Re: [PATCH v5 5/9] patch-id: document new behaviour
On Thu, Apr 24, 2014 at 03:12:14PM -0700, Junio C Hamano wrote: > "Michael S. Tsirkin" writes: > > >> > +--unstable:: > >> > +Use a non-symmetrical sum of hashes, such that reordering > >> > >> What is a non-symmetrical sum? > > > > Non-symmetrical combination function is better? > > I do not think either is very good X-<. > > The primary points to convey for "--stable" are: > > - Two patches produced by comparing the same two trees with two >different settings for "-O" will result in the same >patchc signature, thereby allowing the computed result to be used >as a key to index some metainformation about the change between >the two trees; > > - It will produce a result different from the plain vanilla >patch-id has always produced even when used on a diff output >taken without any use of "-O", thereby making existing >databases keyed by patch-ids unusable. > > The fact that we happened to use a patch-id that catches that > somebody reordered the same patch into different file order and > declares that they are two different changes is a more historical > accident than a designed goal. > > I would even say that we would have used the "stable" version from > the beginning if we thought that "-O" would be widely > used when these two features both appeared. Even though I was the > guilty one who introduced it, I'd admit that "-O" has > merely been a curiosity from its inception and has been a failed > experiment, not in the sense that the feature does not work as > adverertised (it does), but in the sense that it is not widely used > (evidenced by the lack of complaints on missing diff.orderfile for a > long time) at all. With "-O" being a failed experiment, > the "unstability" did not matter, so it has stuck. > > The only two things worth mentioning about "--unstable", if our > future direction is to see diff.orderfile and "--stable" a lot more > widely used, are: > > (1) it keeps producing the same patch-id as existing versions of > Git, so users with existing databases (who do not deal with > reordered patches) may want to use it; and perhaps > > (2) it will not consider a patch taken with "-O" and > another without it from the same source the same patches. > > Mathmatically speaking, mentioning "non-symmetrial" might be one way > of expressing the latter point (2), but stressing on that alone > without mentioning (1) misses the point. (2) is _not_ a designed > feature, so it is not very interesting. Unless you have an existing > database, there is no reason to use "--unstable". > > On the other hand (1) is a very relevant thing to mention, as we are > talking about a feature that, if unused, may break existing users' > data. OK I did just that, pls take a look. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v5 5/9] patch-id: document new behaviour
"Michael S. Tsirkin" writes: >> > +--unstable:: >> > + Use a non-symmetrical sum of hashes, such that reordering >> >> What is a non-symmetrical sum? > > Non-symmetrical combination function is better? I do not think either is very good X-<. The primary points to convey for "--stable" are: - Two patches produced by comparing the same two trees with two different settings for "-O" will result in the same patchc signature, thereby allowing the computed result to be used as a key to index some metainformation about the change between the two trees; - It will produce a result different from the plain vanilla patch-id has always produced even when used on a diff output taken without any use of "-O", thereby making existing databases keyed by patch-ids unusable. The fact that we happened to use a patch-id that catches that somebody reordered the same patch into different file order and declares that they are two different changes is a more historical accident than a designed goal. I would even say that we would have used the "stable" version from the beginning if we thought that "-O" would be widely used when these two features both appeared. Even though I was the guilty one who introduced it, I'd admit that "-O" has merely been a curiosity from its inception and has been a failed experiment, not in the sense that the feature does not work as adverertised (it does), but in the sense that it is not widely used (evidenced by the lack of complaints on missing diff.orderfile for a long time) at all. With "-O" being a failed experiment, the "unstability" did not matter, so it has stuck. The only two things worth mentioning about "--unstable", if our future direction is to see diff.orderfile and "--stable" a lot more widely used, are: (1) it keeps producing the same patch-id as existing versions of Git, so users with existing databases (who do not deal with reordered patches) may want to use it; and perhaps (2) it will not consider a patch taken with "-O" and another without it from the same source the same patches. Mathmatically speaking, mentioning "non-symmetrial" might be one way of expressing the latter point (2), but stressing on that alone without mentioning (1) misses the point. (2) is _not_ a designed feature, so it is not very interesting. Unless you have an existing database, there is no reason to use "--unstable". On the other hand (1) is a very relevant thing to mention, as we are talking about a feature that, if unused, may break existing users' data. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v5 5/9] patch-id: document new behaviour
On Thu, Apr 24, 2014 at 10:33:25AM -0700, Jonathan Nieder wrote: > Michael S. Tsirkin wrote: > > > Documentation/git-patch-id.txt | 23 ++- > > 1 file changed, 18 insertions(+), 5 deletions(-) > > Ah, there's the documentation. Please squash this with the patch that > introduces the new behavior so they can be reviewed together more > easily (both now and later when people do archeology). > > [...] > > +--stable:: > > + Use a symmetrical sum of hashes as the patch ID. > > + With this option, reordering file diffs that make up a patch or > > + splitting a diff up to multiple diffs that touch the same path > > + does not affect the ID. > > + This is the default if patchid.stable is set to true. > > This doesn't explain to me why I would want to use --stable versus > --unstable. Maybe an EXAMPLES section would help? > > The only reason I can think of to use --unstable is for compatibility > with historical patch-ids. Is there any other reason? > > At this point in the series there is no patchid.stable configuration. > > > +--unstable:: > > + Use a non-symmetrical sum of hashes, such that reordering > > What is a non-symmetrical sum? Non-symmetrical combination function is better? > Thanks, > Jonathan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v5 5/9] patch-id: document new behaviour
Michael S. Tsirkin wrote: > Documentation/git-patch-id.txt | 23 ++- > 1 file changed, 18 insertions(+), 5 deletions(-) Ah, there's the documentation. Please squash this with the patch that introduces the new behavior so they can be reviewed together more easily (both now and later when people do archeology). [...] > +--stable:: > + Use a symmetrical sum of hashes as the patch ID. > + With this option, reordering file diffs that make up a patch or > + splitting a diff up to multiple diffs that touch the same path > + does not affect the ID. > + This is the default if patchid.stable is set to true. This doesn't explain to me why I would want to use --stable versus --unstable. Maybe an EXAMPLES section would help? The only reason I can think of to use --unstable is for compatibility with historical patch-ids. Is there any other reason? At this point in the series there is no patchid.stable configuration. > +--unstable:: > + Use a non-symmetrical sum of hashes, such that reordering What is a non-symmetrical sum? Thanks, Jonathan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
