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Re: Join Filter vs. Index Cond (performance regression 9.1->9.2+/HEAD)
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* Re: Join Filter vs. Index Cond (performance regression 9.1->9.2+/HEAD)
@ 2015-06-01 18:03 Andrew Gierth <[email protected]>
  2015-06-01 19:31 ` Re: Join Filter vs. Index Cond (performance regression 9.1->9.2+/HEAD) Tom Lane <[email protected]>
  0 siblings, 1 reply; 815+ messages in thread

From: Andrew Gierth @ 2015-06-01 18:03 UTC (permalink / raw)
  To: Tom Lane <[email protected]>; +Cc: pgsql-hackers

>>>>> "Tom" == Tom Lane <[email protected]> writes:

 Tom> Once you're down to an estimate of one row retrieved, adding
 Tom> additional index conditions simply increases the cost (not by
 Tom> much, but it increases) without delivering any visible benefit.

OK, but this is a serious problem because "estimate of one row" is a
very common estimation failure mode, and isn't always solvable in the
sense of arranging for better estimates (in the absence of hints, ugh).

 Tom> I believe what probably happened in this case is that the planner
 Tom> considered both forms of the indexscan path and concluded that
 Tom> they were fuzzily the same cost and rowcount, yet the path using
 Tom> only t2.a and t3.b clearly dominated by requiring strictly fewer
 Tom> outer relations for parameters.  So it threw away the path that
 Tom> also had the c = t4.c comparison before it ever got to the join
 Tom> stage.  Even had it kept that path, the join cost estimate
 Tom> wouldn't have looked any better than the one for the join it did
 Tom> pick, so there would have been no certainty of picking the
 Tom> "correct" plan.

 Tom> The real problem in your example is thus the incorrect rowcount
 Tom> estimate; with better rowcount estimates the two cases wouldn't
 Tom> have appeared to have the same output rowcount.

 Tom> For the toy data in your example, this can probably be blamed on
 Tom> the fact that eqjoinsel_inner doesn't have any smarts for the case
 Tom> of having an MCV list for only one side (though as noted in the
 Tom> comments, it's not obvious what it should do instead).  However,
 Tom> it's not very clear what was happening in the real-world case.

In the real-world case, t1 was something like an "overrides" table for
data otherwise obtained from the other tables, i.e. special-case
exceptions for general rules. As such it is highly skew, with many
possible (a,b) values having no row at all, but others having hundreds
of matches on (a,b) (but only one at most on (a,b,c) since this was the
pkey in the real data as well as the testcase).

Accordingly, there was no way that we could identify of getting any kind
of better estimate of rowcount.

-- 
Andrew (irc:RhodiumToad)


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^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* Re: Join Filter vs. Index Cond (performance regression 9.1->9.2+/HEAD)
  2015-06-01 18:03 Re: Join Filter vs. Index Cond (performance regression 9.1->9.2+/HEAD) Andrew Gierth <[email protected]>
@ 2015-06-01 19:31 ` Tom Lane <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Tom Lane @ 2015-06-01 19:31 UTC (permalink / raw)
  To: Andrew Gierth <[email protected]>; +Cc: pgsql-hackers

Andrew Gierth <[email protected]> writes:
> "Tom" == Tom Lane <[email protected]> writes:
>  Tom> Once you're down to an estimate of one row retrieved, adding
>  Tom> additional index conditions simply increases the cost (not by
>  Tom> much, but it increases) without delivering any visible benefit.

> OK, but this is a serious problem because "estimate of one row" is a
> very common estimation failure mode, and isn't always solvable in the
> sense of arranging for better estimates (in the absence of hints, ugh).

Yeah.  I've occasionally wondered about removing the clamp-to-one-row
behavior, so that additional conditions would still look like they
contributed something (ie, 0.1 row is better than 1 row).  However,
that seems likely to break about as many cases as it fixes :-(.

A variant of that would be to only allow the minimum to be 1 row if
we are absolutely certain that's what we'll get (eg, we're searching
on a unique-key equality condition), and otherwise clamp to at least
2 rows.  Again though, this would be destabilizing lots of cases that
work well today.

I doubt there are any simple solutions here.

			regards, tom lane


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^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread

* [PATCH v3 2/2] Error out if one iteration of non-direct DML affects more than one row on the foreign server
@ 2025-07-18 14:52 Jehan-Guillaume de Rorthais <[email protected]>
  0 siblings, 0 replies; 815+ messages in thread

From: Jehan-Guillaume de Rorthais @ 2025-07-18 14:52 UTC (permalink / raw)

When a foreign table points to a partitioned table or an inheritance
parent on the foreign server, a non-direct DML can affect multiple
rows when only one row is intended to be affected. This happens
because postgres_fdw uses only ctid to identify a row to work on.
Though ctid uniquely identifies a row in a single table, in a
partitioned table or in an inheritance hierarchy, there can be be
multiple rows, in different partitions, with the same ctid. So a DML
statement sent to the foreign server by postgres_fdw ends up affecting
more than one rows, only one of which is intended to be affected.

In such a case it's good to throw an error instead of corrupting
remote database with unwanted UPDATE/DELETEs. Subsequent commits will
try to fix this situation.

Author: Ashutosh Bapat <[email protected]>
Author: Kyotaro Horiguchi <[email protected]>

Rebased by Jehan-Guillaume de Rorthais <[email protected]>
---
 .../postgres_fdw/expected/postgres_fdw.out    | 26 ++++++++------
 contrib/postgres_fdw/postgres_fdw.c           | 36 +++++++++++++++----
 2 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 62019eaa881..b0ef54a2889 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8984,10 +8984,11 @@ UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa
 (5 rows)
 
 UPDATE fa SET aa = (CASE WHEN random() <= 1 THEN 'zzzz' ELSE NULL END) WHERE aa = 'aaa';
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  |  aa  
-----------+-------+------
- fa       | (0,2) | zzzz
+ tableoid | ctid  | aa  
+----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
 (2 rows)
 
@@ -9008,11 +9009,13 @@ DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
 (6 rows)
 
 DELETE FROM fa WHERE aa = (CASE WHEN random() <= 1 THEN 'aaa' ELSE 'bbb' END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fa;
- tableoid | ctid  | aa 
+ tableoid | ctid  | aa  
 ----------+-------+-----
+ fa       | (0,1) | aaa
  fa       | (0,1) | bbb
-(1 row)
+(2 rows)
 
 -- cleanup
 DROP FOREIGN TABLE fa;
@@ -9048,10 +9051,11 @@ UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
 (5 rows)
 
 UPDATE fplt SET b = (CASE WHEN random() <= 1 THEN 10 ELSE 20 END) WHERE a = 1;
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
- tableoid | ctid  | a | b  
-----------+-------+---+----
- fplt     | (0,2) | 1 | 10
+ tableoid | ctid  | a | b 
+----------+-------+---+---
+ fplt     | (0,1) | 1 | 1
  fplt     | (0,1) | 2 | 2
 (2 rows)
 
@@ -9071,11 +9075,13 @@ DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
 (6 rows)
 
 DELETE FROM fplt WHERE a = (CASE WHEN random() <=  1 THEN 1 ELSE 10 END);
+ERROR:  foreign server affected 2 rows when only one was expected
 SELECT tableoid::regclass, ctid, * FROM fplt;
  tableoid | ctid  | a | b 
 ----------+-------+---+---
- fplt     | (0,1) | 2 | 2 
-(1 row)
+ fplt     | (0,1) | 1 | 1
+ fplt     | (0,1) | 2 | 2
+(2 rows)
 
 DROP TABLE plt;
 DROP FOREIGN TABLE fplt;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index e0a34b27c7c..09c87d0e5d8 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -4132,7 +4132,8 @@ execute_foreign_modify(EState *estate,
 	ItemPointer ctid = NULL;
 	const char **p_values;
 	PGresult   *res;
-	int			n_rows;
+	int			n_rows_returned;
+	int			n_rows_affected;
 	StringInfoData sql;
 
 	/* The operation should be INSERT, UPDATE, or DELETE */
@@ -4213,27 +4214,50 @@ execute_foreign_modify(EState *estate,
 		pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
 
 	/* Check number of rows affected, and fetch RETURNING tuple if any */
+	n_rows_affected = atoi(PQcmdTuples(res));
 	if (fmstate->has_returning)
 	{
 		Assert(*numSlots == 1);
-		n_rows = PQntuples(res);
-		if (n_rows > 0)
+		n_rows_returned = PQntuples(res);
+		if (n_rows_returned > 0)
 			store_returning_result(fmstate, slots[0], res);
+
+		// FIXME: shouldn't we check the max number of rows returned is one?
 	}
 	else
-		n_rows = atoi(PQcmdTuples(res));
+		n_rows_returned = 0;
 
 	/* And clean up */
 	PQclear(res);
 
 	MemoryContextReset(fmstate->temp_cxt);
 
-	*numSlots = n_rows;
+	/*
+	 * UPDATE & DELETE command can only affect one row, make sure this contract
+	 * is respected.
+	 * CMD_INSERT can insert multiple row when called from ForeignBatchInsert.
+	 */
+	if (operation != CMD_INSERT)
+	{
+		/* No rows should be returned if no rows were affected */
+		if (n_rows_affected == 0 && n_rows_returned != 0)
+			elog(ERROR, "foreign server returned %d rows when no row was affected",
+				 n_rows_returned);
+
+		/* ERROR if more than one row was updated on the remote end */
+		if (n_rows_affected > 1)
+			ereport(ERROR,
+					(errcode (ERRCODE_FDW_ERROR), /* XXX */
+					 errmsg ("foreign server affected %d rows when only one was expected",
+							 n_rows_affected)));
+	}
+
+	*numSlots = n_rows_returned;
 
 	/*
 	 * Return NULL if nothing was inserted/updated/deleted on the remote end
 	 */
-	return (n_rows > 0) ? slots : NULL;
+	return (n_rows_affected > 0) ? slots : NULL;
 }
 
 /*
-- 
2.50.0


--MP_/4ZRYdF7Ah.pt5w65PuZdaPz--





^ permalink  raw  reply  [nested|flat] 815+ messages in thread