Mini-benchmark for indexed blob. (#8440)

app/bin/tools/indexed_blob_benchmark.dart

@@ -0,0 +1,55 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:indexed_blob/indexed_blob.dart';
+import 'package:path/path.dart' as p;
+import 'package:pub_dev/shared/utils.dart';
+
+/// Runs a synthetic benchmark by creating and index file, loading it and running
+/// lookup multiple times.
+///
+/// Note: these are some non-representative numbers from local benchmarking, for future reference:
+/// 27.826 index bytes/entry.
+/// 0.0647 ms/(load+lookup)
+/// 0.060964 ms/lookup
+Future<void> main() async {
+  final index = await withTempDirectory((dir) async {
+    final blobFile = File(p.join(dir.path, 'blob.data'));
+    final builder = IndexedBlobBuilder(blobFile.openWrite());
+    for (var i = 0; i < 1000; i++) {
+      await builder.addFile('doc/$i.html', Stream.value(List.filled(2000, 0)));
+    }
+    final index = await builder.buildIndex('123');
+
+    final blobIndex = File(p.join(dir.path, 'blob.index'));
+    await blobIndex.writeAsBytes(index.asBytes());
+
+    print('${blobIndex.lengthSync() / 1000} index bytes/entry.');
+
+    final bytes = await blobIndex.readAsBytes();
+    final loadSw = Stopwatch()..start();
+    for (var r = 0; r < 10000; r++) {
+      final x = BlobIndex.fromBytes(bytes);
+      final r = x.lookup('doc/555.html');
+      r!.start;
+      x.lookup('doc/555.txt');
+    }
+    loadSw.stop();
+    print('${loadSw.elapsedMilliseconds / 10000} ms/(load+lookup)');
+
+    return index;
+  });
+
+  final lookupSw = Stopwatch()..start();
+  for (var r = 0; r < 1000; r++) {
+    for (var i = 0; i < 1000; i++) {
+      index.lookup('doc/$i.html');
+      index.lookup('doc/$i.txt');
+    }
+  }
+  lookupSw.stop();
+  print('${lookupSw.elapsed.inMilliseconds / 1000 / 1000} ms/lookup');
+}