Manage event sending rate for SubscribeActorEvents

node/impl/full/actor_events.go

@@ -3,6 +3,7 @@ package full
 import (
 	"context"
 	"fmt"
+	"time"
 
 	"github.com/ipfs/go-cid"
 	"go.uber.org/fx"
@@ -10,6 +11,7 @@ import (
 	"github.com/filecoin-project/go-state-types/abi"
 
 	"github.com/filecoin-project/lotus/api"
+	"github.com/filecoin-project/lotus/build"
 	"github.com/filecoin-project/lotus/chain/events/filter"
 	"github.com/filecoin-project/lotus/chain/store"
 	"github.com/filecoin-project/lotus/chain/types"
@@ -62,9 +64,11 @@ func (a *ActorEventHandler) GetActorEvents(ctx context.Context, evtFilter *types
 		return nil, err
 	}
 
-	evs, err := getCollected(ctx, f)
-	_ = a.EventFilterManager.Remove(ctx, f.ID())
-	return evs, err
+	evs, _, _ := getCollected(ctx, f)
+	if err := a.EventFilterManager.Remove(ctx, f.ID()); err != nil {
+		log.Warnf("failed to remove filter: %s", err)
+	}
+	return evs, nil
 }
 
 type filterParams struct {
@@ -172,75 +176,143 @@ func (a *ActorEventHandler) SubscribeActorEvents(ctx context.Context, evtFilter
 		return nil, err
 	}
 
-	out := make(chan *types.ActorEvent, 25)
+	// The goal for the code below is to be able to send events on the `out` channel as fast as
+	// possible and not let it get too far behind the rate at which the events are generated.
+	// For historical events we see the rate at which they were generated by looking the height range;
+	// we then make sure that the client can receive them at least twice as fast as they were
+	// generated so they catch up quick enough to receive new events.
+	// For ongoing events we use an exponential moving average of the events per height to make sure
+	// that the client doesn't fall behind.
+	// In both cases we allow a little bit of slack but need to avoid letting the client bloat the
+	// buffer too much.
+	// There is no special handling for reverts, so they will just look like a lot more events per
+	// epoch and the user has to receive them anyway.
+
+	out := make(chan *types.ActorEvent)
 
 	go func() {
 		defer func() {
-			// Tell the caller we're done
+			// tell the caller we're done
 			close(out)
-
-			// Unsubscribe.
 			fm.ClearSubChannel()
-			_ = a.EventFilterManager.Remove(ctx, fm.ID())
+			if err := a.EventFilterManager.Remove(ctx, fm.ID()); err != nil {
+				log.Warnf("failed to remove filter: %s", err)
+			}
 		}()
 
-		evs, err := getCollected(ctx, fm)
-		if err != nil {
-			log.Errorf("failed to get collected events: %w", err)
-			return
-		}
+		// Handle any historical events that our filter may have picked up -----------------------------
 
-		for _, ev := range evs {
-			ev := ev
-			select {
-			case out <- ev:
-			case <-ctx.Done():
-				return
-			default:
-				// TODO: need to fix this, buffer of 25 isn't going to work for prefill without a _really_ fast client or a small number of events
-				log.Errorf("closing event subscription due to slow reader")
-				return
+		evs, minEpoch, maxEpoch := getCollected(ctx, fm)
+		if len(evs) > 0 {
+			// must be able to send events at least twice as fast as they were generated
+			epochRange := maxEpoch - minEpoch
+			if epochRange <= 0 {
+				epochRange = 1
+			}
+			eventsPerEpoch := float64(len(evs)) / float64(epochRange)
+			eventsPerSecond := 2 * eventsPerEpoch / float64(build.BlockDelaySecs)
+			// a minimum rate of 1 event per second if we don't have many events
+			if eventsPerSecond < 1 {
+				eventsPerSecond = 1
+			}
+
+			// send events from evs to the out channel and ensure we don't do it slower than eventsPerMs
+			ticker := time.NewTicker(time.Second)
+			defer ticker.Stop()
+
+			const maxSlowTicks = 3 // slightly forgiving, allow 3 slow ticks (seconds) before giving up
+			slowTicks := 0
+			sentEvents := 0.0
+
+			for _, ev := range evs {
+				select {
+				case out <- ev:
+					sentEvents++
+				case <-ticker.C:
+					if sentEvents < eventsPerSecond {
+						slowTicks++
+						if slowTicks >= maxSlowTicks {
+							log.Errorf("closing event subscription due to slow event sending rate")
+							return
+						}
+					} else {
+						slowTicks = 0
+					}
+					sentEvents = 0
+				case <-ctx.Done():
+					return
+				}
 			}
 		}
 
+		// Handle ongoing events from the filter -------------------------------------------------------
+
 		in := make(chan interface{}, 256)
 		fm.SetSubChannel(in)
 
+		var buffer []*types.ActorEvent
+		const α = 0.2                        // decay factor for the events per height EMA
+		var eventsPerHeightEma float64 = 256 // exponential moving average of events per height, initially guess at 256
+		var lastHeight abi.ChainEpoch        // last seen event height
+		var eventsAtCurrentHeight int        // number of events at the current height
+
+		collectEvent := func(ev interface{}) bool {
+			ce, ok := ev.(*filter.CollectedEvent)
+			if !ok {
+				log.Errorf("got unexpected value from event filter: %T", ev)
+				return false
+			}
+
+			if ce.Height > lastHeight {
+				// update the EMA of events per height when the height increases
+				if lastHeight != 0 {
+					eventsPerHeightEma = α*float64(eventsAtCurrentHeight) + (1-α)*eventsPerHeightEma
+				}
+				lastHeight = ce.Height
+				eventsAtCurrentHeight = 0
+			}
+			eventsAtCurrentHeight++
+
+			buffer = append(buffer, &types.ActorEvent{
+				Entries:   ce.Entries,
+				Emitter:   ce.EmitterAddr,
+				Reverted:  ce.Reverted,
+				Height:    ce.Height,
+				TipSetKey: ce.TipSetKey,
+				MsgCid:    ce.MsgCid,
+			})
+			return true
+		}
+
 		for ctx.Err() == nil {
-			select {
-			case val, ok := <-in:
-				if !ok {
-					// Shutting down.
+			if len(buffer) > 0 {
+				// check if we need to disconnect the client because they've fallen behind, always allow at
+				// least 8 events in the buffer to provide a little bit of slack
+				if len(buffer) > 8 && float64(len(buffer)) > eventsPerHeightEma/2 {
+					log.Errorf("closing event subscription due to slow event sending rate")
 					return
 				}
 
-				ce, ok := val.(*filter.CollectedEvent)
-				if !ok {
-					log.Errorf("got unexpected value from event filter: %T", val)
-					return
-				}
-
-				ev := &types.ActorEvent{
-					Entries:   ce.Entries,
-					Emitter:   ce.EmitterAddr,
-					Reverted:  ce.Reverted,
-					Height:    ce.Height,
-					TipSetKey: ce.TipSetKey,
-					MsgCid:    ce.MsgCid,
-				}
-
 				select {
-				case out <- ev:
-				default: // TODO: need to fix this to be more intelligent about the consumption rate vs the accumulation rate
-					log.Errorf("closing event subscription due to slow reader")
+				case ev, ok := <-in: // incoming event
+					if !ok || !collectEvent(ev) {
+						return
+					}
+				case out <- buffer[0]: // successful send
+					buffer[0] = nil
+					buffer = buffer[1:]
+				case <-ctx.Done():
 					return
 				}
-				if len(out) > 5 {
-					log.Warnf("event subscription is slow, has %d buffered entries", len(out))
+			} else {
+				select {
+				case ev, ok := <-in: // incoming event
+					if !ok || !collectEvent(ev) {
+						return
+					}
+				case <-ctx.Done():
+					return
 				}
-
-			case <-ctx.Done():
-				return
 			}
 		}
 	}()
@@ -248,12 +320,19 @@ func (a *ActorEventHandler) SubscribeActorEvents(ctx context.Context, evtFilter
 	return out, nil
 }
 
-func getCollected(ctx context.Context, f *filter.EventFilter) ([]*types.ActorEvent, error) {
+func getCollected(ctx context.Context, f *filter.EventFilter) ([]*types.ActorEvent, abi.ChainEpoch, abi.ChainEpoch) {
 	ces := f.TakeCollectedEvents(ctx)
 
 	var out []*types.ActorEvent
+	var min, max abi.ChainEpoch
 
 	for _, e := range ces {
+		if min == 0 || e.Height < min {
+			min = e.Height
+		}
+		if e.Height > max {
+			max = e.Height
+		}
 		out = append(out, &types.ActorEvent{
 			Entries:   e.Entries,
 			Emitter:   e.EmitterAddr,
@@ -264,5 +343,5 @@ func getCollected(ctx context.Context, f *filter.EventFilter) ([]*types.ActorEve
 		})
 	}
 
-	return out, nil
+	return out, min, max
 }