Re: Skipping logical replication transactions on subscriber side

On Tue, Oct 12, 2021 at 7:58 PM Greg Nancarrow <gregn4422(at)gmail(dot)com> wrote:
>
> On Tue, Oct 12, 2021 at 4:00 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > I've attached updated patches.
> >
>
> Some comments for the v16-0003 patch:

Thank you for the comments!

>
> (1) doc/src/sgml/logical-replication.sgml
>
> The output from "SELECT * FROM pg_stat_subscription_errors;" still
> shows "last_failed_time" instead of "last_error_time".

Fixed.

>
> doc/src/sgml/ref/alter_subscription.sgml
> (2)
>
> Suggested update (and fix typo: restrited -> restricted):
>
> BEFORE:
> + Setting and resetting of <literal>skip_xid</literal> option is
> + restrited to superusers.
> AFTER:
> + The setting and resetting of the
> <literal>skip_xid</literal> option is
> + restricted to superusers.

Fixed.

>
> (3)
> Suggested improvement to the wording:
>
> BEFORE:
> + incoming change or by skipping the whole transaction. This option
> + specifies transaction ID that logical replication worker skips to
> + apply. The logical replication worker skips all data modification
> AFTER:
> + incoming changes or by skipping the whole transaction. This option
> + specifies the ID of the transaction whose application is to
> be skipped
> + by the logical replication worker. The logical replication worker
> + skips all data modification

Updated.

>
> (4) src/backend/replication/logical/worker.c
>
> Suggested improvement to the comment wording:
>
> BEFORE:
> + * Stop the skipping transaction if enabled. Otherwise, commit the changes
> AFTER:
> + * Stop skipping the transaction changes, if enabled. Otherwise,
> commit the changes

Fixed.

>
>
> (5) skip_xid value validation
>
> The validation of the specified skip_xid XID value isn't great.
> For example, the following value are accepted:
>
> ALTER SUBSCRIPTION sub SET (skip_xid='123abcz');
> ALTER SUBSCRIPTION sub SET (skip_xid='99$(at)*');

Hmm, this is probably a problem of xid data type. For example, we can do like:

postgres(1:12686)=# select 'aa123'::xid;
xid
-----
0
(1 row)

postgres(1:12686)=# select '123aa'::xid;
xid
-----
123
(1 row)

It seems a problem to me. Perhaps we can fix it in a separate patch.
What do you think?

Regards,

--
Masahiko Sawada
EDB: https://www.enterprisedb.com/