Unfortunately, this method does not work.

Because we cannot have more than one separated group of sl_log items within
a single transaction: sl_event SYNC contain information only about xid, not
about sequence of sl_log item. So, if we have

xid=3D123: (0) SYNC
xid=3D123: (1) DDL_SCRIPT
xid=3D123: (2) SYNC
xid=3D123: (3) DDL_SCRIPT

then slon cannot detect are sl_log items of (2) SYNC were performed
*before*(3) DDL_SCRIPT or
*after* it. And the following sequence becomes broken:

(1) ALTER TABLE a ADD COLUMN id_copy INTEGER;
(2) UPDATE a SET id_copy =3D id;
(3) ALTER TABLE a RENAME COLUMN id_copy TO abcd;

But, while digging the source, I have suddenly found 2 bugs. I reported them
here (with solution patches attached):
http://www.slony.info/bugzilla/show_bug.cgi?id=3D75



On Sat, Mar 7, 2009 at 1:40 AM, Dmitry Koterov <dmitry at koterov.ru> wrote:

> Hello.
>
> I work with Slony for about 2 years in a heavy-loaded web site. I'd like =
to
> mix DDL and DML code to perform them in a single transaction (in deployme=
nt
> procedure it would be very handy and important).
>
> Digging the source of slonik and _schemadoc I assumed that I possibly cou=
ld
> do it via slonik
> (for better readability I replaced FILENAME=3D'xxx' clause by the content=
 of
> xxx itself):
>
>
> -- Perform my DDL modifications.
> EXECUTE SCRIPT {
>   ALTER TABLE tbl ADD COLUMN id_copy INTEGER;
> }
>
> EXECUTE SCRIPT {
>   -- This is needed to deny execution of this SQL in other nodes.
>   EXECUTE ONLY ON =3D <my_origin_node>
>
>   -- Temporariy turn on replication mode.
>   SET session_replication_role TO origin;
>   -- Perform my DML operations. They will be replicated via logTrigger as
> usual.
>   UPDATE tbl SET id_copy =3D id;
>   UPDATE tbl SET abc =3D 123;
>   -- Reset replication mode back.
>   SET session_replication_role TO local;
> }
>
> -- Perform any other DDL modifications.
> EXECUTE SCRIPT {
>   ALTER TABLE tbl ADD COLUMN c INTEGER;
> }
> ...
>
> Please say would this method work without side effects or not?
> Thank you!
>
> B.r.,
>   Dmitry Koterov,
>   chief architect at MoiKrug.Ru, Yandex, Moscow.
>
>
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