Perfomance: Add preallocation for some slices (#61632)

pkg/codegen/jenny_docs.go

@@ -324,11 +324,10 @@ func printProperties(w io.Writer, s *schema) {
 	table.SetAutoWrapText(false)
 
 	// Buffer all property rows so that we can sort them before printing them.
-	var rows [][]string
-
+	rows := make([][]string, 0, len(s.Properties))
 	for k, p := range s.Properties {
 		// Generate relative links for objects and arrays of objects.
-		var propType []string
+		propType := make([]string, 0, len(p.Type))
 		for _, pt := range p.Type {
 			switch pt {
 			case PropertyTypeObject:
@@ -372,7 +371,7 @@ func printProperties(w io.Writer, s *schema) {
 		desc := p.Description
 
 		if len(p.Enum) > 0 {
-			var vals []string
+			vals := make([]string, 0, len(p.Enum))
 			for _, e := range p.Enum {
 				vals = append(vals, e.String())
 			}

pkg/setting/setting.go

@@ -1777,8 +1777,8 @@ func (cfg *Cfg) readDataSourcesSettings() {
 }
 
 func GetAllowedOriginGlobs(originPatterns []string) ([]glob.Glob, error) {
-	var originGlobs []glob.Glob
 	allowedOrigins := originPatterns
+	originGlobs := make([]glob.Glob, 0, len(allowedOrigins))
 	for _, originPattern := range allowedOrigins {
 		g, err := glob.Compile(originPattern)
 		if err != nil {

pkg/tsdb/cloudmonitoring/cloudmonitoring.go

@@ -380,7 +380,7 @@ func queryModel(query backend.DataQuery) (grafanaQuery, error) {
 }
 
 func (s *Service) buildQueryExecutors(logger log.Logger, req *backend.QueryDataRequest) ([]cloudMonitoringQueryExecutor, error) {
-	var cloudMonitoringQueryExecutors []cloudMonitoringQueryExecutor
+	cloudMonitoringQueryExecutors := make([]cloudMonitoringQueryExecutor, 0, len(req.Queries))
 	startTime := req.Queries[0].TimeRange.From
 	endTime := req.Queries[0].TimeRange.To
 	durationSeconds := int(endTime.Sub(startTime).Seconds())

pkg/tsdb/cloudwatch/models/cloudwatch_query.go

@@ -248,7 +248,7 @@ func ParseMetricDataQueries(dataQueries []backend.DataQuery, startTime time.Time
 		metricDataQueries[query.RefID] = metricsDataQuery
 	}
 
-	var result []*CloudWatchQuery
+	result := make([]*CloudWatchQuery, 0, len(metricDataQueries))
 	for refId, mdq := range metricDataQueries {
 		cwQuery := &CloudWatchQuery{
 			logger:            logger,

pkg/tsdb/elasticsearch/parse_query.go

@@ -46,8 +46,9 @@ func parseQuery(tsdbQuery []backend.DataQuery) ([]*Query, error) {
 
 func parseBucketAggs(model *simplejson.Json) ([]*BucketAgg, error) {
 	var err error
-	var result []*BucketAgg
-	for _, t := range model.Get("bucketAggs").MustArray() {
+	bucketAggs := model.Get("bucketAggs").MustArray()
+	result := make([]*BucketAgg, 0, len(bucketAggs))
+	for _, t := range bucketAggs {
 		aggJSON := simplejson.NewFromAny(t)
 		agg := &BucketAgg{}
 
@@ -71,8 +72,9 @@ func parseBucketAggs(model *simplejson.Json) ([]*BucketAgg, error) {
 
 func parseMetrics(model *simplejson.Json) ([]*MetricAgg, error) {
 	var err error
-	var result []*MetricAgg
-	for _, t := range model.Get("metrics").MustArray() {
+	metrics := model.Get("metrics").MustArray()
+	result := make([]*MetricAgg, 0, len(metrics))
+	for _, t := range metrics {
 		metricJSON := simplejson.NewFromAny(t)
 		metric := &MetricAgg{}
 

pkg/tsdb/influxdb/influxdb.go

@@ -101,7 +101,7 @@ func (s *Service) QueryData(ctx context.Context, req *backend.QueryDataRequest)
 	logger.Debug("Making a non-Flux type query")
 
 	var allRawQueries string
-	var queries []Query
+	queries := make([]Query, 0, len(req.Queries))
 
 	for _, reqQuery := range req.Queries {
 		query, err := s.queryParser.Parse(reqQuery)

pkg/tsdb/influxdb/model_parser.go

@@ -70,9 +70,10 @@ func (qp *InfluxdbQueryParser) Parse(query backend.DataQuery) (*Query, error) {
 }
 
 func (qp *InfluxdbQueryParser) parseSelects(model *simplejson.Json) ([]*Select, error) {
-	var result []*Select
+	selectObjs := model.Get("select").MustArray()
+	result := make([]*Select, 0, len(selectObjs))
 
-	for _, selectObj := range model.Get("select").MustArray() {
+	for _, selectObj := range selectObjs {
 		selectJson := simplejson.NewFromAny(selectObj)
 		var parts Select
 
@@ -93,8 +94,9 @@ func (qp *InfluxdbQueryParser) parseSelects(model *simplejson.Json) ([]*Select,
 }
 
 func (*InfluxdbQueryParser) parseTags(model *simplejson.Json) ([]*Tag, error) {
-	var result []*Tag
-	for _, t := range model.Get("tags").MustArray() {
+	tags := model.Get("tags").MustArray()
+	result := make([]*Tag, 0, len(tags))
+	for _, t := range tags {
 		tagJson := simplejson.NewFromAny(t)
 		tag := &Tag{}
 		var err error
@@ -159,8 +161,9 @@ func (*InfluxdbQueryParser) parseQueryPart(model *simplejson.Json) (*QueryPart,
 }
 
 func (qp *InfluxdbQueryParser) parseGroupBy(model *simplejson.Json) ([]*QueryPart, error) {
-	var result []*QueryPart
-	for _, groupObj := range model.Get("groupBy").MustArray() {
+	groupBy := model.Get("groupBy").MustArray()
+	result := make([]*QueryPart, 0, len(groupBy))
+	for _, groupObj := range groupBy {
 		groupJson := simplejson.NewFromAny(groupObj)
 		queryPart, err := qp.parseQueryPart(groupJson)
 		if err != nil {

pkg/tsdb/influxdb/query.go

@@ -44,7 +44,7 @@ func (query *Query) Build(queryContext *backend.QueryDataRequest) (string, error
 }
 
 func (query *Query) renderTags() []string {
-	var res []string
+	res := make([]string, 0, len(query.Tags))
 	for i, tag := range query.Tags {
 		str := ""
 
@@ -91,7 +91,7 @@ func (query *Query) renderTimeFilter(queryContext *backend.QueryDataRequest) str
 func (query *Query) renderSelectors(queryContext *backend.QueryDataRequest) string {
 	res := "SELECT "
 
-	var selectors []string
+	selectors := make([]string, 0, len(query.Selects))
 	for _, sel := range query.Selects {
 		stk := ""
 		for _, s := range *sel {

pkg/tsdb/influxdb/response_parser.go

@@ -189,7 +189,7 @@ func formatFrameName(row Row, column string, query Query) string {
 }
 
 func buildFrameNameFromQuery(row Row, column string) string {
-	var tags []string
+	tags := make([]string, 0, len(row.Tags))
 	for k, v := range row.Tags {
 		tags = append(tags, fmt.Sprintf("%s: %s", k, v))
 	}

pkg/tsdb/loki/frame.go

@@ -178,7 +178,7 @@ func makeIdField(stringTimeField *data.Field, lineField *data.Field, labelsField
 }
 
 func formatNamePrometheusStyle(labels map[string]string) string {
-	var parts []string
+	parts := make([]string, 0, len(labels))
 
 	for k, v := range labels {
 		parts = append(parts, fmt.Sprintf("%s=%q", k, v))

pkg/tsdb/parca/query.go

@@ -142,7 +142,7 @@ type Node struct {
 }
 
 func walkTree(tree *v1alpha1.FlamegraphRootNode, fn func(level int64, value int64, name string, self int64)) {
-	var stack []*Node
+	stack := make([]*Node, 0, len(tree.Children))
 	var childrenValue int64 = 0
 
 	for _, child := range tree.Children {
@@ -217,7 +217,7 @@ func normalizeUnit(unit string) string {
 }
 
 func seriesToDataFrame(seriesResp *connect.Response[v1alpha1.QueryRangeResponse], profileTypeID string) []*data.Frame {
-	var frames []*data.Frame
+	frames := make([]*data.Frame, 0, len(seriesResp.Msg.Series))
 
 	for _, series := range seriesResp.Msg.Series {
 		frame := data.NewFrame("series")

pkg/tsdb/parca/resources.go

@@ -28,7 +28,7 @@ func (d *ParcaDatasource) callProfileTypes(ctx context.Context, req *backend.Cal
 		return err
 	}
 
-	var types []*ProfileType
+	types := make([]*ProfileType, 0, len(res.Msg.Types))
 	for _, t := range res.Msg.Types {
 		var id string
 		if t.Delta {

pkg/tsdb/phlare/query.go

@@ -285,14 +285,14 @@ func walkTree(tree *ProfileTree, fn func(tree *ProfileTree)) {
 }
 
 func seriesToDataFrames(seriesResp *connect.Response[querierv1.SelectSeriesResponse], profileTypeID string) []*data.Frame {
-	var frames []*data.Frame
+	frames := make([]*data.Frame, 0, len(seriesResp.Msg.Series))
 
 	for _, series := range seriesResp.Msg.Series {
 		// We create separate data frames as the series may not have the same length
 		frame := data.NewFrame("series")
 		frame.Meta = &data.FrameMeta{PreferredVisualization: "graph"}
 
-		fields := data.Fields{}
+		fields := make(data.Fields, 0, 2)
 		timeField := data.NewField("time", nil, []time.Time{})
 		fields = append(fields, timeField)