40.5. A Table Rewrite Event Trigger Example
Thanks to the
table_rewrite event, it is possible to implement a table rewriting policy only allowing the rewrite in maintenance windows.
Here's an example implementing such a policy.
CREATE OR REPLACE FUNCTION no_rewrite() RETURNS event_trigger LANGUAGE plpgsql AS $$ --- --- Implement local Table Rewriting policy: --- public.foo is not allowed rewriting, ever --- other tables are only allowed rewriting between 1am and 6am --- unless they have more than 100 blocks --- DECLARE table_oid oid := pg_event_trigger_table_rewrite_oid(); current_hour integer := extract('hour' from current_time); pages integer; max_pages integer := 100; BEGIN IF pg_event_trigger_table_rewrite_oid() = 'public.foo'::regclass THEN RAISE EXCEPTION 'you''re not allowed to rewrite the table %', table_oid::regclass; END IF; SELECT INTO pages relpages FROM pg_class WHERE oid = table_oid; IF pages > max_pages THEN RAISE EXCEPTION 'rewrites only allowed for table with less than % pages', max_pages; END IF; IF current_hour NOT BETWEEN 1 AND 6 THEN RAISE EXCEPTION 'rewrites only allowed between 1am and 6am'; END IF; END; $$; CREATE EVENT TRIGGER no_rewrite_allowed ON table_rewrite EXECUTE FUNCTION no_rewrite();