From c525ce95b46b34f344c360dbef036cec3ea08e53 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?SZEDER=20G=C3=A1bor?= Date: Wed, 1 Jul 2020 13:27:30 +0000 Subject: commit-graph: check all leading directories in changed path Bloom filters MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The file 'dir/subdir/file' can only be modified if its leading directories 'dir' and 'dir/subdir' are modified as well. So when checking modified path Bloom filters looking for commits modifying a path with multiple path components, then check not only the full path in the Bloom filters, but all its leading directories as well. Take care to check these paths in "deepest first" order, because it's the full path that is least likely to be modified, and the Bloom filter queries can short circuit sooner. This can significantly reduce the average false positive rate, by about an order of magnitude or three(!), and can further speed up pathspec-limited revision walks. The table below compares the average false positive rate and runtime of git rev-list HEAD -- "$path" before and after this change for 5000+ randomly* selected paths from each repository: Average false Average Average positive rate runtime runtime before after before after difference ------------------------------------------------------------------ git 3.220% 0.7853% 0.0558s 0.0387s -30.6% linux 2.453% 0.0296% 0.1046s 0.0766s -26.8% tensorflow 2.536% 0.6977% 0.0594s 0.0420s -29.2% *Path selection was done with the following pipeline: git ls-tree -r --name-only HEAD | sort -R | head -n 5000 The improvements in runtime are much smaller than the improvements in average false positive rate, as we are clearly reaching diminishing returns here. However, all these timings depend on that accessing tree objects is reasonably fast (warm caches). If we had a partial clone and the tree objects had to be fetched from a promisor remote, e.g.: $ git clone --filter=tree:0 --bare file://.../webkit.git webkit.notrees.git $ git -C webkit.git -c core.modifiedPathBloomFilters=1 \ commit-graph write --reachable $ cp webkit.git/objects/info/commit-graph webkit.notrees.git/objects/info/ $ git -C webkit.notrees.git -c core.modifiedPathBloomFilters=1 \ rev-list HEAD -- "$path" then checking all leading path component can reduce the runtime from over an hour to a few seconds (and this is with the clone and the promisor on the same machine). This adjusts the tracing values in t4216-log-bloom.sh, which provides a concrete way to notice the improvement. Helped-by: Taylor Blau Helped-by: René Scharfe Signed-off-by: SZEDER Gábor Signed-off-by: Derrick Stolee Signed-off-by: Junio C Hamano diff --git a/revision.c b/revision.c index 667ca36..b911800 100644 --- a/revision.c +++ b/revision.c @@ -668,9 +668,10 @@ static void prepare_to_use_bloom_filter(struct rev_info *revs) { struct pathspec_item *pi; char *path_alloc = NULL; - const char *path; + const char *path, *p; int last_index; - int len; + size_t len; + int path_component_nr = 1; if (!revs->commits) return; @@ -707,8 +708,33 @@ static void prepare_to_use_bloom_filter(struct rev_info *revs) return; } - revs->bloom_key = xmalloc(sizeof(struct bloom_key)); - fill_bloom_key(path, len, revs->bloom_key, revs->bloom_filter_settings); + p = path; + while (*p) { + /* + * At this point, the path is normalized to use Unix-style + * path separators. This is required due to how the + * changed-path Bloom filters store the paths. + */ + if (*p == '/') + path_component_nr++; + p++; + } + + revs->bloom_keys_nr = path_component_nr; + ALLOC_ARRAY(revs->bloom_keys, revs->bloom_keys_nr); + + fill_bloom_key(path, len, &revs->bloom_keys[0], + revs->bloom_filter_settings); + path_component_nr = 1; + + p = path + len - 1; + while (p > path) { + if (*p == '/') + fill_bloom_key(path, p - path, + &revs->bloom_keys[path_component_nr++], + revs->bloom_filter_settings); + p--; + } if (trace2_is_enabled() && !bloom_filter_atexit_registered) { atexit(trace2_bloom_filter_statistics_atexit); @@ -722,7 +748,7 @@ static int check_maybe_different_in_bloom_filter(struct rev_info *revs, struct commit *commit) { struct bloom_filter *filter; - int result; + int result = 1, j; if (!revs->repo->objects->commit_graph) return -1; @@ -737,9 +763,11 @@ static int check_maybe_different_in_bloom_filter(struct rev_info *revs, return -1; } - result = bloom_filter_contains(filter, - revs->bloom_key, - revs->bloom_filter_settings); + for (j = 0; result && j < revs->bloom_keys_nr; j++) { + result = bloom_filter_contains(filter, + &revs->bloom_keys[j], + revs->bloom_filter_settings); + } if (result) count_bloom_filter_maybe++; @@ -779,7 +807,7 @@ static int rev_compare_tree(struct rev_info *revs, return REV_TREE_SAME; } - if (revs->bloom_key && !nth_parent) { + if (revs->bloom_keys_nr && !nth_parent) { bloom_ret = check_maybe_different_in_bloom_filter(revs, commit); if (bloom_ret == 0) diff --git a/revision.h b/revision.h index 7c026fe..abbfb4a 100644 --- a/revision.h +++ b/revision.h @@ -295,8 +295,10 @@ struct rev_info { struct topo_walk_info *topo_walk_info; /* Commit graph bloom filter fields */ - /* The bloom filter key for the pathspec */ - struct bloom_key *bloom_key; + /* The bloom filter key(s) for the pathspec */ + struct bloom_key *bloom_keys; + int bloom_keys_nr; + /* * The bloom filter settings used to generate the key. * This is loaded from the commit-graph being used. diff --git a/t/t4216-log-bloom.sh b/t/t4216-log-bloom.sh index 29338f3..4892364 100755 --- a/t/t4216-log-bloom.sh +++ b/t/t4216-log-bloom.sh @@ -146,7 +146,7 @@ test_expect_success 'setup - add commit-graph to the chain with Bloom filters' ' test_bloom_filters_used_when_some_filters_are_missing () { log_args=$1 - bloom_trace_prefix="statistics:{\"filter_not_present\":3,\"maybe\":8,\"definitely_not\":6" + bloom_trace_prefix="statistics:{\"filter_not_present\":3,\"maybe\":6,\"definitely_not\":8" setup "$log_args" && grep -q "$bloom_trace_prefix" "$TRASH_DIRECTORY/trace.perf" && test_cmp log_wo_bloom log_w_bloom -- cgit v0.10.2-6-g49f6