Re: vacuumdb changes for stats import/export

Out of curiosity, I generated many relations with the following command
(stolen from [0]):

do $$
begin
for i in 1..100000 loop
  execute format('create table t%s (f1 int unique, f2 int unique);', i);
  execute format('insert into t%s select x, x from generate_series(1,1000) x',
                 i);
  if i % 100 = 0 then commit; end if;
end loop;
end
$$;

And then I ran a database-wide ANALYZE.  Without --missing-only, vacuumdb's
catalog query took 65 ms.  With --missing-only, it took 735 ms.  While
that's a big jump, this query will only run once for a given vacuumdb, and
--missing-only is likely to save a lot of time elsewhere.

If no feedback or objections materialize, I'm planning to commit these
early next week.

[0] https://postgr.es/m/3612876.1689443232%40sss.pgh.pa.us

-- 
nathan