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Taylor Blau 8de300e1f7 pack-bitmap.c: propagate namehash values from existing bitmaps When an old bitmap exists while writing a new one, we load it and build a "reposition" table which maps bit positions of objects from the old bitmap to their respective positions in the new bitmap. This can help when we encounter a commit which was selected in both the old and new bitmap, since we only need to permute its bit (not recompute it from scratch). We do not, however, repurpose existing namehash values in the case of the hash-cache extension. There has been thus far no good reason to do so, since all of the namehash values for objects in the new bitmap would be populated during the traversal that was just performed by pack-objects when generating single-pack reachability bitmaps. But this isn't the case for multi-pack bitmaps, which are written via `git multi-pack-index write --bitmap` and do not perform any traversal. In this case all namehash values are set to zero, but we don't even bother to check the `pack.writeBitmapHashcache` option anyway, so it fails to matter. There are two approaches we could take to fill in non-zero hash-cache values: - have either the multi-pack-index builtin run its own traversal to attempt to fill in some values, or let a hypothetical caller (like `pack-objects` when `repack` eventually drives the `multi-pack-index` builtin) fill in the values they found during their traversal - or copy any existing namehash values that were stored in an existing bitmap to their corresponding positions in the new bitmap In a system where a repository is generally repacked with `git repack --geometric=<d>` and occasionally repacked with `git repack -a`, the hash-cache coverage will tend towards all objects. Since populating the hash-cache is additive (i.e., doing so only helps our delta search), any intermediate lack of full coverage is just fine. So let's start by just propagating any values from the existing hash-cache if we see one. The next patch will respect the `pack.writeBitmapHashcache` option while writing MIDX bitmaps, and then test this new behavior. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>		2021-09-14 16:34:17 -07:00
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README.md

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). 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 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