When pushing using a matching refspec or a pattern refspec, each ref
in the local repository must be paired with a ref advertised by the
remote server. This is accomplished by using the refspec to transform
the name of the local ref into the name it should have in the remote
repository, and then performing a linear search through the list of
remote refs to see if the remote ref was advertised by the remote
system.
Each of these lookups has O(n) complexity and makes match_push_refs()
be an O(m*n) operation, where m is the number of local refs and n is
the number of remote refs. If there are many refs 100,000+, then this
ref matching can take a significant amount of time. Let's prepare an
index of the remote refs to allow searching in O(log n) time and
reduce the complexity of match_push_refs() to O(m log n).
We prepare the index lazily so that it is only created when necessary.
So, there should be no impact when _not_ using a matching or pattern
refspec, i.e. when pushing using only explicit refspecs.
Dry-run push of a repository with 121,913 local and remote refs:
before after
real 1m40.582s 0m0.804s
user 1m39.914s 0m0.515s
sys 0m0.125s 0m0.106s
The creation of the index has overhead. So, if there are very few
local refs, then it could take longer to create the index than it
would have taken to just perform n linear lookups into the remote
ref space. Using the index should provide some improvement when
the number of local refs is roughly greater than the log of the
number of remote refs (i.e. m >= log n). The pathological case is
when there is a single local ref and very many remote refs.
Dry-run push of a repository with 121,913 remote refs and a single
local ref:
before after
real 0m0.525s 0m0.566s
user 0m0.243s 0m0.279s
sys 0m0.075s 0m0.099s
Using an index takes 41 ms longer, or roughly 7.8% longer.
Jeff King measured a no-op push of a single ref into a remote repo
with 370,000 refs:
before after
real 0m1.087s 0m1.156s
user 0m1.344s 0m1.412s
sys 0m0.288s 0m0.284s
Using an index takes 69 ms longer, or roughly 6.3% longer.
None of the measurements above required transferring any objects to
the remote repository. If the push required transferring objects and
updating the refs in the remote repository, the impact of preparing
the search index would be even smaller.
A similar operation is performed in the reverse direction when pruning
using a matching or pattern refspec. Let's avoid O(m*n) behavior in
the same way by lazily preparing an index on the local refs.
Signed-off-by: Brandon Casey <drafnel@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
////////////////////////////////////////////////////////////////
Git - the stupid content tracker
////////////////////////////////////////////////////////////////
"git" can mean anything, 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
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
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Please read the file INSTALL for installation instructions.
See Documentation/gittutorial.txt to get started, then see
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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
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CVS users may also want to read Documentation/gitcvs-migration.txt
("man gitcvs-migration" or "git help cvs-migration" if git is
installed).
Many Git online resources are accessible from http://git-scm.com/
including full documentation and Git related tools.
The user discussion and development of Git take place on the Git
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To subscribe to the list, send an email with just "subscribe git" in
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The maintainer frequently sends the "What's cooking" reports that
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project status, development direction and remaining tasks.
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