Up-to-date dictionary of distinct values for column - postgresql

Question

I have a table with many columns and several million rows like
CREATE TABLE foo (
id integer,
thing1 text,
thing2 text,
...
stuff text);
How can I manage the relevance of dictionary of unique values of stuff column that originally populates like this:
INSERT INTO stuff_dict SELECT DISTINCT stuff from foo;
Should I manually synchronize (check if new stuff value already in stuff_dict before every insert/update) or use triggers for each insert/update/delete from foo table. In latter case, what is the best design for such a trigger(s)?
UPDATE: view does not suit here, because the SELECT * FROM stuff_dict should run as fast as possible (even CREATE INDEX ON foo(stuff) does not help much when foo has tens of millions of records).

Answer 1

A materialized view seems to be the simplest option for a large table.
In the trigger function just refresh the view. You can use concurrently option (see the pozs's comment below).
create materialized view stuff_dict as
select distinct stuff
from foo;
create or replace function refresh_stuff_dict()
returns trigger language plpgsql
as $$
begin
refresh materialized view /*concurrently*/ stuff_dict;
return null;
end $$;
create trigger refresh_stuff_dict
after insert or update or delete or truncate
on foo for each statement
execute procedure refresh_stuff_dict();
While the solution with a materialized view is straightforward it may be suboptimal when the table foo is modified frequently. In this case use a table for the dictionary. An index will be helpful.
create table stuff_dict as
select distinct stuff
from foo;
create index on stuff_dict(stuff);
The trigger function is more complicated and should be fired for each row after insert/update/delete:
create or replace function refresh_stuff_dict()
returns trigger language plpgsql
as $$
declare
do_insert boolean := tg_op = 'INSERT' or tg_op = 'UPDATE' and new.stuff <> old.stuff;
do_delete boolean := tg_op = 'DELETE' or tg_op = 'UPDATE' and new.stuff <> old.stuff;
begin
if do_insert and not exists (select 1 from stuff_dict where stuff = new.stuff) then
insert into stuff_dict values(new.stuff);
end if;
if do_delete and not exists (select 1 from foo where stuff = old.stuff) then
delete from stuff_dict
where stuff = old.stuff;
end if;
return case tg_op when 'DELETE' then old else new end;
end $$;
create trigger refresh_stuff_dict
after insert or update or delete
on foo for each row
execute procedure refresh_stuff_dict();