The previous patch made it possible to perform line-level filtering
during history traversal instead of in an expensive preprocessing
step, but it still requires some simpler preprocessing steps, notably
topo-ordering. However, nowadays we have commit-graphs storing
generation numbers, which make it possible to incrementally traverse
the history in topological order, without the preparatory limit_list()
and sort_in_topological_order() steps; see b45424181e (revision.c:
generation-based topo-order algorithm, 2018-11-01).
This patch combines the two, so we can do both the topo-ordering and
the line-level filtering during history traversal, eliminating even
those simpler preprocessing steps, and thus further reducing the delay
before showing the first commit modifying the given line range.
The 'revs->limited' flag plays the central role in this, because, due
to limitations of the current implementation, the generation
number-based topo-ordering is only enabled when this flag remains
unset. Line-level log, however, always sets this flag in
setup_revisions() ever since the feature was introduced in 12da1d1f6f
(Implement line-history search (git log -L), 2013-03-28). The reason
for setting 'limited' is unclear, though, because the line-level log
itself doesn't directly depend on it, and it doesn't affect how the
limit_list() function limits the revision range. However, there is an
indirect dependency: the line-level log requires topo-ordering, and
the "traditional" sort_in_topological_order() requires an already
limited commit list since e6c3505b44 (Make sure we generate the whole
commit list before trying to sort it topologically, 2005-07-06). The
new, generation numbers-based topo-ordering doesn't require a limited
commit list anymore.
So don't set 'revs->limited' for line-level log, unless it is really
necessary, namely:
- The user explicitly requested parent rewriting, because that is
still done in the line_log_filter() preprocessing step (see
previous patch), which requires sort_in_topological_order() and in
turn limit_list() as well.
- A commit-graph file is not available or it doesn't yet contain
generation numbers. In these cases we had to fall back on
sort_in_topological_order() and in turn limit_list(). The
existing condition with generation_numbers_enabled() has already
ensured that the 'limited' flag is set in these cases; this patch
just makes sure that the line-level log sets 'revs->topo_order'
before that condition.
While the reduced delay before showing the first commit is measurable
in git.git, it takes a bigger repository to make it clearly noticable.
In both cases below the line ranges were chosen so that they were
modified rather close to the starting revisions, so the effect of this
change is most noticable.
# git.git
$ time git --no-pager log -L:read_alternate_refs:sha1-file.c -1 v2.23.0
Before:
real 0m0.107s
user 0m0.091s
sys 0m0.013s
After:
real 0m0.058s
user 0m0.050s
sys 0m0.005s
# linux.git
$ time git --no-pager log \
-L:build_restore_work_registers:arch/mips/mm/tlbex.c -1 v5.2
Before:
real 0m1.129s
user 0m1.061s
sys 0m0.069s
After:
real 0m0.096s
user 0m0.087s
sys 0m0.009s
Additional testing by Derrick Stolee: Since this patch improves
the performance for the first result, I repeated the experiment
from the previous patch on the Linux kernel repository, reporting
real time here:
Command: git log -L 100,200:MAINTAINERS -n 1 >/dev/null
Before: 0.71 s
After: 0.05 s
Now, we have dropped the full topo-order of all ~910,000 commits
before reporting the first result. The remaining performance
improvements then are:
1. Update the parent-rewriting logic to be incremental similar to
how "git log --graph" behaves.
2. Use changed-path Bloom filters to reduce the time spend in the
tree-diff to see if the path(s) changed.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.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.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).
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
002933f3fe