need help on TestHLLTC_Merge_Complex

[imacks]

I need a bit of help following TestHLLTC_Merge_Complex in hyperloglog_test.go:

Lines 374 and 384: why is ratio calculated against sk1?

Lines 391 and 395: I tried inserting the 500000 records into sk2 and then merge with empty sk3, like in the source. This gives me a ratio of about 1.18%. I made another version where the 500000 records were inserted into sk3, and then merge with sk2. This gets me 6.52%. Shouldn't they be the same?

My code for ref:

func TestHLLTC_Merge_Complex(t *testing.T) {
	sk1, err := newSketch(14, true)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	sk2, err := newSketch(14, true)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	sk3, err := newSketch(14, true)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	// sk1 will contain flow-[1..10000000]
	// sk2 will contain flow-[2,4,...10000000]
	unique := map[string]bool{}
	for i := 1; len(unique) <= 10000000; i++ {
		str := fmt.Sprintf("flow-%d", i)
		sk1.Insert([]byte(str))
		if i%2 == 0 {
			sk2.Insert([]byte(str))
		}
		unique[str] = true
	}

	// sk1
	exact1 := uint64(len(unique))
	res1 := uint64(sk1.Estimate())
	ratio := 100*estimateError(res1, exact1)
	if ratio > 2 {
		t.Errorf("exact %d, got %d which is %.2f%% error", exact1, res1, ratio)
	}
	t.Logf("sk1 estimate %d; exact %d (%.2f%% err)", res1, exact1, ratio)

	// sk2
	exact2 := uint64(len(unique))/2
	res2 := uint64(sk2.Estimate())
	ratio = 100*estimateError(res2, exact2)
	if ratio > 2 {
		t.Errorf("exact %d, got %d which is %.2f%% error", exact2, res2, ratio)
	}
	t.Logf("sk2 estimate %d; exact %d (%.2f%% err)", res2, exact2, ratio)

	// sk2 merge sk1
	if err := sk2.Merge(sk1); err != nil {
		t.Errorf("unexpected error: %v", err)
	}
	exact2 = uint64(len(unique))
	res2 = uint64(sk2.Estimate())
	ratio = 100*estimateError(res2, exact2)
	if ratio > 2 {
		t.Errorf("exact %d, got %d which is %.2f%% error", exact2, res2, ratio)
	}
	t.Logf("sk2 merge sk1 estimate %d; exact %d (%.2f%% err)", res2, exact2, ratio)

	for i := 1; i <= 500000; i++ {
		str := fmt.Sprintf("stream-%d", i)
		sk3.Insert([]byte(str)) // also try sk2.Insert(...)
		unique[str] = true
	}
	/*
	exact3 := uint64(500000)
	res3 := uint64(sk3.Estimate())
	ratio = 100*estimateError(res3, exact3)
	if ratio > 2 {
		t.Errorf("exact %d, got %d which is %.2f%% error", exact3, res3, ratio)
	}
	t.Logf("sk3 estimate %d; exact %d (%.2f%% err)", res3, exact3, ratio)
	*/

	// sk2 merge sk3
	if err := sk2.Merge(sk3); err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	exact2 = uint64(len(unique))
	res2 = uint64(sk2.Estimate())
	ratio = 100*estimateError(res2, exact2)
	if ratio > 2 {
		t.Errorf("exact %d, got %d which is %.2f%% error", exact2, res2, ratio)
	}
	t.Logf("sk2 merge sk3 estimate %d; exact %d (%.2f%% err)", res2, exact2, ratio)
}