Re: BUG #4596: information_schema.table_privileges is way too slow

[Kirill Simonov <xi(at)gamma(dot)dn(dot)ua>]

Pavel Stehule wrote:
> 2008/12/25 Kirill Simonov <xi(at)gamma(dot)dn(dot)ua>:
> > Tom Lane wrote:
> > > "Kirill Simonov" <xi(at)gamma(dot)dn(dot)ua> writes:
> > > > It takes about 5 minutes to perform the query
> > > > SELECT * FROM information_schema.table_privileges
> > > > on an empty database (i.e. with system tables only).
> > > Not here.  What non-default settings might you be using?
> > Indeed, it is slow because there are a lot of rows in pg_authid (about 700).
> >  Is there a possibility to make table_privileges faster with a large number
> > of roles?
> >
> > Thanks,
> > Kirill
>
> two years ago I tested 50000 users without problems. Try to vacuum and
> reindex your system tables

Neither VACUUM nor REINDEX SYSTEM did help.  The problem could be 
reproduced on a freshly installed Postgres:

-- add a function to generate dummy roles.
create language plpgsql;
create function create_dummy_role(start int, finish int) returns void as $$
begin
    for i in start..finish loop
        execute 'create role dummy_' || cast(i as text);
    end loop;
end;
$$ language plpgsql;

-- no extra roles
select count(*) from information_schema.table_privileges;
>>> Time: 11.467 ms

-- 10 roles
select create_dummy_role(1, 10);
select count(*) from information_schema.table_privileges;
>>> Time: 161.539 ms

-- 100 roles
select create_dummy_role(11, 100);
select count(*) from information_schema.table_privileges;
>>> Time: 7807.675 ms

-- 1000 roles
select create_dummy_role(101, 1000);
select count(*) from information_schema.table_privileges;
>>> Time: 543030.948 ms


Thanks,
Kirill