Rate limit report publishing

So that, if many shortcut reports are produced in quick succession,
they will tend to get merged together.

Expand the queue size for shortcut reports, to avoid holding up the
producer so much.

probe/probe.go

@@ -1,17 +1,20 @@
 package probe
 
 import (
+	"context"
 	"sync"
 	"time"
 
 	"github.com/armon/go-metrics"
 	log "github.com/sirupsen/logrus"
+	"golang.org/x/time/rate"
 
 	"github.com/weaveworks/scope/report"
 )
 
 const (
-	reportBufferSize = 16
+	spiedReportBufferSize    = 16
+	shortcutReportBufferSize = 1024
 )
 
 // ReportPublisher publishes reports, probably to a remote collector.
@@ -23,6 +26,7 @@ type ReportPublisher interface {
 type Probe struct {
 	spyInterval, publishInterval time.Duration
 	publisher                    ReportPublisher
+	rateLimiter                  *rate.Limiter
 	noControls                   bool
 
 	tickers   []Ticker
@@ -79,10 +83,11 @@ func New(
 		spyInterval:     spyInterval,
 		publishInterval: publishInterval,
 		publisher:       publisher,
+		rateLimiter:     rate.NewLimiter(rate.Every(publishInterval)*10, 1),
 		noControls:      noControls,
 		quit:            make(chan struct{}),
-		spiedReports:    make(chan report.Report, reportBufferSize),
-		shortcutReports: make(chan report.Report, reportBufferSize),
+		spiedReports:    make(chan report.Report, spiedReportBufferSize),
+		shortcutReports: make(chan report.Report, shortcutReportBufferSize),
 	}
 	return result
 }
@@ -197,6 +202,7 @@ func (p *Probe) tag(r report.Report) report.Report {
 }
 
 func (p *Probe) drainAndPublish(rpt report.Report, rs chan report.Report) {
+	p.rateLimiter.Wait(context.Background())
 ForLoop:
 	for {
 		select {