Improve speed of contrib/postgres_fdw regression tests.

Commit 7012b13 added some tests that consumed an excessive amount of
time, more than tripling the time needed for "make installcheck" for this
module.  Add filter conditions to reduce the number of rows scanned,
bringing the runtime down to within hailing distance of what it was before.

Jeevan Chalke and Ashutosh Bapat, per a gripe from me

Discussion: https://postgr.es/m/16565.1478104765@sss.pgh.pa.us

Author: tglsfdc

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -2685,9 +2685,9 @@ select sum(c1%3), sum(distinct c1%3 order by c1%3) filter (where c1%3 < 2), c2 f
 
 -- Outer query is aggregation query
 explain (verbose, costs off)
-select distinct (select count(*) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 order by 1;
-                                              QUERY PLAN                                               
--------------------------------------------------------------------------------------------------------
+select distinct (select count(*) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 where t2.c2 % 6 = 0 order by 1;
+                                                          QUERY PLAN                                                          
+------------------------------------------------------------------------------------------------------------------------------
  Unique
    Output: ((SubPlan 1))
    ->  Sort
@@ -2696,22 +2696,22 @@ select distinct (select count(*) filter (where t2.c2 = 6 and t2.c1 < 10) from ft
          ->  Foreign Scan
                Output: (SubPlan 1)
                Relations: Aggregate on (public.ft2 t2)
-               Remote SQL: SELECT count(*) FILTER (WHERE ((c2 = 6) AND ("C 1" < 10))) FROM "S 1"."T 1"
+               Remote SQL: SELECT count(*) FILTER (WHERE ((c2 = 6) AND ("C 1" < 10))) FROM "S 1"."T 1" WHERE (((c2 % 6) = 0))
                SubPlan 1
                  ->  Foreign Scan on public.ft1 t1
                        Output: (count(*) FILTER (WHERE ((t2.c2 = 6) AND (t2.c1 < 10))))
                        Remote SQL: SELECT NULL FROM "S 1"."T 1" WHERE (("C 1" = 6))
 (13 rows)
 
-select distinct (select count(*) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 order by 1;
+select distinct (select count(*) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 where t2.c2 % 6 = 0 order by 1;
  count 
 -------
      1
 (1 row)
 
 -- Inner query is aggregation query
 explain (verbose, costs off)
-select distinct (select count(t1.c1) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 order by 1;
+select distinct (select count(t1.c1) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 where t2.c2 % 6 = 0 order by 1;
                                                                       QUERY PLAN                                                                      
 ------------------------------------------------------------------------------------------------------------------------------------------------------
  Unique
@@ -2721,15 +2721,15 @@ select distinct (select count(t1.c1) filter (where t2.c2 = 6 and t2.c1 < 10) fro
          Sort Key: ((SubPlan 1))
          ->  Foreign Scan on public.ft2 t2
                Output: (SubPlan 1)
-               Remote SQL: SELECT "C 1", c2 FROM "S 1"."T 1"
+               Remote SQL: SELECT "C 1", c2 FROM "S 1"."T 1" WHERE (((c2 % 6) = 0))
                SubPlan 1
                  ->  Foreign Scan
                        Output: (count(t1.c1) FILTER (WHERE ((t2.c2 = 6) AND (t2.c1 < 10))))
                        Relations: Aggregate on (public.ft1 t1)
                        Remote SQL: SELECT count("C 1") FILTER (WHERE (($1::integer = 6) AND ($2::integer < 10))) FROM "S 1"."T 1" WHERE (("C 1" = 6))
 (13 rows)
 
-select distinct (select count(t1.c1) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 order by 1;
+select distinct (select count(t1.c1) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 where t2.c2 % 6 = 0 order by 1;
  count 
 -------
      0
@@ -3086,39 +3086,33 @@ select sum(c2) * (random() <= 1)::int as sum from ft1 order by 1;
 -- LATERAL join, with parameterization
 set enable_hashagg to false;
 explain (verbose, costs off)
-select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum from ft2 t2 group by t2.c1) qry where t1.c2 * 2 = qry.sum and t1.c2 < 10 order by 1;
+select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum from ft2 t2 group by t2.c1) qry where t1.c2 * 2 = qry.sum and t1.c2 < 3 and t1."C 1" < 100 order by 1;
                                                 QUERY PLAN                                                
 ----------------------------------------------------------------------------------------------------------
  Sort
    Output: t1.c2, qry.sum
    Sort Key: t1.c2
    ->  Nested Loop
          Output: t1.c2, qry.sum
-         ->  Seq Scan on "S 1"."T 1" t1
+         ->  Index Scan using t1_pkey on "S 1"."T 1" t1
                Output: t1."C 1", t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-               Filter: (t1.c2 < 10)
+               Index Cond: (t1."C 1" < 100)
+               Filter: (t1.c2 < 3)
          ->  Subquery Scan on qry
                Output: qry.sum, t2.c1
                Filter: ((t1.c2 * 2) = qry.sum)
                ->  Foreign Scan
                      Output: (sum((t2.c1 + t1."C 1"))), t2.c1
                      Relations: Aggregate on (public.ft2 t2)
                      Remote SQL: SELECT sum(("C 1" + $1::integer)), "C 1" FROM "S 1"."T 1" GROUP BY "C 1"
-(15 rows)
+(16 rows)
 
-select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum from ft2 t2 group by t2.c1) qry where t1.c2 * 2 = qry.sum and t1.c2 < 10 order by 1;
+select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum from ft2 t2 group by t2.c1) qry where t1.c2 * 2 = qry.sum and t1.c2 < 3 and t1."C 1" < 100 order by 1;
  c2 | sum 
 ----+-----
   1 |   2
   2 |   4
-  3 |   6
-  4 |   8
-  5 |  10
-  6 |  12
-  7 |  14
-  8 |  16
-  9 |  18
-(9 rows)
+(2 rows)
 
 reset enable_hashagg;
 -- Check with placeHolderVars

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -641,12 +641,12 @@ select sum(c1%3), sum(distinct c1%3 order by c1%3) filter (where c1%3 < 2), c2 f
 
 -- Outer query is aggregation query
 explain (verbose, costs off)
-select distinct (select count(*) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 order by 1;
-select distinct (select count(*) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 order by 1;
+select distinct (select count(*) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 where t2.c2 % 6 = 0 order by 1;
+select distinct (select count(*) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 where t2.c2 % 6 = 0 order by 1;
 -- Inner query is aggregation query
 explain (verbose, costs off)
-select distinct (select count(t1.c1) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 order by 1;
-select distinct (select count(t1.c1) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 order by 1;
+select distinct (select count(t1.c1) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 where t2.c2 % 6 = 0 order by 1;
+select distinct (select count(t1.c1) filter (where t2.c2 = 6 and t2.c1 < 10) from ft1 t1 where t1.c1 = 6) from ft2 t2 where t2.c2 % 6 = 0 order by 1;
 
 -- Aggregate not pushed down as FILTER condition is not pushable
 explain (verbose, costs off)
@@ -802,8 +802,8 @@ select sum(c2) * (random() <= 1)::int as sum from ft1 order by 1;
 -- LATERAL join, with parameterization
 set enable_hashagg to false;
 explain (verbose, costs off)
-select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum from ft2 t2 group by t2.c1) qry where t1.c2 * 2 = qry.sum and t1.c2 < 10 order by 1;
-select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum from ft2 t2 group by t2.c1) qry where t1.c2 * 2 = qry.sum and t1.c2 < 10 order by 1;
+select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum from ft2 t2 group by t2.c1) qry where t1.c2 * 2 = qry.sum and t1.c2 < 3 and t1."C 1" < 100 order by 1;
+select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum from ft2 t2 group by t2.c1) qry where t1.c2 * 2 = qry.sum and t1.c2 < 3 and t1."C 1" < 100 order by 1;
 reset enable_hashagg;
 
 -- Check with placeHolderVars