Re: Current Issues #3

From: Shawn Pearce <spearce@spearce.org>
Date: May 22, 2006, 23:12 UTC
Message-ID: <20060522231257.GA21124@spearce.org>
In-Reply-To: <Pine.LNX.4.64.0605221738090.6713@iabervon.org>

Daniel Barkalow <barkalow@iabervon.org> wrote:

Show 21 quoted lines

> On Mon, 22 May 2006, Junio C Hamano wrote:
> 
> > * reflog
> > 
> >   I still haven't merged this series to "next" -- I do not have
> >   much against what the code does, but I am unconvinced if it is
> >   useful.  Also objections raised on the list that this can be
> >   replaced by making sure that a repository that has hundreds of
> >   tags usable certainly have a point.
> 
> I think it would make gitweb's summary view clearer, and Linus seemed 
> interested in being able to look up what happened in the fast forward 
> which was the first of several merges in a day.
> 
> It could be replaced by a repository with hundreds of machine-readable 
> tags with code to parse dates into queries for suitable tags. But I don't 
> think there's an advantage to using the tag mechanism here, because you 
> never want to look the history up by exactly which history it is (the 
> thing that a tag ref is good for); you'll be looking for whatever reflog 
> item is the newest not after a specified time, where the specified time is 
> almost never a time that a reflog item was created.

The thing is this might also be easily represented as a structure of tags; for example:

	refs/logs/heads/<ref>/<year>/<month>/<day> <hour>:<min>:<sec>:<seq>

where the tag is a tag of the commit which was valid in that ref at that time. Searching for an entry "around a particular time" isn't that much more difficult than parsing a file, you just have to walk backwards through the sorted directory listings then read the tag object which matches; that tag object will point at the tree/commit/tag which is was in that ref..

What's ugly about this is simply the disk storage: a ref file is an expensive thing (relatively speaking) on most UNIX file systems due to the inode overhead. If this was stored in a more compact format (such as a GIT tree) then this would cost very little.

So the alternative that I have been mentaly kicking around for the past two days is storing the GIT_DIR/refs directory within a standard GIT tree. This of course would need to be an option that gets enabled by the user as currently most tools expect the refs directory to actually be a directory, not a tree. The advantage here is that unlike proposed reflog it is a compact ref representation which could be used by other features, such as tagging a GIT commit with the unique name of the same change from another SCM. Or tagging your repository on every automated build, which runs once every 5 minutes.

-- 
Shawn.