Subject: Re: [PATCH] commit-graph: don't show progress percentages while expanding reachable commits

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Fri, 22 Mar 2019 16:11:24 +0100

On Fri, Mar 22 2019, SZEDER Gábor wrote:

> On Fri, Mar 22, 2019 at 03:28:34PM +0100, Ævar Arnfjörð Bjarmason wrote:
>>
>> On Fri, Mar 22 2019, SZEDER Gábor wrote:
>>
>> > On Fri, Mar 22, 2019 at 12:11:26PM +0100, Ævar Arnfjörð Bjarmason wrote:
>> >>
>> >> On Fri, Mar 22 2019, SZEDER Gábor wrote:
>> >>
>> >> > Commit 49bbc57a57 (commit-graph write: emit a percentage for all
>> >> > progress, 2019-01-19) was a bit overeager when it added progress
>> >> > percentages to the "Expanding reachable commits in commit graph" phase
>> >> > as well, because most of the time the number of commits that phase has
>> >> > to iterate over is not known in advance and grows significantly, and,
>> >> > consequently, we end up with nonsensical numbers:
>> >> >
>> >> >   $ git commit-graph write --reachable
>> >> >   Expanding reachable commits in commit graph: 138606% (824706/595), done.
>> >> >   [...]
>> >> >
>> >> >   $ git rev-parse v5.0 | git commit-graph write --stdin-commits
>> >> >   Expanding reachable commits in commit graph: 81264400% (812644/1), done.
>> >> >   [...]
>> >> >
>> >> > Therefore, don't show progress percentages in the "Expanding reachable
>> >> > commits in commit graph" phase.
>> >>
>> >> There's indeed a bug here as your examples show, but there *are* cases
>> >> where it's correct, as the commit message for my patch on "master" shows
>> >> there's cases where we correctly.
>> >>
>> >> So this "fixes" things by always removing the progress, why not instead
>> >> pass down the state to close_reachable() about what we're walking over,
>> >> so we can always show progress, or at least in some cases?
>> >
>> > The cases where it does display correct percentages are exceptional,
>> > and doesn't worth the effort to try to find out whether ther current
>> > operation happens to be such a case.
>>
>> It's the "write" entry point without arguments that displays the correct
>> progress. So not exceptional, but yeah, it's not what we use on "gc".
>
> Bit it displays the correct number only if all the reachable commits
> are in packfiles, which is not necessarily the case (e.g. unpacked
> small packs during 'git fetch').

No, argument-less "write" only considers packed commits.

>> In any case, the problem is that sometimes we've walked the full set of
>> commits already, and some other times we haven't.
>
> ... and that we can't really be sure whether we've walked the full set
> of commits until after this loop.

I'm fairly sure we can when we start with a full walk. See my
explanation in <[email-masked]>, but I may have
missed something.

>> So in cases where we have we can show progress, and as a TODO (I think
>> this came up in previous discussions), we could do better if we had a
>> approximate_commit_count().
>>
>> In any case, the below fix seems correct to me, but I haven't poked it
>> much. It *does* suffer from a theoretical race with the progress bar
>> similar to d9b1b309cf ("commit-graph write: show progress for object
>> search", 2019-01-19), but I work around it in the same way:
>>
>> diff --git a/commit-graph.c b/commit-graph.c
>> index 47e9be0a3a..0fab3d8b2b 100644
>> --- a/commit-graph.c
>> +++ b/commit-graph.c
>> @@ -693,7 +693,8 @@ static void add_missing_parents(struct packed_oid_list *oids, struct commit *com
>>  	}
>>  }
>>
>> -static void close_reachable(struct packed_oid_list *oids, int report_progress)
>> +static void close_reachable(struct packed_oid_list *oids, int report_progress,
>> +			    uint64_t oids_count_for_progress)
>>  {
>>  	int i;
>>  	struct commit *commit;
>> @@ -717,7 +718,8 @@ static void close_reachable(struct packed_oid_list *oids, int report_progress)
>>  	 */
>>  	if (report_progress)
>>  		progress = start_delayed_progress(
>> -			_("Expanding reachable commits in commit graph"), oids->nr);
>> +			_("Expanding reachable commits in commit graph"),
>> +			oids_count_for_progress);
>>  	for (i = 0; i < oids->nr; i++) {
>>  		display_progress(progress, i + 1);
>>  		commit = lookup_commit(the_repository, &oids->list[i]);
>> @@ -725,6 +727,8 @@ static void close_reachable(struct packed_oid_list *oids, int report_progress)
>>  		if (commit && !parse_commit(commit))
>>  			add_missing_parents(oids, commit);
>>  	}
>> +	if (oids->nr < oids_count_for_progress)
>> +		display_progress(progress, oids_count_for_progress);
>>  	stop_progress(&progress);
>>
>>  	if (report_progress)
>> @@ -829,6 +833,7 @@ void write_commit_graph(const char *obj_dir,
>>  	uint64_t progress_cnt = 0;
>>  	struct strbuf progress_title = STRBUF_INIT;
>>  	unsigned long approx_nr_objects;
>> +	uint64_t oids_count_for_progress = 0;
>>
>>  	if (!commit_graph_compatible(the_repository))
>>  		return;
>> @@ -934,9 +939,10 @@ void write_commit_graph(const char *obj_dir,
>>  		if (oids.progress_done < approx_nr_objects)
>>  			display_progress(oids.progress, approx_nr_objects);
>>  		stop_progress(&oids.progress);
>> +		oids_count_for_progress = oids.nr;
>>  	}
>>
>> -	close_reachable(&oids, report_progress);
>> +	close_reachable(&oids, report_progress, oids_count_for_progress);
>>
>>  	if (report_progress)
>>  		progress = start_delayed_progress(
>>