9f75e7a150
Defer the actual removal in prio_queue_get() until the next
operation. If that next operation is a prio_queue_put(), the
removal and insertion are fused into a single replace — writing
the new element at the root and sifting it down — which avoids
a full remove-rebalance-insert cycle.
This matches the dominant usage pattern in git's commit traversal:
get a commit, then put its parents. The first parent insertion
after each get is now a replace operation automatically.
This generalizes the lazy_queue pattern from builtin/describe.c
(introduced in 08bb69d70f) into prio_queue itself. Three callers
independently implemented the same get+put fusion:
- builtin/describe.c had a full lazy_queue wrapper
- commit.c:pop_most_recent_commit() used peek+replace
- builtin/show-branch.c:join_revs() used peek+replace
All three now collapse to plain _get() and _put(), with the data
structure handling the fusion internally. This simplifies callers
and means every prio_queue user gets the optimization for free
without needing to implement it manually.
Remove prio_queue_replace() since no external callers remain.
Benchmarked on a 1.8M-commit monorepo (30 interleaved runs,
paired t-test, Xeon @ 2.20GHz):
Code paths that previously did eager get+put (new optimization):
Command base patched change p
merge-base --all A A~1000 3828ms 3725ms -2.69% 0.0001
rev-list --count A~1000..A 3055ms 2986ms -2.27% 0.0601
log --oneline A~1000..A 3408ms 3350ms -1.71% 0.0482
Code paths that already had manual get+put fusion (expect
neutral — the optimization moves into prio_queue but the number
of heap operations stays the same):
Command base patched change p
show-branch A A~1000 9156ms 9127ms -0.32% 0.3470
describe (4751 revs, 81K repo) 1983ms 1963ms -1.02% <0.001
No regressions in any scenario.
Suggested-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Kristofer Karlsson <krka@spotify.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