Re: posgres 12 bug (partitioned table)

On Thu, Apr 22, 2021 at 4:10 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Amit Langote <amitlangote09(at)gmail(dot)com> writes:
> > Forgot to ask in the last reply: for HEAD, should we consider simply
> > preventing accessing system columns when querying through a parent
> > partitioned table, as was also mentioned upthread?
>
> Indeed, it seems like this thread is putting a fair amount of work
> into a goal that we shouldn't even be trying to do. We gave up the
> assumption that a partitioned table's children would have consistent
> system columns the moment we decided to allow foreign tables as
> partition leaf tables; and it's only going to get worse as alternate
> table AMs become more of a thing. So now I'm thinking the right thing
> to be working on is banning access to system columns via partition
> parent tables (other than tableoid, which ought to work).

Accessing both tableoid and ctid works currently. Based on the
discussion, it seems we're not so sure whether that will remain the
case for the 2nd going forward.

> I'm not quite sure whether the right way to do that is just not
> make pg_attribute entries for system columns of partitioned tables,
> as we do for views; or make them but have a code-driven error if
> you try to use one in a query. The second way is uglier, but
> it should allow a more on-point error message. OTOH, if we start
> to have different sets of system columns for different table AMs,
> we can't have partitioned tables covering all of those sets.

I tend to agree with Andres that not having any pg_attribute entries
may be better.

> In the meantime, if the back branches fail with something like
> "virtual tuple table slot does not have system attributes" when
> trying to do this, that's not great but I'm not sure we should
> be putting effort into improving it.

Got it. That sounds like an acceptable compromise.

--
Amit Langote
EDB: http://www.enterprisedb.com