Re: postgres_fdw bug in 9.6

On Fri, Jan 13, 2017 at 6:22 AM, Etsuro Fujita
<fujita.etsuro@lab.ntt.co.jp> wrote:
> My biggest concern about GetExistingLocalJoinPath is that might not be
> extendable to the case of foreign-join paths with parameterization; in which
> case, fdw_outerpath for a given foreign-join path would need to have the
> same parameterization as the foreign-join path, but there might not be any
> existing paths with the same parameterization in the path list.

I agree that this is a problem.

> You might
> think we could get the fdw_outerpath by getting an existing path with no
> parameterization as in GetExistingLocalJoinPath and then modifying the
> path's param_info to match the parameterization of the foreign-join path.  I
> don't know that really works, but that might be inefficient.

I am not sure about this.

> What I have in mind to support foreign-join paths with parameterization for
> postgres_fdw like this: (1) generate parameterized paths from any joinable
> combination of the outer/inner cheapest-parameterized paths that have pushed
> down the outer/inner relation to the remote server, in a similar way as
> postgresGetForeignJoinPaths creates unparameterized paths, and (2) create
> fdw_outerpath for each parameterized path from the outer/inner paths used to
> generate the parameterized path, by create_nestloop_path (or,
> create_hashjoin_path or create_mergejoin_path if full join), so that the
> resulting fdw_outerpath has the same parameterization as the paramterized
> path.  This would probably work and might be more efficient.  And the patch
> I proposed would be easily extended to this, by replacing the outer/inner
> cheapest-total paths with the outer/inner cheapest-parameterized paths.
> Attached is the latest version of the patch.

Yes, I think that's broadly the approach Tom was recommending.

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