Allow FDWs to push down quals without breaking EvalPlanQual rechecks.

This fixes a long-standing bug which was discovered while investigating
the interaction between the new join pushdown code and the EvalPlanQual
machinery: if a ForeignScan appears on the inner side of a paramaterized
nestloop, an EPQ recheck would re-return the original tuple even if
it no longer satisfied the pushed-down quals due to changed parameter
values.

This fix adds a new member to ForeignScan and ForeignScanState and a
new argument to make_foreignscan, and requires changes to FDWs which
push down quals to populate that new argument with a list of quals they
have chosen to push down.  Therefore, I'm only back-patching to 9.5,
even though the bug is not new in 9.5.

Etsuro Fujita, reviewed by me and by Kyotaro Horiguchi.

1 files changed, 11 insertions, 3 deletions

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e4d799cecd5..1902f1f4eae 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -748,6 +748,7 @@ postgresGetForeignPlan(PlannerInfo *root,
 	Index		scan_relid = baserel->relid;
 	List	   *fdw_private;
 	List	   *remote_conds = NIL;
+	List	   *remote_exprs = NIL;
 	List	   *local_exprs = NIL;
 	List	   *params_list = NIL;
 	List	   *retrieved_attrs;
@@ -769,8 +770,8 @@ postgresGetForeignPlan(PlannerInfo *root,
 	 *
 	 * This code must match "extract_actual_clauses(scan_clauses, false)"
 	 * except for the additional decision about remote versus local execution.
-	 * Note however that we only strip the RestrictInfo nodes from the
-	 * local_exprs list, since appendWhereClause expects a list of
+	 * Note however that we don't strip the RestrictInfo nodes from the
+	 * remote_conds list, since appendWhereClause expects a list of
 	 * RestrictInfos.
 	 */
 	foreach(lc, scan_clauses)
@@ -784,11 +785,17 @@ postgresGetForeignPlan(PlannerInfo *root,
 			continue;
 
 		if (list_member_ptr(fpinfo->remote_conds, rinfo))
+		{
 			remote_conds = lappend(remote_conds, rinfo);
+			remote_exprs = lappend(remote_exprs, rinfo->clause);
+		}
 		else if (list_member_ptr(fpinfo->local_conds, rinfo))
 			local_exprs = lappend(local_exprs, rinfo->clause);
 		else if (is_foreign_expr(root, baserel, rinfo->clause))
+		{
 			remote_conds = lappend(remote_conds, rinfo);
+			remote_exprs = lappend(remote_exprs, rinfo->clause);
+		}
 		else
 			local_exprs = lappend(local_exprs, rinfo->clause);
 	}
@@ -874,7 +881,8 @@ postgresGetForeignPlan(PlannerInfo *root,
 							scan_relid,
 							params_list,
 							fdw_private,
-							NIL /* no custom tlist */ );
+							NIL,	/* no custom tlist */
+							remote_exprs);
 }
 
 /*