Thread: BUG #13978: xmin,xmax not current for foreign table

The following bug has been logged on the website:

Bug reference:      13978
Logged by:          digoal
Email address:      digoal@126.com
PostgreSQL version: 9.5.0
Operating system:   CentOS 6.x x64
Description:

tbl0 is a foreign table with postgres_fdw
master=# select tableoid,ctid,xmin,xmax,* from tbl0;
 tableoid |  ctid  | xmin |    xmax    | id | info |          crt_time

----------+--------+------+------------+----+------+----------------------------
    20304 | (0,11) |  192 | 4294967295 |  4 | test | 2016-02-23
11:25:20.440349
    20304 | (0,12) |  192 | 4294967295 |  8 | test | 2016-02-23
11:25:20.440349
(2 rows)

but the right values is:
db0=# select tableoid,ctid,xmin,xmax,* from tbl0;
 tableoid |  ctid  |   xmin   |   xmax   | id | info |          crt_time

----------+--------+----------+----------+----+------+----------------------------
    20280 | (0,11) | 38232587 | 38232588 |  4 | test | 2016-02-23
11:25:20.440349
    20280 | (0,12) | 38232587 | 38232588 |  8 | test | 2016-02-23
11:25:20.440349
(2 rows)

digoal@126.com writes:
> tbl0 is a foreign table with postgres_fdw
> master=# select tableoid,ctid,xmin,xmax,* from tbl0;
> ...
> but the right values is:

xmin/xmax are not meaningful in foreign tables.  Even in the case of a
postgres_fdw foreign table, they cannot be useful because there's no way
to map between the remote server's XID numbering and local XIDs.  So I do
not believe your claim that there's a "right" value for them to have.

Ideally, those columns wouldn't even exist in foreign tables; but fixing
that has so far not seemed worth the trouble it would require.

            regards, tom lane