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From: Philip Oakley <philipoakley@iee.org>
To: Derrick Stolee <stolee@gmail.com>,
	Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>,
	git@vger.kernel.org
Cc: peff@peff.net, avarab@gmail.com, git@jeffhostetler.com,
	jrnieder@google.com, steadmon@google.com,
	Junio C Hamano <gitster@pobox.com>,
	Derrick Stolee <dstolee@microsoft.com>
Subject: Re: [PATCH v3 01/14] commit-graph: document commit-graph chains
Date: Thu, 6 Jun 2019 22:59:00 +0100	[thread overview]
Message-ID: <504867ac-557e-7c9c-3d0f-076c1a7f0e58@iee.org> (raw)
In-Reply-To: <909f355c-4c44-1556-71c7-168b28abddfc@gmail.com>

Hi Stolee,

We may be talking at cross-purposes.
On 06/06/2019 18:09, Derrick Stolee wrote:
> On 6/6/2019 8:10 AM, Philip Oakley wrote:
>> Hi Derrick ,
>>
>> On 03/06/2019 17:03, Derrick Stolee via GitGitGadget wrote:
>>> From: Derrick Stolee <dstolee@microsoft.com>
>>>
>>> Add a basic description of commit-graph chains.
>> Not really your problem, but I did notice that we don't actually explain what we mean here by a commit graph (before we start chaining them), and the distinction between the generic concept and the specific implementation.
The purpose of my comment is here. We have/had not explained why we need 
(another) commit graph, either within the man page, or the technical 
docs. It's an understanding gap.
>>
>> If I understand it correctly, the regular DAG (directed acyclic graph) already inherently contains the commit graph, showing the parent(s) of each commit. Hence, why do we need another? (which then needs explaining the what/why/how)
>>
>> So, in one sense, another commit chain is potentially duplicated redundant data. What hasn't been surfaced (for the reader coming later) is probably that accessing the DAG commit graph can be (a) slow, (b) one way (no child relationships), and (c) accesses large amounts of other data that isn't relevant to the task at hand.
>>
>> So the commit graph (implementation) is [I think] a fast, compact, sorted(?), list of commit oids that provides two way linkage through the commit graph (?) to allow fast queries within the Git codebase.
>>
>> The commit graph is normally considered immutable,
> _Commits_ are immutable. The graph grows as commits are added.
I was aware that individual commits are immutable. However the tips, 
grafts and replacements can change the topology of the graph (especially 
the grafts and replacements, hence the desire to have something that 
acts as a guide as to what, generally, is trying to be achieved).
>
> This may be the crux of your confusion, since the commit-graph
> file can become stale as commits are added by 'git commit' or
> 'git fetch'. The point of the incremental file format is to
> update the commit-graph data without rewriting the entire thing
> every time.
>
> Does this help clarify what's going on?
Only slightly, see below.
>
>> however the DAG commit graph can be extended by new commits, trimmed by branch deletion, rebasing, forced push, etc, or even reorganised via 'replace' or grafts commits, which must then be reflected in the commit graph (implementation).
> These things create new commit objects, which would not be in
> the commit-graph file until it is rewritten.
>
>> It just felt that there is a gap between the high level DAG, explained in the glossary, and the commit-graph That perhaps the technical/commit-graph.txt ought to summarise.
> I do think that technical/commit-graph.txt does summarize a lot
> about the commit-graph _file_ and how that accelerates walks on
> the high-level DAG. The added content in this patch does assume
> a full understanding of the previous contents of that file.
The current (prior) documentation is a bit Catch 22 with regard to that 
assumed full understanding, hence my comment, including the "Not really 
your problem," bit.
>
> Thanks,
> -Stolee
>
Philip

  reply	other threads:[~2019-06-06 21:59 UTC|newest]

Thread overview: 136+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-08 15:53 [PATCH 00/17] [RFC] Commit-graph: Write incremental files Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 01/17] commit-graph: fix the_repository reference Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 02/17] commit-graph: return with errors during write Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 04/17] commit-graph: remove Future Work section Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 03/17] commit-graph: collapse parameters into flags Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 05/17] commit-graph: create write_commit_graph_context Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 06/17] commit-graph: extract fill_oids_from_packs() Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 07/17] commit-graph: extract fill_oids_from_commit_hex() Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 08/17] commit-graph: extract fill_oids_from_all_packs() Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 09/17] commit-graph: extract count_distinct_commits() Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 10/17] commit-graph: extract copy_oids_to_commits() Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 11/17] commit-graph: extract write_commit_graph_file() Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 12/17] Documentation: describe split commit-graphs Derrick Stolee via GitGitGadget
2019-05-08 17:20   ` SZEDER Gábor
2019-05-08 19:00     ` Derrick Stolee
2019-05-08 20:11       ` Ævar Arnfjörð Bjarmason
2019-05-09  4:49         ` Junio C Hamano
2019-05-09 12:25           ` Derrick Stolee
2019-05-09 13:45         ` Derrick Stolee
2019-05-09 15:48           ` Ævar Arnfjörð Bjarmason
2019-05-09 17:08             ` Derrick Stolee
2019-05-09 21:45               ` Ævar Arnfjörð Bjarmason
2019-05-10 12:44                 ` Derrick Stolee
2019-05-08 15:53 ` [PATCH 13/17] commit-graph: lay groundwork for incremental files Derrick Stolee via GitGitGadget
2019-05-08 15:53 ` [PATCH 14/17] commit-graph: load split commit-graph files Derrick Stolee via GitGitGadget
2019-05-08 15:54 ` [PATCH 15/17] commit-graph: write " Derrick Stolee via GitGitGadget
2019-05-08 15:54 ` [PATCH 16/17] commit-graph: add --split option Derrick Stolee via GitGitGadget
2019-05-08 15:54 ` [PATCH 17/17] fetch: add fetch.writeCommitGraph config setting Derrick Stolee via GitGitGadget
2019-05-09  8:07   ` Ævar Arnfjörð Bjarmason
2019-05-09 14:21     ` Derrick Stolee
2019-05-08 19:27 ` [PATCH 00/17] [RFC] Commit-graph: Write incremental files Ævar Arnfjörð Bjarmason
2019-05-22 19:53 ` [PATCH v2 00/11] " Derrick Stolee via GitGitGadget
2019-05-22 19:53   ` [PATCH v2 01/11] commit-graph: document commit-graph chains Derrick Stolee via GitGitGadget
2019-05-22 19:53   ` [PATCH v2 02/11] commit-graph: prepare for " Derrick Stolee via GitGitGadget
2019-05-22 19:53   ` [PATCH v2 03/11] commit-graph: rename commit_compare to oid_compare Derrick Stolee via GitGitGadget
2019-05-22 19:53   ` [PATCH v2 04/11] commit-graph: load commit-graph chains Derrick Stolee via GitGitGadget
2019-05-22 19:53   ` [PATCH v2 05/11] commit-graph: add base graphs chunk Derrick Stolee via GitGitGadget
2019-05-22 19:53   ` [PATCH v2 06/11] commit-graph: rearrange chunk count logic Derrick Stolee via GitGitGadget
2019-05-22 19:53   ` [PATCH v2 07/11] commit-graph: write commit-graph chains Derrick Stolee via GitGitGadget
2019-05-22 19:53   ` [PATCH v2 08/11] commit-graph: add --split option to builtin Derrick Stolee via GitGitGadget
2019-05-27 11:28     ` SZEDER Gábor
2019-05-22 19:53   ` [PATCH v2 09/11] commit-graph: merge commit-graph chains Derrick Stolee via GitGitGadget
2019-05-23  0:43     ` Ævar Arnfjörð Bjarmason
2019-05-23 13:00       ` Derrick Stolee
2019-05-22 19:53   ` [PATCH v2 10/11] commit-graph: allow cross-alternate chains Derrick Stolee via GitGitGadget
2019-05-22 19:53   ` [PATCH v2 11/11] commit-graph: expire commit-graph files Derrick Stolee via GitGitGadget
2019-06-03 16:03   ` [PATCH v3 00/14] Commit-graph: Write incremental files Derrick Stolee via GitGitGadget
2019-06-03 16:03     ` [PATCH v3 01/14] commit-graph: document commit-graph chains Derrick Stolee via GitGitGadget
2019-06-05 17:22       ` Junio C Hamano
2019-06-05 18:09         ` Derrick Stolee
2019-06-06 12:10       ` Philip Oakley
2019-06-06 17:09         ` Derrick Stolee
2019-06-06 21:59           ` Philip Oakley [this message]
2019-06-03 16:03     ` [PATCH v3 02/14] commit-graph: prepare for " Derrick Stolee via GitGitGadget
2019-06-03 16:03     ` [PATCH v3 03/14] commit-graph: rename commit_compare to oid_compare Derrick Stolee via GitGitGadget
2019-06-03 16:03     ` [PATCH v3 04/14] commit-graph: load commit-graph chains Derrick Stolee via GitGitGadget
2019-06-03 16:03     ` [PATCH v3 06/14] commit-graph: rearrange chunk count logic Derrick Stolee via GitGitGadget
2019-06-03 16:03     ` [PATCH v3 05/14] commit-graph: add base graphs chunk Derrick Stolee via GitGitGadget
2019-06-03 16:03     ` [PATCH v3 07/14] commit-graph: write commit-graph chains Derrick Stolee via GitGitGadget
2019-06-03 16:03     ` [PATCH v3 08/14] commit-graph: add --split option to builtin Derrick Stolee via GitGitGadget
2019-06-03 16:03     ` [PATCH v3 09/14] commit-graph: merge commit-graph chains Derrick Stolee via GitGitGadget
2019-06-03 16:03     ` [PATCH v3 10/14] commit-graph: allow cross-alternate chains Derrick Stolee via GitGitGadget
2019-06-03 16:03     ` [PATCH v3 11/14] commit-graph: expire commit-graph files Derrick Stolee via GitGitGadget
2019-06-03 16:04     ` [PATCH v3 13/14] commit-graph: verify chains with --shallow mode Derrick Stolee via GitGitGadget
2019-06-03 16:04     ` [PATCH v3 12/14] commit-graph: create options for split files Derrick Stolee via GitGitGadget
2019-06-03 16:04     ` [PATCH v3 14/14] commit-graph: clean up chains after flattened write Derrick Stolee via GitGitGadget
2019-06-06 14:15     ` [PATCH v4 00/14] Commit-graph: Write incremental files Derrick Stolee via GitGitGadget
2019-06-06 14:15       ` [PATCH v4 01/14] commit-graph: document commit-graph chains Derrick Stolee via GitGitGadget
2019-06-06 14:15       ` [PATCH v4 02/14] commit-graph: prepare for " Derrick Stolee via GitGitGadget
2019-06-06 15:19         ` Philip Oakley
2019-06-06 21:28         ` Junio C Hamano
2019-06-07 12:44           ` Derrick Stolee
2019-06-06 14:15       ` [PATCH v4 03/14] commit-graph: rename commit_compare to oid_compare Derrick Stolee via GitGitGadget
2019-06-06 14:15       ` [PATCH v4 04/14] commit-graph: load commit-graph chains Derrick Stolee via GitGitGadget
2019-06-06 22:20         ` Junio C Hamano
2019-06-07 12:53           ` Derrick Stolee
2019-06-06 14:15       ` [PATCH v4 05/14] commit-graph: add base graphs chunk Derrick Stolee via GitGitGadget
2019-06-07 18:15         ` Junio C Hamano
2019-06-06 14:15       ` [PATCH v4 06/14] commit-graph: rearrange chunk count logic Derrick Stolee via GitGitGadget
2019-06-07 18:23         ` Junio C Hamano
2019-06-06 14:15       ` [PATCH v4 07/14] commit-graph: write commit-graph chains Derrick Stolee via GitGitGadget
2019-06-06 14:15       ` [PATCH v4 08/14] commit-graph: add --split option to builtin Derrick Stolee via GitGitGadget
2019-06-07 21:57         ` Junio C Hamano
2019-06-11 12:51           ` Derrick Stolee
2019-06-11 19:45             ` Junio C Hamano
2019-06-06 14:15       ` [PATCH v4 09/14] commit-graph: merge commit-graph chains Derrick Stolee via GitGitGadget
2019-06-06 14:15       ` [PATCH v4 10/14] commit-graph: allow cross-alternate chains Derrick Stolee via GitGitGadget
2019-06-06 17:00         ` Philip Oakley
2019-06-06 14:15       ` [PATCH v4 11/14] commit-graph: expire commit-graph files Derrick Stolee via GitGitGadget
2019-06-06 14:15       ` [PATCH v4 12/14] commit-graph: create options for split files Derrick Stolee via GitGitGadget
2019-06-06 18:41         ` Ramsay Jones
2019-06-06 14:15       ` [PATCH v4 13/14] commit-graph: verify chains with --shallow mode Derrick Stolee via GitGitGadget
2019-06-06 14:15       ` [PATCH v4 14/14] commit-graph: clean up chains after flattened write Derrick Stolee via GitGitGadget
2019-06-06 16:57       ` [PATCH v4 00/14] Commit-graph: Write incremental files Junio C Hamano
2019-06-07 12:37         ` Derrick Stolee
2019-06-07 18:38       ` [PATCH v5 00/16] " Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 01/16] commit-graph: document commit-graph chains Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 02/16] commit-graph: prepare for " Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 04/16] commit-graph: load " Derrick Stolee via GitGitGadget
2019-06-10 21:47           ` Junio C Hamano
2019-06-10 23:41             ` Derrick Stolee
2019-06-07 18:38         ` [PATCH v5 03/16] commit-graph: rename commit_compare to oid_compare Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 05/16] commit-graph: add base graphs chunk Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 06/16] commit-graph: rearrange chunk count logic Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 07/16] commit-graph: write commit-graph chains Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 08/16] commit-graph: add --split option to builtin Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 09/16] commit-graph: merge commit-graph chains Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 10/16] commit-graph: allow cross-alternate chains Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 11/16] commit-graph: expire commit-graph files Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 12/16] commit-graph: create options for split files Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 13/16] commit-graph: verify chains with --shallow mode Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 14/16] commit-graph: clean up chains after flattened write Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 15/16] commit-graph: test octopus merges with --split Derrick Stolee via GitGitGadget
2019-06-07 18:38         ` [PATCH v5 16/16] commit-graph: test --split across alternate without --split Derrick Stolee via GitGitGadget
2019-06-17 15:02         ` [PATCH] commit-graph: normalize commit-graph filenames Derrick Stolee
2019-06-17 15:07           ` Derrick Stolee
2019-06-17 18:07           ` [PATCH v2] " Derrick Stolee
2019-06-18 18:14         ` [PATCH v6 00/18] Commit-graph: Write incremental files Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 01/18] commit-graph: document commit-graph chains Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 03/18] commit-graph: rename commit_compare to oid_compare Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 02/18] commit-graph: prepare for commit-graph chains Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 04/18] commit-graph: load " Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 05/18] commit-graph: add base graphs chunk Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 07/18] commit-graph: write commit-graph chains Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 06/18] commit-graph: rearrange chunk count logic Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 08/18] commit-graph: add --split option to builtin Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 09/18] commit-graph: merge commit-graph chains Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 10/18] commit-graph: allow cross-alternate chains Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 11/18] commit-graph: expire commit-graph files Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 13/18] commit-graph: verify chains with --shallow mode Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 12/18] commit-graph: create options for split files Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 14/18] commit-graph: clean up chains after flattened write Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 15/18] commit-graph: test octopus merges with --split Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 16/18] commit-graph: test --split across alternate without --split Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 18/18] commit-graph: test verify across alternates Derrick Stolee via GitGitGadget
2019-06-18 18:14           ` [PATCH v6 17/18] commit-graph: normalize commit-graph filenames Derrick Stolee via GitGitGadget

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