得益于table_rewrite
事件的存在,我们可以实现一种只允许在
维护窗口中重写的表重写策略。
这里是实现这种策略的例子。
CREATE OR REPLACE FUNCTION no_rewrite() RETURNS event_trigger LANGUAGE plpgsql AS $$ --- --- 实现本地表重写策略: --- public.foo 不允许重写,其他表只允许在 1am 和 6am 之间重写, --- 且前提是它们拥有不超过 100 块 --- DECLARE table_oid oid := pg_event_trigger_table_rewrite_oid(); current_hour integer := extract('hour' from current_time); pages integer; max_pages integer := 100; BEGIN IF pg_event_trigger_table_rewrite_oid() = 'public.foo'::regclass THEN RAISE EXCEPTION 'you''re not allowed to rewrite the table %', table_oid::regclass; END IF; SELECT INTO pages relpages FROM pg_class WHERE oid = table_oid; IF pages > max_pages THEN RAISE EXCEPTION 'rewrites only allowed for table with less than % pages', max_pages; END IF; IF current_hour NOT BETWEEN 1 AND 6 THEN RAISE EXCEPTION 'rewrites only allowed between 1am and 6am'; END IF; END; $$; CREATE EVENT TRIGGER no_rewrite_allowed ON table_rewrite EXECUTE PROCEDURE no_rewrite();