read-cache: avoid allocating every ondisk entry when writing

When writing the index for each entry an ondisk struct will be
allocated and freed in ce_write_entry.  We can do better by
using a ondisk struct on the stack for each entry.

This is accomplished by using a stack ondisk_cache_entry_extended
outside looping through the entries in do_write_index.  Only the
fixed fields of this struct are used when writing and depending on
whether it is extended or not the flags2 field will be written.
The name field is not used and instead the cache_entry name field
is used directly when writing out the name.  Because ce_write is
using a buffer and memcpy to fill the buffer before flushing to disk,
we don't have to worry about doing multiple ce_write calls.

Running the p0007-write-cache.sh tests would save anywhere
between 3-7% when the index had over a million entries with no
performance degradation on small repos.

Signed-off-by: Kevin Willford <kewillf@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
1 file changed
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  352. unpack-trees.c
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  354. upload-pack.c
  355. url.c
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  366. version.c
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  375. wrap-for-bin.sh
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  379. wt-status.c
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  381. xdiff-interface.c
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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-.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://public-inbox.org/git/, http://marc.info/?l=git and other archival sites.

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