Re: postgres_fdw join pushdown (was Re: Custom/Foreign-Join-APIs)

On 2016/02/16 15:22, Ashutosh Bapat wrote:
> During join planning, the planner tries multiple combinations of joining
> relations, thus the same base or join relation can be part of multiple
> of combination. Hence remote_conds or joinclauses will get linked
> multiple times as they are bidirectional lists, thus breaking linkages
> of previous join combinations tried. E.g. while planning A join B join C
> join D planner will come up with combinations like A(B(CD)) or (AB)(CD)
> or ((AB)C)D etc. and remote_conds from A will first be linked into
> A(B(CD)), then AB breaking the first linkages.

Exactly, but I don't think that that needs to be considered because we 
have this at the beginning of postgresGetGForeignJoinPaths:
    /*     * Skip if this join combination has been considered already.     */    if (joinrel->fdw_private)
return;

Best regards,
Etsuro Fujita