Re: Git Notes - Track rebase/etc + reverse-lookup for bugs ideas
On Mon, Nov 10, 2008 at 12:37:20PM -0500, Thomas Harning wrote:
> Just wondering, has there been any looking into whether the git-notes
> concept can track rebases?
Not that I know of, but then again, I'm not sure exactly what you mean by "track rebases".
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> Reading over what git-notes is leads me to think it could be a good
> mechanism for the distributed bug-tracking idea I had some time ago.
> The only gotcha I see is that there would have to be some reverse mapping
> / fast lookup to track the commit objects that given notes are attached
> to.... and to facilitate individual assignment... notes applied to notes.
You can really think of the notes facility as a way of mapping SHA1 -> SHA1. So the oft-discussed concept of "attach some text to this commit" would be a commit sha1 mapping to a blob that contains the text. You have the commit, and you want to look up the attached text.
How fast you can do a reverse lookup depends on what you are given. If you are saying "I want to look through the list of all notes, and see which commits they are attached to" that is quick. You are iterating through the mapping, so you just look at the left hand side.
But if you are given a SHA-1 (say, of a blob with some text) and ask "which commits map to this blob", then you will have to linearly search through the mapping. Which really _isn't_ that painful, if you are doing one such search per user request, but can be slow if you want to do it for 10,000 notes.
And in the latter case, I would suggest simply building a reverse mapping. Which you _could_ make as a parallel notes namespace, but then you have to keep the two in sync. I would suggest instead simply building a hash table on the fly for the reverse mapping (which is basically what the forward-lookup does, anyway, since our tree lookup is necessarily linear).
As far as attaching notes to notes, again it depends what you mean. If you mean "map a blob SHA-1 to another blob SHA-1", then that is simple. E.g., if you have some commit mapping to the text note "foo", then you can map another note "bar" onto "foo".
But if you want to put a note onto the actual mapping, that is a bit different. Since notes are a commit history of trees, I would think you would simply make a new commit, and put your note into the commit message. And if you need to do so after the fact, then of course it is just putting a note onto the commit in the notes history.
But bear in mind that the whole point of notes is annotating commits after the fact, since commits must remain immutable. So might it not be simpler to just update the note itself, with the new information, rather than creating a note of a note?
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> Operations for bug-tracking:
>
> 1) List all 'BUG'-type items that would refer to individual notes
> 2) List 'BUG' items reachable from a point
> Perhaps with criterion that a certain 'bug note' attribute is not
> set...
> or that a 'BUG_CLOSED' note is not attached to the given 'bug note'
I'm not sure that doing bug tracking in this way makes sense with notes. If notes are a mapping of a commit sha-1 to a blob, then how do I have a commit with _two_ bugs? I think a bug database should be indexed by bug id, not by commit id which has the bug.
-Peff
Thomas Harning
