Re: What's so special about objects/17/ ?

From: Stefan Beller <sbeller@google.com>
Date: Oct 9, 2018, 17:37 UTC
Message-ID: <CAGZ79ka5kKrSqPCWFMDetRLYxDqcguJUzJXDex9q-VMwT-ABAw@mail.gmail.com>
In-Reply-To: <xmqq4ldwszh8.fsf@gitster-ct.c.googlers.com>

On Mon, Oct 8, 2018 at 6:03 PM Junio C Hamano <gitster@pobox.com> wrote:

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>
> Stefan Beller <sbeller@google.com> writes:
>
> > On Sun, Oct 7, 2018 at 1:07 PM Junio C Hamano <gitster@pobox.com> wrote:
> >>
> >> Junio C Hamano <gitster@pobox.com> writes:
> >
> >> > ...
> >> > by general public and I do not have to explain the choice to the
> >> > general public ;-)
> >>
> >> One thing that is more important than "why not 00 but 17?" to answer
> >> is why a hardcoded number rather than a runtime random.  It is for
> >> repeatability.
> >
> > Let's talk about repeatability vs statistics for a second. ;-)
>
> Oh, I think I misled you by saying "more important".
>
> I didn't mean that it is more important to stick to the "use
> hardcoded value" design decision than sticking to "use 17".  I've
> made sure that everybody would understnd choosing any arbitrary byte
> value other than "17" does not make the resulting Git any better nor
> worse.

Yes, I totally get that. We could have chosen 42 just because.

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>  But discussing the design decision to use hardcoded value is
> "more important", as that affects the balance between the end-user
> experience and debuggability, and I tried to help those who do not
> know the history by giving the fact that choice was made for the
> latter and not for other hidden reasons, that those who would
> propose to change the system may have to keep in mind.

From an end users point of view, the auto gc kicks in at random. (Maybe it's just me, but I don't keep track of the loose object count ;-)

For debuggability, we could design a system that allows for debugging, e.g. "When GIT_AUTO_GC_BIN is set, use the number as set, otherwise take a random slot".

> Sorry if you mistook it as if I were saying that it is important to
> keep the design to use a hardcoded byte value.  That wasn't what the
> message was about.

I understood very well that the choice of value was arbitrary and you do not have a convincing story as to why 17 (and not say 23, but such a story is not required, as all slots are equal from a design perspective).

I do challenge the decision to take a hardcoded value, though, as it yields better properties for the end users IMHO, whereas debugging this specific case does not seem to be important to me.