Postgres trigger refreshing a materialized view not working after some time

Question

I have a materialized view created and a trigger to refresh it after any update on the source table.

Everything seems to work oke, but after a while seems that the trigger stops working since the materialized view remains with stale data.

At some point after I recreated the trigger the functionality started to work again.

The postgres version used in 11.

CREATE OR REPLACE FUNCTION refresh_some_view()
    RETURNS TRIGGER
    LANGUAGE PLPGSQL
AS
$$
BEGIN
    REFRESH MATERIALIZED VIEW some_view;
    RETURN NEW;
END;
$$;


CREATE TRIGGER on_source_table_update
    AFTER UPDATE OR INSERT OR DELETE
    ON source_table
    FOR EACH ROW
EXECUTE PROCEDURE refresh_some_view();

Answer 1

Use FOR EACH STATEMENT instead of FOR EACH ROW . This will prevent the view to be refreshed after every single row of your insert statements, which most likely isn't what you want.

CREATE TRIGGER on_source_table_update 
AFTER UPDATE OR INSERT OR DELETE ON source_table 
FOR EACH STATEMENT EXECUTE PROCEDURE refresh_some_view();

You can check it in the query planner. If you use FOR EACH STATEMENT the refresh in the function will be called only once - see number of calls at Trigger on_source_table_update . This query plan shows what happens with an insert containing 1000 rows - see the number rows at ProjectSet :

                                QUERY PLAN 
------------------------------------------------------------------------------

Insert on source_table (actual time=7.097..7.140 rows=0 loops=1)
  ->  ProjectSet (actual time=0.005..0.398 rows=1000 loops=1)
        ->  Result (actual time=0.002..0.044 rows=1 loops=1)
Planning Time: 0.264 ms
Trigger on_source_table_update: time=11.628 calls=1
Execution Time: 19.011 ms

.. but if you stick to FOR EACH ROW things get much slower, as the trigger calls the function once per row (1000 times!):

                                QUERY PLAN 
------------------------------------------------------------------------------
Insert on source_table (actual time=4.187..4.188 rows=0 loops=1)
  ->  ProjectSet (actual time=0.004..0.204 rows=1000 loops=1)
        ->  Result (actual time=0.002..0.002 rows=1 loops=1)
Planning Time: 0.122 ms
Trigger on_source_table_update: time=13815.499 calls=1000
Execution Time: 13820.529 ms

Demo: db<>fiddle