desc STG_XML
Name                           Null     Type
------------------------------ -------- ------------------------
ENTITY_ID                      NOT NULL VARCHAR2(100 CHAR) 
ENTITY_TYPE_ID                 NOT NULL NUMBER
SOURCE_ID                      NOT NULL VARCHAR2(512 CHAR) 
XML_SCHEMA_ID                  NOT NULL NUMBER
JOB_ID                         NOT NULL NUMBER
FINGERPRINT                    NOT NULL VARCHAR2(100 CHAR)
ENTITY_XML_DATA                         CLOB()
ARCHIVED                                NUMBER(1)
CREATION_DATE                           TIMESTAMP(6)
MODIFICATION_DATE                       TIMESTAMP(6)
ARCHIVING_DATE                          TIMESTAMP(6)
CREATED_BY                              VARCHAR2(50 CHAR)
MODIFIED_BY                             VARCHAR2(50 CHAR)

select sum(bytes)/1024 SIZE_KB, SEGMENT_NAME 
from user_segments group by SEGMENT_NAME order by SIZE_KB desc; 

select TABLE_NAME, ROUND((AVG_ROW_LEN * NUM_ROWS / 1024), 2) SIZE_KB 
from USER_TABLES order by SIZE_KB desc; 

create table t1(c2 varchar2(10));
alter table t1 enable row movement;
insert into t1 select '1234567890' from dual connect by level < 1000000;
select bytes from user_segments where segment_name='T1';
delete from t1;
alter table t1 shrink space compact;
select bytes from user_segments where segment_name='T1';
alter table t1 shrink space;
select bytes from user_segments where segment_name='T1';