ReadWrite: faster Has() by using the in-memory index instead of reading on disk

[MichaelMure]

Before:
BenchmarkHas-12 205046 6404 ns/op 744 B/op 16 allocs/op

After
BenchmarkHas-12 2354449 481.3 ns/op 160 B/op 3 allocs/op

func BenchmarkHas(b *testing.B) {
	ctx := context.TODO()

	path := filepath.Join(b.TempDir(), "bench-large-v2.car")
	generateRandomCarV2File(b, path, 200<<20) // 10 MiB
	defer os.Remove(path)

	subject, err := blockstore.OpenReadWrite(path, nil)

	c, err := subject.AllKeysChan(ctx)
	require.NoError(b, err)

	var allCids []cid.Cid

	for c2 := range c {
		allCids = append(allCids, c2)
	}

	b.ReportAllocs()
	b.ResetTimer()

	var idx int
	for i := 0; i < b.N; i++ {
		_, _ = subject.Has(ctx, allCids[idx])
		// require.NoError(b, err)
		// require.True(b, has)
		idx = (idx + 1) % len(allCids)
	}
}

[MichaelMure]

I keep falling into the same trap. go.mod files act as boundaries for tests, so if your run tests from the root of that package, the whole /v2 is not tested ...

[MichaelMure]

Before

BenchmarkHas-8 190216 6368 ns/op 744 B/op 16 allocs/op

After

BenchmarkHas-8 1419169 845.6 ns/op 320 B/op 6 allocs/op

7.5x faster, 2.32x less allocation. That's still 6 allocations due to decoding multihashes and friends, there might be a better way.

[rvagg]

👌