Cloning a table

This is possibly a very basic question, but I am not able to figure it out. Imagine a large table TAB1(col1 number, col2 varchar2(50)) with few million rows. Compare the following two methods.

1. create table TAB1_CLONE ( col1, col2, constraint PK_TAB1_CLONE primary key(col1) ) as select col1, col2 from tab1;
2. create table TAB1_CLONE col1 number, col2 varchar2(50), constraint PK_TAB1_CLONE primary key(col1) );

   insert into TAB1_CLONE (col1, col2) select col1, col2 from TAB1;    commit;

Now my understanding is that if TAB1 is very large, using method 2 might give some sort of "rollback segment too small" or "transaction log full" kind of error, since we commit only after all rows have been inserted. On the other hand, method 1 does not seem to have any such errors, and seems faster. How does this work ?

Thanks.

• Silver