Keeping Materialized Views Updated
The reason our materialized view is so much faster than the regular view is because it essentially caches the results of the backing query into a real table. The trade-off is that the contents of the table could lag behind what’s in the tables that the backing query queries.
Postgres provides a way to refresh the view via REFRESH MATERIALIZED VIEW. Before Postgres 9.4, refreshing materialized views like this was a problem, because it would lock the view while it was being refreshed. That meant that any application that wanted to query the view would have to wait until the update was completed. Since this could potentially be a long time, it meant that materialized views were mostly useless before 9.4.
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