Re: Handle infinite recursion in logical replication setup

On Tue, Sep 6, 2022 at 9:31 AM wangw(dot)fnst(at)fujitsu(dot)com
<wangw(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Tues, 6 Sept 2022 at 11:14, vignesh C <vignesh21(at)gmail(dot)com> wrote:
> > Thanks for the comments, the attached patch has the changes for the same.
>
> Thanks for updating the patch.
>
> Here is one comment for 0001 patch.
> 1. The query in function check_publications_origin.
> + appendStringInfoString(&cmd,
> + "SELECT DISTINCT P.pubname AS pubname\n"
> + "FROM pg_publication P,\n"
> + " LATERAL pg_get_publication_tables(P.pubname) GPT\n"
> + " LEFT JOIN pg_subscription_rel PS ON (GPT.relid = PS.srrelid),\n"
> + " pg_class C JOIN pg_namespace N ON (N.oid = C.relnamespace)\n"
> + "WHERE C.oid = GPT.relid AND PS.srrelid IS NOT NULL AND P.pubname IN (");
>
> Since I found that we only use "PS.srrelid" in the WHERE statement by
> specifying "PS.srrelid IS NOT NULL", could we just use "[INNER] JOIN" to join
> the table pg_subscription_rel?
>

I also think we can use INNER JOIN here but maybe there is a reason
why that is not used in the first place. If we change it in the code
then also let's change the same in the docs section as well.

Few minor points:
===============
1.
This scenario is detected and a WARNING is logged to the
+ user, but the warning is only an indication of a potential problem; it is
+ the user responsibility to make the necessary checks to ensure the copied
+ data origins are really as wanted or not.
+ </para>

/user/user's

2. How about a commit message like:
Raise a warning if there is a possibility of data from multiple origins.

This commit raises a warning message for a combination of options
('copy_data = true' and 'origin = none') during CREATE/ALTER subscription
operations if the publication tables were also replicated from other
publishers.

During replication, we can skip the data from other origins as we have that
information in WAL but that is not possible during initial sync so we raise
a warning if there is such a possibility.

--
With Regards,
Amit Kapila.