Fast Dual in Oracle

Oracle 10g introduces FAST DUAL. Now, when the the DUAL table is accessed, no logical I/O is performed which improves performance.

We can demonstrate this by generating a million rows using the DUAL table.

set timi on
set autot trace stat

SELECT rownum FROM dual CONNECT BY LEVEL <= 1000000;

1000000 rows selected.

Elapsed: 00:00:08.07

Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          0  consistent gets
          0  physical reads
          0  redo size
   14380219  bytes sent via SQL*Net to client
     733838  bytes received via SQL*Net from client
      66668  SQL*Net roundtrips to/from client
          1  sorts (memory)
          0  sorts (disk)
    1000000  rows processed

The statistics trace shows that 1 million rows have been processed without any logical I/O being performed.