mat views stats

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.

-- Jim