From: Johannes Sixt Date: Sun, 07 Oct 2018 18:35:57 GMT Subject: Re: What's so special about objects/17/ ? Message-ID: In-Reply-To: <87k1mta9x5.fsf@evledraar.gmail.com> Am 07.10.18 um 20:28 schrieb Ævar Arnfjörð Bjarmason: > In 2007 Junio wrote > (https://public-inbox.org/git/7vr6lcj2zi.fsf@gitster.siamese.dyndns.org/): > > +static int need_to_gc(void) > +{ > + /* > + * Quickly check if a "gc" is needed, by estimating how > + * many loose objects there are. Because SHA-1 is evenly > + * distributed, we can check only one and get a reasonable > + * estimate. > + */ > 1. We still have this check of objects/17/ in builtin/gc.c today. Why > objects/17/ and not e.g. objects/00/ to go with other 000* magic such > as the 0000000000000000000000000000000000000000 SHA-1? Statistically > it doesn't matter, but 17 seems like an odd thing to pick at random > out of 00..ff, does it have any significance? The reason is explained in the comment. And, BTW, you do know about this one: https://xkcd.com/221/ don't you? (TLDR: the title is "Random Number") > 2. It seems overly paranoid to be checking that the files in > .git/objects/17/ look like a SHA-1. If we have stuff not generated by > git in .git/objects/??/ we probably have bigger problems than > prematurely triggering auto gc, can this just be removed as > redundant. Was this some check e.g. expecting that this would need to > deal with tempfiles in these directories that we created at the time > (but no longer do?)? It's not about that there are SHA-1s in there, it's about how many there are. -- Hannes