02a7f6ffab
When approximating the number of objects in a repository we only take
into account two data sources, the multi-pack index and the packfile
indices, as both of these data structures allow us to easily figure out
how many objects they contain.
But the way we currently approximate the number of objects is broken in
presence of a multi-pack index. This is due to two separate reasons:
- We have recently introduced initial infrastructure for incremental
multi-pack indices. Starting with that series, `num_objects` only
counts the number of objects of a specific layer of the MIDX chain,
so we do not take into account objects from parent layers.
This issue is fixed by adding `num_objects_in_base`, which contains
the sum of all objects in previous layers.
- When using the multi-pack index we may count objects contained in
packfiles twice: once via the multi-pack index, but then we again
count them via the packfile itself.
This issue is fixed by skipping any packfiles that have an MIDX.
Overall, given that we _always_ count the packs, we can only end up
overestimating the number of objects, and the overestimation is limited
to a factor of two at most.
The consequences of those issues are very limited though, as we only
approximate object counts in a small number of cases:
- When writing a commit-graph we use the approximate object count to
display the upper limit of a progress display.
- In `repo_find_unique_abbrev_r()` we use it to specify a lower limit
of how many hex digits we want to abbreviate to. Given that we use
power-of-two here to derive the lower limit we may end up with an
abbreviated hash that is one digit longer than required.
- In `estimate_repack_memory()` we may end up overestimating how much
memory a repack needs to pack objects. Conseuqently, we may end up
dropping some packfiles from a repack.
None of these are really game-changing. But it's nice to fix those
issues regardless.
While at it, convert the code to use `repo_for_each_pack()`.
Furthermore, use `odb_prepare_alternates()` instead of explicitly
preparing the packfile store. We really only want to prepare the object
database sources, and `get_multi_pack_index()` already knows to prepare
the packfile store for us.
Helped-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
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).
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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