*** a/src/backend/executor/nodeModifyTable.c
--- b/src/backend/executor/nodeModifyTable.c
***************
*** 354,359 **** ldelete:;
--- 354,379 ----
  		switch (result)
  		{
  			case HeapTupleSelfUpdated:
+ 				/*
+ 				 * There is no sensible action to take if the BEFORE DELETE
+ 				 * trigger for a row issues an UPDATE for the same row, either
+ 				 * directly or by performing DML which fires other triggers
+ 				 * which do the update.  We don't want to discard the original
+ 				 * DELETE while keeping the triggered actions based on its
+ 				 * deletion; and it would be no better to allow the original
+ 				 * DELETE while discarding some of its triggered actions.
+ 				 * Updating the row which is being deleted risks losing some
+ 				 * information which might be important according to business
+ 				 * rules; so throwing an error is the only safe course.
+ 				 */
+ 				if (!ItemPointerEquals(tupleid, &update_ctid)
+ 					&& GetCurrentCommandId(false) != estate->es_output_cid)
+ 				{
+ 					ereport(ERROR,
+ 							(errcode(ERRCODE_TRIGGERED_DATA_CHANGE_VIOLATION),
+ 							 errmsg("cannot update or delete a row from its BEFORE DELETE trigger"),
+ 							 errhint("Consider moving code to an AFTER DELETE trigger.")));
+ 				}
  				/* already deleted by self; nothing to do */
  				return NULL;
  
***************
*** 570,575 **** lreplace:;
--- 590,613 ----
  		switch (result)
  		{
  			case HeapTupleSelfUpdated:
+ 				/*
+ 				 * There is no sensible action to take if the BEFORE UPDATE
+ 				 * trigger for a row issues another UPDATE for the same row,
+ 				 * either directly or by performing DML which fires other
+ 				 * triggers which do the update.  We don't want to discard the
+ 				 * original UPDATE while keeping the triggered actions based
+ 				 * on its update; and it would be no better to allow the
+ 				 * original UPDATE while discarding some of its triggered
+ 				 * actions.
+ 				 */
+ 				if (!ItemPointerEquals(tupleid, &update_ctid)
+ 					&& GetCurrentCommandId(false) != estate->es_output_cid)
+ 				{
+ 					ereport(ERROR,
+ 							(errcode(ERRCODE_TRIGGERED_DATA_CHANGE_VIOLATION),
+ 							 errmsg("cannot update or delete a row from its BEFORE UPDATE trigger"),
+ 							 errhint("Consider moving code to an AFTER UPDATE trigger.")));
+ 				}
  				/* already deleted by self; nothing to do */
  				return NULL;
  
*** a/src/test/regress/expected/triggers.out
--- b/src/test/regress/expected/triggers.out
***************
*** 1443,1445 **** NOTICE:  drop cascades to 2 other objects
--- 1443,1566 ----
  DETAIL:  drop cascades to view city_view
  drop cascades to view european_city_view
  DROP TABLE country_table;
+ --
+ -- Test updates to rows during firing of BEFORE ROW triggers.
+ --
+ create table parent (aid int not null primary key,
+                      val1 text,
+                      val2 text,
+                      val3 text,
+                      val4 text,
+                      bcnt int not null default 0);
+ NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "parent_pkey" for table "parent"
+ create table child (bid int not null primary key,
+                     aid int not null,
+                     val1 text);
+ NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "child_pkey" for table "child"
+ create function parent_upd_func()
+   returns trigger language plpgsql as
+ $$
+ begin
+   if old.val1 <> new.val1 then
+     new.val2 = new.val1;
+     delete from child where child.aid = new.aid and child.val1 = new.val1;
+   end if;
+   return new;
+ end;
+ $$;
+ create trigger parent_upd_trig before update On parent
+   for each row execute procedure parent_upd_func();
+ create function parent_del_func()
+   returns trigger language plpgsql as
+ $$
+ begin
+   delete from child where aid = old.aid;
+   return old;
+ end;
+ $$;
+ create trigger parent_del_trig before delete On parent
+   for each row execute procedure parent_del_func();
+ create function child_ins_func()
+   returns trigger language plpgsql as
+ $$
+ begin
+   update parent set bcnt = bcnt + 1 where aid = new.aid;
+   return new;
+ end;
+ $$;
+ create trigger child_ins_trig after insert on child
+   for each row execute procedure child_ins_func();
+ create function child_del_func()
+   returns trigger language plpgsql as
+ $$
+ begin
+   update parent set bcnt = bcnt - 1 where aid = old.aid;
+   return old;
+ end;
+ $$;
+ create trigger child_del_trig after delete on child
+   for each row execute procedure child_del_func();
+ insert into parent values (1, 'a', 'a', 'a', 'a', 0);
+ insert into child values (10, 1, 'b');
+ select * from parent; select * from child;
+  aid | val1 | val2 | val3 | val4 | bcnt 
+ -----+------+------+------+------+------
+    1 | a    | a    | a    | a    |    1
+ (1 row)
+ 
+  bid | aid | val1 
+ -----+-----+------
+   10 |   1 | b
+ (1 row)
+ 
+ update parent set val1 = 'b' where aid = 1;
+ ERROR:  cannot update or delete a row from its BEFORE UPDATE trigger
+ HINT:  Consider moving code to an AFTER UPDATE trigger.
+ select * from parent; select * from child;
+  aid | val1 | val2 | val3 | val4 | bcnt 
+ -----+------+------+------+------+------
+    1 | a    | a    | a    | a    |    1
+ (1 row)
+ 
+  bid | aid | val1 
+ -----+-----+------
+   10 |   1 | b
+ (1 row)
+ 
+ delete from parent where aid = 1;
+ ERROR:  cannot update or delete a row from its BEFORE DELETE trigger
+ HINT:  Consider moving code to an AFTER DELETE trigger.
+ select * from parent; select * from child;
+  aid | val1 | val2 | val3 | val4 | bcnt 
+ -----+------+------+------+------+------
+    1 | a    | a    | a    | a    |    1
+ (1 row)
+ 
+  bid | aid | val1 
+ -----+-----+------
+   10 |   1 | b
+ (1 row)
+ 
+ create or replace function parent_del_func()
+   returns trigger language plpgsql as
+ $$
+ begin
+   delete from child where aid = old.aid;
+   if found then
+     delete from parent where aid = old.aid;
+     return null;
+   end if;
+   return old;
+ end;
+ $$;
+ delete from parent where aid = 1;
+ select * from parent; select * from child;
+  aid | val1 | val2 | val3 | val4 | bcnt 
+ -----+------+------+------+------+------
+ (0 rows)
+ 
+  bid | aid | val1 
+ -----+-----+------
+ (0 rows)
+ 
+ drop table parent, child;
*** a/src/test/regress/sql/triggers.sql
--- b/src/test/regress/sql/triggers.sql
***************
*** 961,963 **** SELECT * FROM city_view;
--- 961,1050 ----
  
  DROP TABLE city_table CASCADE;
  DROP TABLE country_table;
+ 
+ --
+ -- Test updates to rows during firing of BEFORE ROW triggers.
+ --
+ 
+ create table parent (aid int not null primary key,
+                      val1 text,
+                      val2 text,
+                      val3 text,
+                      val4 text,
+                      bcnt int not null default 0);
+ create table child (bid int not null primary key,
+                     aid int not null,
+                     val1 text);
+ 
+ create function parent_upd_func()
+   returns trigger language plpgsql as
+ $$
+ begin
+   if old.val1 <> new.val1 then
+     new.val2 = new.val1;
+     delete from child where child.aid = new.aid and child.val1 = new.val1;
+   end if;
+   return new;
+ end;
+ $$;
+ create trigger parent_upd_trig before update On parent
+   for each row execute procedure parent_upd_func();
+ 
+ create function parent_del_func()
+   returns trigger language plpgsql as
+ $$
+ begin
+   delete from child where aid = old.aid;
+   return old;
+ end;
+ $$;
+ create trigger parent_del_trig before delete On parent
+   for each row execute procedure parent_del_func();
+ 
+ create function child_ins_func()
+   returns trigger language plpgsql as
+ $$
+ begin
+   update parent set bcnt = bcnt + 1 where aid = new.aid;
+   return new;
+ end;
+ $$;
+ create trigger child_ins_trig after insert on child
+   for each row execute procedure child_ins_func();
+ 
+ create function child_del_func()
+   returns trigger language plpgsql as
+ $$
+ begin
+   update parent set bcnt = bcnt - 1 where aid = old.aid;
+   return old;
+ end;
+ $$;
+ create trigger child_del_trig after delete on child
+   for each row execute procedure child_del_func();
+ 
+ insert into parent values (1, 'a', 'a', 'a', 'a', 0);
+ insert into child values (10, 1, 'b');
+ select * from parent; select * from child;
+ update parent set val1 = 'b' where aid = 1;
+ select * from parent; select * from child;
+ delete from parent where aid = 1;
+ select * from parent; select * from child;
+ 
+ create or replace function parent_del_func()
+   returns trigger language plpgsql as
+ $$
+ begin
+   delete from child where aid = old.aid;
+   if found then
+     delete from parent where aid = old.aid;
+     return null;
+   end if;
+   return old;
+ end;
+ $$;
+ 
+ delete from parent where aid = 1;
+ select * from parent; select * from child;
+ 
+ drop table parent, child;