Add RoomInfo cache, remove RoomServerRoomNIDsCache (#1646)

* Add RoomInfo cache, remove RoomServerRoomNID cache, ensure caches are thread-safe

* Don't panic if the roomInfo isn't known yet

* LRU package is already threadsafe

* Use RoomInfo cache to find room version if possible in Events()

* Adding comments about RoomInfoCache safety

6 files changed, 88 insertions, 41 deletions

diff --git a/internal/caching/cache_roominfo.go b/internal/caching/cache_roominfo.go
new file mode 100644
index 00000000..f32d6ba9
--- /dev/null
+++ b/internal/caching/cache_roominfo.go
@@ -0,0 +1,45 @@
+package caching
+
+import (
+	"github.com/matrix-org/dendrite/roomserver/types"
+)
+
+// WARNING: This cache is mutable because it's entirely possible that
+// the IsStub or StateSnaphotNID fields can change, even though the
+// room version and room NID fields will not. This is only safe because
+// the RoomInfoCache is used ONLY within the roomserver and because it
+// will be kept up-to-date by the latest events updater. It MUST NOT be
+// used from other components as we currently have no way to invalidate
+// the cache in downstream components.
+
+const (
+	RoomInfoCacheName       = "roominfo"
+	RoomInfoCacheMaxEntries = 1024
+	RoomInfoCacheMutable    = true
+)
+
+// RoomInfosCache contains the subset of functions needed for
+// a room Info cache. It must only be used from the roomserver only
+// It is not safe for use from other components.
+type RoomInfoCache interface {
+	GetRoomInfo(roomID string) (roomInfo types.RoomInfo, ok bool)
+	StoreRoomInfo(roomID string, roomInfo types.RoomInfo)
+}
+
+// GetRoomInfo must only be called from the roomserver only. It is not
+// safe for use from other components.
+func (c Caches) GetRoomInfo(roomID string) (types.RoomInfo, bool) {
+	val, found := c.RoomInfos.Get(roomID)
+	if found && val != nil {
+		if roomInfo, ok := val.(types.RoomInfo); ok {
+			return roomInfo, true
+		}
+	}
+	return types.RoomInfo{}, false
+}
+
+// StoreRoomInfo must only be called from the roomserver only. It is not
+// safe for use from other components.
+func (c Caches) StoreRoomInfo(roomID string, roomInfo types.RoomInfo) {
+	c.RoomInfos.Set(roomID, roomInfo)
+}
diff --git a/internal/caching/cache_roomservernids.go b/internal/caching/cache_roomservernids.go
index cac59549..bf4fe85e 100644
--- a/internal/caching/cache_roomservernids.go
+++ b/internal/caching/cache_roomservernids.go
@@ -15,10 +15,6 @@ const (
 	RoomServerEventTypeNIDsCacheMaxEntries = 64
 	RoomServerEventTypeNIDsCacheMutable    = false
 
-	RoomServerRoomNIDsCacheName       = "roomserver_room_nids"
-	RoomServerRoomNIDsCacheMaxEntries = 1024
-	RoomServerRoomNIDsCacheMutable    = false
-
 	RoomServerRoomIDsCacheName       = "roomserver_room_ids"
 	RoomServerRoomIDsCacheMaxEntries = 1024
 	RoomServerRoomIDsCacheMutable    = false
@@ -27,6 +23,7 @@ const (
 type RoomServerCaches interface {
 	RoomServerNIDsCache
 	RoomVersionCache
+	RoomInfoCache
 }
 
 // RoomServerNIDsCache contains the subset of functions needed for
@@ -38,9 +35,6 @@ type RoomServerNIDsCache interface {
 	GetRoomServerEventTypeNID(eventType string) (types.EventTypeNID, bool)
 	StoreRoomServerEventTypeNID(eventType string, nid types.EventTypeNID)
 
-	GetRoomServerRoomNID(roomID string) (types.RoomNID, bool)
-	StoreRoomServerRoomNID(roomID string, nid types.RoomNID)
-
 	GetRoomServerRoomID(roomNID types.RoomNID) (string, bool)
 	StoreRoomServerRoomID(roomNID types.RoomNID, roomID string)
 }
@@ -73,21 +67,6 @@ func (c Caches) StoreRoomServerEventTypeNID(eventType string, nid types.EventTyp
 	c.RoomServerEventTypeNIDs.Set(eventType, nid)
 }
 
-func (c Caches) GetRoomServerRoomNID(roomID string) (types.RoomNID, bool) {
-	val, found := c.RoomServerRoomNIDs.Get(roomID)
-	if found && val != nil {
-		if roomNID, ok := val.(types.RoomNID); ok {
-			return roomNID, true
-		}
-	}
-	return 0, false
-}
-
-func (c Caches) StoreRoomServerRoomNID(roomID string, roomNID types.RoomNID) {
-	c.RoomServerRoomNIDs.Set(roomID, roomNID)
-	c.RoomServerRoomIDs.Set(strconv.Itoa(int(roomNID)), roomID)
-}
-
 func (c Caches) GetRoomServerRoomID(roomNID types.RoomNID) (string, bool) {
 	val, found := c.RoomServerRoomIDs.Get(strconv.Itoa(int(roomNID)))
 	if found && val != nil {
@@ -99,5 +78,5 @@ func (c Caches) GetRoomServerRoomID(roomNID types.RoomNID) (string, bool) {
 }
 
 func (c Caches) StoreRoomServerRoomID(roomNID types.RoomNID, roomID string) {
-	c.StoreRoomServerRoomNID(roomID, roomNID)
+	c.RoomServerRoomIDs.Set(strconv.Itoa(int(roomNID)), roomID)
 }
diff --git a/internal/caching/caches.go b/internal/caching/caches.go
index e7b7f550..f04d05d4 100644
--- a/internal/caching/caches.go
+++ b/internal/caching/caches.go
@@ -10,6 +10,7 @@ type Caches struct {
 	RoomServerEventTypeNIDs Cache // RoomServerNIDsCache
 	RoomServerRoomNIDs      Cache // RoomServerNIDsCache
 	RoomServerRoomIDs       Cache // RoomServerNIDsCache
+	RoomInfos               Cache // RoomInfoCache
 	FederationEvents        Cache // FederationEventsCache
 }
 
diff --git a/internal/caching/impl_inmemorylru.go b/internal/caching/impl_inmemorylru.go
index f05e8f3c..cf05a8b5 100644
--- a/internal/caching/impl_inmemorylru.go
+++ b/internal/caching/impl_inmemorylru.go
@@ -45,19 +45,19 @@ func NewInMemoryLRUCache(enablePrometheus bool) (*Caches, error) {
 	if err != nil {
 		return nil, err
 	}
-	roomServerRoomNIDs, err := NewInMemoryLRUCachePartition(
-		RoomServerRoomNIDsCacheName,
-		RoomServerRoomNIDsCacheMutable,
-		RoomServerRoomNIDsCacheMaxEntries,
+	roomServerRoomIDs, err := NewInMemoryLRUCachePartition(
+		RoomServerRoomIDsCacheName,
+		RoomServerRoomIDsCacheMutable,
+		RoomServerRoomIDsCacheMaxEntries,
 		enablePrometheus,
 	)
 	if err != nil {
 		return nil, err
 	}
-	roomServerRoomIDs, err := NewInMemoryLRUCachePartition(
-		RoomServerRoomIDsCacheName,
-		RoomServerRoomIDsCacheMutable,
-		RoomServerRoomIDsCacheMaxEntries,
+	roomInfos, err := NewInMemoryLRUCachePartition(
+		RoomInfoCacheName,
+		RoomInfoCacheMutable,
+		RoomInfoCacheMaxEntries,
 		enablePrometheus,
 	)
 	if err != nil {
@@ -77,8 +77,8 @@ func NewInMemoryLRUCache(enablePrometheus bool) (*Caches, error) {
 		ServerKeys:              serverKeys,
 		RoomServerStateKeyNIDs:  roomServerStateKeyNIDs,
 		RoomServerEventTypeNIDs: roomServerEventTypeNIDs,
-		RoomServerRoomNIDs:      roomServerRoomNIDs,
 		RoomServerRoomIDs:       roomServerRoomIDs,
+		RoomInfos:               roomInfos,
 		FederationEvents:        federationEvents,
 	}, nil
 }
diff --git a/roomserver/storage/shared/latest_events_updater.go b/roomserver/storage/shared/latest_events_updater.go
index 8825dc46..36865081 100644
--- a/roomserver/storage/shared/latest_events_updater.go
+++ b/roomserver/storage/shared/latest_events_updater.go
@@ -105,6 +105,13 @@ func (u *LatestEventsUpdater) SetLatestEvents(
 		if err := u.d.RoomsTable.UpdateLatestEventNIDs(u.ctx, txn, roomNID, eventNIDs, lastEventNIDSent, currentStateSnapshotNID); err != nil {
 			return fmt.Errorf("u.d.RoomsTable.updateLatestEventNIDs: %w", err)
 		}
+		if roomID, ok := u.d.Cache.GetRoomServerRoomID(roomNID); ok {
+			if roomInfo, ok := u.d.Cache.GetRoomInfo(roomID); ok {
+				roomInfo.StateSnapshotNID = currentStateSnapshotNID
+				roomInfo.IsStub = false
+				u.d.Cache.StoreRoomInfo(roomID, roomInfo)
+			}
+		}
 		return nil
 	})
 }
diff --git a/roomserver/storage/shared/storage.go b/roomserver/storage/shared/storage.go
index d61fa61d..b4d9d562 100644
--- a/roomserver/storage/shared/storage.go
+++ b/roomserver/storage/shared/storage.go
@@ -124,7 +124,15 @@ func (d *Database) StateEntriesForTuples(
 }
 
 func (d *Database) RoomInfo(ctx context.Context, roomID string) (*types.RoomInfo, error) {
-	return d.RoomsTable.SelectRoomInfo(ctx, roomID)
+	if roomInfo, ok := d.Cache.GetRoomInfo(roomID); ok {
+		return &roomInfo, nil
+	}
+	roomInfo, err := d.RoomsTable.SelectRoomInfo(ctx, roomID)
+	if err == nil && roomInfo != nil {
+		d.Cache.StoreRoomServerRoomID(roomInfo.RoomNID, roomID)
+		d.Cache.StoreRoomInfo(roomID, *roomInfo)
+	}
+	return roomInfo, err
 }
 
 func (d *Database) AddState(
@@ -322,14 +330,24 @@ func (d *Database) Events(
 	for _, n := range roomNIDs {
 		uniqueRoomNIDs[n] = struct{}{}
 	}
-	roomNIDList := make([]types.RoomNID, 0, len(uniqueRoomNIDs))
+	roomVersions := make(map[types.RoomNID]gomatrixserverlib.RoomVersion)
+	fetchNIDList := make([]types.RoomNID, 0, len(uniqueRoomNIDs))
 	for n := range uniqueRoomNIDs {
-		roomNIDList = append(roomNIDList, n)
+		if roomID, ok := d.Cache.GetRoomServerRoomID(n); ok {
+			if roomInfo, ok := d.Cache.GetRoomInfo(roomID); ok {
+				roomVersions[n] = roomInfo.RoomVersion
+				continue
+			}
+		}
+		fetchNIDList = append(fetchNIDList, n)
 	}
-	roomVersions, err := d.RoomsTable.SelectRoomVersionsForRoomNIDs(ctx, roomNIDList)
+	dbRoomVersions, err := d.RoomsTable.SelectRoomVersionsForRoomNIDs(ctx, fetchNIDList)
 	if err != nil {
 		return nil, err
 	}
+	for n, v := range dbRoomVersions {
+		roomVersions[n] = v
+	}
 	results := make([]types.Event, len(eventJSONs))
 	for i, eventJSON := range eventJSONs {
 		result := &results[i]
@@ -556,8 +574,8 @@ func (d *Database) assignRoomNID(
 	ctx context.Context, txn *sql.Tx,
 	roomID string, roomVersion gomatrixserverlib.RoomVersion,
 ) (types.RoomNID, error) {
-	if roomNID, ok := d.Cache.GetRoomServerRoomNID(roomID); ok {
-		return roomNID, nil
+	if roomInfo, ok := d.Cache.GetRoomInfo(roomID); ok {
+		return roomInfo.RoomNID, nil
 	}
 	// Check if we already have a numeric ID in the database.
 	roomNID, err := d.RoomsTable.SelectRoomNID(ctx, txn, roomID)
@@ -569,9 +587,6 @@ func (d *Database) assignRoomNID(
 			roomNID, err = d.RoomsTable.SelectRoomNID(ctx, txn, roomID)
 		}
 	}
-	if err == nil {
-		d.Cache.StoreRoomServerRoomNID(roomID, roomNID)
-	}
 	return roomNID, err
 }