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




On Mon, Oct 8, 2018 at 6:03 PM Junio C Hamano <gitster@xxxxxxxxx> wrote:
>
> Stefan Beller <sbeller@xxxxxxxxxx> writes:
>
> > On Sun, Oct 7, 2018 at 1:07 PM Junio C Hamano <gitster@xxxxxxxxx> wrote:
> >>
> >> Junio C Hamano <gitster@xxxxxxxxx> 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.


>  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.