app/vmselect/promql: avoid memory allocations and copying from source timeseries to the returned result at timeseriesToResult()

app/vmselect/promql/exec.go

@@ -129,9 +129,11 @@ func timeseriesToResult(tss []*timeseries, maySort bool) ([]netstorage.Result, e
 		m[k] = struct{}{}
 
 		rs := &result[i]
-		rs.MetricName.CopyFrom(&ts.MetricName)
-		rs.Values = append(rs.Values[:0], ts.Values...)
-		rs.Timestamps = append(rs.Timestamps[:0], ts.Timestamps...)
+		rs.MetricName.MoveFrom(&ts.MetricName)
+		rs.Values = ts.Values
+		ts.Values = nil
+		rs.Timestamps = ts.Timestamps
+		ts.Timestamps = nil
 	}
 	bbPool.Put(bb)
 

app/vmselect/promql/rollup_result_cache.go

@@ -497,11 +497,9 @@ func mergeTimeseries(a, b []*timeseries, bStart int64, ec *EvalConfig) []*timese
 		tmp.denyReuse = true
 		tmp.Timestamps = sharedTimestamps
 		tmp.Values = make([]float64, 0, len(tmp.Timestamps))
-		// Do not use MetricName.CopyFrom for performance reasons.
-		// It is safe to make shallow copy, since tsB must no longer used.
-		tmp.MetricName = tsB.MetricName
+		tmp.MetricName.MoveFrom(&tsB.MetricName)
 
-		bb.B = marshalMetricNameSorted(bb.B[:0], &tsB.MetricName)
+		bb.B = marshalMetricNameSorted(bb.B[:0], &tmp.MetricName)
 		tsA := m[string(bb.B)]
 		if tsA == nil {
 			tStart := ec.Start
@@ -525,9 +523,7 @@ func mergeTimeseries(a, b []*timeseries, bStart int64, ec *EvalConfig) []*timese
 		var tmp timeseries
 		tmp.denyReuse = true
 		tmp.Timestamps = sharedTimestamps
-		// Do not use MetricName.CopyFrom for performance reasons.
-		// It is safe to make shallow copy, since tsA must no longer used.
-		tmp.MetricName = tsA.MetricName
+		tmp.MetricName.MoveFrom(&tsA.MetricName)
 		tmp.Values = append(tmp.Values, tsA.Values...)
 
 		tStart := bStart

lib/storage/metric_name.go

@@ -165,6 +165,14 @@ func (mn *MetricName) Reset() {
 	mn.Tags = mn.Tags[:0]
 }
 
+// MoveFrom moves src to mn.
+//
+// The src is reset after the call.
+func (mn *MetricName) MoveFrom(src *MetricName) {
+	*mn = *src
+	*src = MetricName{}
+}
+
 // CopyFrom copies src to mn.
 func (mn *MetricName) CopyFrom(src *MetricName) {
 	if cap(mn.MetricGroup) > 0 {