I've come across a number of times where the statistics on materialized views become stale producing bad plans. It turns out that autovacuum only touches a materialized view when it is first created and ignores it on a refresh. When you have a materialized view like yesterdays_sales the data in the materialized view turns over every day.
Attached is a patch to trigger autovacuum based on a matview refresh along with a system view pg_stat_all_matviews to show information more meaningful for materialized views.
