Re: [HACKERS] postgres_fdw bug in 9.6

On Wed, Dec 21, 2016 at 11:04 AM, Ashutosh Bapat
<ashutosh.bapat@enterprisedb.com> wrote:
> Some review comments
>
> 1. postgres_fdw doesn't push down semi and anti joins so you may want to
> discount these two too.
> +           jointype == JOIN_SEMI ||
> +           jointype == JOIN_ANTI);

But in the future, it might.  We shouldn't randomly leave foot-guns
lying around if there's an easy alternative.

> 3. Adding new members to JoinPathExtraData may save some work for postgres_fdw
> and other FDWs which would use CreateLocalJoinPath(), but it will add few bytes
> to the structure even when there is no "FULL foreign join which requires EPQ"
> involved in the query. That may not be so much of memory overhead since the
> structure is used locally to add_paths_to_joinrel(), but it might be something
> to think about. Instead, what if we call select_mergejoin_clauses() within
> CreateLocalJoinPath() to get that information?

I think that's exactly backwards.  The few bytes of storage don't
matter, but extra CPU cycles might.

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