可能会大一点。

1. 用这个表名去查大小,你会发现这个表的大小没有变，下面我模拟了存入一个BLOB对象并让它变大
   

https://dbfiddle.uk/?rdbms=oracle_21&fiddle=948ce4fca7881bf70b8dc08f91e02928

2. BLOB/CLOB的数据其实是存储在另外的segment里的，原表里其实只存了一个位置，指明这个值是存到哪去了。
3. 另外，oracle数据库并不是存多少占多少，因为它是按段按块来的。

测试sql：

create table test_blob_0531 (a blob);
select BYTES from USER_segments where segment_name='TEST_BLOB_0531';
insert into test_blob_0531 values (empty_blob());
select BYTES from USER_segments where segment_name='TEST_BLOB_0531';
declare
  a_blob blob;
  tmp varchar2(50):='3131313131313131313131313131';
begin
  select a into a_blob from test_blob_0531 for update;
  dbms_lob.open(a_blob, dbms_lob.lob_readwrite);
  dbms_lob.writeappend( a_blob,length(to_blob(tmp)), to_blob(tmp));
  dbms_lob.close(a_blob);
  commit;
end;
/
select BYTES from USER_segments where segment_name='TEST_BLOB_0531';
select length(a) from TEST_BLOB_0531;
declare
  a_blob blob;
    tmp varchar2(50):='3131313131313131313131313131';
  I NUMBER:=0;
begin
  select a into a_blob from test_blob_0531 for update;
   dbms_lob.open(a_blob, dbms_lob.lob_readwrite);
 LOOP 
  dbms_lob.writeappend( a_blob,length(to_blob(tmp)), to_blob(tmp));
  I:=I+1;
  IF I=10000 THEN EXIT;
  END IF;
  END LOOP;
  dbms_lob.close(a_blob);
  commit;
end;
/
select BYTES from USER_segments where segment_name='TEST_BLOB_0531';
select length(a) from TEST_BLOB_0531;