Allow foreign and custom joins to handle EvalPlanQual rechecks.

Commit e7cb7ee14555cc9c5773e2c102efd6371f6f2005 provided basic
infrastructure for allowing a foreign data wrapper or custom scan
provider to replace a join of one or more tables with a scan.
However, this infrastructure failed to take into account the need
for possible EvalPlanQual rechecks, and ExecScanFetch would fail
an assertion (or just overwrite memory) if such a check was attempted
for a plan containing a pushed-down join.  To fix, adjust the EPQ
machinery to skip some processing steps when scanrelid == 0, making
those the responsibility of scan's recheck method, which also has
the responsibility in this case of correctly populating the relevant
slot.

To allow foreign scans to gain control in the right place to make
use of this new facility, add a new, optional RecheckForeignScan
method.  Also, allow a foreign scan to have a child plan, which can
be used to correctly populate the slot (or perhaps for something
else, but this is the only use currently envisioned).

KaiGai Kohei, reviewed by Robert Haas, Etsuro Fujita, and Kyotaro
Horiguchi.

4 files changed, 10 insertions, 2 deletions

diff --git a/src/include/foreign/fdwapi.h b/src/include/foreign/fdwapi.h
index 69b48b46778..e9fdacd4498 100644
--- a/src/include/foreign/fdwapi.h
+++ b/src/include/foreign/fdwapi.h
@@ -36,13 +36,17 @@ typedef ForeignScan *(*GetForeignPlan_function) (PlannerInfo *root,
 														  Oid foreigntableid,
 													  ForeignPath *best_path,
 															 List *tlist,
-														 List *scan_clauses);
+														  List *scan_clauses,
+														   Plan *outer_plan);
 
 typedef void (*BeginForeignScan_function) (ForeignScanState *node,
 													   int eflags);
 
 typedef TupleTableSlot *(*IterateForeignScan_function) (ForeignScanState *node);
 
+typedef bool (*RecheckForeignScan_function) (ForeignScanState *node,
+													   TupleTableSlot *slot);
+
 typedef void (*ReScanForeignScan_function) (ForeignScanState *node);
 
 typedef void (*EndForeignScan_function) (ForeignScanState *node);
@@ -162,6 +166,7 @@ typedef struct FdwRoutine
 	/* Functions for SELECT FOR UPDATE/SHARE row locking */
 	GetForeignRowMarkType_function GetForeignRowMarkType;
 	RefetchForeignRow_function RefetchForeignRow;
+	RecheckForeignScan_function RecheckForeignScan;
 
 	/* Support functions for EXPLAIN */
 	ExplainForeignScan_function ExplainForeignScan;
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 6de07a1fbd0..32321238ae4 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -911,6 +911,7 @@ typedef struct TidPath
 typedef struct ForeignPath
 {
 	Path		path;
+	Path	   *fdw_outerpath;
 	List	   *fdw_private;
 } ForeignPath;
 
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index eea75d0d1ec..f41847f4093 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -86,6 +86,7 @@ extern ForeignPath *create_foreignscan_path(PlannerInfo *root, RelOptInfo *rel,
 						double rows, Cost startup_cost, Cost total_cost,
 						List *pathkeys,
 						Relids required_outer,
+						Path *fdw_outerpath,
 						List *fdw_private);
 
 extern Relids calc_nestloop_required_outer(Path *outer_path, Path *inner_path);
diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index 1fb850489fb..f96e9ee5054 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -45,7 +45,8 @@ extern SubqueryScan *make_subqueryscan(List *qptlist, List *qpqual,
 				  Index scanrelid, Plan *subplan);
 extern ForeignScan *make_foreignscan(List *qptlist, List *qpqual,
 				 Index scanrelid, List *fdw_exprs, List *fdw_private,
-				 List *fdw_scan_tlist, List *fdw_recheck_quals);
+				 List *fdw_scan_tlist, List *fdw_recheck_quals,
+				 Plan *outer_plan);
 extern Append *make_append(List *appendplans, List *tlist);
 extern RecursiveUnion *make_recursive_union(List *tlist,
 					 Plan *lefttree, Plan *righttree, int wtParam,