update: add benchmark test

benchmark result:
(1) master branch
$ go test -bench='BenchmarkIndexPut$' -count=5
goos: darwin
goarch: amd64
pkg: go.etcd.io/etcd/server/v3/storage/mvcc
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkIndexPut-12             1000000              2591 ns/op
BenchmarkIndexPut-12             1000000              2531 ns/op
BenchmarkIndexPut-12             1000000              2536 ns/op
BenchmarkIndexPut-12             1000000              2546 ns/op
BenchmarkIndexPut-12             1000000              2538 ns/op
PASS
ok      go.etcd.io/etcd/server/v3/storage/mvcc  167.439s

$ go test -bench='BenchmarkIndexGet$' -count=5
goos: darwin
goarch: amd64
pkg: go.etcd.io/etcd/server/v3/storage/mvcc
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkIndexGet-12             1000000              2021 ns/op
BenchmarkIndexGet-12             1000000              2029 ns/op
BenchmarkIndexGet-12             1000000              2044 ns/op
BenchmarkIndexGet-12             1000000              1973 ns/op
BenchmarkIndexGet-12             1000000              2027 ns/op
PASS
ok      go.etcd.io/etcd/server/v3/storage/mvcc  177.815s

(2) google/btree in the generic way
$ go test -bench='BenchmarkIndexPut$' -count=5
goos: darwin
goarch: amd64
pkg: go.etcd.io/etcd/server/v3/storage/mvcc
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkIndexPut-12             1000000              2477 ns/op
BenchmarkIndexPut-12             1000000              2380 ns/op
BenchmarkIndexPut-12             1000000              2360 ns/op
BenchmarkIndexPut-12             1000000              2396 ns/op
BenchmarkIndexPut-12             1000000              2382 ns/op
PASS
ok      go.etcd.io/etcd/server/v3/storage/mvcc  165.841s

$ go test -bench='BenchmarkIndexGet$' -count=5
goos: darwin
goarch: amd64
pkg: go.etcd.io/etcd/server/v3/storage/mvcc
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkIndexGet-12             1000000              1985 ns/op
BenchmarkIndexGet-12             1000000              1914 ns/op
BenchmarkIndexGet-12             1000000              1900 ns/op
BenchmarkIndexGet-12             1000000              1905 ns/op
BenchmarkIndexGet-12             1000000              1894 ns/op
PASS
ok      go.etcd.io/etcd/server/v3/storage/mvcc  177.573s

Signed-off-by: wathenjiang <wathenjiang@tencent.com>

server/storage/mvcc/index_bench_test.go

@@ -40,3 +40,30 @@ func benchmarkIndexCompact(b *testing.B, size int) {
 		kvindex.Compact(int64(i))
 	}
 }
+
+func BenchmarkIndexPut(b *testing.B) {
+	log := zap.NewNop()
+	kvindex := newTreeIndex(log)
+
+	bytesN := 64
+	keys := createBytesSlice(bytesN, b.N)
+	b.ResetTimer()
+	for i := 1; i < b.N; i++ {
+		kvindex.Put(keys[i], revision{main: int64(i), sub: int64(i)})
+	}
+}
+
+func BenchmarkIndexGet(b *testing.B) {
+	log := zap.NewNop()
+	kvindex := newTreeIndex(log)
+
+	bytesN := 64
+	keys := createBytesSlice(bytesN, b.N)
+	for i := 1; i < b.N; i++ {
+		kvindex.Put(keys[i], revision{main: int64(i), sub: int64(i)})
+	}
+	b.ResetTimer()
+	for i := 1; i < b.N; i++ {
+		kvindex.Get(keys[i], int64(i))
+	}
+}