postgres_fdw: Push down UPDATE/DELETE joins to remote servers.

Commit 0bf3ae88 allowed direct
foreign table modification; instead of fetching each row, updating
it locally, and then pushing the modification back to the remote
side, we would instead do all the work on the remote server via a
single remote UPDATE or DELETE command.  However, that commit only
enabled this optimization when join tree consisted only of the
target table.

This change allows the same optimization when an UPDATE statement
has a FROM clause or a DELETE statement has a USING clause.  This
works much like ordinary foreign join pushdown, in that the tables
must be on the same remote server, relevant parts of the query
must be pushdown-safe, and so forth.

Etsuro Fujita, reviewed by Ashutosh Bapat, Rushabh Lathia, and me.
Some formatting corrections by me.

Discussion: http://postgr.es/m/5A57193A.2080003@lab.ntt.co.jp
Discussion: http://postgr.es/m/b9cee735-62f8-6c07-7528-6364ce9347d0@lab.ntt.co.jp

contrib/postgres_fdw/postgres_fdw.h

@@ -150,6 +150,7 @@ extern void deparseUpdateSql(StringInfo buf, PlannerInfo *root,
 				 List **retrieved_attrs);
 extern void deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 					   Index rtindex, Relation rel,
+					   RelOptInfo *foreignrel,
 					   List *targetlist,
 					   List *targetAttrs,
 					   List *remote_conds,
@@ -162,6 +163,7 @@ extern void deparseDeleteSql(StringInfo buf, PlannerInfo *root,
 				 List **retrieved_attrs);
 extern void deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 					   Index rtindex, Relation rel,
+					   RelOptInfo *foreignrel,
 					   List *remote_conds,
 					   List **params_list,
 					   List *returningList,

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -1082,14 +1082,14 @@ UPDATE ft2 SET c2 = c2 + 400, c3 = c3 || '_update7' WHERE c1 % 10 = 7 RETURNING
 UPDATE ft2 SET c2 = c2 + 400, c3 = c3 || '_update7' WHERE c1 % 10 = 7 RETURNING *;
 EXPLAIN (verbose, costs off)
 UPDATE ft2 SET c2 = ft2.c2 + 500, c3 = ft2.c3 || '_update9', c7 = DEFAULT
-  FROM ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 9;                               -- can't be pushed down
+  FROM ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 9;                               -- can be pushed down
 UPDATE ft2 SET c2 = ft2.c2 + 500, c3 = ft2.c3 || '_update9', c7 = DEFAULT
   FROM ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 9;
 EXPLAIN (verbose, costs off)
   DELETE FROM ft2 WHERE c1 % 10 = 5 RETURNING c1, c4;                               -- can be pushed down
 DELETE FROM ft2 WHERE c1 % 10 = 5 RETURNING c1, c4;
 EXPLAIN (verbose, costs off)
-DELETE FROM ft2 USING ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 2;                -- can't be pushed down
+DELETE FROM ft2 USING ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 2;                -- can be pushed down
 DELETE FROM ft2 USING ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 2;
 SELECT c1,c2,c3,c4 FROM ft2 ORDER BY c1;
 EXPLAIN (verbose, costs off)
@@ -1102,6 +1102,58 @@ EXPLAIN (verbose, costs off)
 DELETE FROM ft2 WHERE c1 = 9999 RETURNING tableoid::regclass;                       -- can be pushed down
 DELETE FROM ft2 WHERE c1 = 9999 RETURNING tableoid::regclass;
 
+-- Test UPDATE/DELETE with RETURNING on a three-table join
+INSERT INTO ft2 (c1,c2,c3)
+  SELECT id, id - 1200, to_char(id, 'FM00000') FROM generate_series(1201, 1300) id;
+EXPLAIN (verbose, costs off)
+UPDATE ft2 SET c3 = 'foo'
+  FROM ft4 INNER JOIN ft5 ON (ft4.c1 = ft5.c1)
+  WHERE ft2.c1 > 1200 AND ft2.c2 = ft4.c1
+  RETURNING ft2.ctid, ft2, ft2.*, ft4.ctid, ft4, ft4.*;                             -- can be pushed down
+UPDATE ft2 SET c3 = 'foo'
+  FROM ft4 INNER JOIN ft5 ON (ft4.c1 = ft5.c1)
+  WHERE ft2.c1 > 1200 AND ft2.c2 = ft4.c1
+  RETURNING ft2.ctid, ft2, ft2.*, ft4.ctid, ft4, ft4.*;
+EXPLAIN (verbose, costs off)
+DELETE FROM ft2
+  USING ft4 LEFT JOIN ft5 ON (ft4.c1 = ft5.c1)
+  WHERE ft2.c1 > 1200 AND ft2.c1 % 10 = 0 AND ft2.c2 = ft4.c1
+  RETURNING 100;                                                                    -- can be pushed down
+DELETE FROM ft2
+  USING ft4 LEFT JOIN ft5 ON (ft4.c1 = ft5.c1)
+  WHERE ft2.c1 > 1200 AND ft2.c1 % 10 = 0 AND ft2.c2 = ft4.c1
+  RETURNING 100;
+DELETE FROM ft2 WHERE ft2.c1 > 1200;
+
+-- Test UPDATE/DELETE with WHERE or JOIN/ON conditions containing
+-- user-defined operators/functions
+ALTER SERVER loopback OPTIONS (DROP extensions);
+INSERT INTO ft2 (c1,c2,c3)
+  SELECT id, id % 10, to_char(id, 'FM00000') FROM generate_series(2001, 2010) id;
+EXPLAIN (verbose, costs off)
+UPDATE ft2 SET c3 = 'bar' WHERE postgres_fdw_abs(c1) > 2000 RETURNING *;            -- can't be pushed down
+UPDATE ft2 SET c3 = 'bar' WHERE postgres_fdw_abs(c1) > 2000 RETURNING *;
+EXPLAIN (verbose, costs off)
+UPDATE ft2 SET c3 = 'baz'
+  FROM ft4 INNER JOIN ft5 ON (ft4.c1 = ft5.c1)
+  WHERE ft2.c1 > 2000 AND ft2.c2 === ft4.c1
+  RETURNING ft2.*, ft4.*, ft5.*;                                                    -- can't be pushed down
+UPDATE ft2 SET c3 = 'baz'
+  FROM ft4 INNER JOIN ft5 ON (ft4.c1 = ft5.c1)
+  WHERE ft2.c1 > 2000 AND ft2.c2 === ft4.c1
+  RETURNING ft2.*, ft4.*, ft5.*;
+EXPLAIN (verbose, costs off)
+DELETE FROM ft2
+  USING ft4 INNER JOIN ft5 ON (ft4.c1 === ft5.c1)
+  WHERE ft2.c1 > 2000 AND ft2.c2 = ft4.c1
+  RETURNING ft2.ctid, ft2.c1, ft2.c2, ft2.c3;                                       -- can't be pushed down
+DELETE FROM ft2
+  USING ft4 INNER JOIN ft5 ON (ft4.c1 === ft5.c1)
+  WHERE ft2.c1 > 2000 AND ft2.c2 = ft4.c1
+  RETURNING ft2.ctid, ft2.c1, ft2.c2, ft2.c3;
+DELETE FROM ft2 WHERE ft2.c1 > 2000;
+ALTER SERVER loopback OPTIONS (ADD extensions 'postgres_fdw');
+
 -- Test that trigger on remote table works as expected
 CREATE OR REPLACE FUNCTION "S 1".F_BRTRIG() RETURNS trigger AS $$
 BEGIN