From cfa0253ed8ca449d803fc34aa4461f49c2de0db9 Mon Sep 17 00:00:00 2001
From: Frederic Branczyk <fbranczyk@gmail.com>
Date: Fri, 26 Jan 2018 14:57:33 +0100
Subject: [PATCH] discovery: Schedule updates to throttle

---
 discovery/manager.go | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/discovery/manager.go b/discovery/manager.go
index ae10de5cb..dd1e9b533 100644
--- a/discovery/manager.go
+++ b/discovery/manager.go
@@ -17,6 +17,7 @@ import (
 	"context"
 	"fmt"
 	"sync"
+	"time"
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
@@ -81,6 +82,10 @@ type Manager struct {
 	targets map[poolKey]map[string]*targetgroup.Group
 	// The sync channels sends the updates in map[targetSetName] where targetSetName is the job value from the scrape config.
 	syncCh chan map[string][]*targetgroup.Group
+	// True if updates were received in the last 5 seconds.
+	recentlyUpdated bool
+	// Protects recentlyUpdated.
+	recentlyUpdatedMtx sync.Mutex
 }
 
 // Run starts the background processing
@@ -123,6 +128,7 @@ func (m *Manager) startProvider(ctx context.Context, poolKey poolKey, worker Dis
 
 	go worker.Run(ctx, updates)
 	go m.runProvider(ctx, poolKey, updates)
+	go m.runUpdater(ctx)
 }
 
 func (m *Manager) runProvider(ctx context.Context, poolKey poolKey, updates chan []*targetgroup.Group) {
@@ -137,7 +143,26 @@ func (m *Manager) runProvider(ctx context.Context, poolKey poolKey, updates chan
 				return
 			}
 			m.updateGroup(poolKey, tgs)
-			m.syncCh <- m.allGroups()
+			m.recentlyUpdatedMtx.Lock()
+			m.recentlyUpdated = true
+			m.recentlyUpdatedMtx.Unlock()
+		}
+	}
+}
+
+func (m *Manager) runUpdater(ctx context.Context) {
+	ticker := time.NewTicker(5 * time.Second)
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			m.recentlyUpdatedMtx.Lock()
+			if m.recentlyUpdated {
+				m.syncCh <- m.allGroups()
+				m.recentlyUpdated = false
+			}
+			m.recentlyUpdatedMtx.Unlock()
 		}
 	}
 }