postgres_fdw: Account for triggers in non-direct remote UPDATE planning.

Previously, in postgresPlanForeignModify, we planned an UPDATE operation
on a foreign table so that we transmit only columns that were explicitly
targets of the UPDATE, so as to avoid unnecessary data transmission, but
if there were BEFORE ROW UPDATE triggers on the foreign table, those
triggers might change values for non-target columns, in which case we
would miss sending changed values for those columns.  Prevent optimizing
away transmitting all columns if there are BEFORE ROW UPDATE triggers on
the foreign table.

This is an oversight in commit 7cbe57c34 which added triggers on foreign
tables, so apply the patch all the way back to 9.4 where that came in.

Author: Shohei Mochizuki
Reviewed-by: Amit Langote
Discussion: https://postgr.es/m/201905270152.x4R1q3qi014550@toshiba.co.jp

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index f19f982e0ac9b23a82471cd212050417594c6c5e..01f11487ef2e7a2c58eed7932dcf15fe828bf84d 100644 (file)
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -6577,6 +6577,25 @@ SELECT * from loc1;
   2 | skidoo triggered !
 (2 rows)
 
+EXPLAIN (verbose, costs off)
+UPDATE rem1 set f1 = 10;          -- all columns should be transmitted
+                              QUERY PLAN                               
+-----------------------------------------------------------------------
+ Update on public.rem1
+   Remote SQL: UPDATE public.loc1 SET f1 = $2, f2 = $3 WHERE ctid = $1
+   ->  Foreign Scan on public.rem1
+         Output: 10, f2, ctid, rem1.*
+         Remote SQL: SELECT f1, f2, ctid FROM public.loc1 FOR UPDATE
+(5 rows)
+
+UPDATE rem1 set f1 = 10;
+SELECT * from loc1;
+ f1 |               f2               
+----+--------------------------------
+ 10 | skidoo triggered ! triggered !
+ 10 | skidoo triggered ! triggered !
+(2 rows)
+
 DELETE FROM rem1;
 -- Add a second trigger, to check that the changes are propagated correctly
 -- from trigger to trigger
@@ -6689,7 +6708,7 @@ NOTICE:  trig_row_after(23, skidoo) AFTER ROW INSERT ON rem1
 NOTICE:  NEW: (13,"test triggered !")
   ctid  
 --------
- (0,27)
+ (0,29)
 (1 row)
 
 -- cleanup
@@ -6793,10 +6812,10 @@ BEFORE UPDATE ON rem1
 FOR EACH ROW EXECUTE PROCEDURE trigger_data(23,'skidoo');
 EXPLAIN (verbose, costs off)
 UPDATE rem1 set f2 = '';          -- can't be pushed down
-                             QUERY PLAN                              
----------------------------------------------------------------------
+                              QUERY PLAN                               
+-----------------------------------------------------------------------
  Update on public.rem1
-   Remote SQL: UPDATE public.loc1 SET f2 = $2 WHERE ctid = $1
+   Remote SQL: UPDATE public.loc1 SET f1 = $2, f2 = $3 WHERE ctid = $1
    ->  Foreign Scan on public.rem1
          Output: f1, ''::text, ctid, rem1.*
          Remote SQL: SELECT f1, f2, ctid FROM public.loc1 FOR UPDATE
@@ -7423,12 +7442,12 @@ AFTER UPDATE OR DELETE ON bar2
 FOR EACH ROW EXECUTE PROCEDURE trigger_data(23,'skidoo');
 explain (verbose, costs off)
 update bar set f2 = f2 + 100;
-                                      QUERY PLAN                                      
---------------------------------------------------------------------------------------
+                                               QUERY PLAN                                               
+--------------------------------------------------------------------------------------------------------
  Update on public.bar
    Update on public.bar
    Foreign Update on public.bar2
-     Remote SQL: UPDATE public.loct2 SET f2 = $2 WHERE ctid = $1 RETURNING f1, f2, f3
+     Remote SQL: UPDATE public.loct2 SET f1 = $2, f2 = $3, f3 = $4 WHERE ctid = $1 RETURNING f1, f2, f3
    ->  Seq Scan on public.bar
          Output: bar.f1, (bar.f2 + 100), bar.ctid
    ->  Foreign Scan on public.bar2

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index ae1deab4eecb3a90923f94b51cc3d582f3ed38a5..025f922b4c670b643a0c15518b2a38e72e89a959 100644 (file)
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -1620,12 +1620,19 @@ postgresPlanForeignModify(PlannerInfo *root,
 
        /*
         * In an INSERT, we transmit all columns that are defined in the foreign
-        * table.  In an UPDATE, we transmit only columns that were explicitly
-        * targets of the UPDATE, so as to avoid unnecessary data transmission.
-        * (We can't do that for INSERT since we would miss sending default values
-        * for columns not listed in the source statement.)
-        */
-       if (operation == CMD_INSERT)
+        * table.  In an UPDATE, if there are BEFORE ROW UPDATE triggers on the
+        * foreign table, we transmit all columns like INSERT; else we transmit
+        * only columns that were explicitly targets of the UPDATE, so as to avoid
+        * unnecessary data transmission.  (We can't do that for INSERT since we
+        * would miss sending default values for columns not listed in the source
+        * statement, and for UPDATE if there are BEFORE ROW UPDATE triggers since
+        * those triggers might change values for non-target columns, in which
+        * case we would miss sending changed values for those columns.)
+        */
+       if (operation == CMD_INSERT ||
+               (operation == CMD_UPDATE &&
+                rel->trigdesc &&
+                rel->trigdesc->trig_update_before_row))
        {
                TupleDesc       tupdesc = RelationGetDescr(rel);
                int                     attnum;

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 934b6ffaf2c192e3b85347704981a67eadd63060..a87c57df7bf08d7ad732f020fc31112d10959648 100644 (file)
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -1481,6 +1481,11 @@ SELECT * from loc1;
 UPDATE rem1 set f2 = 'skidoo' RETURNING f2;
 SELECT * from loc1;
 
+EXPLAIN (verbose, costs off)
+UPDATE rem1 set f1 = 10;          -- all columns should be transmitted
+UPDATE rem1 set f1 = 10;
+SELECT * from loc1;
+
 DELETE FROM rem1;
 
 -- Add a second trigger, to check that the changes are propagated correctly