Re: AlterSubscription_refresh "wrconn" wrong variable?

On Thu, May 6, 2021 at 7:18 PM Japin Li <japinli(at)hotmail(dot)com> wrote:
>
>
> On Thu, 06 May 2021 at 17:08, Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> > On Wed, May 5, 2021 at 12:35 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >>
> >> Peter Smith <smithpb2250(at)gmail(dot)com> writes:
> >> > This patch replaces the global "wrconn" in AlterSubscription_refresh with a local variable of the same name, making it consistent with other functions in subscriptioncmds.c (e.g. DropSubscription).
> >> > The global wrconn is only meant to be used for logical apply/tablesync worker.
> >> > Using the global/incorrect wrconn in AlterSubscription_refresh doesn't normally cause any problems, but harm is still posslble if the apply worker ever manages to do a subscription refresh. e.g. see [1]
> >>
> >> Hm. I would actually place the blame for this on whoever thought
> >> it was okay to name a global variable something as generic as
> >> "wrconn". Let's rename that while we're at it, say to something
> >> like "tablesync_wrconn" (feel free to bikeshed).
> >
> > PSA v3 of the patch. Same as before, but now also renames the global
> > variable from "wrconn" to "lrep_worker_wrconn".
> >
>
> Thanks for updating patch. I'm confused why we move the walrcv_connect() out of
> PG_TRY() block?
> + /* Try to connect to the publisher. */
> + wrconn = walrcv_connect(sub->conninfo, true, sub->name, &err);
> + if (!wrconn)
> + ereport(ERROR,
> + (errmsg("could not connect to the publisher: %s", err)));
> +
> PG_TRY();
> {
> - /* Try to connect to the publisher. */
> - wrconn = walrcv_connect(sub->conninfo, true, sub->name, &err);
> - if (!wrconn)
> - ereport(ERROR,
> - (errmsg("could not connect to the publisher: %s", err)));
> -
> /* Get the table list from publisher. */
> pubrel_names = fetch_table_list(wrconn, sub->publications);

Thanks for your review. Reason for moving that out of the PG_TRY are:

a) It makes code now consistent with other functions using wrconn. See
CreateSubscription, DropSubscription etc

b) It means don't need the wrconn NULL check anymore in the PG_FINALLY
so it simplifies the disconnect.

------
Kind Regards,
Peter Smith.
Fujitsu Australia