v3rpc: add jitter to progress notification

etcdserver/api/v3rpc/watch.go

@@ -17,6 +17,7 @@ package v3rpc
 import (
 	"context"
 	"io"
+	"math/rand"
 	"sync"
 	"time"
 
@@ -58,7 +59,9 @@ var (
 func GetProgressReportInterval() time.Duration {
 	progressReportIntervalMu.RLock()
 	defer progressReportIntervalMu.RUnlock()
-	return progressReportInterval
+	// add rand(1/10*progressReportInterval) as jitter so that etcdserver will not
+	// send progress notification to watches around the same time.
+	return progressReportInterval + time.Duration(rand.Int63n(int64(progressReportInterval)/10))
 }
 
 func SetProgressReportInterval(newTimeout time.Duration) {