ALTER TABLE transaction isolation problem

[DT <kurt023@xxxxxxxxxxx>]

Hi,

  I'm reading code of ALTER TABLE, and I found when target table needs rewrite, tuple inserted into new heap uses current transaction's xid as xmin. Does this behavior satisfy serializable isolation? I wrote some test cases:

CREATE TABLE t1(a INT);

CREATE TABLE t2(a INT);

INSERT INTO t1 VALUES(1);

INSERT INTO t2 VALUES(1);

transaction one:

postgres=# commit;

COMMIT

postgres=# BEGIN;

BEGIN

postgres=# SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;

SET

postgres=# SELECT * FROM t1;

 a

---

 1

(1 rows)

        transaction two execute SQL:  ALTER TABLE t2 ADD COLUMN b INT DEFAULT 1;

postgres=# SELECT * FROM t2;

 a | b

---+---

(0 rows)

Transaction one sees nothing in t2, and i can not give any serial execution order of these two transactions, does it still  satisfy serializable isolation?