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b9849a1ab6
This updates git-rev-list --objects to be a bit more careful when listing a blob object to make sure the blob actually exists, and uses it to make sure the quick-fetch optimization we introduced earlier is not fooled by a previous incomplete fetch. The quick-fetch optimization works by running this command: git rev-list --objects <<commit-list>> --not --all where <<commit-list>> is a list of commits that we are going to fetch from the other side. If there is any object missing to complete the <<commit-list>>, the rev-list would fail and die (say, the commit was in our repository, but its tree wasn't -- then it will barf while trying to list the blobs the tree contains because it cannot read that tree). Usually we do not have the objects (otherwise why would we fetching?), but in one important special case we do: when the remote repository is used as an alternate object store (i.e. pointed by .git/objects/info/alternates). We could check .git/objects/info/alternates to see if the remote we are interacting with is one of them (or is used as an alternate, recursively, by one of them), but that check is more cumbersome than it is worth. The above check however did not catch missing blob, because object listing code did not read nor check blob objects, knowing that blobs do not contain any further references to other objects. This commit fixes it with practically unmeasurable overhead. I've benched this with git rev-list --objects --all >/dev/null in the kernel repository, with three different implementations of the "check-blob". - Checking with has_sha1_file() has negligible (unmeasurable) performance penalty. - Checking with sha1_object_info() makes it somewhat slower, perhaps by 5%. - Checking with read_sha1_file() to cause a fully re-validation is prohibitively expensive (about 4 times as much runtime). In my original patch, I had this as a command line option, but the overhead is small enough that it is not really worth it. Signed-off-by: Junio C Hamano <junkio@cox.net>
//////////////////////////////////////////////////////////////// GIT - the stupid content tracker //////////////////////////////////////////////////////////////// "git" can mean anything, depending on your mood. - random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant. - stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang. - "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room. - "goddamn idiotic truckload of sh*t": when it breaks Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals. Git is an Open Source project covered by the GNU General Public License. It was originally written by Linus Torvalds with help of a group of hackers around the net. It is currently maintained by Junio C Hamano. Please read the file INSTALL for installation instructions. See Documentation/tutorial.txt to get started, then see Documentation/everyday.txt for a useful minimum set of commands, and "man git-commandname" for documentation of each command. CVS users may also want to read Documentation/cvs-migration.txt. Many Git online resources are accessible from http://git.or.cz/ including full documentation and Git related tools. The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org. To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org. The mailing list archives are available at http://marc.theaimsgroup.com/?l=git and other archival sites. The messages titled "A note from the maintainer", "What's in git.git (stable)" and "What's cooking in git.git (topics)" and the discussion following them on the mailing list give a good reference for project status, development direction and remaining tasks.