Re: [PATCH 12/12] builtin/commit-graph.c: introduce '--max-new-filters=<n>'

From: Taylor Blau <me@ttaylorr.com>
To: Derrick Stolee <stolee@gmail.com>
Cc: Junio C Hamano <gitster@pobox.com>,
	git@vger.kernel.org, dstolee@microsoft.com, szeder.dev@gmail.com,
	Jeff King <peff@peff.net>
Subject: Re: [PATCH 12/12] builtin/commit-graph.c: introduce '--max-new-filters=<n>'
Date: Mon, 14 Sep 2020 16:36:59 -0400	[thread overview]
Message-ID: <20200914203659.GA12855@nand.local> (raw)
In-Reply-To: <134d64a0-abb6-bdc9-2c05-7aded01a906a@gmail.com>

On Mon, Sep 14, 2020 at 04:31:03PM -0400, Derrick Stolee wrote:
> On 9/14/2020 4:12 PM, Taylor Blau wrote:
> >   - This patch (attached below the scisors) instead of 12/12, and
> >
> >   - This [1] patch instead of 10/12.
> >
> > [1]: https://lore.kernel.org/git/20200910154516.GA32117@nand.local/
> >
> > Let me know if you'd rather have a full re-roll.
>
> It's getting a bit difficult to track all of these "use this instead"
> patches. But, I'm not the one applying them, so maybe that's not actually
> a problem.

The above list is the only changes that I've made, so I'm happy if Junio
wants to follow what's written there, but I'm equally happy to send a
new reroll.

> You might need a re-roll, anyway, as I have a few comments here:

Let's take a look...

> You also introduce commitGraph.maxNewFitlers here, which is not
> mentioned in the commit message anywhere. In fact, it might be
> good to include it as a separate patch so its implementation and
> tests can be isolated from the command-line functionality.

I could go either way on both of these, to be honest. I don't think
there's anything interesting that isn't said in the documentation
changes introduced by that commit that is worth convering there, so I'm
not sue 'commitGraph.maxNewFilters' needs the additional call-out.

> > +length zero Bloom filter. Overrides the `commitGraph.maxNewFilters`
> > +configuration.
>
> We have found it valuable to demonstrate these overrides in tests.
> Let's inspect your tests for this.
>
> > +test_bloom_filters_computed () {
> > +	commit_graph_args=$1
> > +	rm -f "$TRASH_DIRECTORY/trace.event" &&
> > +	GIT_TRACE2_EVENT="$TRASH_DIRECTORY/trace.event" git commit-graph write \
> > +		$commit_graph_args &&
> > +	grep "\"filter_not_computed\":$2" "$TRASH_DIRECTORY/trace.event" &&
> > +	grep "\"filter_trunc_large\":$3" "$TRASH_DIRECTORY/trace.event" &&
> > +	grep "\"filter_computed\":$4" "$TRASH_DIRECTORY/trace.event"
> > +}
>
> If the arguments were moved to the last parameter, then we could do a few
> interesting things here.
>
> test_bloom_filters_computed () {
> 	NOT_COMPUTED="\"filter_not_computed\":$1" &&
> 	shift &&
> 	TRUNCATED="\"filter_trunc_large\":$1" &&
> 	shift &&
> 	COMPUTED="\"filter_computed\":$1" &&
> 	shift &&
> 	rm -f "$TRASH_DIRECTORY/trace.event" &&
> 	GIT_TRACE2_EVENT="$TRASH_DIRECTORY/trace.event" git commit-graph write $@ &&
> 	grep "$NOT_COMPUTED" "$TRASH_DIRECTORY/trace.event" &&
> 	grep "$TRUNCATED" "$TRASH_DIRECTORY/trace.event" &&
> 	grep "$COMPUTED" "$TRASH_DIRECTORY/trace.event"
> }
>
>
> (I have not tested this script. It might need some work.)
> This would make your callers a bit cleaner-looking, for example:
>
> test_expect_success 'Bloom generation is limited by --max-new-filters' '
> 	(
> 		cd limits &&
> 		test_commit c2 filter &&
> 		test_commit c3 filter &&
> 		test_commit c4 no-filter &&
> 		test_bloom_filters_computed 3 0 2 \
> 			--reachable --changed-paths --split=replace --max-new-filters=2
> 	)
> '
>
> At least, this looks nicer to me.

Yeah, but I think we're still stuck with the test_config below unless
you write "git $@" instead of "git commit-graph write $@". I don't think
that I have strong feelings about this unless you do.

> > +test_expect_success 'Bloom generation backfills previously-skipped filters' '
> > +	# Check specifying commitGraph.maxNewFilters over "git config" works.
> > +	test_config -C limits commitGraph.maxNewFilters 1 &&
> > +	(
> > +		cd limits &&
> > +		test_bloom_filters_computed "--reachable --changed-paths --split=replace" \
> > +			4 0 1
> > +	)
> > +'
>
> Adding a case for `commitGraph.maxNewFilters=1` and `--max-new-filters=2` might
> be interesting for the override rules.

Potentially. I'm equally happy to do it in a follow-up series. I worry
slightly about adding too many test-cases for somewhat trivial behavior.

> > +
> > +test_expect_success 'Bloom generation backfills empty commits' '
> > +	git init empty &&
> > +	test_when_finished "rm -fr empty" &&
> > +	(
> > +		cd empty &&
> > +		for i in $(test_seq 1 6)
> > +		do
> > +			git commit --allow-empty -m "$i"
> > +		done &&
> > +
> > +		# Generate Bloom filters for empty commits 1-6, two at a time.
> > +		test_bloom_filters_computed "--reachable --changed-paths --max-new-filters=2" \
> > +			4 0 2 &&
> > +		test_bloom_filters_computed "--reachable --changed-paths --max-new-filters=2" \
> > +			4 0 2 &&
> > +		test_bloom_filters_computed "--reachable --changed-paths --max-new-filters=2" \
> > +			4 0 2 &&
>
> I'm concerned that the max-new-filters limit (2) is a divisor
> of the full number of commits (6). It might be good to add one
> more commit here and test again with a limit of 2. That would
> handle both "equal to limit" and "less than limit" cases.

That case is already covered in the test two above this one ("Bloom
generation is limited by --max-new-filters").

> Thanks,
> -Stolee

Thanks,
Taylor