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;