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The parse_object() function checks the object hash of any object it parses. This is a nice feature, as it means we may catch bit corruption during normal use, rather than waiting for specific fsck operations. But it also can be slow. It's particularly noticeable for blobs, where except for the hash check, we could return without loading the object contents at all. Now one may wonder what is the point of calling parse_object() on a blob in the first place then, but usually it's not intentional: we were fed an oid from somewhere, don't know the type, and want an object struct. For commits and trees, the parsing is usually helpful; we're about to look at the contents anyway. But this is less true for blobs, where we may be collecting them as part of a reachability traversal, etc, and don't actually care what's in them. And blobs, of course, tend to be larger. We don't want to just throw out the hash-checks for blobs, though. We do depend on them in some circumstances (e.g., rev-list --verify-objects uses parse_object() to check them). It's only the callers that know how they're going to use the result. And so we can help them by providing a special flag to skip the hash check. We could just apply this to blobs, as they're going to be the main source of performance improvement. But if a caller doesn't care about checking the hash, we might as well skip it for other object types, too. Even though we can't avoid reading the object contents, we can still skip the actual hash computation. If this seems like it is making Git a little bit less safe against corruption, it may be. But it's part of a series of tradeoffs we're already making. For instance, "rev-list --objects" does not open the contents of blobs it prints. And when a commit graph is present, we skip opening most commits entirely. The important thing will be to use this flag in cases where it's safe to skip the check. For instance, when serving a pack for a fetch, we know the client will fully index the objects and do a connectivity check itself. There's little to be gained from the server side re-hashing a blob itself. And indeed, most of the time we don't! The revision machinery won't open up a blob reached by traversal, but only one requested directly with a "want" line. So applied properly, this new feature shouldn't make anything less safe in practice. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git - fast, scalable, distributed revision control system
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 version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-<commandname>.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with man gittutorial or git help tutorial, and the
documentation of each command with man git-<commandname> or git help <commandname>.
CVS users may also want to read Documentation/gitcvs-migration.txt
(man gitcvs-migration or git help cvs-migration if git is
installed).
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 (read Documentation/SubmittingPatches for instructions on patch submission and Documentation/CodingGuidelines).
Those wishing to help with error message, usage and informational message
string translations (localization l10) should see po/README.md
(a po file is a Portable Object file that holds the translations).
To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org (not the Git list). The mailing list archives are available at https://lore.kernel.org/git/, http://marc.info/?l=git and other archival sites.
Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.
The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (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