how to make selecting random rows in oracle faster with table with millions of rows

Question

Is there a way to make selecting random rows faster in oracle with a table that has million of rows. I tried to use sample(x) and dbms_random.value and its taking a long time to

Answer 1

Version with retries when no rows returned:

WITH gen AS ((SELECT --+ inline leading(e) use_nl(e t) rowid(t)
                     MAX(t.ROWID) KEEP(DENSE_RANK FIRST ORDER BY dbms_random.value) Row_Id
                FROM (SELECT o.Data_Object_Id,
                             e.Relative_Fno,
                             e.Block_Id + TRUNC(Dbms_Random.Value(0, e.Blocks)) AS Block_Id 
                        FROM Dba_Extents e
                        JOIN Dba_Objects o ON o.Owner = e.Owner AND o.Object_Type = e.Segment_Type AND o.Object_Name = e.Segment_Name
                       WHERE e.Segment_Name = 'MY_TABLE'
                         AND(e.Segment_Type, e.Owner, e.Extent_Id) =
                            (SELECT MAX(e.Segment_Type) AS Segment_Type,
                                    MAX(e.Owner)        AS Owner,
                                    MAX(e.Extent_Id) KEEP(DENSE_RANK FIRST ORDER BY Dbms_Random.Value) AS Extent_Id
                               FROM Dba_Extents e
                              WHERE e.Segment_Name = 'MY_TABLE'
                                AND e.Owner = 'MY_USER'
                                AND e.Segment_Type = 'TABLE')) e
                JOIN MY_USER.MY_TABLE t ON t.ROWID BETWEEN Dbms_Rowid.Rowid_Create(1, Data_Object_Id, Relative_Fno, Block_Id, 0)
                                                  AND Dbms_Rowid.Rowid_Create(1, Data_Object_Id, Relative_Fno, Block_Id, 32767))),
  Retries(Cnt, Row_Id) AS (SELECT 1, gen.Row_Id
                             FROM Dual
                             LEFT JOIN gen ON 1=1
                            UNION ALL
                           SELECT Cnt + 1, gen.Row_Id
                             FROM Retries
                             LEFT JOIN gen ON 1=1
                            WHERE Retries.Row_Id IS NULL AND Retries.Cnt < 10)
SELECT *
  FROM MY_USER.MY_TABLE
 WHERE ROWID = (SELECT Row_Id
                  FROM Retries
                 WHERE Row_Id IS NOT NULL)