diff --git a/src/resources/extensions/sf/sf-db.ts b/src/resources/extensions/sf/sf-db.ts
index 5929b5b7e..f89800b06 100644
--- a/src/resources/extensions/sf/sf-db.ts
+++ b/src/resources/extensions/sf/sf-db.ts
@@ -313,6 +313,12 @@ function initSchema(db: DbAdapter, fileBacked: boolean): void {
         FOREIGN KEY (to_id) REFERENCES memories(id) ON DELETE CASCADE
       )
     `);
+		// PK covers from_id as leading column already; reverse lookups
+		// (memory-relations.ts queries WHERE to_id = ?) need their own index
+		// to avoid a full table scan as the relation count grows.
+		db.exec(
+			"CREATE INDEX IF NOT EXISTS idx_memory_relations_to ON memory_relations(to_id)",
+		);
 
 		db.exec(`
       CREATE TABLE IF NOT EXISTS memory_sources (