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'--object-only' is an alias for '--format=%(objectname)'. It cannot
be used together other format-altering options like '--name-only',
'--long' or '--format', they are mutually exclusive.
The "--name-only" option outputs <filepath> only. Likewise, <objectName>
is another high frequency used field, so implement '--object-only' option
will bring intuitive and clear semantics for this scenario. Using
'--format=%(objectname)' we can achieve a similar effect, but the former
is with a lower learning cost(without knowing the format requirement
of '--format' option).
Even so, if a user is prefer to use "--format=%(objectname)", this is entirely
welcome because they are not only equivalent in function, but also have almost
identical performance. The reason is this commit also add the specific of
"--format=%(objectname)" to the current fast-pathes (builtin formats) to
avoid running unnecessary parsing mechanisms.
The following performance benchmarks are based on torvalds/linux.git:
When hit the fast-path:
Benchmark 1: /opt/git/ls-tree-oid-only/bin/git ls-tree -r --object-only HEAD
Time (mean ± σ): 83.6 ms ± 2.0 ms [User: 59.4 ms, System: 24.1 ms]
Range (min … max): 80.4 ms … 87.2 ms 35 runs
Benchmark 1: /opt/git/ls-tree-oid-only/bin/git ls-tree -r --format='%(objectname)' HEAD
Time (mean ± σ): 84.1 ms ± 1.8 ms [User: 61.7 ms, System: 22.3 ms]
Range (min … max): 80.9 ms … 87.5 ms 35 runs
But for a customized format, it will be slower:
Benchmark 1: /opt/git/ls-tree-oid-only/bin/git ls-tree -r --format='oid: %(objectname)' HEAD
Time (mean ± σ): 96.5 ms ± 2.5 ms [User: 72.9 ms, System: 23.5 ms]
Range (min … max): 93.1 ms … 104.1 ms 31 runs
Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Teng Long <dyroneteng@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Add a --format option to ls-tree. It has an existing default output,
and then --long and --name-only options to emit the default output
along with the objectsize and, or to only emit object paths.
Rather than add --type-only, --object-only etc. we can just support a
--format using a strbuf_expand() similar to "for-each-ref
--format". We might still add such options in the future for
convenience.
The --format implementation is slower than the existing code, but this
change does not cause any performance regressions. We'll leave the
existing show_tree() unchanged, and only run show_tree_fmt() in if
a --format different than the hardcoded built-in ones corresponding to
the existing modes is provided.
I.e. something like the "--long" output would be much slower with
this, mainly due to how we need to allocate various things to do with
quote.c instead of spewing the output directly to stdout.
The new option of '--format' comes from Ævar Arnfjörð Bjarmasonn's
idea and suggestion, this commit makes modifications in terms of the
original discussion on community [1].
In [1] there was a "GIT_TEST_LS_TREE_FORMAT_BACKEND" variable to
ensure that we had test coverage for passing tests that would
otherwise use show_tree() through show_tree_fmt(), and thus that the
formatting mechanism could handle all the same cases as the
non-formatting options.
Somewhere in subsequent re-rolls of that we seem to have drifted away
from what the goal of these tests should be. We're trying to ensure
correctness of show_tree_fmt(). We can't tell if we "hit [the]
fast-path" here, and instead of having an explicit test for that, we
can just add it to something our "test_ls_tree_format" tests for.
Here is the statistics about performance tests:
1. Default format (hitten the builtin formats):
"git ls-tree <tree-ish>" vs "--format='%(mode) %(type) %(object)%x09%(file)'"
$hyperfine --warmup=10 "/opt/git/master/bin/git ls-tree -r HEAD"
Benchmark 1: /opt/git/master/bin/git ls-tree -r HEAD
Time (mean ± σ): 105.2 ms ± 3.3 ms [User: 84.3 ms, System: 20.8 ms]
Range (min … max): 99.2 ms … 113.2 ms 28 runs
$hyperfine --warmup=10 "/opt/git/ls-tree-oid-only/bin/git ls-tree -r --format='%(mode) %(type) %(object)%x09%(file)' HEAD"
Benchmark 1: /opt/git/ls-tree-oid-only/bin/git ls-tree -r --format='%(mode) %(type) %(object)%x09%(file)' HEAD
Time (mean ± σ): 106.4 ms ± 2.7 ms [User: 86.1 ms, System: 20.2 ms]
Range (min … max): 100.2 ms … 110.5 ms 29 runs
2. Default format includes object size (hitten the builtin formats):
"git ls-tree -l <tree-ish>" vs "--format='%(mode) %(type) %(object) %(size:padded)%x09%(file)'"
$hyperfine --warmup=10 "/opt/git/master/bin/git ls-tree -r -l HEAD"
Benchmark 1: /opt/git/master/bin/git ls-tree -r -l HEAD
Time (mean ± σ): 335.1 ms ± 6.5 ms [User: 304.6 ms, System: 30.4 ms]
Range (min … max): 327.5 ms … 348.4 ms 10 runs
$hyperfine --warmup=10 "/opt/git/ls-tree-oid-only/bin/git ls-tree -r --format='%(mode) %(type) %(object) %(size:padded)%x09%(file)' HEAD"
Benchmark 1: /opt/git/ls-tree-oid-only/bin/git ls-tree -r --format='%(mode) %(type) %(object) %(size:padded)%x09%(file)' HEAD
Time (mean ± σ): 337.2 ms ± 8.2 ms [User: 309.2 ms, System: 27.9 ms]
Range (min … max): 328.8 ms … 349.4 ms 10 runs
Links:
[1] https://public-inbox.org/git/RFC-patch-6.7-eac299f06ff-20211217T131635Z-avarab@gmail.com/
[2] https://lore.kernel.org/git/cb717d08be87e3239117c6c667cb32caabaad33d.1646390152.git.dyroneteng@gmail.com/
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Teng Long <dyroneteng@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Teng Long
Ævar Arnfjörð Bjarmason