On Fri, Jul 23, 2010 at 11:19 AM, Marc Branchaud <marcnarc@xxxxxxxxxxx> wrote: > On 10-07-22 03:41 PM, Avery Pennarun wrote: >> 1) Sometimes I want to clone only some subdirs of a project >> 2) Sometimes I don't want the entire history because it's too big. >> 3) Super huge git repositories start to degrade in performance. > > The reason we turned to submodules is precisely to deal with repository size. I believe that's very common. However, I wonder whether that's actually a good reason for git to develop better submodules, or actually just a good reason for git to get better support for handling huge repositories. My bup project (http://github.com/apenwarr/bup) is all about huge repositories. It handles repositories with hundreds of gigabytes, and trees containing millions of files (entire filesystems), quite nicely. Of course, it's not a version control system, so it won't solve your problems. It's just evidence that large repositories are actually quite manageable without changing the fundamentals of git. > Our code base encompasses the entire FreeBSD tree plus different versions of > the Linux kernel, along with various third-party libraries & apps. You don't > need everything to build a given product (a FreeBSD product doesn't use any > Linux kernels, for example) but because all the products share common code we > need to be able to branch and tag the common code along with the uncommon code. Honest question: do you care about the wasted disk space and download time for these extra files? Or just the fact that git gets slow when you have them? How people answer that question very much affects the way git should be designed. > So a straight "git clone" that would need to fetch all of FreeBSD plus 4 > different Linux kernels and check all that out is a major problem, especially > for our automated build system (which could definitely be implemented better, > but still). To be absolutely pedantic, the four linux kernels likely share most of their objects and so you're only paying the cost (at least during fetch) of including it once :) (If you're actually using git-submodule and each copy of the kernel is its own module, then it might be cloning the kernel four times separately, in which case the objects *don't* get shared, so this ends up being much more expensive than it should be. That could be fixed by slightly improving git-submodule to share some objects rather than rearchitecting it though.) > In truth it's the checkout that takes the most time by far, > though commands like git-status also take inconveniently long. Yeah, git could stand to be optimized a bit here. And since Windows stats files about 10x slower than Linux, this problem occurs about 10x sooner on Windows, which makes using git on Windows (which sadly I have to do sometimes) extremely painful compared to Linux. IMHO, the correct answer here is to have an inotify-based daemon prod at the .git/index automatically when files get updated, so that git itself doesn't have to stat/readdir through the entire tree in order to do any of its operations. (Windows also has something like inotify that would work.) If you had this, then git status/diff/checkout/commit would be just as fast with zillions of files as with 10 files. Sooner or later, if nobody implements this, I promise I'll get around to it since inotify is actually easy to code for :) Also note that the only reason submodules are faster here is that they're ignoring possibly important changes. Notably, when you do 'git status' from the top level, it won't warn you if you have any not-yet-committed files in any of your submodules. Personally, I consider that to be really important information, but to obtain it would make 'git status' take just as long as without submodules, so you wouldn't get any benefit. (I think nowadays there's a way to get this recursive status information if you want it, but it'll be slow of course.) > We chose git-submodule over git-subtree mainly because git-submodule lets us > selectively checkout different parts of our code. (AFAIK sparse checkouts > aren't yet an option.) Fair enough. If you could confirm or deny my theory that this is *entirely* a performance related concern (as opposed to disk space / download time), that would be helpful. > We didn't really consider git-subtree because it's > not an official part of git, and we didn't want to have to teach (and nag) > all our developers to install and maintain it in addition to keeping up with > git itself. Arguably, this is a vote for including git-subtree into the core (which was Bryan's point when he started this thread); it obviously is being rejected sometimes by git users simply because it's not in the core, even though it could help them. Have fun, Avery -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html