Performance impact due to varchar2 length

Question

hi,
We know varchar2 stores data dynamically. means it takes storage space only for the data it has. Then what is the requirement of defining varchar2 length. It shd be default to 4000. Pls take data consistency /security/maintenence etc fundas as another issue.
Take an e.g
Is there any other performance/storage/etc impact of given table designs ?
SQL>Create table T1
(sex varchar2(1));
SQL>Create table T2
(sex varchar2(4000));
SQL>Insert into T1 values('M');
SQL>Insert into T2 values('M');
SQL>select * from t1;
s
M
SQL>select * from t2;
sex
M
Is there any other performance/storage/etc impact of given table designs ?
Any comments.... ?
Rgds,
Rup

Answer 1

Well Pls chk this explain plan.
SQL> desc test1;
Name Null? Type
A1 VARCHAR2(1)
A2 VARCHAR2(1)
A3 VARCHAR2(1)
A4 VARCHAR2(1)
A5 VARCHAR2(1)
A6 VARCHAR2(1)
A7 VARCHAR2(1)
A8 VARCHAR2(1)
A9 VARCHAR2(1)
A10 VARCHAR2(1)
A11 VARCHAR2(1)
A12 VARCHAR2(1)
A14 VARCHAR2(1)
A15 VARCHAR2(1)
SQL> desc test2;
Name Null? Type
A1 VARCHAR2(4000)
A2 VARCHAR2(4000)
A3 VARCHAR2(4000)
A4 VARCHAR2(4000)
A5 VARCHAR2(4000)
A6 VARCHAR2(4000)
A7 VARCHAR2(4000)
A8 VARCHAR2(4000)
A9 VARCHAR2(4000)
A10 VARCHAR2(4000)
A11 VARCHAR2(4000)
A12 VARCHAR2(4000)
A13 VARCHAR2(4000)
A14 VARCHAR2(4000)
SQL> set autotrace on
SQL> select a1 from test1 where rownum<=1;
A
a
Execution Plan
0 SELECT STATEMENT Optimizer=ALL_ROWS (Cost=2 Card=1 Bytes=2)
1 0 COUNT (STOPKEY)
2 1 TABLE ACCESS (FULL) OF 'TEST1' (TABLE) (Cost=2 Card=80 Bytes=160)
SQL> select a1 from test2 where rownum<=1;
A1
a
Execution Plan
0 SELECT STATEMENT Optimizer=ALL_ROWS (Cost=2 Card=1 Bytes=2002)
1 0 COUNT (STOPKEY)
2 1 TABLE ACCESS (FULL) OF 'TEST2' (TABLE) (Cost=2 Card=80 Bytes=160160)
what is this??? Explain plan has major difference in the Bytes accessed field.
Is this a major performance issue...
Rgds,