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When iterating through the `packed-refs` file in order to answer a query
like:
$ git for-each-ref --exclude=refs/__hidden__
it would be useful to avoid walking over all of the entries in
`refs/__hidden__/*` when possible, since we know that the ref-filter
code is going to throw them away anyways.
In certain circumstances, doing so is possible. The algorithm for doing
so is as follows:
- For each excluded pattern, find the first record that matches it,
and the first record that *doesn't* match it (i.e. the location
you'd next want to consider when excluding that pattern).
- Sort the set of excluded regions from the previous step in ascending
order of the first location within the `packed-refs` file that
matches.
- Clean up the results from the previous step: discard empty regions,
and combine adjacent regions. The set of regions which remains is
referred to as the "jump list", and never contains any references
which should be included in the result set.
Then when iterating through the `packed-refs` file, if `iter->pos` is
ever contained in one of the regions from the previous steps, advance
`iter->pos` past the end of that region, and continue enumeration.
Note that we only perform this optimization when none of the excluded
pattern(s) have special meta-characters in them. For a pattern like
"refs/foo[ac]", the excluded regions ("refs/fooa", "refs/fooc", and
everything underneath them) are not connected. A future implementation
that handles this case may split the character class (pretending as if
two patterns were excluded: "refs/fooa", and "refs/fooc").
There are a few other gotchas worth considering. First, note that the
jump list is sorted, so once we jump past a region, we can avoid
considering it (or any regions preceding it) again. The member
`jump_pos` is used to track the first next-possible region to jump
through.
Second, note that the jump list is best-effort, since we do not handle
loose references, and because of the meta-character issue above. The
jump list may not skip past all references which won't appear in the
results, but will never skip over a reference which does appear in the
result set.
In repositories with a large number of hidden references, the speed-up
can be significant. Tests here are done with a copy of linux.git with a
reference "refs/pull/N" pointing at every commit, as in:
$ git rev-list HEAD | awk '{ print "create refs/pull/" NR " " $0 }' |
git update-ref --stdin
$ git pack-refs --all
, it is significantly faster to have `for-each-ref` jump over the
excluded references, as opposed to filtering them out after the fact:
$ hyperfine \
'git for-each-ref --format="%(objectname) %(refname)" | grep -vE "^[0-9a-f]{40} refs/pull/"' \
'git.prev for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"' \
'git.compile for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"'
Benchmark 1: git for-each-ref --format="%(objectname) %(refname)" | grep -vE "^[0-9a-f]{40} refs/pull/"
Time (mean ± σ): 798.1 ms ± 3.3 ms [User: 687.6 ms, System: 146.4 ms]
Range (min … max): 794.5 ms … 805.5 ms 10 runs
Benchmark 2: git.prev for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"
Time (mean ± σ): 98.9 ms ± 1.4 ms [User: 93.1 ms, System: 5.7 ms]
Range (min … max): 97.0 ms … 104.0 ms 29 runs
Benchmark 3: git.compile for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"
Time (mean ± σ): 4.5 ms ± 0.2 ms [User: 0.7 ms, System: 3.8 ms]
Range (min … max): 4.1 ms … 5.8 ms 524 runs
Summary
'git.compile for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"' ran
21.87 ± 1.05 times faster than 'git.prev for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"'
176.52 ± 8.19 times faster than 'git for-each-ref --format="%(objectname) %(refname)" | grep -vE "^[0-9a-f]{40} refs/pull/"'
(Comparing stock git and this patch isn't quite fair, since an earlier
commit in this series adds a naive implementation of the `--exclude`
option. `git.prev` is built from the previous commit and includes this
naive implementation).
Using the jump list is fairly straightforward (see the changes to
`refs/packed-backend.c::next_record()`), but constructing the list is
not. To ensure that the construction is correct, add a new suite of
tests in t1419 covering various corner cases (overlapping regions,
partially overlapping regions, adjacent regions, etc.).
Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
102 lines
2.5 KiB
Bash
Executable file
102 lines
2.5 KiB
Bash
Executable file
#!/bin/sh
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test_description='test exclude_patterns functionality in main ref store'
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GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
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export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
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TEST_PASSES_SANITIZE_LEAK=true
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. ./test-lib.sh
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for_each_ref__exclude () {
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test-tool ref-store main for-each-ref--exclude "$@" >actual.raw
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cut -d ' ' -f 2 actual.raw
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}
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for_each_ref () {
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git for-each-ref --format='%(refname)' "$@"
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}
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test_expect_success 'setup' '
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test_commit --no-tag base &&
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base="$(git rev-parse HEAD)" &&
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for name in foo bar baz quux
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do
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for i in 1 2 3
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do
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echo "create refs/heads/$name/$i $base" || return 1
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done || return 1
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done >in &&
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echo "delete refs/heads/main" >>in &&
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git update-ref --stdin <in &&
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git pack-refs --all
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'
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test_expect_success 'excluded region in middle' '
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for_each_ref__exclude refs/heads refs/heads/foo >actual &&
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for_each_ref refs/heads/bar refs/heads/baz refs/heads/quux >expect &&
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test_cmp expect actual
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'
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test_expect_success 'excluded region at beginning' '
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for_each_ref__exclude refs/heads refs/heads/bar >actual &&
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for_each_ref refs/heads/baz refs/heads/foo refs/heads/quux >expect &&
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test_cmp expect actual
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'
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test_expect_success 'excluded region at end' '
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for_each_ref__exclude refs/heads refs/heads/quux >actual &&
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for_each_ref refs/heads/foo refs/heads/bar refs/heads/baz >expect &&
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test_cmp expect actual
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'
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test_expect_success 'disjoint excluded regions' '
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for_each_ref__exclude refs/heads refs/heads/bar refs/heads/quux >actual &&
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for_each_ref refs/heads/baz refs/heads/foo >expect &&
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test_cmp expect actual
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'
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test_expect_success 'adjacent, non-overlapping excluded regions' '
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for_each_ref__exclude refs/heads refs/heads/bar refs/heads/baz >actual &&
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for_each_ref refs/heads/foo refs/heads/quux >expect &&
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test_cmp expect actual
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'
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test_expect_success 'overlapping excluded regions' '
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for_each_ref__exclude refs/heads refs/heads/ba refs/heads/baz >actual &&
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for_each_ref refs/heads/foo refs/heads/quux >expect &&
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test_cmp expect actual
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'
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test_expect_success 'several overlapping excluded regions' '
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for_each_ref__exclude refs/heads \
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refs/heads/bar refs/heads/baz refs/heads/foo >actual &&
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for_each_ref refs/heads/quux >expect &&
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test_cmp expect actual
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'
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test_expect_success 'non-matching excluded section' '
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for_each_ref__exclude refs/heads refs/heads/does/not/exist >actual &&
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for_each_ref >expect &&
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test_cmp expect actual
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'
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test_expect_success 'meta-characters are discarded' '
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for_each_ref__exclude refs/heads "refs/heads/ba*" >actual &&
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for_each_ref >expect &&
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test_cmp expect actual
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'
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test_done
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