MySQL query optimization. Added loading component.

sql/schema.postgresql.sql

@@ -65,6 +65,7 @@ create index pageview_created_at_idx on pageview(created_at);
 create index pageview_website_id_idx on pageview(website_id);
 create index pageview_session_id_idx on pageview(session_id);
 create index pageview_website_id_created_at_idx on pageview(website_id, created_at);
+create index pageview_website_id_session_id_created_at_idx on pageview(website_id, session_id, created_at);
 
 create index event_created_at_idx on event(created_at);
 create index event_website_id_idx on event(website_id);