cx_oracle: Issues moving large volume of data from one table to another

Question

I am trying to move 20 million records using from one oracle database to another using python cx_Oracle libraries. Unfortunately I cannot use the oracle cli utility tool because some minor transformation is required on some rows.

Here is the code I am using

def execute(in_query, out_query, batch_size=10000):
    in_conn = create_src_db_connection()
    out_conn = create_dest_db_connection()
    
    out_conn.autocommit = True
    in_cursor = in_conn.cursor()
    out_cursor = out_conn.cursor()
    in_cursor.execute(in_query)
    
    white True:
        try:
            rows = in_cursor.fetchmany(batch_size)
            if not rows:
                break
            # transformation of rows done here
            out_cursor.execute_many(out_query, rows, batcherrors=True)
            
            for error in out_cursor.getbatcherrors():
                print("Error", error.message, "at row offset", error.offset)
        except cx_Oracle.Error as err:
            print(err)
            
    in_conn.close()
    out_conn.close()

in_query = "select * from table" out_query = "insert into table(a, b, c, d) values (:1,:2,:3,:4)"

Unfortunately this is either not performing well about 6000 rows per minute or is sometimes failing with error

cx_Oracle DIP-1080: connection was closed by ORA-3135C50

Is the re a better approach? Any reason why this keeps failing? Seems like one of the connections is idling for too long.