diff --git a/src/github.com/matrix-org/dendrite/roomserver/input/events.go b/src/github.com/matrix-org/dendrite/roomserver/input/events.go
index d26c95d1c..adc25661d 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/input/events.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/input/events.go
@@ -38,9 +38,9 @@ type RoomEventDatabase interface {
 	// The RoomRecentEventsUpdater must have Commit or Rollback called on it if this doesn't return an error.
 	// Returns the latest events in the room and the last eventID sent to the log along with an updater.
 	// If this returns an error then no further action is required.
-	GetLatestEventsForUpdate(roomNID types.RoomNID) (
-		latestEvents []types.StateAtEventAndReference, lastEventIDSent string, updater types.RoomRecentEventsUpdater, err error,
-	)
+	GetLatestEventsForUpdate(roomNID types.RoomNID) (updater types.RoomRecentEventsUpdater, err error)
+	// Lookup the string event IDs for a list of numeric event IDs
+	EventIDs(eventNIDs []types.EventNID) (map[types.EventNID]string, error)
 }
 
 // OutputRoomEventWriter has the APIs needed to write an event to the output logs.
@@ -91,7 +91,7 @@ func processRoomEvent(db RoomEventDatabase, ow OutputRoomEventWriter, input api.
 			}
 		} else {
 			// We haven't been told what the state at the event is so we need to calculate it from the prev_events
-			if stateAtEvent.BeforeStateSnapshotNID, err = calculateAndStoreState(db, event, roomNID); err != nil {
+			if stateAtEvent.BeforeStateSnapshotNID, err = calculateAndStoreStateBeforeEvent(db, event, roomNID); err != nil {
 				return err
 			}
 		}
diff --git a/src/github.com/matrix-org/dendrite/roomserver/input/latest_events.go b/src/github.com/matrix-org/dendrite/roomserver/input/latest_events.go
index 55b712d82..feaeccdb0 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/input/latest_events.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/input/latest_events.go
@@ -26,7 +26,7 @@ import (
 func updateLatestEvents(
 	db RoomEventDatabase, ow OutputRoomEventWriter, roomNID types.RoomNID, stateAtEvent types.StateAtEvent, event gomatrixserverlib.Event,
 ) (err error) {
-	oldLatest, lastEventIDSent, updater, err := db.GetLatestEventsForUpdate(roomNID)
+	updater, err := db.GetLatestEventsForUpdate(roomNID)
 	if err != nil {
 		return
 	}
@@ -44,16 +44,19 @@ func updateLatestEvents(
 		}
 	}()
 
-	err = doUpdateLatestEvents(updater, ow, oldLatest, lastEventIDSent, roomNID, stateAtEvent, event)
+	err = doUpdateLatestEvents(db, updater, ow, roomNID, stateAtEvent, event)
 	return
 }
 
 func doUpdateLatestEvents(
-	updater types.RoomRecentEventsUpdater, ow OutputRoomEventWriter, oldLatest []types.StateAtEventAndReference, lastEventIDSent string, roomNID types.RoomNID, stateAtEvent types.StateAtEvent, event gomatrixserverlib.Event,
+	db RoomEventDatabase, updater types.RoomRecentEventsUpdater, ow OutputRoomEventWriter, roomNID types.RoomNID, stateAtEvent types.StateAtEvent, event gomatrixserverlib.Event,
 ) error {
 	var err error
 	var prevEvents []gomatrixserverlib.EventReference
 	prevEvents = event.PrevEvents()
+	oldLatest := updater.LatestEvents()
+	lastEventIDSent := updater.LastEventIDSent()
+	oldStateNID := updater.CurrentStateSnapshotNID()
 
 	if hasBeenSent, err := updater.HasEventBeenSent(stateAtEvent.EventNID); err != nil {
 		return err
@@ -78,6 +81,20 @@ func doUpdateLatestEvents(
 		StateAtEvent:   stateAtEvent,
 	})
 
+	latestStateAtEvents := make([]types.StateAtEvent, len(newLatest))
+	for i := range newLatest {
+		latestStateAtEvents[i] = newLatest[i].StateAtEvent
+	}
+	newStateNID, err := calculateAndStoreStateAfterEvents(db, roomNID, latestStateAtEvents)
+	if err != nil {
+		return err
+	}
+
+	removed, added, err := differenceBetweeenStateSnapshots(db, oldStateNID, newStateNID)
+	if err != nil {
+		return err
+	}
+
 	// Send the event to the output logs.
 	// We do this inside the database transaction to ensure that we only mark an event as sent if we sent it.
 	// (n.b. this means that it's possible that the same event will be sent twice if the transaction fails but
@@ -86,11 +103,11 @@ func doUpdateLatestEvents(
 	// send the event asynchronously but we would need to ensure that 1) the events are written to the log in
 	// the correct order, 2) that pending writes are resent across restarts. In order to avoid writing all the
 	// necessary bookkeeping we'll keep the event sending synchronous for now.
-	if err = writeEvent(ow, lastEventIDSent, event, newLatest); err != nil {
+	if err = writeEvent(db, ow, lastEventIDSent, event, newLatest, removed, added); err != nil {
 		return err
 	}
 
-	if err = updater.SetLatestEvents(roomNID, newLatest, stateAtEvent.EventNID); err != nil {
+	if err = updater.SetLatestEvents(roomNID, newLatest, stateAtEvent.EventNID, newStateNID); err != nil {
 		return err
 	}
 
@@ -134,18 +151,41 @@ func calculateLatest(oldLatest []types.StateAtEventAndReference, alreadyReferenc
 	return newLatest
 }
 
-func writeEvent(ow OutputRoomEventWriter, lastEventIDSent string, event gomatrixserverlib.Event, latest []types.StateAtEventAndReference) error {
+func writeEvent(
+	db RoomEventDatabase, ow OutputRoomEventWriter, lastEventIDSent string,
+	event gomatrixserverlib.Event, latest []types.StateAtEventAndReference,
+	removed, added []types.StateEntry,
+) error {
 
 	latestEventIDs := make([]string, len(latest))
 	for i := range latest {
 		latestEventIDs[i] = latest[i].EventID
 	}
 
-	// TODO: Fill out AddsStateEventIDs and RemovesStateEventIDs
-	// TODO: Fill out VisibilityStateIDs
-	return ow.WriteOutputRoomEvent(api.OutputRoomEvent{
+	ore := api.OutputRoomEvent{
 		Event:           event.JSON(),
 		LastSentEventID: lastEventIDSent,
 		LatestEventIDs:  latestEventIDs,
-	})
+	}
+
+	var stateEventNIDs []types.EventNID
+	for _, entry := range added {
+		stateEventNIDs = append(stateEventNIDs, entry.EventNID)
+	}
+	for _, entry := range removed {
+		stateEventNIDs = append(stateEventNIDs, entry.EventNID)
+	}
+	eventIDMap, err := db.EventIDs(stateEventNIDs)
+	if err != nil {
+		return err
+	}
+	for _, entry := range added {
+		ore.AddsStateEventIDs = append(ore.AddsStateEventIDs, eventIDMap[entry.EventNID])
+	}
+	for _, entry := range removed {
+		ore.RemovesStateEventIDs = append(ore.RemovesStateEventIDs, eventIDMap[entry.EventNID])
+	}
+
+	// TODO: Fill out VisibilityStateIDs
+	return ow.WriteOutputRoomEvent(ore)
 }
diff --git a/src/github.com/matrix-org/dendrite/roomserver/input/state.go b/src/github.com/matrix-org/dendrite/roomserver/input/state.go
index c46dc6e14..36ab43b1c 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/input/state.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/input/state.go
@@ -9,8 +9,8 @@ import (
 
 // calculateAndStoreState calculates a snapshot of the state of a room before an event.
 // Stores the snapshot of the state in the database.
-// Returns a numeric ID for that snapshot.
-func calculateAndStoreState(
+// Returns a numeric ID for the snapshot of the state before the event.
+func calculateAndStoreStateBeforeEvent(
 	db RoomEventDatabase, event gomatrixserverlib.Event, roomNID types.RoomNID,
 ) (types.StateSnapshotNID, error) {
 	// Load the state at the prev events.
@@ -25,6 +25,13 @@ func calculateAndStoreState(
 		return 0, err
 	}
 
+	// The state before this event will be the state after the events that came before it.
+	return calculateAndStoreStateAfterEvents(db, roomNID, prevStates)
+}
+
+// calculateAndStoreStateAfterEvents finds the room state after the given events.
+// Stores the resulting state in the database and returns a numeric ID for that snapshot.
+func calculateAndStoreStateAfterEvents(db RoomEventDatabase, roomNID types.RoomNID, prevStates []types.StateAtEvent) (types.StateSnapshotNID, error) {
 	if len(prevStates) == 0 {
 		// 2) There weren't any prev_events for this event so the state is
 		// empty.
@@ -55,9 +62,9 @@ func calculateAndStoreState(
 			)
 		}
 		// If there are too many deltas then we need to calculate the full state
-		// So fall through to calculateAndStoreStateMany
+		// So fall through to calculateAndStoreStateAfterManyEvents
 	}
-	return calculateAndStoreStateMany(db, roomNID, prevStates)
+	return calculateAndStoreStateAfterManyEvents(db, roomNID, prevStates)
 }
 
 // maxStateBlockNIDs is the maximum number of state data blocks to use to encode a snapshot of room state.
@@ -67,10 +74,10 @@ func calculateAndStoreState(
 // TODO: Tune this to get the right balance between size and lookup performance.
 const maxStateBlockNIDs = 64
 
-// calculateAndStoreStateMany calculates the state of the room before an event
-// using the states at each of the event's prev events.
+// calculateAndStoreStateAfterManyEvents finds the room state after the given events.
+// This handles the slow path of calculateAndStoreStateAfterEvents for when there is more than one event.
 // Stores the resulting state and returns a numeric ID for the snapshot.
-func calculateAndStoreStateMany(db RoomEventDatabase, roomNID types.RoomNID, prevStates []types.StateAtEvent) (types.StateSnapshotNID, error) {
+func calculateAndStoreStateAfterManyEvents(db RoomEventDatabase, roomNID types.RoomNID, prevStates []types.StateAtEvent) (types.StateSnapshotNID, error) {
 	// Conflict resolution.
 	// First stage: load the state after each of the prev events.
 	combined, err := loadCombinedStateAfterEvents(db, prevStates)
@@ -107,6 +114,98 @@ func calculateAndStoreStateMany(db RoomEventDatabase, roomNID types.RoomNID, pre
 	return db.AddState(roomNID, nil, state)
 }
 
+// differenceBetweeenStateSnapshots works out which state entries have been added and removed between two snapshots.
+func differenceBetweeenStateSnapshots(db RoomEventDatabase, oldStateNID, newStateNID types.StateSnapshotNID) (
+	removed, added []types.StateEntry, err error,
+) {
+	if oldStateNID == newStateNID {
+		// If the snapshot NIDs are the same then nothing has changed
+		return nil, nil, nil
+	}
+
+	var oldEntries []types.StateEntry
+	var newEntries []types.StateEntry
+	if oldStateNID != 0 {
+		oldEntries, err = loadStateAtSnapshot(db, oldStateNID)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+	if newStateNID != 0 {
+		newEntries, err = loadStateAtSnapshot(db, newStateNID)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+
+	var oldI int
+	var newI int
+	for {
+		switch {
+		case oldI == len(oldEntries):
+			// We've reached the end of the old entries.
+			// The rest of the new list must have been newly added.
+			added = append(added, newEntries[newI:]...)
+			return
+		case newI == len(newEntries):
+			// We've reached the end of the new entries.
+			// The rest of the old list must be have been removed.
+			removed = append(removed, oldEntries[oldI:]...)
+			return
+		case oldEntries[oldI] == newEntries[newI]:
+			// The entry is in both lists so skip over it.
+			oldI++
+			newI++
+		case oldEntries[oldI].LessThan(newEntries[newI]):
+			// The lists are sorted so the old entry being less than the new entry means that it only appears in the old list.
+			removed = append(removed, oldEntries[oldI])
+			oldI++
+		default:
+			// Reaching the default case implies that the new entry is less than the old entry.
+			// Since the lists are sorted this means that it only appears in the new list.
+			added = append(added, newEntries[newI])
+			newI++
+		}
+	}
+}
+
+// loadStateAtSnapshot loads the full state of a room at a particular snapshot.
+// This is typically the state before an event or the current state of a room.
+// Returns a sorted list of state entries or an error if there was a problem talking to the database.
+func loadStateAtSnapshot(db RoomEventDatabase, stateNID types.StateSnapshotNID) ([]types.StateEntry, error) {
+	stateBlockNIDLists, err := db.StateBlockNIDs([]types.StateSnapshotNID{stateNID})
+	if err != nil {
+		return nil, err
+	}
+	stateBlockNIDList := stateBlockNIDLists[0]
+
+	stateEntryLists, err := db.StateEntries(stateBlockNIDList.StateBlockNIDs)
+	if err != nil {
+		return nil, err
+	}
+	stateEntriesMap := stateEntryListMap(stateEntryLists)
+
+	// Combined all the state entries for this snapshot.
+	// The order of state block NIDs in the list tells us the order to combine them in.
+	var fullState []types.StateEntry
+	for _, stateBlockNID := range stateBlockNIDList.StateBlockNIDs {
+		entries, ok := stateEntriesMap.lookup(stateBlockNID)
+		if !ok {
+			// This should only get hit if the database is corrupt.
+			// It should be impossible for an event to reference a NID that doesn't exist
+			panic(fmt.Errorf("Corrupt DB: Missing state block numeric ID %d", stateBlockNID))
+		}
+		fullState = append(fullState, entries...)
+	}
+
+	// Stable sort so that the most recent entry for each state key stays
+	// remains later in the list than the older entries for the same state key.
+	sort.Stable(stateEntryByStateKeySorter(fullState))
+	// Unique returns the last entry and hence the most recent entry for each state key.
+	fullState = fullState[:unique(stateEntryByStateKeySorter(fullState))]
+	return fullState, nil
+}
+
 // loadCombinedStateAfterEvents loads a snapshot of the state after each of the events
 // and combines those snapshots together into a single list.
 func loadCombinedStateAfterEvents(db RoomEventDatabase, prevStates []types.StateAtEvent) ([]types.StateEntry, error) {
@@ -146,18 +245,18 @@ func loadCombinedStateAfterEvents(db RoomEventDatabase, prevStates []types.State
 		if !ok {
 			// This should only get hit if the database is corrupt.
 			// It should be impossible for an event to reference a NID that doesn't exist
-			panic(fmt.Errorf("Corrupt DB: Missing state numeric ID %d", prevState.BeforeStateSnapshotNID))
+			panic(fmt.Errorf("Corrupt DB: Missing state snapshot numeric ID %d", prevState.BeforeStateSnapshotNID))
 		}
 
 		// Combined all the state entries for this snapshot.
-		// The order of state data NIDs in the list tells us the order to combine them in.
+		// The order of state block NIDs in the list tells us the order to combine them in.
 		var fullState []types.StateEntry
 		for _, stateBlockNID := range stateBlockNIDs {
 			entries, ok := stateEntriesMap.lookup(stateBlockNID)
 			if !ok {
 				// This should only get hit if the database is corrupt.
 				// It should be impossible for an event to reference a NID that doesn't exist
-				panic(fmt.Errorf("Corrupt DB: Missing state numeric ID %d", prevState.BeforeStateSnapshotNID))
+				panic(fmt.Errorf("Corrupt DB: Missing state block numeric ID %d", stateBlockNID))
 			}
 			fullState = append(fullState, entries...)
 		}
diff --git a/src/github.com/matrix-org/dendrite/roomserver/roomserver-integration-tests/main.go b/src/github.com/matrix-org/dendrite/roomserver/roomserver-integration-tests/main.go
index b8766ca87..e7cd2d1fa 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/roomserver-integration-tests/main.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/roomserver-integration-tests/main.go
@@ -356,7 +356,7 @@ func main() {
 			},
 			"VisibilityEventIDs":null,
 			"LatestEventIDs":["$1463671339126270PnVwC:matrix.org"],
-			"AddsStateEventIDs":null,
+			"AddsStateEventIDs":["$1463671337126266wrSBX:matrix.org", "$1463671339126270PnVwC:matrix.org"],
 			"RemovesStateEventIDs":null,
 			"LastSentEventID":""
 		}`,
diff --git a/src/github.com/matrix-org/dendrite/roomserver/storage/events_table.go b/src/github.com/matrix-org/dendrite/roomserver/storage/events_table.go
index 471bdcfbb..63cfa266b 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/storage/events_table.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/storage/events_table.go
@@ -87,6 +87,9 @@ const bulkSelectStateAtEventAndReferenceSQL = "" +
 const bulkSelectEventReferenceSQL = "" +
 	"SELECT event_id, reference_sha256 FROM events WHERE event_nid = ANY($1)"
 
+const bulkSelectEventIDSQL = "" +
+	"SELECT event_nid, event_id FROM events WHERE event_nid = ANY($1)"
+
 type eventStatements struct {
 	insertEventStmt                        *sql.Stmt
 	selectEventStmt                        *sql.Stmt
@@ -98,6 +101,7 @@ type eventStatements struct {
 	selectEventIDStmt                      *sql.Stmt
 	bulkSelectStateAtEventAndReferenceStmt *sql.Stmt
 	bulkSelectEventReferenceStmt           *sql.Stmt
+	bulkSelectEventIDStmt                  *sql.Stmt
 }
 
 func (s *eventStatements) prepare(db *sql.DB) (err error) {
@@ -105,36 +109,30 @@ func (s *eventStatements) prepare(db *sql.DB) (err error) {
 	if err != nil {
 		return
 	}
-	if s.insertEventStmt, err = db.Prepare(insertEventSQL); err != nil {
-		return
+
+	statements := []struct {
+		statement **sql.Stmt
+		sql       string
+	}{
+		{&s.insertEventStmt, insertEventSQL},
+		{&s.selectEventStmt, selectEventSQL},
+		{&s.bulkSelectStateEventByIDStmt, bulkSelectStateEventByIDSQL},
+		{&s.bulkSelectStateAtEventByIDStmt, bulkSelectStateAtEventByIDSQL},
+		{&s.updateEventStateStmt, updateEventStateSQL},
+		{&s.updateEventSentToOutputStmt, updateEventSentToOutputSQL},
+		{&s.selectEventSentToOutputStmt, selectEventSentToOutputSQL},
+		{&s.selectEventIDStmt, selectEventIDSQL},
+		{&s.bulkSelectStateAtEventAndReferenceStmt, bulkSelectStateAtEventAndReferenceSQL},
+		{&s.bulkSelectEventReferenceStmt, bulkSelectEventReferenceSQL},
+		{&s.bulkSelectEventIDStmt, bulkSelectEventIDSQL},
 	}
-	if s.selectEventStmt, err = db.Prepare(selectEventSQL); err != nil {
-		return
-	}
-	if s.bulkSelectStateEventByIDStmt, err = db.Prepare(bulkSelectStateEventByIDSQL); err != nil {
-		return
-	}
-	if s.bulkSelectStateAtEventByIDStmt, err = db.Prepare(bulkSelectStateAtEventByIDSQL); err != nil {
-		return
-	}
-	if s.updateEventStateStmt, err = db.Prepare(updateEventStateSQL); err != nil {
-		return
-	}
-	if s.updateEventSentToOutputStmt, err = db.Prepare(updateEventSentToOutputSQL); err != nil {
-		return
-	}
-	if s.selectEventSentToOutputStmt, err = db.Prepare(selectEventSentToOutputSQL); err != nil {
-		return
-	}
-	if s.selectEventIDStmt, err = db.Prepare(selectEventIDSQL); err != nil {
-		return
-	}
-	if s.bulkSelectStateAtEventAndReferenceStmt, err = db.Prepare(bulkSelectStateAtEventAndReferenceSQL); err != nil {
-		return
-	}
-	if s.bulkSelectEventReferenceStmt, err = db.Prepare(bulkSelectEventReferenceSQL); err != nil {
-		return
+
+	for _, statement := range statements {
+		if *statement.statement, err = db.Prepare(statement.sql); err != nil {
+			return
+		}
 	}
+
 	return
 }
 
@@ -297,6 +295,29 @@ func (s *eventStatements) bulkSelectEventReference(eventNIDs []types.EventNID) (
 	return results, nil
 }
 
+// bulkSelectEventID returns a map from numeric event ID to string event ID.
+func (s *eventStatements) bulkSelectEventID(eventNIDs []types.EventNID) (map[types.EventNID]string, error) {
+	rows, err := s.bulkSelectEventIDStmt.Query(eventNIDsAsArray(eventNIDs))
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	results := make(map[types.EventNID]string, len(eventNIDs))
+	i := 0
+	for ; rows.Next(); i++ {
+		var eventNID int64
+		var eventID string
+		if err = rows.Scan(&eventNID, &eventID); err != nil {
+			return nil, err
+		}
+		results[types.EventNID(eventNID)] = eventID
+	}
+	if i != len(eventNIDs) {
+		return nil, fmt.Errorf("storage: event NIDs missing from the database (%d != %d)", i, len(eventNIDs))
+	}
+	return results, nil
+}
+
 func eventNIDsAsArray(eventNIDs []types.EventNID) pq.Int64Array {
 	nids := make([]int64, len(eventNIDs))
 	for i := range eventNIDs {
diff --git a/src/github.com/matrix-org/dendrite/roomserver/storage/rooms_table.go b/src/github.com/matrix-org/dendrite/roomserver/storage/rooms_table.go
index a6be8fcb5..93a65e473 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/storage/rooms_table.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/storage/rooms_table.go
@@ -18,7 +18,10 @@ CREATE TABLE IF NOT EXISTS rooms (
     -- (The server will be in that state while it stores the events for the initial state of the room)
     latest_event_nids BIGINT[] NOT NULL DEFAULT '{}'::BIGINT[],
     -- The last event written to the output log for this room.
-    last_event_sent_nid BIGINT NOT NULL DEFAULT 0
+    last_event_sent_nid BIGINT NOT NULL DEFAULT 0,
+    -- The state of the room after the current set of latest events.
+    -- This will be 0 if there are no latest events in the room.
+    state_snapshot_nid BIGINT NOT NULL DEFAULT 0
 );
 `
 
@@ -35,10 +38,10 @@ const selectLatestEventNIDsSQL = "" +
 	"SELECT latest_event_nids FROM rooms WHERE room_nid = $1"
 
 const selectLatestEventNIDsForUpdateSQL = "" +
-	"SELECT latest_event_nids, last_event_sent_nid FROM rooms WHERE room_nid = $1 FOR UPDATE"
+	"SELECT latest_event_nids, last_event_sent_nid, state_snapshot_nid FROM rooms WHERE room_nid = $1 FOR UPDATE"
 
 const updateLatestEventNIDsSQL = "" +
-	"UPDATE rooms SET latest_event_nids = $2, last_event_sent_nid = $3 WHERE room_nid = $1"
+	"UPDATE rooms SET latest_event_nids = $2, last_event_sent_nid = $3, state_snapshot_nid = $4 WHERE room_nid = $1"
 
 type roomStatements struct {
 	insertRoomNIDStmt                  *sql.Stmt
@@ -96,21 +99,29 @@ func (s *roomStatements) selectLatestEventNIDs(roomNID types.RoomNID) ([]types.E
 	return eventNIDs, nil
 }
 
-func (s *roomStatements) selectLatestEventsNIDsForUpdate(txn *sql.Tx, roomNID types.RoomNID) ([]types.EventNID, types.EventNID, error) {
+func (s *roomStatements) selectLatestEventsNIDsForUpdate(txn *sql.Tx, roomNID types.RoomNID) (
+	[]types.EventNID, types.EventNID, types.StateSnapshotNID, error,
+) {
 	var nids pq.Int64Array
 	var lastEventSentNID int64
-	err := txn.Stmt(s.selectLatestEventNIDsForUpdateStmt).QueryRow(int64(roomNID)).Scan(&nids, &lastEventSentNID)
+	var stateSnapshotNID int64
+	err := txn.Stmt(s.selectLatestEventNIDsForUpdateStmt).QueryRow(int64(roomNID)).Scan(&nids, &lastEventSentNID, &stateSnapshotNID)
 	if err != nil {
-		return nil, 0, err
+		return nil, 0, 0, err
 	}
 	eventNIDs := make([]types.EventNID, len(nids))
 	for i := range nids {
 		eventNIDs[i] = types.EventNID(nids[i])
 	}
-	return eventNIDs, types.EventNID(lastEventSentNID), nil
+	return eventNIDs, types.EventNID(lastEventSentNID), types.StateSnapshotNID(stateSnapshotNID), nil
 }
 
-func (s *roomStatements) updateLatestEventNIDs(txn *sql.Tx, roomNID types.RoomNID, eventNIDs []types.EventNID, lastEventSentNID types.EventNID) error {
-	_, err := txn.Stmt(s.updateLatestEventNIDsStmt).Exec(roomNID, eventNIDsAsArray(eventNIDs), int64(lastEventSentNID))
+func (s *roomStatements) updateLatestEventNIDs(
+	txn *sql.Tx, roomNID types.RoomNID, eventNIDs []types.EventNID, lastEventSentNID types.EventNID,
+	stateSnapshotNID types.StateSnapshotNID,
+) error {
+	_, err := txn.Stmt(s.updateLatestEventNIDsStmt).Exec(
+		roomNID, eventNIDsAsArray(eventNIDs), int64(lastEventSentNID), int64(stateSnapshotNID),
+	)
 	return err
 }
diff --git a/src/github.com/matrix-org/dendrite/roomserver/storage/storage.go b/src/github.com/matrix-org/dendrite/roomserver/storage/storage.go
index bede936ad..989d91b0b 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/storage/storage.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/storage/storage.go
@@ -205,38 +205,62 @@ func (d *Database) StateEntries(stateBlockNIDs []types.StateBlockNID) ([]types.S
 	return d.statements.bulkSelectStateDataEntries(stateBlockNIDs)
 }
 
+// EventIDs implements input.RoomEventDatabase
+func (d *Database) EventIDs(eventNIDs []types.EventNID) (map[types.EventNID]string, error) {
+	return d.statements.bulkSelectEventID(eventNIDs)
+}
+
 // GetLatestEventsForUpdate implements input.EventDatabase
-func (d *Database) GetLatestEventsForUpdate(roomNID types.RoomNID) ([]types.StateAtEventAndReference, string, types.RoomRecentEventsUpdater, error) {
+func (d *Database) GetLatestEventsForUpdate(roomNID types.RoomNID) (types.RoomRecentEventsUpdater, error) {
 	txn, err := d.db.Begin()
 	if err != nil {
-		return nil, "", nil, err
+		return nil, err
 	}
-	eventNIDs, lastEventNIDSent, err := d.statements.selectLatestEventsNIDsForUpdate(txn, roomNID)
+	eventNIDs, lastEventNIDSent, currentStateSnapshotNID, err := d.statements.selectLatestEventsNIDsForUpdate(txn, roomNID)
 	if err != nil {
 		txn.Rollback()
-		return nil, "", nil, err
+		return nil, err
 	}
 	stateAndRefs, err := d.statements.bulkSelectStateAtEventAndReference(txn, eventNIDs)
 	if err != nil {
 		txn.Rollback()
-		return nil, "", nil, err
+		return nil, err
 	}
 	var lastEventIDSent string
 	if lastEventNIDSent != 0 {
 		lastEventIDSent, err = d.statements.selectEventID(txn, lastEventNIDSent)
 		if err != nil {
 			txn.Rollback()
-			return nil, "", nil, err
+			return nil, err
 		}
 	}
-	return stateAndRefs, lastEventIDSent, &roomRecentEventsUpdater{txn, d}, nil
+	return &roomRecentEventsUpdater{txn, d, stateAndRefs, lastEventIDSent, currentStateSnapshotNID}, nil
 }
 
 type roomRecentEventsUpdater struct {
-	txn *sql.Tx
-	d   *Database
+	txn                     *sql.Tx
+	d                       *Database
+	latestEvents            []types.StateAtEventAndReference
+	lastEventIDSent         string
+	currentStateSnapshotNID types.StateSnapshotNID
 }
 
+// LatestEvents implements types.RoomRecentEventsUpdater
+func (u *roomRecentEventsUpdater) LatestEvents() []types.StateAtEventAndReference {
+	return u.latestEvents
+}
+
+// LastEventIDSent implements types.RoomRecentEventsUpdater
+func (u *roomRecentEventsUpdater) LastEventIDSent() string {
+	return u.lastEventIDSent
+}
+
+// CurrentStateSnapshotNID implements types.RoomRecentEventsUpdater
+func (u *roomRecentEventsUpdater) CurrentStateSnapshotNID() types.StateSnapshotNID {
+	return u.currentStateSnapshotNID
+}
+
+// StorePreviousEvents implements types.RoomRecentEventsUpdater
 func (u *roomRecentEventsUpdater) StorePreviousEvents(eventNID types.EventNID, previousEventReferences []gomatrixserverlib.EventReference) error {
 	for _, ref := range previousEventReferences {
 		if err := u.d.statements.insertPreviousEvent(u.txn, ref.EventID, ref.EventSHA256, eventNID); err != nil {
@@ -246,6 +270,7 @@ func (u *roomRecentEventsUpdater) StorePreviousEvents(eventNID types.EventNID, p
 	return nil
 }
 
+// IsReferenced implements types.RoomRecentEventsUpdater
 func (u *roomRecentEventsUpdater) IsReferenced(eventReference gomatrixserverlib.EventReference) (bool, error) {
 	err := u.d.statements.selectPreviousEventExists(u.txn, eventReference.EventID, eventReference.EventSHA256)
 	if err == nil {
@@ -257,26 +282,34 @@ func (u *roomRecentEventsUpdater) IsReferenced(eventReference gomatrixserverlib.
 	return false, err
 }
 
-func (u *roomRecentEventsUpdater) SetLatestEvents(roomNID types.RoomNID, latest []types.StateAtEventAndReference, lastEventNIDSent types.EventNID) error {
+// SetLatestEvents implements types.RoomRecentEventsUpdater
+func (u *roomRecentEventsUpdater) SetLatestEvents(
+	roomNID types.RoomNID, latest []types.StateAtEventAndReference, lastEventNIDSent types.EventNID,
+	currentStateSnapshotNID types.StateSnapshotNID,
+) error {
 	eventNIDs := make([]types.EventNID, len(latest))
 	for i := range latest {
 		eventNIDs[i] = latest[i].EventNID
 	}
-	return u.d.statements.updateLatestEventNIDs(u.txn, roomNID, eventNIDs, lastEventNIDSent)
+	return u.d.statements.updateLatestEventNIDs(u.txn, roomNID, eventNIDs, lastEventNIDSent, currentStateSnapshotNID)
 }
 
+// HasEventBeenSent implements types.RoomRecentEventsUpdater
 func (u *roomRecentEventsUpdater) HasEventBeenSent(eventNID types.EventNID) (bool, error) {
 	return u.d.statements.selectEventSentToOutput(u.txn, eventNID)
 }
 
+// MarkEventAsSent implements types.RoomRecentEventsUpdater
 func (u *roomRecentEventsUpdater) MarkEventAsSent(eventNID types.EventNID) error {
 	return u.d.statements.updateEventSentToOutput(u.txn, eventNID)
 }
 
+// Commit implements types.RoomRecentEventsUpdater
 func (u *roomRecentEventsUpdater) Commit() error {
 	return u.txn.Commit()
 }
 
+// Rollback implements types.RoomRecentEventsUpdater
 func (u *roomRecentEventsUpdater) Rollback() error {
 	return u.txn.Rollback()
 }
diff --git a/src/github.com/matrix-org/dendrite/roomserver/types/types.go b/src/github.com/matrix-org/dendrite/roomserver/types/types.go
index 0a90d40d1..1d268e1f4 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/types/types.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/types/types.go
@@ -133,6 +133,12 @@ type StateEntryList struct {
 // (On postgresql this wraps a database transaction that holds a "FOR UPDATE"
 //  lock on the row holding the latest events for the room.)
 type RoomRecentEventsUpdater interface {
+	// The latest event IDs and state in the room.
+	LatestEvents() []StateAtEventAndReference
+	// The event ID of the latest event written to the output log in the room.
+	LastEventIDSent() string
+	// The current state of the room.
+	CurrentStateSnapshotNID() StateSnapshotNID
 	// Store the previous events referenced by an event.
 	// This adds the event NID to an entry in the database for each of the previous events.
 	// If there isn't an entry for one of previous events then an entry is created.
@@ -143,7 +149,10 @@ type RoomRecentEventsUpdater interface {
 	IsReferenced(eventReference gomatrixserverlib.EventReference) (bool, error)
 	// Set the list of latest events for the room.
 	// This replaces the current list stored in the database with the given list
-	SetLatestEvents(roomNID RoomNID, latest []StateAtEventAndReference, lastEventNIDSent EventNID) error
+	SetLatestEvents(
+		roomNID RoomNID, latest []StateAtEventAndReference, lastEventNIDSent EventNID,
+		currentStateSnapshotNID StateSnapshotNID,
+	) error
 	// Check if the event has already be written to the output logs.
 	HasEventBeenSent(eventNID EventNID) (bool, error)
 	// Mark the event as having been sent to the output logs.