drop table hits_user_daily_count;

create table hits_user_daily_count (
 userid                     integer  not null,
 date                       date     not null,
 num_hits                   integer  default 0,
 num_cover_page_hits        integer  default 0,
 num_additional_files_hits  integer  default 0,
 primary key (userid, date));
create index hits_user_daily_count_date on hits_user_daily_count(date);

create or replace function fill_for_date(d date, n int) returns void
language plpgsql as $$
begin
  insert into hits_user_daily_count
    select uid, d, random()*10, random()*10 from
      generate_series(1,n) uid order by random();
end
$$;

select fill_for_date('today'::date - 5, 100000);
select fill_for_date('today'::date - 4, 100000);
select fill_for_date('today'::date - 3, 100000);
select fill_for_date('today'::date - 2, 100000);
select fill_for_date('today'::date - 1, 100000);

analyze hits_user_daily_count;

-- If you include this step, the query for today actually takes a long time;
-- but you risk auto-analyze changing the stats and making the problem go away.
-- select fill_for_date('today'::date - 0, 20000);

explain analyze select 1
        from hits_user_daily_count
        where userid = 15901 and date = 'yesterday'::date;

explain analyze select 1
        from hits_user_daily_count
        where userid = 15901 and date = 'today'::date;