Re: Question about the ahead-behind computation and status

From: Derrick Stolee <stolee@gmail.com>
Date: Dec 15, 2017, 15:43 UTC
Message-ID: <d16339e0-54bd-073b-fa4a-7c3a84a025e9@gmail.com>
In-Reply-To: <88175f57-082d-ad61-c2dd-53ae50540460@jeffhostetler.com>

On 12/15/2017 10:08 AM, Jeff Hostetler wrote:

Show 14 quoted lines

> On 12/15/2017 5:08 AM, Jeff King wrote:
>> On Thu, Dec 14, 2017 at 04:49:31PM -0500, Jeff Hostetler wrote:
>>> [*] Sadly, the local repo was only about 20 days out of
>>>      date (including the Thanksgiving holidays)....
>>
>> Taking 20 seconds to traverse 20 days worth of history sounds pretty
>> awful. How many commits is it?
>
> 150,000 commits, give or take.  The graph is many thousands of lanes
> wide because of the merges and that isn't helping.
>
> (But I should give you folks lots of credit -- it *only* took 20
> seconds to find, unzip and decode 150,000 commit objects and walk
> the commit graph.)

To give a few more data points, I created similar situation by checking out a big repo I hadn't updated in three months and it was 16,000 commits behind. That took 1.5s to calculate the ahead/behind. Moving it 100,000 commits behind it took 5s. This repo has about 300,000 total commits versus the 1.5 million commits in the Windows repo.

The biggest reason for the 20 seconds is not just the number of commits in the ahead/behind but how many commits are walked (including common to both branches) before paint_down_to_common() breaks its while loop due to queue_has_nonstale().

Thanks, -Stolee