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Both 'git for-each-ref --merged=<X>' and 'git branch --merged=<X>' use the ref-filter machinery to select references or branches (respectively) that are reachable from a set of commits presented by one or more --merged arguments. This happens within reach_filter(), which uses the revision-walk machinery to walk history in a standard way. However, the commit-reach.c file is full of custom searches that are more efficient, especially for reachability queries that can terminate early when reachability is discovered. Add a new tips_reachable_from_bases() method to commit-reach.c and call it from within reach_filter() in ref-filter.c. This affects both 'git branch' and 'git for-each-ref' as tested in p1500-graph-walks.sh. For the Linux kernel repository, we take an already-fast algorithm and make it even faster: Test HEAD~1 HEAD ------------------------------------------------------------------- 1500.5: contains: git for-each-ref --merged 0.13 0.02 -84.6% 1500.6: contains: git branch --merged 0.14 0.02 -85.7% 1500.7: contains: git tag --merged 0.15 0.03 -80.0% (Note that we remove the iterative 'git rev-list' test from p1500 because it no longer makes sense as a comparison to 'git for-each-ref' and would just waste time running it for these comparisons.) The algorithm is implemented in commit-reach.c in the method tips_reachable_from_base(). This method takes a string_list of tips and assigns the 'util' for each item with the value 1 if the base commit can reach those tips. Like other reachability queries in commit-reach.c, the fastest way to search for "can A reach B?" is to do a depth-first search up to the generation number of B, preferring to explore first parents before later parents. While we must walk all reachable commits up to that generation number when the answer is "no", the depth-first search can answer "yes" much faster than other approaches in most cases. This search becomes trickier when there are multiple targets for the depth-first search. The commits with lower generation number are more likely to be within the history of the start commit, but we don't want to waste time searching commits of low generation number if the commit target with lowest generation number has already been found. The trick here is to take the input commits and sort them by generation number in ascending order. Track the index within this order as min_generation_index. When we find a commit, if its index in the list is equal to min_generation_index, then we can increase the generation number boundary of our search to the next-lowest value in the list. With this mechanism, the number of commits to search is minimized with respect to the depth-first search heuristic. We will walk all commits up to the minimum generation number of a commit that is _not_ reachable from the start, but we will walk only the necessary portion of the depth-first search for the reachable commits of lower generation. Add extra tests for this behavior in t6600-test-reach.sh as the interesting data shape of that repository can sometimes demonstrate corner case bugs. Signed-off-by: Derrick Stolee <derrickstolee@github.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
51 lines
1.1 KiB
Bash
Executable file
51 lines
1.1 KiB
Bash
Executable file
#!/bin/sh
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test_description='Commit walk performance tests'
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. ./perf-lib.sh
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test_perf_large_repo
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test_expect_success 'setup' '
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git for-each-ref --format="%(refname)" "refs/heads/*" "refs/tags/*" >allrefs &&
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sort -r allrefs | head -n 50 >refs &&
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for ref in $(cat refs)
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do
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git branch -f ref-$ref $ref &&
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echo ref-$ref ||
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return 1
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done >branches &&
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for ref in $(cat refs)
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do
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git tag -f tag-$ref $ref &&
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echo tag-$ref ||
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return 1
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done >tags &&
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git commit-graph write --reachable
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'
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test_perf 'ahead-behind counts: git for-each-ref' '
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git for-each-ref --format="%(ahead-behind:HEAD)" --stdin <refs
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'
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test_perf 'ahead-behind counts: git branch' '
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xargs git branch -l --format="%(ahead-behind:HEAD)" <branches
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'
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test_perf 'ahead-behind counts: git tag' '
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xargs git tag -l --format="%(ahead-behind:HEAD)" <tags
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'
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test_perf 'contains: git for-each-ref --merged' '
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git for-each-ref --merged=HEAD --stdin <refs
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'
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test_perf 'contains: git branch --merged' '
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xargs git branch --merged=HEAD <branches
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'
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test_perf 'contains: git tag --merged' '
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xargs git tag --merged=HEAD <tags
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'
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test_done
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