Re: git annotate runs out of memory

From: Steven Grimm <koreth@midwinter.com>
Date: Dec 11, 2007, 19:29 UTC
Message-ID: <74ED838F-4966-42A9-BC8A-906FD0B4B46F@midwinter.com>
In-Reply-To: <alpine.LFD.0.9999.0712111018540.25032@woody.linux-foundation.org>

On Dec 11, 2007, at 10:40 AM, Linus Torvalds wrote:

Show 7 quoted lines

> To git, "git annotate" is just about the *last* thing you ever want  
> to do.
> It's not a common operation, it's a "last resort" operation. In git,  
> the
> whole workflow is designed for "git log -p <pathnamepattern>" rather  
> than
> annotate/blame.

My use of "git blame" is perhaps not typical, but I use it fairly often when I'm looking at a part of my company's code base that I'm not terribly familiar with. I've found it's the fastest way to figure out who to go ask about a particular block of code that I think is responsible for a bug, or more commonly, who to ask to review a change I'm making.

"git log" is too coarse-grained to be useful for that purpose; it usually doesn't tell me which of the 500 revisions to the file I'm looking at introduced the actual line of code I want to change.

To me that really has nothing whatsoever to do with git workflow or svn workflow; it happens well before I'm ready to do any kind of integration or commit or even, sometimes, before I've made any changes to any code at all.

Given infinite spare time, one of the things I'd be strongly tempted to try to build would be some kind of blame cache. You could theoretically make blame pretty much instantaneous by doing something as simple as caching the per-line revision ID for each file in each revision in a shadow repository (or a shadow branch in the main repo) and keeping a map between shadow-repo revisions and real-repo ones. If the cache was of the form "one SHA1 hash per line in the original file" it would delta-compress pretty well. It'd be easy to update incrementally since you only need to walk back in history until you get to the most recently cached revision for each file, at which point you use the cached value for all the lines that haven't changed.

Yeah, I know, code talks louder than words...

-Steve