fix(multipart): defer persistent listing from public requests

Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/erasure-multipart-listing-benchmark_test.go

@@ -14,7 +14,7 @@ import (
 // Run explicitly with -benchtime=1x. Fixture creation is excluded from timing;
 // each request still discovers real on-disk metadata. The 16-drive/10k case
 // deliberately exceeds the existing aggregate directory-entry budget.
-func BenchmarkMultipartListingCapacity(b *testing.B) {
+func BenchmarkMultipartDiagnosticScanCapacity(b *testing.B) {
 	for _, tc := range []struct {
 		drives, uploads int
 		mixed, limited  bool
@@ -67,7 +67,7 @@ func BenchmarkMultipartListingCapacity(b *testing.B) {
 			}
 			b.ResetTimer()
 			for range b.N {
-				got, err := z.ListMultipartUploads(b.Context(), bucket, "dir/", "", "", "", 1000)
+				got, err := z.scanMultipartUploadsForTest(b.Context(), bucket, "dir/", "", "", "", 1000)
 				if tc.limited {
 					var limited SlowDown
 					if !errors.As(err, &limited) || len(got.Uploads) != 0 {
@@ -83,3 +83,88 @@ func BenchmarkMultipartListingCapacity(b *testing.B) {
 		})
 	}
 }
+
+// The public path is measured with a populated cache as well as after cache
+// loss. An empty post-restart response alone is not capacity acceptance.
+func BenchmarkMultipartPublicListingCapacity(b *testing.B) {
+	for _, tc := range []struct {
+		drives, uploads int
+		sameKey         bool
+	}{
+		{4, 10_000, false},
+		{16, 3_126, false},
+		{16, 10_000, true},
+	} {
+		b.Run(fmt.Sprintf("drives=%d/uploads=%d/same-key=%t", tc.drives, tc.uploads, tc.sameKey), func(b *testing.B) {
+			obj, dirs, err := prepareErasure(b.Context(), tc.drives)
+			if err != nil {
+				b.Fatal(err)
+			}
+			z := obj.(*erasureServerPools)
+			b.Cleanup(func() { z.Shutdown(context.Background()); removeRoots(dirs) })
+			const bucket, other = "multipart-public-capacity", "multipart-public-other"
+			for _, name := range []string{bucket, other} {
+				if err := z.MakeBucket(b.Context(), name, MakeBucketOptions{}); err != nil {
+					b.Fatal(err)
+				}
+			}
+			wantCached, wantExact := 0, 1
+			for n := range tc.uploads {
+				target, key := bucket, fmt.Sprintf("dir/%05d", n)
+				if tc.sameKey {
+					key = "dir/00000"
+				} else if n%2 != 0 {
+					target = other
+				}
+				if target == bucket {
+					wantCached++
+				}
+				if _, err := z.NewMultipartUpload(b.Context(), target, key, ObjectOptions{}); err != nil {
+					b.Fatal(err)
+				}
+			}
+			if tc.sameKey {
+				wantExact = 1000
+			}
+			if tc.drives == 16 && !tc.sameKey {
+				_, err := z.scanMultipartUploadsForTest(b.Context(), bucket, "", "", "", "", 1000)
+				var limited SlowDown
+				if !errors.As(err, &limited) {
+					b.Fatalf("fixture did not reproduce the previous global budget failure: %v", err)
+				}
+			}
+			var directoryCalls, metadataCalls atomic.Int64
+			for _, set := range z.serverPools[0].sets {
+				original := set.getDisks
+				set.getDisks = func() []StorageAPI {
+					disks := append([]StorageAPI(nil), original()...)
+					for i, disk := range disks {
+						disks[i] = multipartListingCountingDisk{disk, &directoryCalls, &metadataCalls}
+					}
+					return disks
+				}
+				b.Cleanup(func() { set.getDisks = original })
+			}
+			measure := func(name, prefix string, want int) {
+				b.Run(name, func(b *testing.B) {
+					directoryCalls.Store(0)
+					metadataCalls.Store(0)
+					b.ResetTimer()
+					for range b.N {
+						got, err := z.ListMultipartUploads(b.Context(), bucket, prefix, "", "", "", 1000)
+						if err != nil || len(got.Uploads) != want {
+							b.Fatalf("public listing: count=%d want=%d err=%v", len(got.Uploads), want, err)
+						}
+					}
+					b.StopTimer()
+					b.ReportMetric(float64(directoryCalls.Load())/float64(b.N), "ListDir/op")
+					b.ReportMetric(float64(metadataCalls.Load())/float64(b.N), "ReadVersion/op")
+				})
+			}
+			measure("populated-cache", "", wantCached)
+			z.mpCache.Clear()
+			measure("lost-cache", "", 0)
+			measure("known-key", "dir/00000", wantExact)
+		})
+	}
+}