Re: Skipping logical replication transactions on subscriber side

On Thu, Mar 10, 2022 at 9:02 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Tue, Mar 1, 2022 at 8:31 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > I've attached an updated patch along with two patches for cfbot tests
> > since the main patch (0003) depends on the other two patches. Both
> > 0001 and 0002 patches are the same ones I attached on another
> > thread[2].
> >
>
> Few comments on 0003:
> =====================
> 1.
> +     <row>
> +      <entry role="catalog_table_entry"><para role="column_definition">
> +       <structfield>subskiplsn</structfield> <type>pg_lsn</type>
> +      </para>
> +      <para>
> +       Commit LSN of the transaction whose changes are to be skipped,
> if a valid
> +       LSN; otherwise <literal>0/0</literal>.
> +      </para></entry>
> +     </row>
>
> Can't this be prepared LSN or rollback prepared LSN? Can we say
> Finish/End LSN and then add some details which all LSNs can be there?

Right, changed to finish LSN.

>
> 2. The conflict resolution explanation needs an update after the
> latest commits and we should probably change the commit LSN
> terminology as mentioned in the previous point.

Updated.

>
> 3. The text in alter_subscription.sgml looks a bit repetitive to me
> (similar to what we have in logical-replication.sgml related to
> conflicts). Here also we refer to only commit LSN which needs to be
> changed as mentioned in the previous two points.

Updated.

>
> 4.
> if (strcmp(lsn_str, "none") == 0)
> + {
> + /* Setting lsn = NONE is treated as resetting LSN */
> + lsn = InvalidXLogRecPtr;
> + }
> + else
> + {
> + /* Parse the argument as LSN */
> + lsn = DatumGetTransactionId(DirectFunctionCall1(pg_lsn_in,
> + CStringGetDatum(lsn_str)));
> +
> + if (XLogRecPtrIsInvalid(lsn))
> + ereport(ERROR,
> + (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
> + errmsg("invalid WAL location (LSN): %s", lsn_str)));
>
> Is there a reason that we don't want to allow setting 0
> (InvalidXLogRecPtr) for skip LSN?

0 is obviously an invalid value for skip LSN, which should not be
allowed similar to other options (like setting '' to slot_name). Also,
we use 0 (InvalidXLogRecPtr) internally to reset the subskipxid when
NONE is specified.

>
> 5.
> +# The subscriber will enter an infinite error loop, so we don't want
> +# to overflow the server log with error messages.
> +$node_subscriber->append_conf(
> + 'postgresql.conf',
> + qq[
> +wal_retrieve_retry_interval = 2s
> +]);
>
> Can we change this test to use disable_on_error feature? I am thinking
> if the disable_on_error feature got committed first, maybe we can have
> one test file for this and disable_on_error feature (something like
> conflicts.pl).

Good idea. Updated.

I've attached an updated version patch. This patch can be applied on
top of the latest disable_on_error patch[1].

Regards,

[1] https://www.postgresql.org/message-id/CAA4eK1Kes9TsMpGL6m%2BAJNHYCGRvx6piYQt5v6TEbH_t9jh8nA%40mail.gmail.com

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