Simplify backpressure handling

cmd/send-all-events-to-relay/main.go

@@ -148,7 +148,7 @@ func (u *EventUploader) worker(ctx context.Context) {
 func (u *EventUploader) sendEvent(ctx context.Context, event domain.Event) error {
 	for {
 		if err := u.eventSender.SendEvent(ctx, u.address, event); err != nil {
-			if errors.Is(err, relays.BackPressureError) {
+			if errors.Is(err, relays.ErrEventReplaced) {
 				u.eventsRelayReplaced.Add(1)
 				u.allEvents.Add(1)
 			} else {

service/domain/relays/relay_connection.go

@@ -70,7 +70,6 @@ type RelayConnection struct {
 	eventsToSendMutex             sync.Mutex
 	newEventsCh                   chan domain.Event
 	rateLimitNoticeBackoffManager *RateLimitNoticeBackoffManager
-	cancelBackPressure            context.CancelFunc
 }
 
 func NewRelayConnection(
@@ -90,7 +89,6 @@ func NewRelayConnection(
 		eventsToSend:                  make(map[domain.EventId]*eventToSend),
 		newEventsCh:                   make(chan domain.Event),
 		rateLimitNoticeBackoffManager: rateLimitNoticeBackoffManager,
-		cancelBackPressure:            nil,
 	}
 }
 
@@ -108,10 +106,6 @@ func (r *RelayConnection) Run(ctx context.Context) {
 		if r.Address().HostWithoutPort() == "relay.nos.social" {
 			// We control relay.nos.social, so we don't backoff here
 			backoff = 0
-		} else if errors.Is(err, BackPressureError) {
-			// Only calling r.cancelBackPressure() can resolve the backpressure
-			r.WaitUntilNoBackPressure(ctx)
-			backoff = 0
 		}
 
 		select {
@@ -123,20 +117,6 @@ func (r *RelayConnection) Run(ctx context.Context) {
 	}
 }
 
-func (r *RelayConnection) WaitUntilNoBackPressure(ctx context.Context) {
-	var resolvedBackPressureCtx context.Context
-	var cancelBackPressure context.CancelFunc
-
-	r.setStateWithFn(RelayConnectionStateBackPressured, func() {
-		resolvedBackPressureCtx, cancelBackPressure = context.WithCancel(ctx)
-		r.cancelBackPressure = cancelBackPressure
-	})
-
-	<-resolvedBackPressureCtx.Done()
-
-	r.setState(RelayConnectionStateDisconnected)
-}
-
 func (r *RelayConnection) State() RelayConnectionState {
 	r.stateMutex.Lock()
 	defer r.stateMutex.Unlock()
@@ -356,8 +336,8 @@ func (r *RelayConnection) run(ctx context.Context) error {
 		}
 
 		if r.state == RelayConnectionStateBackPressured {
-			// Load shedding under backpressure
-			continue
+			// Load shedding under backpressure, we just disconnect
+			return BackPressureError
 		}
 
 		if err := r.handleMessage(messageBytes); err != nil {
@@ -613,14 +593,6 @@ func (r *RelayConnection) setState(state RelayConnectionState) {
 	r.state = state
 }
 
-func (r *RelayConnection) setStateWithFn(state RelayConnectionState, fn func()) {
-	r.stateMutex.Lock()
-	defer r.stateMutex.Unlock()
-
-	r.state = state
-	fn()
-}
-
 func (r *RelayConnection) manageSubs(ctx context.Context, conn Connection) error {
 	defer conn.Close()
 

service/domain/relays/relay_connections.go

@@ -76,17 +76,16 @@ func (d *RelayConnections) SendEvent(ctx context.Context, relayAddress domain.Re
 
 func (d *RelayConnections) NotifyBackPressure() {
 	for _, connection := range d.connections {
-		if connection.Address().HostWithoutPort() != "relay.nos.social" {
+		if connection.Address().HostWithoutPort() != "relay.nos.social" && connection.State() == RelayConnectionStateConnected {
 			connection.setState(RelayConnectionStateBackPressured)
 		}
 	}
 }
 
 func (d *RelayConnections) ResolveBackPressure() {
 	for _, connection := range d.connections {
-		if connection.cancelBackPressure != nil {
-			connection.cancelBackPressure()
-			connection.cancelBackPressure = nil
+		if connection.Address().HostWithoutPort() != "relay.nos.social" && connection.State() == RelayConnectionStateBackPressured {
+			connection.setState(RelayConnectionStateConnected)
 		}
 	}
 }
@@ -115,6 +114,7 @@ func (d *RelayConnections) storeMetrics() {
 	}
 	d.metrics.ReportRelayConnectionsState(m)
 }
+
 func (r *RelayConnections) getRateLimitNoticeBackoffManager(relayAddress domain.RelayAddress) *RateLimitNoticeBackoffManager {
 	rateLimitNoticeBackoffManager, exists := r.rateLimitNoticeBackoffManagers[relayAddress.HostWithoutPort()]
 	if !exists {

service/ports/sqlitepubsub/event_saved.go

@@ -57,7 +57,7 @@ func (s *EventSavedEventSubscriber) Run(ctx context.Context) error {
 					fmt.Sprintf("Queue size %d > %d. Sending backpressure signal to slow down", queueSize, backPressureThreshold),
 				)
 				s.handler.NotifyBackPressure()
-			} else if queueSize < backPressureThreshold/2 {
+			} else {
 				s.handler.ResolveBackPressure()
 			}