create table t1(
    c1 number not null
  , c2 number
  , c3 number
  , c4 number
  , constraint  t1_pk primary key (c1) )
organization index ;               -- IOT 

create index t1_x1 on t1 (c2) ;    -- Secondary ε 

insert into t1
select rownum, rownum, rownum, rownum
from all_objects
where  rownum <= 1000;

commit;

select index_name, PCT_DIRECT_ACCESS
from user_indexes
where index_name = 'T1_X1';

exec dbms_stats.gather_index_stats(user, 't1_x1');

select index_name, PCT_DIRECT_ACCESS
from user_indexes
where index_name = 'T1_X1';

alter index t1_x1 UPDATE BLOCK REFERENCES;

select index_name, PCT_DIRECT_ACCESS
from user_indexes
where index_name = 'T1_X1';

exec dbms_stats.gather_index_stats(user, 't1_x1');

select index_name, blevel, PCT_DIRECT_ACCESS
from user_indexes
where index_name = 'T1_X1';

exec dbms_stats.set_index_stats (user, 't1_x1', guessq => 100);

