git/t/t4216-log-bloom.sh
Derrick Stolee b16a827764 bloom/diff: properly short-circuit on max_changes
Commit e3696980 (diff: halt tree-diff early after max_changes,
2020-03-30) intended to create a mechanism to short-circuit a diff
calculation after a certain number of paths were modified. By
incrementing a "num_changes" counter throughout the recursive
ll_diff_tree_paths(), this was supposed to match the number of changes
that would be written into the changed-path Bloom filters.
Unfortunately, this was not implemented correctly and instead misses
simple cases like file modifications. This then does not stop very
large changed-path filters from being written (unless they add or remove
many files).

To start, change the implementation in ll_diff_tree_paths() to instead
use the global diff_queue_diff struct's 'nr' member as the count. This
is a way to simplify the logic instead of making more mistakes in the
complicated diff code.

This has a drawback: the diff_queue_diff struct only lists the paths
corresponding to blob changes, not their leading directories. Thus,
get_or_compute_bloom_filter() needs an additional check to see if the
hashmap with the leading directories becomes too large.

One reason why this was not caught by test cases was that the test in
t4216-log-bloom.sh that was supposed to check this "too many changes"
condition only checked this on the initial commit of a repository. The
old logic counted these values correctly. Update this test in a few
ways:

1. Use GIT_TEST_BLOOM_SETTINGS_MAX_CHANGED_PATHS to reduce the limit,
   allowing smaller commits to engage with this logic.

2. Create several interesting cases of edits, adds, removes, and mode
   changes (in the second commit). By testing both sides of the
   inequality with the *_MAX_CHANGED_PATHS variable, we can see that
   the count is exactly correct, so none of these changes are missed
   or over-counted.

3. Use the trace2 data value filter_found_large to verify that these
   commits are on the correct side of the limit.

Another way to verify the behavior is correct is through performance
tests. By testing on my local copies of the Git repository and the Linux
kernel repository, I could measure the effect of these short-circuits
when computing a fresh commit-graph file with changed-path Bloom filters
using the command

  GIT_TEST_BLOOM_SETTINGS_MAX_CHANGED_PATHS=N time \
    git commit-graph write --reachable --changed-paths

and reporting the wall time and resulting commit-graph size.

For Git, the results are

|        |      N=1       |       N=10     |      N=512     |
|--------|----------------|----------------|----------------|
| HEAD~1 | 10.90s  9.18MB | 11.11s  9.34MB | 11.31s  9.35MB |
| HEAD   |  9.21s  8.62MB | 11.11s  9.29MB | 11.29s  9.34MB |

For Linux, the results are

|        |       N=1      |     N=20      |     N=512     |
|--------|----------------|---------------|---------------|
| HEAD~1 | 61.28s  64.3MB | 76.9s  72.6MB | 77.6s  72.6MB |
| HEAD   | 49.44s  56.3MB | 68.7s  65.9MB | 69.2s  65.9MB |

Naturally, the improvement becomes much less as the limit grows, as
fewer commits satisfy the short-circuit.

Reported-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-09-17 09:31:25 -07:00

282 lines
8.4 KiB
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Executable file

#!/bin/sh
test_description='git log for a path with Bloom filters'
. ./test-lib.sh
GIT_TEST_COMMIT_GRAPH=0
GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
test_expect_success 'setup test - repo, commits, commit graph, log outputs' '
git init &&
mkdir A A/B A/B/C &&
test_commit c1 A/file1 &&
test_commit c2 A/B/file2 &&
test_commit c3 A/B/C/file3 &&
test_commit c4 A/file1 &&
test_commit c5 A/B/file2 &&
test_commit c6 A/B/C/file3 &&
test_commit c7 A/file1 &&
test_commit c8 A/B/file2 &&
test_commit c9 A/B/C/file3 &&
test_commit c10 file_to_be_deleted &&
git checkout -b side HEAD~4 &&
test_commit side-1 file4 &&
git checkout master &&
git merge side &&
test_commit c11 file5 &&
mv file5 file5_renamed &&
git add file5_renamed &&
git commit -m "rename" &&
rm file_to_be_deleted &&
git add . &&
git commit -m "file removed" &&
git commit-graph write --reachable --changed-paths
'
graph_read_expect () {
NUM_CHUNKS=5
cat >expect <<- EOF
header: 43475048 1 1 $NUM_CHUNKS 0
num_commits: $1
chunks: oid_fanout oid_lookup commit_metadata bloom_indexes bloom_data
EOF
test-tool read-graph >actual &&
test_cmp expect actual
}
test_expect_success 'commit-graph write wrote out the bloom chunks' '
graph_read_expect 15
'
# Turn off any inherited trace2 settings for this test.
sane_unset GIT_TRACE2 GIT_TRACE2_PERF GIT_TRACE2_EVENT
sane_unset GIT_TRACE2_PERF_BRIEF
sane_unset GIT_TRACE2_CONFIG_PARAMS
setup () {
rm -f "$TRASH_DIRECTORY/trace.perf" &&
git -c core.commitGraph=false log --pretty="format:%s" $1 >log_wo_bloom &&
GIT_TRACE2_PERF="$TRASH_DIRECTORY/trace.perf" git -c core.commitGraph=true log --pretty="format:%s" $1 >log_w_bloom
}
test_bloom_filters_used () {
log_args=$1
bloom_trace_prefix="statistics:{\"filter_not_present\":${2:-0},\"maybe\""
setup "$log_args" &&
grep -q "$bloom_trace_prefix" "$TRASH_DIRECTORY/trace.perf" &&
test_cmp log_wo_bloom log_w_bloom &&
test_path_is_file "$TRASH_DIRECTORY/trace.perf"
}
test_bloom_filters_not_used () {
log_args=$1
setup "$log_args" &&
! grep -q "statistics:{\"filter_not_present\":" "$TRASH_DIRECTORY/trace.perf" &&
test_cmp log_wo_bloom log_w_bloom
}
for path in A A/B A/B/C A/file1 A/B/file2 A/B/C/file3 file4 file5 file5_renamed file_to_be_deleted
do
for option in "" \
"--all" \
"--full-history" \
"--full-history --simplify-merges" \
"--simplify-merges" \
"--simplify-by-decoration" \
"--follow" \
"--first-parent" \
"--topo-order" \
"--date-order" \
"--author-date-order" \
"--ancestry-path side..master"
do
test_expect_success "git log option: $option for path: $path" '
test_bloom_filters_used "$option -- $path" &&
test_config commitgraph.readChangedPaths false &&
test_bloom_filters_not_used "$option -- $path"
'
done
done
test_expect_success 'git log -- folder works with and without the trailing slash' '
test_bloom_filters_used "-- A" &&
test_bloom_filters_used "-- A/"
'
test_expect_success 'git log for path that does not exist. ' '
test_bloom_filters_used "-- path_does_not_exist"
'
test_expect_success 'git log with --walk-reflogs does not use Bloom filters' '
test_bloom_filters_not_used "--walk-reflogs -- A"
'
test_expect_success 'git log -- multiple path specs does not use Bloom filters' '
test_bloom_filters_not_used "-- file4 A/file1"
'
test_expect_success 'git log -- "." pathspec at root does not use Bloom filters' '
test_bloom_filters_not_used "-- ."
'
test_expect_success 'git log with wildcard that resolves to a single path uses Bloom filters' '
test_bloom_filters_used "-- *4" &&
test_bloom_filters_used "-- *renamed"
'
test_expect_success 'git log with wildcard that resolves to a multiple paths does not uses Bloom filters' '
test_bloom_filters_not_used "-- *" &&
test_bloom_filters_not_used "-- file*"
'
test_expect_success 'setup - add commit-graph to the chain without Bloom filters' '
test_commit c14 A/anotherFile2 &&
test_commit c15 A/B/anotherFile2 &&
test_commit c16 A/B/C/anotherFile2 &&
git commit-graph write --reachable --split --no-changed-paths &&
test_line_count = 2 .git/objects/info/commit-graphs/commit-graph-chain
'
test_expect_success 'use Bloom filters even if the latest graph does not have Bloom filters' '
# Ensure that the number of empty filters is equal to the number of
# filters in the latest graph layer to prove that they are loaded (and
# ignored).
test_bloom_filters_used "-- A/B" 3
'
test_expect_success 'setup - add commit-graph to the chain with Bloom filters' '
test_commit c17 A/anotherFile3 &&
git commit-graph write --reachable --changed-paths --split &&
test_line_count = 3 .git/objects/info/commit-graphs/commit-graph-chain
'
test_bloom_filters_used_when_some_filters_are_missing () {
log_args=$1
bloom_trace_prefix="statistics:{\"filter_not_present\":3,\"maybe\":6,\"definitely_not\":8"
setup "$log_args" &&
grep -q "$bloom_trace_prefix" "$TRASH_DIRECTORY/trace.perf" &&
test_cmp log_wo_bloom log_w_bloom
}
test_expect_success 'Use Bloom filters if they exist in the latest but not all commit graphs in the chain.' '
test_bloom_filters_used_when_some_filters_are_missing "-- A/B"
'
test_expect_success 'persist filter settings' '
test_when_finished rm -rf .git/objects/info/commit-graph* &&
rm -rf .git/objects/info/commit-graph* &&
GIT_TRACE2_EVENT="$(pwd)/trace2.txt" \
GIT_TRACE2_EVENT_NESTING=5 \
GIT_TEST_BLOOM_SETTINGS_NUM_HASHES=9 \
GIT_TEST_BLOOM_SETTINGS_BITS_PER_ENTRY=15 \
git commit-graph write --reachable --changed-paths &&
grep "{\"hash_version\":1,\"num_hashes\":9,\"bits_per_entry\":15,\"max_changed_paths\":512" trace2.txt &&
GIT_TRACE2_EVENT="$(pwd)/trace2-auto.txt" \
GIT_TRACE2_EVENT_NESTING=5 \
git commit-graph write --reachable --changed-paths &&
grep "{\"hash_version\":1,\"num_hashes\":9,\"bits_per_entry\":15,\"max_changed_paths\":512" trace2-auto.txt
'
test_max_changed_paths () {
grep "\"max_changed_paths\":$1" $2
}
test_filter_computed () {
grep "\"key\":\"filter-computed\",\"value\":\"$1\"" $2
}
test_filter_trunc_large () {
grep "\"key\":\"filter-trunc-large\",\"value\":\"$1\"" $2
}
test_expect_success 'correctly report changes over limit' '
git init limits &&
(
cd limits &&
mkdir d &&
mkdir d/e &&
for i in $(test_seq 1 2)
do
printf $i >d/file$i.txt &&
printf $i >d/e/file$i.txt || return 1
done &&
mkdir mode &&
printf bash >mode/script.sh &&
mkdir foo &&
touch foo/bar &&
touch foo.txt &&
git add d foo foo.txt mode &&
git commit -m "files" &&
# Commit has 7 file and 4 directory adds
GIT_TEST_BLOOM_SETTINGS_MAX_CHANGED_PATHS=10 \
GIT_TRACE2_EVENT="$(pwd)/trace" \
git commit-graph write --reachable --changed-paths &&
test_max_changed_paths 10 trace &&
test_filter_computed 1 trace &&
test_filter_trunc_large 1 trace &&
for path in $(git ls-tree -r --name-only HEAD)
do
git -c commitGraph.readChangedPaths=false log \
-- $path >expect &&
git log -- $path >actual &&
test_cmp expect actual || return 1
done &&
# Make a variety of path changes
printf new1 >d/e/file1.txt &&
printf new2 >d/file2.txt &&
rm d/e/file2.txt &&
rm -r foo &&
printf text >foo &&
mkdir f &&
printf new1 >f/file1.txt &&
# including a mode-only change (counts as modified)
git update-index --chmod=+x mode/script.sh &&
git add foo d f &&
git commit -m "complicated" &&
# start from scratch and rebuild
rm -f .git/objects/info/commit-graph &&
GIT_TEST_BLOOM_SETTINGS_MAX_CHANGED_PATHS=10 \
GIT_TRACE2_EVENT="$(pwd)/trace-edit" \
git commit-graph write --reachable --changed-paths &&
test_max_changed_paths 10 trace-edit &&
test_filter_computed 2 trace-edit &&
test_filter_trunc_large 2 trace-edit &&
for path in $(git ls-tree -r --name-only HEAD)
do
git -c commitGraph.readChangedPaths=false log \
-- $path >expect &&
git log -- $path >actual &&
test_cmp expect actual || return 1
done &&
# start from scratch and rebuild
rm -f .git/objects/info/commit-graph &&
GIT_TEST_BLOOM_SETTINGS_MAX_CHANGED_PATHS=11 \
GIT_TRACE2_EVENT="$(pwd)/trace-update" \
git commit-graph write --reachable --changed-paths &&
test_max_changed_paths 11 trace-update &&
test_filter_computed 2 trace-update &&
test_filter_trunc_large 0 trace-update &&
for path in $(git ls-tree -r --name-only HEAD)
do
git -c commitGraph.readChangedPaths=false log \
-- $path >expect &&
git log -- $path >actual &&
test_cmp expect actual || return 1
done
)
'
test_done