diff --git a/federationsender/queue/destinationqueue.go b/federationsender/queue/destinationqueue.go
index 6a00abb4a..dd8243845 100644
--- a/federationsender/queue/destinationqueue.go
+++ b/federationsender/queue/destinationqueue.go
@@ -205,10 +205,9 @@ func (oq *destinationQueue) backgroundSend() {
 				// There are new PDUs waiting in the database.
 				hydrate()
 			case edu := <-oq.incomingEDUs:
-				// Likewise for EDUs, although we should probably not try
-				// too hard with some EDUs (like typing notifications) after
-				// a certain amount of time has passed.
-				// TODO: think about EDU expiry some more
+				// EDUs are handled in-memory for now. We will try to keep
+				// the ordering intact.
+				// TODO: Certain EDU types need persistence, e.g. send-to-device
 				oq.pendingEDUs = append(oq.pendingEDUs, edu)
 				// If there are any more things waiting in the channel queue
 				// then read them. This is safe because we guarantee only
@@ -322,41 +321,29 @@ func (oq *destinationQueue) backgroundSend() {
 // cleanPendingPDUs cleans out the pending PDU buffer, removing
 // all references so that the underlying objects can be GC'd.
 func (oq *destinationQueue) cleanPendingPDUs() {
-	numPDUs := len(oq.pendingPDUs)
-	for i := 0; i < numPDUs; i++ {
+	for i := 0; i < len(oq.pendingPDUs); i++ {
 		oq.pendingPDUs[i] = nil
 	}
-	oq.pendingPDUs = append(
-		[]*gomatrixserverlib.HeaderedEvent{},
-		oq.pendingPDUs[numPDUs:]...,
-	)
+	oq.pendingPDUs = []*gomatrixserverlib.HeaderedEvent{}
 }
 
 // cleanPendingEDUs cleans out the pending EDU buffer, removing
 // all references so that the underlying objects can be GC'd.
 func (oq *destinationQueue) cleanPendingEDUs() {
-	numEDUs := len(oq.pendingEDUs)
-	for i := 0; i < numEDUs; i++ {
+	for i := 0; i < len(oq.pendingEDUs); i++ {
 		oq.pendingEDUs[i] = nil
 	}
-	oq.pendingEDUs = append(
-		[]*gomatrixserverlib.EDU{},
-		oq.pendingEDUs[numEDUs:]...,
-	)
+	oq.pendingEDUs = []*gomatrixserverlib.EDU{}
 }
 
 // cleanPendingInvites cleans out the pending invite buffer,
 // removing all references so that the underlying objects can
 // be GC'd.
 func (oq *destinationQueue) cleanPendingInvites() {
-	numInvites := len(oq.pendingInvites)
-	for i := 0; i < numInvites; i++ {
+	for i := 0; i < len(oq.pendingInvites); i++ {
 		oq.pendingInvites[i] = nil
 	}
-	oq.pendingInvites = append(
-		[]*gomatrixserverlib.InviteV2Request{},
-		oq.pendingInvites[numInvites:]...,
-	)
+	oq.pendingInvites = []*gomatrixserverlib.InviteV2Request{}
 }
 
 // nextTransaction creates a new transaction from the pending event
diff --git a/federationsender/storage/postgres/queue_json_table.go b/federationsender/storage/postgres/queue_json_table.go
index c2fa46455..eac2ea988 100644
--- a/federationsender/storage/postgres/queue_json_table.go
+++ b/federationsender/storage/postgres/queue_json_table.go
@@ -1,5 +1,4 @@
-// Copyright 2017-2018 New Vector Ltd
-// Copyright 2019-2020 The Matrix.org Foundation C.I.C.
+// Copyright 2020 The Matrix.org Foundation C.I.C.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -25,7 +24,7 @@ import (
 )
 
 const queueJSONSchema = `
--- The queue_retry_json table contains event contents that
+-- The federationsender_queue_json table contains event contents that
 -- we failed to send. 
 CREATE TABLE IF NOT EXISTS federationsender_queue_json (
 	-- The JSON NID. This allows the federationsender_queue_retry table to
diff --git a/federationsender/storage/postgres/queue_pdus_table.go b/federationsender/storage/postgres/queue_pdus_table.go
index 13b3b49c2..ef7a9f41e 100644
--- a/federationsender/storage/postgres/queue_pdus_table.go
+++ b/federationsender/storage/postgres/queue_pdus_table.go
@@ -1,5 +1,4 @@
-// Copyright 2017-2018 New Vector Ltd
-// Copyright 2019-2020 The Matrix.org Foundation C.I.C.
+// Copyright 2020 The Matrix.org Foundation C.I.C.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -28,7 +27,7 @@ const queuePDUsSchema = `
 CREATE TABLE IF NOT EXISTS federationsender_queue_pdus (
     -- The transaction ID that was generated before persisting the event.
 	transaction_id TEXT NOT NULL,
-    -- The domain part of the user ID the m.room.member event is for.
+    -- The destination server that we will send the event to.
 	server_name TEXT NOT NULL,
 	-- The JSON NID from the federationsender_queue_pdus_json table.
 	json_nid BIGINT NOT NULL
@@ -137,7 +136,10 @@ func (s *queuePDUsStatements) selectQueueReferenceJSONCount(
 	stmt := sqlutil.TxStmt(txn, s.selectQueueReferenceJSONCountStmt)
 	err := stmt.QueryRowContext(ctx, jsonNID).Scan(&count)
 	if err == sql.ErrNoRows {
-		return -1, nil
+		// It's acceptable for there to be no rows referencing a given
+		// JSON NID but it's not an error condition. Just return as if
+		// there's a zero count.
+		return 0, nil
 	}
 	return count, err
 }