From 93130ba5c3bd52e920b7709c12c2a9a7cfb4af70 Mon Sep 17 00:00:00 2001
From: "Matt T. Proud" <matt.proud@gmail.com>
Date: Sun, 21 Jul 2013 17:34:37 +0200
Subject: [PATCH] Introduce histogram purging support.

---
 prometheus/histogram.go | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/prometheus/histogram.go b/prometheus/histogram.go
index 5a806bb..3d5f9e7 100644
--- a/prometheus/histogram.go
+++ b/prometheus/histogram.go
@@ -13,6 +13,7 @@ import (
 	"math"
 	"strconv"
 	"sync"
+	"time"
 
 	dto "github.com/prometheus/client_model/go"
 
@@ -54,6 +55,7 @@ type HistogramSpecification struct {
 	BucketBuilder         BucketBuilder
 	ReportablePercentiles []float64
 	Starts                []float64
+	PurgeInterval         time.Duration
 }
 
 type Histogram interface {
@@ -82,6 +84,9 @@ type histogram struct {
 	values map[uint64]*histogramVector
 	// These are the percentile values that will be reported on marshalling.
 	reportablePercentiles []float64
+
+	purgeInterval time.Duration
+	lastPurge     time.Time
 }
 
 type histogramVector struct {
@@ -249,6 +254,8 @@ func formatFloat(value float64) string {
 }
 
 func (h *histogram) MarshalJSON() ([]byte, error) {
+	h.Purge()
+
 	h.mutex.RLock()
 	defer h.mutex.RUnlock()
 
@@ -274,10 +281,29 @@ func (h *histogram) MarshalJSON() ([]byte, error) {
 	})
 }
 
+func (h *histogram) Purge() {
+	if h.purgeInterval == 0 {
+		return
+	}
+
+	h.mutex.Lock()
+	defer h.mutex.Unlock()
+	if time.Since(h.lastPurge) < h.purgeInterval {
+		return
+	}
+
+	h.resetAll()
+	h.lastPurge = time.Now()
+}
+
 func (h *histogram) ResetAll() {
 	h.mutex.Lock()
 	defer h.mutex.Unlock()
 
+	h.resetAll()
+}
+
+func (h *histogram) resetAll() {
 	for signature, value := range h.values {
 		for _, bucket := range value.buckets {
 			bucket.Reset()
@@ -294,6 +320,8 @@ func NewHistogram(specification *HistogramSpecification) Histogram {
 		bucketStarts:          specification.Starts,
 		reportablePercentiles: specification.ReportablePercentiles,
 		values:                map[uint64]*histogramVector{},
+		lastPurge:             time.Now(),
+		purgeInterval:         specification.PurgeInterval,
 	}
 
 	return metric
@@ -307,11 +335,14 @@ func NewDefaultHistogram() Histogram {
 			Starts:                LogarithmicSizedBucketsFor(0, 4096),
 			BucketBuilder:         AccumulatingBucketBuilder(EvictAndReplaceWith(10, AverageReducer), 50),
 			ReportablePercentiles: []float64{0.01, 0.05, 0.5, 0.90, 0.99},
+			PurgeInterval:         15 * time.Minute,
 		},
 	)
 }
 
 func (metric *histogram) dumpChildren(f *dto.MetricFamily) {
+	metric.Purge()
+
 	metric.mutex.RLock()
 	defer metric.mutex.RUnlock()