Problem:

drop table t1;
CREATE TABLE t1 (col1 number);

SQL> INSERT INTO t1
2 WITH w1 AS
3 (SELECT ROWNUM r FROM dual CONNECT BY ROWNUM <= 2000000)
4 SELECT ROWNUM
5 FROM w1
6 /
INSERT INTO t1
*
ERROR at line 1:
ORA-30009: Not enough memory for CONNECT BY operation
… 48 more words