Update comments

roomserver/internal/input/input.go

@@ -159,10 +159,17 @@ func (r *Inputer) startWorkerForRoom(roomID string) {
 
 		// The consumer already exists, try to update if necessary.
 		if info != nil {
+			// Not using reflect.DeepEqual here, since consumerConfig does not explicitly set
+			// e.g. the consumerName, which is added by NATS later. So this would result
+			// in constantly updating/recreating the consumer.
 			switch {
 			case info.Config.AckWait.Nanoseconds() != consumerConfig.AckWait.Nanoseconds():
+				// Initially we had a AckWait of 2m 10s, now we have 5m 10s, so we need to update
+				// existing consumers.
 				fallthrough
 			case info.Config.AckPolicy != consumerConfig.AckPolicy:
+				// We've changed the AckPolicy from AckAll to AckExplicit, this needs a
+				// recreation of the consumer. (Note: Only a few changes actually need a recreat)
 				logger.Warn("Consumer already exists, trying to update it.")
 				// Try updating the consumer first
 				if _, err = w.r.JetStream.UpdateConsumer(streamName, consumerConfig); err != nil {
@@ -172,6 +179,7 @@ func (r *Inputer) startWorkerForRoom(roomID string) {
 						logger.WithError(err).Fatal("Unable to delete consumer")
 						return
 					}
+					// Set info to nil, so it can be recreated with the correct config.
 					info = nil
 				}
 			}
@@ -310,7 +318,7 @@ func (w *worker) _next() {
 	msg := msgs[0]
 	var inputRoomEvent api.InputRoomEvent
 	if err = json.Unmarshal(msg.Data, &inputRoomEvent); err != nil {
-		// using AckWait here makes the call synchronous; 5 seconds is default value
+		// using AckWait here makes the call synchronous; 5 seconds is the default value used by NATS
 		_ = msg.Term(nats.AckWait(time.Second * 5))
 		return
 	}

roomserver/internal/input/input_events.go

@@ -48,7 +48,9 @@ import (
 	"github.com/matrix-org/dendrite/roomserver/types"
 )
 
-// TODO: Does this value make sense?
+// MaximumMissingProcessingTime is the maximum time we allow "processRoomEvent" to fetch
+// e.g. missing auth/prev events. This duration is used for AckWait, and if it is exceeded
+// NATS queues the event for redelivery.
 const MaximumMissingProcessingTime = time.Minute * 5
 
 var processRoomEventDuration = prometheus.NewHistogramVec(