RE: pg_get_publication_tables() output duplicate relid

On Sat, Nov 20, 2021 7:31 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Fri, Nov 19, 2021 at 10:58 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
> >
> > On Fri, Nov 19, 2021 at 7:19 AM Amit Langote <amitlangote09(at)gmail(dot)com>
> wrote:
> > >
> > > The problematic case is attaching the partition *after* the
> > > subscriber has already marked the root parent as synced and/or ready
> > > for replication. Refreshing the subscription doesn't help it
> > > discover the newly attached partition, because a
> > > publish_via_partition_root only ever tells about the root parent,
> > > which would be already synced, so the subscriber would think there's
> > > nothing to copy.
> > >
> >
> > Okay, I see this could be a problem but I haven't tried to reproduce it.
>
> One more thing you mentioned is that the initial sync won't work after refresh
> but later changes will be replicated but I noticed that later changes also don't
> get streamed till we restart the subscriber server.
> I am not sure but we might not be invalidating apply workers cache due to
> which it didn't notice the same.

I investigated this bug recently, and I think the reason is that when receiving
relcache invalidation message, the callback function[1] in walsender only reset
the schema sent status while it doesn't reset the replicate_valid flag. So, it
won’t rebuild the publication actions of the relation.

[1]
static void
rel_sync_cache_relation_cb(Datum arg, Oid relid)
...
/*
* Reset schema sent status as the relation definition may have changed.
* Also free any objects that depended on the earlier definition.
*/
if (entry != NULL)
{
entry->schema_sent = false;
list_free(entry->streamed_txns);
...

Also, when you DETACH a partition, the publication won’t be rebuilt too because
of the same reason. Which could cause unexpected behavior if we modify the
detached table's data . And the bug happens regardless of whether pubviaroot is
set or not.

For the fix:

I think if we also reset replicate_valid flag in rel_sync_cache_relation_cb,
then the bug can be fixed. I have a bit hesitation about this approach, because
it could increase the frequency of invalidating and rebuilding the publication
action. But I haven't produced some other better approaches.

Another possibility could be that we add a syscache callback function for
pg_inherits table, but we currently don't have syscache for pg_inherits. We
might need to add the cache pg_inherits first which doesn't seems better
than the above approach.

What do you think ?

Attach an initial patch which reset the replicate_valid flag in
rel_sync_cache_relation_cb and add some reproduction tests in 013_partition.pl.

Best regards,
Hou zj