From: Kyle J. McKay Date: Thu, 29 Sep 2016 13:01:44 GMT Subject: Re: Changing the default for "core.abbrev"? Message-ID: <80D70A8B-0EB6-4118-8193-8D113621C57D@gmail.com> In-Reply-To: On Sep 25, 2016, at 18:39, Linus Torvalds wrote: > The kernel, these days, is at roughly 5 million objects, and while the > seven hex digits are still often enough for uniqueness (and git will > always add digits *until* it is unique), it's long been at the point > where I tell people to do > > git config --global core.abbrev 12 > > because even though git will extend the seven hex digits until the > object name is unique, that only reflects the *current* situation in > the repository. With 5 million objects and a very healthy growth rate, > a 7-8 hex digit number that is unique today is not necessarily unique > a month or two from now, and then it gets annoying when a commit > message has a short git ID that is no longer unique when you go back > and try to figure out what went wrong in that commit. On Sep 25, 2016, at 20:46, Junio C Hamano wrote: > Linus Torvalds writes: > >> I can just keep reminding kernel maintainers and developers to update >> their git config, but maybe it would be a good idea to just admit >> that >> the defaults picked in 2005 weren't necessarily the best ones >> possible, and those could be bumped up a bit? > > I am not quite sure how good any new default would be, though. Just > like any timeout is not long enough for somebody, growing projects > will eventually hit whatever abbreviation length they start with. This made me curious what the situation is really like. So I crunched some data. Using a recent clone of $korg/torvalds/linux: $ git rev-parse --verify d597639e203 error: short SHA1 d597639e203 is ambiguous. fatal: Needed a single revision So the kernel already has 11-character "short" SHA1s that are ambiguous. Is a core.abbrev setting of 12 really good enough? Here are the stats on the kernel's repository: Ambiguous length 11 (but not at length 12) info: prefixes: 2 0 (with 1 or more commit disambiguations) Ambiguous length 10 (but not at length 11) info: prefixes: 12 3 (with 1 or more commit disambiguations) 0 (with 2 or more commit disambiguations) Ambiguous length 9 (but not at length 10) info: prefixes: 186 43 (with 1 or more commit disambiguations) 1 (with 2 or more commit disambiguations) 0 (with 3 or more disambiguations) Ambiguous length 8 (but not at length 9) info: prefixes: 2723 651 (with 1 or more commit disambiguations) 40 (with 2 or more commit disambiguations) 1 (with 3 or more disambiguations) maxambig: 3 (there is 1 of them) Ambiguous length 7 (but not at length 8) info: prefixes: 41864 9842 (with 1 or more commit disambiguations) 680 (with 2 or more commit disambiguations) 299 (with 3 or more disambiguations) maxambig: 3 (there are 299 of them) The "maxambig" value is the maximum number of disambiguations for any single prefix at that prefix length. So for prefixes of length 7 there are 299 that disambiguate into 3 objects. Just out of curiosity, generating stats on the Git repository gives: Ambiguous length 8 (but not at length 9) info: prefixes: 7 3 (with 1 or more commit disambiguations) 2 (with 2 or more commit disambiguations) 0 (with 3 or more disambiguations) Ambiguous length 7 (but not at length 8) info: prefixes: 87 36 (with 1 or more commit disambiguations) 3 (with 2 or more commit disambiguations) 0 (with 3 or more disambiguations) Running the stats on $github/gitster/git produces some ambiguous length 9 prefixes (one of which contains a commit disambiguation). --Kyle