GODRIVER-1563 Reduce allocations in bsoncore.Document.LookupErr (#376)

bartle-stripe · web-flow · commit 5e7e89cbca40 · 2020-04-20T13:07:25.000-04:00
diff --git a/benchmark/harness.go b/benchmark/harness.go
@@ -38,6 +38,7 @@ func WrapCase(bench BenchCase) BenchFunction {
 	return func(b *testing.B) {
 		ctx := context.Background()
 		b.ResetTimer()
+		b.ReportAllocs()
 		err := bench(ctx, b, b.N)
 		require.NoError(b, err, "case='%s'", name)
 	}
diff --git a/x/bsonx/bsoncore/document.go b/x/bsonx/bsoncore/document.go
@@ -181,7 +181,8 @@ func (d Document) LookupErr(key ...string) (Value, error) {
 		if !ok {
 			return Value{}, NewInsufficientBytesError(d, rem)
 		}
-		if elem.Key() != key[0] {
+		// We use `KeyBytes` rather than `Key` to avoid a needless string alloc.
+		if string(elem.KeyBytes()) != key[0] {
 			continue
 		}
 		if len(key) > 1 {

Original file line number	Diff line number	Diff line change
`@@ -38,6 +38,7 @@ func WrapCase(bench BenchCase) BenchFunction {`
`38`	`38`	`return func(b *testing.B) {`
`39`	`39`	`ctx := context.Background()`
`40`	`40`	`b.ResetTimer()`
	`41`	`+ b.ReportAllocs()`
`41`	`42`	`err := bench(ctx, b, b.N)`
`42`	`43`	`require.NoError(b, err, "case='%s'", name)`
`43`	`44`	`}`
Original file line number	Diff line number	Diff line change
`@@ -181,7 +181,8 @@ func (d Document) LookupErr(key ...string) (Value, error) {`
`181`	`181`	`if !ok {`
`182`	`182`	`return Value{}, NewInsufficientBytesError(d, rem)`
`183`	`183`	`}`
`184`		`- if elem.Key() != key[0] {`
	`184`	+ // We use `KeyBytes` rather than `Key` to avoid a needless string alloc.
	`185`	`+ if string(elem.KeyBytes()) != key[0] {`
`185`	`186`	`continue`
`186`	`187`	`}`
`187`	`188`	`if len(key) > 1 {`