Search notes:

Oracle: X$KCB…

Kernel Cache Buffer…
The following statements show that these tables have the same amount of records and seem therefore to be related: 
select count(*) from x$kcbwh;
select count(*) from x$kcbsw;
select count(*) from x$kcbuwhy;

select
   wh.kcbwhdes     des,
   sw.other_wait,
   wy.why0, wy.why1, wy.why2, wy.why3, wy.why4
from
   x$kcbwh    wh   join
   x$kcbsw    sw on wh.indx = sw.indx join
   x$kcbuwhy  wy on wh.indx = wy.indx
order by
   sw.other_wait desc;

See also

fixed table

Index