Re: pg_partition_tree crashes for a non-defined relation

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: Michael Paquier <michael(at)paquier(dot)xyz>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Stephen Frost <sfrost(at)snowman(dot)net>, Postgres hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_partition_tree crashes for a non-defined relation
Date: 2019-03-01 04:38:28
Message-ID: de05e459-0562-f113-e82f-2627bc736b1d@lab.ntt.co.jp
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Hi,

On 2019/03/01 9:22, Michael Paquier wrote:
> On Thu, Feb 28, 2019 at 04:32:03PM -0300, Alvaro Herrera wrote:
>> Yeah, looks good, please push.
>
> Done for this part.
>
>> I would opt for returning the empty set for legacy inheritance too.
>>
>> More generally, I think we should return empty for anything that's
>> either not RELKIND_PARTITIONED_TABLE or has relispartition set.
>
> I think that one option is to make the function return only the table
> itself if it is not a partitioned table, which would be more
> consistent with what pg_partition_root() does.
>
> What I am writing next sounds perhaps a bit fancy, but in my opinion a
> normal table is itself a partition tree, made of one single member:
> itself.

That's what we discussed, but it seems that we ended up allowing regular
standalone tables (possibly in inheritance trees) only because it
*appeared* to work. Alvaro already pointed out what appears to be a bug
in how we compute the value of level. Instead of trying to fix it, I
agree we should just disallow tables that are not a partitioned
table/index or a partition (relispartition). Maybe there won't be any use
cases, so we should change that while we still can.

So, maybe change the check in check_rel_can_be_partition() as follows:

relkind = get_rel_relkind(relid);
relispartition = get_rel_relispartition(relid);

/* Only allow relation types that can appear in partition trees. */
if (!relispartition &&
relkind != RELKIND_PARTITIONED_TABLE &&
relkind != RELKIND_PARTITIONED_INDEX)
return false;

Thanks,
Amit

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