fetch: parametrize success rate threshold (#5161)

this threshold used to determine if peers are seen as equally responsive within certain threshold.
parametrizing it to run some experiments

fetch/fetch.go

@@ -84,6 +84,7 @@ type Config struct {
 	BatchSize, QueueSize int
 	RequestTimeout       time.Duration // in seconds
 	MaxRetriesForRequest int
+	PeersRateThreshold   float64 `mapstructure:"peers-rate-threshold"`
 }
 
 // DefaultConfig is the default config for the fetch component.
@@ -94,6 +95,7 @@ func DefaultConfig() Config {
 		BatchSize:            20,
 		RequestTimeout:       time.Second * time.Duration(10),
 		MaxRetriesForRequest: 100,
+		PeersRateThreshold:   0.02,
 	}
 }
 
@@ -174,12 +176,12 @@ func NewFetch(
 	opts ...Option,
 ) *Fetch {
 	bs := datastore.NewBlobStore(cdb.Database)
+
 	f := &Fetch{
 		cfg:         DefaultConfig(),
 		logger:      log.NewNop(),
 		bs:          bs,
 		host:        host,
-		peers:       peers.New(),
 		servers:     map[string]requester{},
 		unprocessed: make(map[types.Hash32]*request),
 		ongoing:     make(map[types.Hash32]*request),
@@ -189,6 +191,11 @@ func NewFetch(
 	for _, opt := range opts {
 		opt(f)
 	}
+	popts := []peers.Opt{}
+	if f.cfg.PeersRateThreshold != 0 {
+		popts = append(popts, peers.WithRateThreshold(f.cfg.PeersRateThreshold))
+	}
+	f.peers = peers.New(popts...)
 	// NOTE(dshulyak) this is to avoid tests refactoring.
 	// there is one test that covers this part.
 	if host != nil {

fetch/peers/peers.go

@@ -21,11 +21,10 @@ func (p *data) successRate() float64 {
 	return float64(p.success) / float64(p.success+p.failures)
 }
 
-func (p *data) cmp(other *data) int {
+func (p *data) cmp(other *data, rateThreshold float64) int {
 	if p == nil && other != nil {
 		return -1
 	}
-	const rateThreshold = 0.1
 	switch {
 	case p.rate-other.rate > rateThreshold:
 		return 1
@@ -41,13 +40,30 @@ func (p *data) cmp(other *data) int {
 	return strings.Compare(string(p.id), string(other.id))
 }
 
-func New() *Peers {
-	return &Peers{peers: map[peer.ID]*data{}}
+type Opt func(*Peers)
+
+func WithRateThreshold(rate float64) Opt {
+	return func(p *Peers) {
+		p.rateThreshold = rate
+	}
+}
+
+func New(opts ...Opt) *Peers {
+	p := &Peers{
+		peers:         map[peer.ID]*data{},
+		rateThreshold: 0.1,
+	}
+	for _, opt := range opts {
+		opt(p)
+	}
+	return p
 }
 
 type Peers struct {
 	mu    sync.Mutex
 	peers map[peer.ID]*data
+
+	rateThreshold float64
 }
 
 func (p *Peers) Add(id peer.ID) {
@@ -107,7 +123,7 @@ func (p *Peers) SelectBestFrom(peers []peer.ID) peer.ID {
 		if !exist {
 			continue
 		}
-		if best.cmp(pdata) == -1 {
+		if best.cmp(pdata, p.rateThreshold) == -1 {
 			best = pdata
 		}
 	}
@@ -134,7 +150,7 @@ func (p *Peers) SelectBest(n int) []peer.ID {
 	for _, peer := range p.peers {
 		worst := peer
 		for i := range cache {
-			if cache[i].cmp(worst) == -1 {
+			if cache[i].cmp(worst, p.rateThreshold) == -1 {
 				cache[i], worst = worst, cache[i]
 			}
 		}

fetch/peers/peers_test.go

@@ -19,7 +19,7 @@ type event struct {
 }
 
 func withEvents(events []event) *Peers {
-	tracker := New()
+	tracker := New(WithRateThreshold(0.1))
 	for _, ev := range events {
 		if ev.delete {
 			tracker.Delete(ev.id)