From: Derrick Stolee <stolee@gmail.com>
Date: Tue, 03 Apr 2018 18:31:18 GMT
Subject: Re: [PATCH 2/6] commit: add generation number to struct commmit
Message-ID: <2b5a08da-6b15-194e-4336-ce7c84240a9b@gmail.com>
In-Reply-To: <20180403182800.GA8377@sigill.intra.peff.net>

On 4/3/2018 2:28 PM, Jeff King wrote:
> On Tue, Apr 03, 2018 at 11:05:36AM -0700, Brandon Williams wrote:
>
>> On 04/03, Derrick Stolee wrote:
>>> The generation number of a commit is defined recursively as follows:
>>>
>>> * If a commit A has no parents, then the generation number of A is one.
>>> * If a commit A has parents, then the generation number of A is one
>>>    more than the maximum generation number among the parents of A.
>>>
>>> Add a uint32_t generation field to struct commit so we can pass this
>> Is there any reason to believe this would be too small of a value in the
>> future?  Or is a 32 bit unsigned good enough?
> The linux kernel took ~10 years to produce 500k commits. Even assuming
> those were all linear (and they're not), that gives us ~80,000 years of
> leeway. So even if the pace of development speeds up or we have a
> quicker project, it still seems we have a pretty reasonable safety
> margin.

That, and larger projects do not have linear histories. Despite having 
almost 2 million reachable commits, the Windows repository has maximum 
generation number ~100,000.

Thanks,
-Stolee