DECLARE
  i NUMBER := 0;
  CURSOR G1 IS SELECT * FROM sometable WHERE col1 = 'somevalue'
               FOR UPDATE;
BEGIN
  FOR c1 IN S1 LOOP
      UPDATE tab1 SET col1 = 'somevalue1'
             WHERE CURRENT OF G1;
 
      i := i + 1;              -- Commits after every X number of records
      IF i > 1000 THEN
         COMMIT;
         i := 0;
      END IF;
 
  END LOOP;
  COMMIT;
END;