refactor: add config value

.config/example.yml

@@ -64,6 +64,20 @@ db:
 #   keyspace: firefish
 #   replicationFactor: 1
 #   localDataCentre: "datacenter1"
+#
+#   # <sparseTimelineDays> determines how many days ScyllaDB searches posts within
+#   # one pagination when user's timelines are "sparse". As the user follows more
+#   # accounts and more posts appear in the feeds, user's timelines will no longer
+#   # be sparse.  The bigger this value is, the slower the responses of timeline
+#   # APIs would be.
+#   #
+#   # Let's say <sparseTimelineDays> is 14 and a user signed up and only created one
+#   # post. Suppose that this user follows no accounts, and created the second post
+#   # 15 days after signing up. In this case, the user's first post does not
+#   # appear in their home timeline.
+#   #
+#   # (default: 14)
+#   sparseTimelineDays: 14
 
 #   ┌─────────────────────┐
 #───┘ Redis configuration └─────────────────────────────────────

packages/backend/src/config/types.ts

@@ -22,6 +22,7 @@ export type Source = {
 		keyspace: string;
 		replicationFactor: number;
 		localDataCentre: string;
+		sparseTimelineDays?: number;
 	};
 	redis: {
 		host: string;

packages/backend/src/db/scylla.ts

@@ -238,7 +238,7 @@ export interface ScyllaNoteReaction extends NoteReaction {
 	emoji: PopulatedEmoji;
 }
 
-const QUERY_LIMIT = 1000;
+const QUERY_LIMIT = 1000; // TODO: should this be configurable?
 
 export function parseScyllaReaction(row: types.Row): ScyllaNoteReaction {
 	return {
@@ -303,7 +303,7 @@ export async function execNotePaginationQuery(
 		noteId?: string;
 	},
 	filter?: (_: ScyllaNote[]) => Promise<ScyllaNote[]>,
-	maxPartitions = 30,
+	maxPartitions = config.scylla?.sparseTimelineDays ?? 14,
 ): Promise<ScyllaNote[]> {
 	if (!scyllaClient) return [];