Problem of full table scan on a partitioned table

Question

hi all
There is a table called "si_sync_operation" that have 171040 number of rows.
I partitioned that table into a new table called "si_sync_operation_par" with 7 partitoins.
I issued the following statements
SELECT * FROM si_sync_operation_par.
SELECT * FROM si_sync_operation.
The explain plan show that the cost of the first statement is 1626 and that of the second statments is 1810.
The "cost" of full table scan on partitioned table is lower than the that of non-partitioned table.That's fine.
But the "Bytes" of full table scan on partitioned table is 5761288680 and that of the non-partitioned table is 263743680.
Why full table scan on partitioned table access more bytes than non-partitioned table?
And how could a statment that access more bytes results a lower cost?
Thank u very much

Answer 1

As Hemant metioned bytes reported are approximate number of bytes. As far as Cost is concerned, according to Tom its just a number and we should not compare queries by their cost. (search asktom.oracle.com for more information)
SQL> drop table non_part purge;
Table dropped.
SQL> drop table part purge;
Table dropped.
SQL>
SQL> CREATE TABLE non_part
  2        (id  NUMBER(5),
  3         dt    DATE);
Table created.
SQL>
SQL> CREATE TABLE part
  2        (id  NUMBER(5),
  3         dt    DATE)
  4         PARTITION BY RANGE(dt)
  5         (
  6         PARTITION part1_jan2008 VALUES LESS THAN(TO_DATE('01/02/2008','DD/MM/YYYY')),
  7         PARTITION part2_feb2008 VALUES LESS THAN(TO_DATE('01/03/2008','DD/MM/YYYY')),
  8         PARTITION part3_mar2008 VALUES LESS THAN(TO_DATE('01/04/2008','DD/MM/YYYY')),
  9         PARTITION part4_apr2008 VALUES LESS THAN(TO_DATE('01/05/2008','DD/MM/YYYY')),
10         PARTITION part5_may2008 VALUES LESS THAN(TO_DATE('01/06/2008','DD/MM/YYYY'))
11       );
Table created.
SQL>
SQL>
SQL> insert into non_part select rownum, trunc(sysdate) - rownum from dual connect by level <= 140;
140 rows created.
Execution Plan
Plan hash value: 1731520519
| Id  | Operation                     | Name | Rows  | Cost (%CPU)| Time     |
|   0 | INSERT STATEMENT              |      |     1 |     2   (0)| 00:00:01 |
|   1 |  COUNT                        |      |       |            |          |
|*  2 |   CONNECT BY WITHOUT FILTERING|      |       |            |          |
|   3 |    FAST DUAL                  |      |     1 |     2   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   2 - filter(LEVEL<=140)
SQL>
SQL> insert into part select * from non_part;
140 rows created.
Execution Plan
Plan hash value: 1654070669
| Id  | Operation         | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | INSERT STATEMENT  |          |   140 |  3080 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| NON_PART |   140 |  3080 |     3   (0)| 00:00:01 |
Note
   - dynamic sampling used for this statement
SQL>
SQL> commit;
Commit complete.
SQL>
SQL> set line 10000
SQL> set autotrace traceonly exp
SQL> select * from non_part;
Execution Plan
Plan hash value: 1654070669
| Id  | Operation         | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |          |   140 |  3080 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| NON_PART |   140 |  3080 |     3   (0)| 00:00:01 |
Note
   - dynamic sampling used for this statement
SQL> select * from part;
Execution Plan
Plan hash value: 3392317243
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
|   0 | SELECT STATEMENT    |      |   140 |  3080 |     9   (0)| 00:00:01 |       |       |
|   1 |  PARTITION RANGE ALL|      |   140 |  3080 |     9   (0)| 00:00:01 |     1 |     5 |
|   2 |   TABLE ACCESS FULL | PART |   140 |  3080 |     9   (0)| 00:00:01 |     1 |     5 |
Note
   - dynamic sampling used for this statement
SQL>
SQL> exec dbms_stats.gather_table_stats(user, 'non_part');
PL/SQL procedure successfully completed.
SQL> exec dbms_stats.gather_table_stats(user, 'part');
PL/SQL procedure successfully completed.
SQL>
SQL>
SQL> select * from non_part;
Execution Plan
Plan hash value: 1654070669
| Id  | Operation         | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |          |   140 |  1540 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| NON_PART |   140 |  1540 |     3   (0)| 00:00:01 |
SQL> select * from part;
Execution Plan
Plan hash value: 3392317243
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
|   0 | SELECT STATEMENT    |      |   140 |  1540 |     9   (0)| 00:00:01 |       |       |
|   1 |  PARTITION RANGE ALL|      |   140 |  1540 |     9   (0)| 00:00:01 |     1 |     5 |
|   2 |   TABLE ACCESS FULL | PART |   140 |  1540 |     9   (0)| 00:00:01 |     1 |     5 |
SQL>After analyzing the tables, notice that the Bytes column has changed value