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When managing a MIDX chain with many layers, it is convenient to combine a sequence of adjacent layers into a single layer to prevent the chain from growing too long. While it is conceptually possible to "compact" a sequence of MIDX layers together by running "git multi-pack-index write --stdin-packs", there are a few drawbacks that make this less than desirable: - Preserving the MIDX chain is impossible, since there is no way to write a MIDX layer that contains objects or packs found in an earlier MIDX layer already part of the chain. So callers would have to write an entirely new (non-incremental) MIDX containing only the compacted layers, discarding all other objects/packs from the MIDX. - There is (currently) no way to write a MIDX layer outside of the MIDX chain to work around the above, such that the MIDX chain could be reassembled substituting the compacted layers with the MIDX that was written. - The `--stdin-packs` command-line option does not allow us to specify the order of packs as they appear in the MIDX. Therefore, even if there were workarounds for the previous two challenges, any bitmaps belonging to layers which come after the compacted layer(s) would no longer be valid. This commit introduces a way to compact a sequence of adjacent MIDX layers into a single layer while preserving the MIDX chain, as well as any bitmap(s) in layers which are newer than the compacted ones. Implementing MIDX compaction does not require a significant number of changes to how MIDX layers are written. The main changes are as follows: - Instead of calling `fill_packs_from_midx()`, we call a new function `fill_packs_from_midx_range()`, which walks backwards along the portion of the MIDX chain which we are compacting, and adds packs one layer a time. In order to preserve the pseudo-pack order, the concatenated pack order is preserved, with the exception of preferred packs which are always added first. - After adding entries from the set of packs in the compaction range, `compute_sorted_entries()` must adjust the `pack_int_id`'s for all objects added in each fanout layer to match their original `pack_int_id`'s (as opposed to the index at which each pack appears in `ctx.info`). - When writing out the new 'multi-pack-index-chain' file, discard any layers in the compaction range, replacing them with the newly written layer, instead of keeping them and placing the new layer at the end of the chain. This ends up being sufficient to implement MIDX compaction in such a way that preserves bitmaps corresponding to more recent layers in the MIDX chain. The tests for MIDX compaction are so far fairly spartan, since the main interesting behavior here is ensuring that the right packs/objects are selected from each layer, and that the pack order is preserved despite whether or not they are sorted in lexicographic order in the original MIDX chain. Signed-off-by: Taylor Blau <me@ttaylorr.com> 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.adoc to get started, then see
Documentation/giteveryday.adoc for a useful minimum set of commands, and
Documentation/git-<commandname>.adoc 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.adoc
(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 to git+subscribe@vger.kernel.org (see https://subspace.kernel.org/subscribing.html for details). The mailing list archives are available at https://lore.kernel.org/git/, https://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