create table t ( x number, y char(1) ) pctfree 99 pctused 1;

insert into t
select mod(rownum,3), 'x' from dual connect by level <= 1000000;

commit;

select min(count(*)), max(count(*)), avg(count(*))
from   t
group by dbms_rowid.rowid_block_number(rowid);


create bitmap index t_idx on t(x);

select extents, blocks, bytes/1024 "SIZE(KB)"
from   user_segments
where  segment_name = 'T_IDX';

drop index t_idx;
alter table t minimize records_per_block;

create bitmap index t_idx on t(x);

select extents, blocks, bytes/1024 "SIZE(KB)"
from   user_segments
where  segment_name = 'T_IDX';
