From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
cc: Andres Freund <andres@anarazel.de>, buschmann@nidsa.net,
        pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #16045: vacuum_db crash and illegal memory alloc after
 pg_upgrade from PG11 to PG12
In-reply-to: <20191010163350.2rtcjtje6tkgilqi@development>
References: <20191009132436.uugh4r3be6vw6ex4@development>
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 <20191009141841.my6k44wfiaquj3ks@development>
 <20191009230759.ge66neof5qj627a2@development>
 <19314.1570663125@sss.pgh.pa.us>
 <20191009232836.jg77wccqwy5fgs6s@development>
 <20265.1570664514@sss.pgh.pa.us>
 <20191010014813.3b2btmkakhrskwgd@alap3.anarazel.de>
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 <20191010163350.2rtcjtje6tkgilqi@development>
Comments: In-reply-to Tomas Vondra <tomas.vondra@2ndquadrant.com>
	message dated "Thu, 10 Oct 2019 18:33:50 +0200"
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Date: Thu, 10 Oct 2019 16:14:20 -0400
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Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> On Thu, Oct 10, 2019 at 10:19:12AM -0400, Tom Lane wrote:
>> To identify such domains, I think we'd need something like
>> WHERE attypid IN (recursive-WITH-query), which makes me nervous.
>> We did support those starting with 8.4, which is as far back as
>> pg_upgrade will go, so in theory it should work.  But I think we
>> had bugs with such cases in old releases.  Do we want to assume
>> that the source server has been updated enough to avoid any such
>> bugs?  The expense of such a query might be daunting, too.

> For the query cost, I think we can assume the domain hierarchies are not
> particularly deep (in practice I'd expect just domains directly on the
> sql_identifier type). And I doubt people are using that very widely,
> it's probably more like this report - ad-hoc CTAS, so just a couple of
> items. So I wouldn't expect it to be a huge deal in most cases. But even
> if it takes a second or two, it's a one-time cost.

What I was worried about was the planner possibly trying to apply the
atttypid restriction as a scan qual using a subplan, which might be rather
awful.  But it doesn't look like that happens.  I get a hash semijoin to
the CTE output, in all branches back to 8.4, on this trial query:

explain
with recursive sqlidoids(toid) as (
select 'information_schema.sql_identifier'::pg_catalog.regtype as toid
union
select oid from pg_catalog.pg_type, sqlidoids
  where typtype = 'd' and typbasetype = sqlidoids.toid
)                       
SELECT n.nspname, c.relname, a.attname 
FROM    pg_catalog.pg_class c, 
        pg_catalog.pg_namespace n, 
        pg_catalog.pg_attribute a 
WHERE   c.oid = a.attrelid AND 
        NOT a.attisdropped AND 
        a.atttypid in (select toid from sqlidoids) AND
        c.relkind IN ('r','v','i') and
        c.relnamespace = n.oid AND 
        n.nspname !~ '^pg_temp_' AND 
        n.nspname !~ '^pg_toast_temp_' AND 
        n.nspname NOT IN ('pg_catalog', 'information_schema');

			regards, tom lane