t/perf: add perf tests for for-each-ref

Add performance tests for 'for-each-ref'. The tests exercise different
combinations of filters/formats/options, as well as the overall performance
of 'git for-each-ref | git cat-file --batch-check' to demonstrate the
performance difference vs. 'git for-each-ref --full-deref'.

All tests are run against a repository with 40k loose refs - 10k commits,
each having a unique:

- branch
- custom ref (refs/custom/special_*)
- annotated tag pointing at the commit
- annotated tag pointing at the other annotated tag (i.e., a nested tag)

After those tests are finished, the refs are packed with 'pack-refs --all'
and the same tests are rerun.

Signed-off-by: Victoria Dye <vdye@github.com>

t/perf/p6300-for-each-ref.sh

@@ -0,0 +1,87 @@
+#!/bin/sh
+
+test_description='performance of for-each-ref'
+. ./perf-lib.sh
+
+test_perf_fresh_repo
+
+ref_count_per_type=10000
+test_iteration_count=10
+
+test_expect_success "setup" '
+	test_commit_bulk $(( 1 + $ref_count_per_type )) &&
+
+	# Create refs
+	test_seq $ref_count_per_type |
+		sed "s,.*,update refs/heads/branch_& HEAD~&\nupdate refs/custom/special_& HEAD~&," |
+		git update-ref --stdin &&
+
+	# Create annotated tags
+	for i in $(test_seq $ref_count_per_type)
+	do
+		# Base tags
+		echo "tag tag_$i" &&
+		echo "mark :$i" &&
+		echo "from HEAD~$i" &&
+		printf "tagger %s <%s> %s\n" \
+			"$GIT_COMMITTER_NAME" \
+			"$GIT_COMMITTER_EMAIL" \
+			"$GIT_COMMITTER_DATE" &&
+		echo "data <<EOF" &&
+		echo "tag $i" &&
+		echo "EOF" &&
+
+		# Nested tags
+		echo "tag nested_$i" &&
+		echo "from :$i" &&
+		printf "tagger %s <%s> %s\n" \
+			"$GIT_COMMITTER_NAME" \
+			"$GIT_COMMITTER_EMAIL" \
+			"$GIT_COMMITTER_DATE" &&
+		echo "data <<EOF" &&
+		echo "nested tag $i" &&
+		echo "EOF" || return 1
+	done | git fast-import
+'
+
+test_for_each_ref () {
+	title="for-each-ref"
+	if test $# -gt 0; then
+		title="$title ($1)"
+		shift
+	fi
+	args="$@"
+
+	test_perf "$title" "
+		for i in \$(test_seq $test_iteration_count); do
+			git for-each-ref $args >/dev/null
+		done
+	"
+}
+
+run_tests () {
+	test_for_each_ref "$1"
+	test_for_each_ref "$1, no sort" --no-sort
+	test_for_each_ref "$1, tags" refs/tags/
+	test_for_each_ref "$1, tags, no sort" --no-sort refs/tags/
+	test_for_each_ref "$1, tags, shallow deref" '--format="%(refname) %(objectname) %(*objectname)"' refs/tags/
+	test_for_each_ref "$1, tags, shallow deref, no sort" --no-sort '--format="%(refname) %(objectname) %(*objectname)"' refs/tags/
+	test_for_each_ref "$1, tags, full deref" --full-deref '--format="%(refname) %(objectname) %(*objectname)"' refs/tags/
+	test_for_each_ref "$1, tags, full deref, no sort" --no-sort --full-deref '--format="%(refname) %(objectname) %(*objectname)"' refs/tags/
+
+	test_perf "for-each-ref ($1, tags) + cat-file --batch-check (full deref)" "
+		for i in \$(test_seq $test_iteration_count); do
+			git for-each-ref --format='%(objectname)^{} %(refname) %(objectname)' refs/tags/ | \
+				git cat-file --batch-check='%(objectname) %(rest)' >/dev/null
+		done
+	"
+}
+
+run_tests "loose"
+
+test_expect_success 'pack refs' '
+	git pack-refs --all
+'
+run_tests "packed"
+
+test_done