@@ -26,0 +23,4 @@
+	let max_depth = body.max_depth.unwrap_or(max_max_depth).min(max_max_depth);
+	let limit = body.limit.map_or(DEFAULT_LIMIT, usize_from_ruma);
+	if limit == 0 {
+		return Err!(Request(InvalidParam("limit must be greater than zero.")));

@@ -60,2 +84,4 @@
 impl crate::Service for Service {
 	fn build(args: crate::Args<'_>) -> Result<Arc<Self>> {
+		let config = &args.server.config;
+		let cache_capacity = f64::from(config.roomid_spacehierarchy_cache_capacity)

@@ -71,6 +99,7 @@ impl crate::Service for Service {
 				state_cache: args.depend::<rooms::state_cache::Service>("rooms::state_cache"),
 				timeline: args.depend::<rooms::timeline::Service>("rooms::timeline"),
 			},
+			hierarchy_cache: LruCache::new(usize_from_f64(cache_capacity)?.max(1)).into(),

@@ -293,0 +334,4 @@
+		room_id: OwnedRoomId,
+		max_depth: UInt,
+		suggested_only: bool,
+		from: Option<&str>,

@@ -169,2 +173,2 @@
-            .map(|child| SpaceChild { room_id: child.state_key, via: child.content.via })
-            .collect();
+			.collect();
+		children.sort();