Re: [PATCH v3 6/6] commit-graph: remove Future Work section

From: Derrick Stolee <stolee@gmail.com>
Date: May 1, 2019, 19:59 UTC
Message-ID: <c1c91314-477e-ffc7-25f5-fb46bc64db4e@gmail.com>
In-Reply-To: <87o94mql0a.fsf@evledraar.gmail.com>

On 5/1/2019 10:58 AM, Ævar Arnfjörð Bjarmason wrote:

Show 24 quoted lines

> 
> On Wed, May 01 2019, Derrick Stolee via GitGitGadget wrote:
> 
>> The commit-graph feature began with a long list of planned
>> benefits, most of which are now complete. The future work
>> section has only a few items left.
>>
>> As for making more algorithms aware of generation numbers,
>> some are only waiting for generation number v2 to ensure the
>> performance matches the existing behavior using commit date.
>>
>> It is unlikely that we will ever send a commit-graph file
>> as part of the protocol, since we would need to verify the
>> data, and that is as expensive as writing a commit-graph from
>> scratch. If we want to start trusting remote content, then
>> that item can be investigated again.
> 
> My best of 3 times for "write" followed by "verify" on linux.git are
> 8.7/7.9 real/user for "write" and 5.2/4.9 real/user for "write".
> 
> So that's a reduction of ~40%. I have another big in-house repo where I
> get similar numbers of 17/16 for "write" and 10/9 for "verify". Both for
> a commit-graph file on the order of 50MB where it would be quicker for
> me to download and verify it if the protocol supported it.

Keep in mind that your first "write" may have warmed up the file system and your pack-files parsed faster the second time around.

You are right though, 'verify' doesn't do these things:

1. Sort a list of OIDs.
2. Write a file.

And perhaps some other things. I should mean that "the main task of 'git commit-graph verify' is to parse commits from the object store, and this is the most expensive operation in 'git commit-graph write'."

Thanks, -Stolee