Re: Expression errors with "FOR UPDATE" and postgres_fdw with partition wise join enabled.

On Mon, Aug 13, 2018 at 12:32 PM, Etsuro Fujita
<fujita.etsuro@lab.ntt.co.jp> wrote:
> One thing I noticed might be an improvement is to skip
> build_joinrel_partition_info if the given joinrel will be to have
> consider_partitionwise_join=false; in the previous patch, that function
> created the joinrel's partition info such as part_scheme and part_rels if
> the joinrel is considered as partitioned, independently of the flag
> consider_partitionwise_join for it, but if that flag is false, we don't
> generate PWJ paths for the joinrel, so we would not need to create that
> partition info at all.  This would not only avoid unnecessary processing in
> that function, but also make unnecessary the changes I made to
> try_partitionwise_join, generate_partitionwise_join_paths,
> apply_scanjoin_target_to_paths, and create_ordinary_grouping_paths.  So I
> updated the patch that way.  Please find attached an updated version of the
> patch.

I guess the question is whether there are (or might be in the future)
other dependencies on part_scheme.  For example, it looks like
partition pruning uses it.  I'm not sure whether partition pruning
supports a plan like:

Append
-> Nested Loop
  -> Seq Scan on p1
  -> Index Scan on q1
<repeat the above for p2/q2 etc.>

If it doesn't, that's just an implementation restriction; somebody
might want to fix things so it works, if it doesn't already.

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