Re: multi-level partitions and partition-wise joins

On Wed, Dec 21, 2016 at 11:31 PM, Ashutosh Bapat
<ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
> Given the scenario described above, it looks like we have to retain
> partition hierarchy in the form of inheritance hierarchy in order to
> implement partition-wise joins for multi-leveled partition tables. Is
> that the right thing to do? PFA a patch retained by Amit Langote to
> translate partition hierarchy into inheritance hierarchy. Is this
> something on the right direction?

I am not sure whether Amit's patch is the right way to go. I don't
fully understand it, and I remember complaining about some aspects of
it before, such as this unexplained and fairly random-looking
exception:

+ /*
+ * Do not flatten the inheritance hierarchy if partitioned table, unless
+ * this is the result relation.
+ */

However, I think the overall idea of doing flattening later in the
process for partitioned tables is probably correct. It's not that we
shouldn't do flattening at all -- the final Plan shouldn't involve
nested Append nodes -- but maybe we should delay it. Perhaps the Path
tree retains the structure and the final Plan flattens it. We might
consider doing that way for both inheritance trees and partitioning,
just so we don't have two different code paths to validate.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company