Re: FDW join pushdown and scanclauses

On 2016/01/08 22:05, Ashutosh Bapat wrote:

In add_paths_to_joinrel(), the FDW specific hook GetForeignJoinPaths()
is called. This hook if implemented should add ForeignPaths for pushed
down joins. create_plan_recurse() calls create_scan_plan() on seeing
these paths.

create_scan_plan() generates a list of clauses to be applied on scan
from rel->baserestrictinfo and parameterization clauses. This list is
passed to create_*scan_plan routine as scanclauses. This code is very
specific for single relations scans. Now that we are using
create_scan_plan() for creating plan for join relations, it needs some
changes so that quals relevant to a join can be passed to
create_foreignscan_plan().

Do we really need that?  The relevant join quals are passed to GetForeignJoinPaths as extra->restrictlist, so I think we can get those quals during GetForeignPlan, by looking at the selected ForeignPath that is passed to that function as a parameter.

A related problem is in
create_foreignscan_plan(), which sets ForeignScan::fsSystemCol if a
system column is being used in the targetlist or quals. Right now it
only checks rel->baserestrictinfo, which is NULL for a joinrel. Thus in
case a system column appears in the joinclauses it will not be considered.

IIUC, we assume that such system columns are assumed to be contained in fdw_scan_tlist in the joinrel case.