` Junio C Hamano
2021-03-04 21:40         ` Taylor Blau
2021-03-04 21:55       ` Taylor Blau
2021-02-23  3:39   ` [PATCH v4 0/8] repack: support repacking into a geometric sequence Jeff King
2021-02-23  7:43   ` Junio C Hamano
2021-02-23 18:44     ` Jeff King
2021-02-23 19:54       ` Martin Fick
2021-02-23 20:06         ` Taylor Blau
2021-02-23 21:57           ` Martin Fick
2021-02-23 20:15         ` Jeff King
2021-02-23 21:41           ` Martin Fick
2021-02-23 21:53             ` Jeff King
2021-02-24 18:13               ` Martin Fick
2021-02-26  6:23                 ` Jeff King

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