Re: Somebody has not thought through subscription locking considerations

Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com> writes:
> On 31/03/17 20:23, Tom Lane wrote:
>> No, the problematic part is that there is any heap_open happening at
>> all. That open could very easily result in a recursive attempt to read
>> pg_class, for example, which is going to be fatal if we're in the midst
>> of vacuum full'ing or reindex'ing pg_class. It's frankly astonishing
>> to me that this patch seems to have survived testing under
>> CLOBBER_CACHE_ALWAYS, because it's only the catalog caches that are
>> preventing such recursive lookups.

> Hmm okay, so the solution is to either use standard dependency info for
> this so that it's only called for tables that are actually know to be
> subscribed or have some exceptions in the current code to call the
> function only for user catalogs. Any preferences?

Looking at dependency info isn't going to fix this, it only moves the
unsafe catalog access somewhere else (ie pg_depend instead of
pg_subscription_rel). I suspect the only safe solution is doing an
IsCatalogRelation or similar test pretty early in the logical replication
code paths.

regards, tom lane