On 05/03/2013 07:28 PM, Jeff King wrote: > On Fri, May 03, 2013 at 11:26:11AM +0200, Johan Herland wrote: > >> You don't really need to be sure that packed-refs is up-to-date. You >> only need to make sure that don't rely on lazily loading loose refs >> _after_ you have loaded packed-refs. > > True. As long as you load them both together, and always make sure you > do loose first, you'd be fine. But I think there will be corner cases > where you have loaded _part_ of the loose ref namespace. I think part of > the point of Michael's ref work is that if you call "for_each_tag_ref", > we would not waste time loading refs/remotes/ at all. If you then follow > that with a call to "for_each_ref", you would want to re-use the cached > work from traversing refs/tags/, and then traverse refs/remotes/. You > know that your cached packed-refs is good with respect to refs/tags/, > but you don't with respect to refs/remotes.
Correct. [I wonder if there really are a lot of iterations over overlapping parts of the reference namespace within a single git process...] >> The following solution might work in both the resolve-a-single-ref and >> enumerating-refs case: >> >> 0. Look for ref already cached in memory. If found, OK. >> >> 1. Look for loose ref. If found, OK. >> >> 2. If not found, load all loose refs and packed-refs from disk (in >> that order), and store in memory for remainder of this process. Never >> reload packed-refs from disk (unless you also reload all loose refs >> first). > > I think that would be correct (modulo that step 1 cannot happen for > enumeration). But we would like to avoid loading all loose refs if we > can. Especially on a cold cache, it can be quite slow, and you may not > even care about those refs for the current operation (I do not recall > the exact original motivation for the lazy loading, but it was something > along those lines). Lazy loading was first inspired by the observation that effectively every git invocation was loading *all* loose references to do an iteration over refs/replace/ (which I've never even used!) This was absolutely killing the performance of filter-branch, which creates a lot of loose references and invokes git many times--even though the cache was warm. Michael -- Michael Haggerty mhag...@alum.mit.edu http://softwareswirl.blogspot.com/ -- 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