10g CBO的一个问题

 declare
     type rc is ref cursor;
     l_rc rc;
     l_dummy all_objects.object_name%type;
     l_start number default dbms_utility.get_time;
     y all_objects.object_name%type;
 begin
     for i in 1 .. 1000
     loop
         open l_rc for
         'select object_name
            from all_objects
           where object_id = :x and object_name=:y' using i,y;
         fetch l_rc into l_dummy;
         close l_rc;
     end loop;
     dbms_output.put_line
     ( round( (dbms_utility.get_time-l_start)/100, 2 ) ||
       ' seconds...' );
 end;

转Eygle的话:我想具体原因应该在优化器上,10g缺省采用的是CBO优化器.
9i如果没有统计信息那么缺省的是RBO.

对于这类大批量循环测试,CBO的影响会非常明显.

请参考我在10g下的测试结果:

代码:
     
SQL> select * from v$version; 
 
BANNER 
---------------------------------------------------------------- 
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod 
PL/SQL Release 10.2.0.1.0 - Production 
CORE    10.2.0.1.0      Production 
TNS for Linux: Version 10.2.0.1.0 - Production 
NLSRTL Version 10.2.0.1.0 - Production 
 
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  / 
26.99 seconds... 
 
PL/SQL procedure successfully completed. 
 
SQL> 
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  / 
16.37 seconds... 
 
PL/SQL procedure successfully completed. 
 
SQL>