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From: Derrick Stolee <stolee@gmail.com>
To: Junio C Hamano <gitster@pobox.com>,
	Derrick Stolee <dstolee@microsoft.com>
Cc: "git@vger.kernel.org" <git@vger.kernel.org>,
	"peff@peff.net" <peff@peff.net>,
	"avarab@gmail.com" <avarab@gmail.com>,
	"sbeller@google.com" <sbeller@google.com>,
	"larsxschneider@gmail.com" <larsxschneider@gmail.com>,
	"bmwill@google.com" <bmwill@google.com>
Subject: Re: [PATCH v2 04/10] commit-graph: compute generation numbers
Date: Wed, 11 Apr 2018 09:02:09 -0400	[thread overview]
Message-ID: <9ba7d27f-ce65-7f2c-601a-1bea3274104e@gmail.com> (raw)
In-Reply-To: <xmqqa7uazc9e.fsf@gitster-ct.c.googlers.com>

On 4/10/2018 10:51 PM, Junio C Hamano wrote:
> Derrick Stolee <dstolee@microsoft.com> writes:
>
>> +		if ((*list)->generation != GENERATION_NUMBER_INFINITY) {
>> +			if ((*list)->generation > GENERATION_NUMBER_MAX)
>> +				die("generation number %u is too large to store in commit-graph",
>> +				    (*list)->generation);
>> +			packedDate[0] |= htonl((*list)->generation << 2);
>> +		}
>
> How serious do we want this feature to be?  On one extreme, we could
> be irresponsible and say it will be a problem for our descendants in
> the future if their repositories have more than billion pearls on a
> single strand, and the above certainly is a reasonable way to punt.
> Those who actually encounter the problem will notice by Git dying
> somewhere rather deep in the callchain.
>
> Or we could say Git actually does support a history that is
> arbitrarily long, even though such a deep portion of history will
> not benefit from having generation numbers in commit-graph.
>
> I've been assuming that our stance is the latter and that is why I
> made noises about overflowing 30-bit generation field in my review
> of the previous step.
>
> In case we want to do the "we know this is very large, but we do not
> know the exact value", we may actually want a mode where we can
> pretend that GENERATION_NUMBER_MAX is set to quite low (say 256) and
> make sure that the code to handle overflow behaves sensibly.

I agree. I wonder how we can effectively expose this value into a test. 
It's probably not sufficient to manually test using compiler flags ("-D 
GENERATION_NUMBER_MAX=8").

>
>> +	for (i = 0; i < nr_commits; i++) {
>> +		if (commits[i]->generation != GENERATION_NUMBER_INFINITY &&
>> +		    commits[i]->generation != GENERATION_NUMBER_ZERO)
>> +			continue;
>> +
>> +		commit_list_insert(commits[i], &list);
>> +		while (list) {
>> +...
>> +		}
>> +	}
> So we go over the list of commits just _once_ and make sure each of
> them gets the generation assigned correctly by (conceptually
> recursively but iteratively in implementation by using a commit
> list) making sure that all its parents have generation assigned and
> compute the generation for the commit, before moving to the next
> one.  Which sounds correct.

Yes, we compute the generation number of a commit exactly once. We use 
the list as a stack so we do not have recursion limits during our 
depth-first search (DFS). We rely on the object cache to ensure we store 
the computed generation numbers, and computed generation numbers provide 
termination conditions to the DFS.

Thanks,
-Stolee

  reply	other threads:[~2018-04-11 13:02 UTC|newest]

Thread overview: 162+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-03 16:51 [PATCH 0/6] Compute and consume generation numbers Derrick Stolee
2018-04-03 16:51 ` [PATCH 1/6] object.c: parse commit in graph first Derrick Stolee
2018-04-03 18:21   ` Jonathan Tan
2018-04-03 18:28     ` Jeff King
2018-04-03 18:32       ` Derrick Stolee
2018-04-03 16:51 ` [PATCH 2/6] commit: add generation number to struct commmit Derrick Stolee
2018-04-03 18:05   ` Brandon Williams
2018-04-03 18:28     ` Jeff King
2018-04-03 18:31       ` Derrick Stolee
2018-04-03 18:32       ` Brandon Williams
2018-04-03 18:44       ` Stefan Beller
2018-04-03 23:17       ` Ramsay Jones
2018-04-03 23:19         ` Jeff King
2018-04-03 18:24   ` Jonathan Tan
2018-04-03 16:51 ` [PATCH 3/6] commit-graph: compute generation numbers Derrick Stolee
2018-04-03 18:30   ` Jonathan Tan
2018-04-03 18:49     ` Stefan Beller
2018-04-03 16:51 ` [PATCH 4/6] commit: use generations in paint_down_to_common() Derrick Stolee
2018-04-03 18:31   ` Stefan Beller
2018-04-03 18:31   ` Jonathan Tan
2018-04-03 16:51 ` [PATCH 5/6] commit.c: use generation to halt paint walk Derrick Stolee
2018-04-03 19:01   ` Jonathan Tan
2018-04-03 16:51 ` [PATCH 6/6] commit-graph.txt: update future work Derrick Stolee
2018-04-03 19:04   ` Jonathan Tan
2018-04-03 16:56 ` [PATCH 0/6] Compute and consume generation numbers Derrick Stolee
2018-04-03 18:03 ` Brandon Williams
2018-04-03 18:29   ` Derrick Stolee
2018-04-03 18:47     ` Jeff King
2018-04-03 19:05       ` Jeff King
2018-04-04 15:45         ` [PATCH 7/6] ref-filter: use generation number for --contains Derrick Stolee
2018-04-04 15:45           ` [PATCH 8/6] commit: use generation numbers for in_merge_bases() Derrick Stolee
2018-04-04 15:48             ` Derrick Stolee
2018-04-04 17:01               ` Brandon Williams
2018-04-04 18:24               ` Jeff King
2018-04-04 18:53                 ` Derrick Stolee
2018-04-04 18:59                   ` Jeff King
2018-04-04 18:22           ` [PATCH 7/6] ref-filter: use generation number for --contains Jeff King
2018-04-04 19:06             ` Derrick Stolee
2018-04-04 19:16               ` Jeff King
2018-04-04 19:22                 ` Derrick Stolee
2018-04-04 19:42                   ` Jeff King
2018-04-04 19:45                     ` Derrick Stolee
2018-04-04 19:46                       ` Jeff King
2018-04-07 17:09     ` [PATCH 0/6] Compute and consume generation numbers Jakub Narebski
2018-04-07 16:55 ` Jakub Narebski
2018-04-08  1:06   ` Derrick Stolee
2018-04-11 19:32     ` Jakub Narebski
2018-04-11 19:58       ` Derrick Stolee
2018-04-14 16:52         ` Jakub Narebski
2018-04-21 20:44           ` Jakub Narebski
2018-04-23 13:54             ` Derrick Stolee
2018-04-09 16:41 ` [PATCH v2 00/10] " Derrick Stolee
2018-04-09 16:41   ` [PATCH v2 01/10] object.c: parse commit in graph first Derrick Stolee
2018-04-09 16:41   ` [PATCH v2 02/10] merge: check config before loading commits Derrick Stolee
2018-04-11  2:12     ` Junio C Hamano
2018-04-11 12:49       ` Derrick Stolee
2018-04-09 16:42   ` [PATCH v2 03/10] commit: add generation number to struct commmit Derrick Stolee
2018-04-09 17:59     ` Stefan Beller
2018-04-11  2:31     ` Junio C Hamano
2018-04-11 12:57       ` Derrick Stolee
2018-04-11 23:28         ` Junio C Hamano
2018-04-09 16:42   ` [PATCH v2 04/10] commit-graph: compute generation numbers Derrick Stolee
2018-04-11  2:51     ` Junio C Hamano
2018-04-11 13:02       ` Derrick Stolee [this message]
2018-04-11 18:49         ` Stefan Beller
2018-04-11 19:26         ` Eric Sunshine
2018-04-09 16:42   ` [PATCH v2 05/10] commit: use generations in paint_down_to_common() Derrick Stolee
2018-04-09 16:42   ` [PATCH v2 06/10] commit.c: use generation to halt paint walk Derrick Stolee
2018-04-11  3:02     ` Junio C Hamano
2018-04-11 13:24       ` Derrick Stolee
2018-04-09 16:42   ` [PATCH v2 07/10] commit-graph.txt: update future work Derrick Stolee
2018-04-12  9:12     ` Junio C Hamano
2018-04-12 11:35       ` Derrick Stolee
2018-04-13  9:53         ` Jakub Narebski
2018-04-09 16:42   ` [PATCH v2 08/10] ref-filter: use generation number for --contains Derrick Stolee
2018-04-09 16:42   ` [PATCH v2 09/10] commit: use generation numbers for in_merge_bases() Derrick Stolee
2018-04-09 16:42   ` [PATCH v2 10/10] commit: add short-circuit to paint_down_to_common() Derrick Stolee
2018-04-17 17:00   ` [PATCH v3 0/9] Compute and consume generation numbers Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 1/9] commit: add generation number to struct commmit Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 2/9] commit-graph: compute generation numbers Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 3/9] commit: use generations in paint_down_to_common() Derrick Stolee
2018-04-18 14:31       ` Jakub Narebski
2018-04-18 14:46         ` Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 4/9] commit-graph.txt: update design document Derrick Stolee
2018-04-18 19:47       ` Jakub Narebski
2018-04-17 17:00     ` [PATCH v3 5/9] ref-filter: use generation number for --contains Derrick Stolee
2018-04-18 21:02       ` Jakub Narebski
2018-04-23 14:22         ` Derrick Stolee
2018-04-24 18:56           ` Jakub Narebski
2018-04-25 14:11             ` Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 6/9] commit: use generation numbers for in_merge_bases() Derrick Stolee
2018-04-18 22:15       ` Jakub Narebski
2018-04-23 14:31         ` Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 7/9] commit: add short-circuit to paint_down_to_common() Derrick Stolee
2018-04-18 23:19       ` Jakub Narebski
2018-04-23 14:40         ` Derrick Stolee
2018-04-23 21:38           ` Jakub Narebski
2018-04-24 12:31             ` Derrick Stolee
2018-04-19  8:32       ` Jakub Narebski
2018-04-17 17:00     ` [PATCH v3 8/9] commit-graph: always load commit-graph information Derrick Stolee
2018-04-17 17:50       ` Derrick Stolee
2018-04-19  0:02       ` Jakub Narebski
2018-04-23 14:49         ` Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 9/9] merge: check config before loading commits Derrick Stolee
2018-04-19  0:04     ` [PATCH v3 0/9] Compute and consume generation numbers Jakub Narebski
2018-04-23 14:54       ` Derrick Stolee
2018-04-25 14:37     ` [PATCH v4 00/10] " Derrick Stolee
2018-04-25 14:37       ` [PATCH v4 01/10] ref-filter: fix outdated comment on in_commit_list Derrick Stolee
2018-04-28 17:54         ` Jakub Narebski
2018-04-25 14:37       ` [PATCH v4 02/10] commit: add generation number to struct commmit Derrick Stolee
2018-04-28 22:35         ` Jakub Narebski
2018-04-30 12:05           ` Derrick Stolee
2018-04-25 14:37       ` [PATCH v4 03/10] commit-graph: compute generation numbers Derrick Stolee
2018-04-26  2:35         ` Junio C Hamano
2018-04-26 12:58           ` Derrick Stolee
2018-04-26 13:49             ` Derrick Stolee
2018-04-29  9:08         ` Jakub Narebski
2018-05-01 12:10           ` Derrick Stolee
2018-05-02 16:15             ` Jakub Narebski
2018-04-25 14:37       ` [PATCH v4 04/10] commit: use generations in paint_down_to_common() Derrick Stolee
2018-04-26  3:22         ` Junio C Hamano
2018-04-26  9:02           ` Jakub Narebski
2018-04-28 14:38             ` Jakub Narebski
2018-04-29 15:40         ` Jakub Narebski
2018-04-25 14:37       ` [PATCH v4 05/10] commit-graph: always load commit-graph information Derrick Stolee
2018-04-29 22:14         ` Jakub Narebski
2018-05-01 12:19           ` Derrick Stolee
2018-04-29 22:18         ` Jakub Narebski
2018-04-25 14:37       ` [PATCH v4 06/10] ref-filter: use generation number for --contains Derrick Stolee
2018-04-30 16:34         ` Jakub Narebski
2018-04-25 14:37       ` [PATCH v4 07/10] commit: use generation numbers for in_merge_bases() Derrick Stolee
2018-04-30 17:05         ` Jakub Narebski
2018-04-25 14:38       ` [PATCH v4 08/10] commit: add short-circuit to paint_down_to_common() Derrick Stolee
2018-04-30 22:19         ` Jakub Narebski
2018-05-01 11:47           ` Derrick Stolee
2018-05-02 13:05             ` Jakub Narebski
2018-05-02 13:42               ` Derrick Stolee
2018-04-25 14:38       ` [PATCH v4 09/10] merge: check config before loading commits Derrick Stolee
2018-04-30 22:54         ` Jakub Narebski
2018-05-01 11:52           ` Derrick Stolee
2018-05-02 11:41             ` Jakub Narebski
2018-04-25 14:38       ` [PATCH v4 10/10] commit-graph.txt: update design document Derrick Stolee
2018-04-30 23:32         ` Jakub Narebski
2018-05-01 12:00           ` Derrick Stolee
2018-05-02  7:57             ` Jakub Narebski
2018-04-25 14:40       ` [PATCH v4 00/10] Compute and consume generation numbers Derrick Stolee
2018-04-28 17:28         ` Jakub Narebski
2018-05-01 12:47       ` [PATCH v5 00/11] " Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 01/11] ref-filter: fix outdated comment on in_commit_list Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 02/11] commit: add generation number to struct commmit Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 03/11] commit-graph: compute generation numbers Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 04/11] commit: use generations in paint_down_to_common() Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 05/11] commit-graph: always load commit-graph information Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 06/11] ref-filter: use generation number for --contains Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 07/11] commit: use generation numbers for in_merge_bases() Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 08/11] commit: add short-circuit to paint_down_to_common() Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 09/11] commit: use generation number in remove_redundant() Derrick Stolee
2018-05-01 15:37           ` Derrick Stolee
2018-05-03 18:45           ` Jakub Narebski
2018-05-01 12:47         ` [PATCH v5 10/11] merge: check config before loading commits Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 11/11] commit-graph.txt: update design document Derrick Stolee
2018-05-03 11:18         ` [PATCH v5 00/11] Compute and consume generation numbers Jakub Narebski

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