From 17443d288bcf7b0d704ccc3ad1759fd938a8e433 Mon Sep 17 00:00:00 2001
From: beorn7 <beorn@soundcloud.com>
Date: Sun, 22 Feb 2015 00:25:02 +0100
Subject: [PATCH] Avoid copying of the COWMetric if we already have the metric
 available.

---
 rules/ast/functions.go |  7 +++----
 rules/ast/quantile.go  | 45 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/rules/ast/functions.go b/rules/ast/functions.go
index 0c5fcafd9..3a207b976 100644
--- a/rules/ast/functions.go
+++ b/rules/ast/functions.go
@@ -514,12 +514,11 @@ func histogramQuantileImpl(timestamp clientmodel.Timestamp, args []Node) interfa
 			// TODO(beorn7): Issue a warning somehow.
 			continue
 		}
-		// TODO avoid copying each time by using a custom fingerprint
-		el.Metric.Delete(clientmodel.BucketLabel)
-		el.Metric.Delete(clientmodel.MetricNameLabel)
-		fp := el.Metric.Metric.Fingerprint()
+		fp := bucketFingerprint(el.Metric.Metric)
 		mb, ok := fpToMetricWithBuckets[fp]
 		if !ok {
+			el.Metric.Delete(clientmodel.BucketLabel)
+			el.Metric.Delete(clientmodel.MetricNameLabel)
 			mb = &metricWithBuckets{el.Metric, nil}
 			fpToMetricWithBuckets[fp] = mb
 		}
diff --git a/rules/ast/quantile.go b/rules/ast/quantile.go
index f38313313..0f628153f 100644
--- a/rules/ast/quantile.go
+++ b/rules/ast/quantile.go
@@ -14,6 +14,8 @@
 package ast
 
 import (
+	"encoding/binary"
+	"hash/fnv"
 	"math"
 	"sort"
 
@@ -97,3 +99,46 @@ func quantile(q clientmodel.SampleValue, buckets buckets) float64 {
 	}
 	return bucketStart + (bucketEnd-bucketStart)*float64(rank/count)
 }
+
+// bucketFingerprint works like the Fingerprint method of Metric, but ignores
+// the name and the bucket label.
+func bucketFingerprint(m clientmodel.Metric) clientmodel.Fingerprint {
+	numLabels := 0
+	if len(m) > 2 {
+		numLabels = len(m) - 2
+	}
+	labelNames := make([]string, 0, numLabels)
+	maxLength := 0
+
+	for labelName, labelValue := range m {
+		if labelName == clientmodel.MetricNameLabel || labelName == clientmodel.BucketLabel {
+			continue
+		}
+		labelNames = append(labelNames, string(labelName))
+		if len(labelName) > maxLength {
+			maxLength = len(labelName)
+		}
+		if len(labelValue) > maxLength {
+			maxLength = len(labelValue)
+		}
+	}
+
+	sort.Strings(labelNames)
+
+	summer := fnv.New64a()
+	buf := make([]byte, maxLength)
+
+	for _, labelName := range labelNames {
+		labelValue := m[clientmodel.LabelName(labelName)]
+
+		copy(buf, labelName)
+		summer.Write(buf[:len(labelName)])
+		summer.Write([]byte{clientmodel.SeparatorByte})
+
+		copy(buf, labelValue)
+		summer.Write(buf[:len(labelValue)])
+		summer.Write([]byte{clientmodel.SeparatorByte})
+	}
+
+	return clientmodel.Fingerprint(binary.LittleEndian.Uint64(summer.Sum(nil)))
+}