ORA-01628: max # extents (%s) reached for rollback segment %s
 *Cause:  An attempt was made to extend a rollback segment that was
          already at the MAXEXTENTS value.
 *Action: If the value of the MAXEXTENTS storage parameter is less than
          the maximum allowed by the system, raise this value

SELECT MAX_EXTENTS FROM DBA_rollback_SEGS

select
   substr(s.username,1,18) username,
   substr(s.program,1,15) program,
   decode(s.command,
       0,'No Command',
       1,'Create Table',
       2,'Insert',
       3,'Select',
       6,'Update',
       7,'Delete',
       9,'Create Index',
      15,'Alter Table',
      21,'Create View',
      23,'Validate Index',
      35,'Alter Database',
      39,'Create Tablespace',
      41,'Drop Tablespace',
      40,'Alter Tablespace',
      53,'Drop User',
      62,'Analyze Table',
      63,'Analyze Index',
    s.command||': Other') command, s.status, s.osuser
from v$session s, v$process p, v$transaction t, v$rollstat r, v$rollname n
where s.paddr = p.addr
and   s.taddr = t.addr (+)
and   t.xidusn = r.usn (+)
and   r.usn = n.usn (+)
order by 1

SQL> select distinct sid from v$mystat;

       SID
----------
       159