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[email protected]

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 20b627b74ce349e09ccab4d1baf107d9d178d671..c87a33d5da72fa55b0a8999095ee4d44caf12a23 100644 (file)
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -3063,6 +3063,25 @@ 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
@@ -3175,6 +3194,6 @@ NOTICE:  trig_row_after(23, skidoo) AFTER ROW INSERT ON rem1
 NOTICE:  NEW: (13,"test triggered !")
   ctid  
 --------
- (0,27)
+ (0,29)
 (1 row)
 

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index c5d9ee43dd9905873dc63423df6074e58d2447be..597b825ac890e03962762611543cd8d89726d20b 100644 (file)
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -1176,12 +1176,19 @@ 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 440e69099d7c883ab8b942bd46b5de8f63b14381..b93b9d27e40721c84a9163606de94d968b3d76f7 100644 (file)
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -638,6 +638,11 @@ 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