Re: Somebody has not thought through subscription lockingconsiderations

On 01/04/17 00:52, Tom Lane wrote:
> Petr Jelinek <petr.jelinek@2ndquadrant.com> writes:
>> On 31/03/17 21:00, Tom Lane wrote:
>>> 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.
> 
>> I don't follow, everything else does dependency info check in this
>> situation, how is this any different?
> 
> What do you mean by "everything else"?  The key point here is that
> access to the bootstrap catalogs like pg_class and pg_attribute can't
> be dependent on accesses to other catalogs, or we get into circularities.
> We certainly aren't trying to look in pg_depend when we do a heap_open.
> 
> (Or, if you tell me that we are now because the logical replication
> patch added it, I'm going to start agitating for reverting the patch
> and sending it back for redesign.)

But the pg_subscription_rel is also not accessed on heap_open, the
problematic code is called from heap_drop_with_catalog. And VACUUM FULL
pg_class calls heap_drop_with_catalog() when doing the heap swap (and it
goes through performDeletion so through dependency info which is what I
mean by everything else does this).

--  Petr Jelinek                  http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training &
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