CBO RBO Oracle10g and Speed

[oracle@danaly udump]$ sqlplus "/ as sysdba"

SQL*Plus: Release 10.2.0.1.0 - Production on Sat Dec 31 10:31:47 2005

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, Oracle Label Security, OLAP and Data Mining Scoring Engine options

SQL> alter system flush shared_pool;

System altered.

SQL> set serveroutput on
SQL> declare
  2       type rc is ref cursor;
  3       l_rc rc;
  4       l_dummy all_objects.object_name%type;
  5       l_start number default dbms_utility.get_time;
  6   begin
  7       for i in 1 .. 1000
  8       loop
  9           open l_rc for
 10           'select object_name
 11              from all_objects
 12             where object_id = ' || i;
 13           fetch l_rc into l_dummy;
 14           close l_rc;
 15       end loop;
 16       dbms_output.put_line
 17       ( round( (dbms_utility.get_time-l_start)/100, 2 ) ||
 18         ' seconds...' );
 19   end;
 20  /
27.01 seconds...

PL/SQL procedure successfully completed. 

SQL> declare
  2       type rc is ref cursor;
  3       l_rc rc;
  4       l_dummy all_objects.object_name%type;
  5       l_start number default dbms_utility.get_time;
  6   begin
  7       for i in 1 .. 1000
  8       loop
  9           open l_rc for
 10           'select /*+ rule */ object_name
 11              from all_objects
 12             where object_id = ' || i;
 13           fetch l_rc into l_dummy;
 14           close l_rc;
 15       end loop;
 16       dbms_output.put_line
 17       ( round( (dbms_utility.get_time-l_start)/100, 2 ) ||
 18         ' seconds...' );
 19   end;
 20  /
16.56 seconds...

PL/SQL procedure successfully completed. 

SQL> declare
  2       type rc is ref cursor;
  3       l_rc rc;
  4       l_dummy all_objects.object_name%type;
  5       l_start number default dbms_utility.get_time;
  6   begin
  7       for i in 1 .. 1000
  8       loop
  9           open l_rc for
 10           'select object_name
 11              from all_objects
 12             where object_id = :x'
 13           using i;
 14           fetch l_rc into l_dummy;
 15           close l_rc;
 16       end loop;
 17       dbms_output.put_line
 18       ( round( (dbms_utility.get_time-l_start)/100, 2 ) ||
 19         ' seconds...' );
 20   end;
 21  /
.19 seconds...

PL/SQL procedure successfully completed.

SQL>