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backend/utils/adt/float.c uses non-existent NAN value
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* backend/utils/adt/float.c uses non-existent NAN value
@ 1999-01-16 05:27  Taral <[email protected]>
  0 siblings, 2 replies; 822+ messages in thread

From: Taral @ 1999-01-16 05:27 UTC (permalink / raw)
  To: [email protected]

Seems at some point someone decided not to be machine-independent in
backend/utils/adt/float.c

Redhat 5.2 system with gcc 2.8.1 doesn't define NAN unless _GNU_SOURCE is
defined first. Although include/utils/dt.h *does* check for NAN (and HUGE_VAL)
before using them, the float.c doesn't.

What happened?

Taral



^ permalink  raw  reply  [nested|flat] 822+ messages in thread

* Re: [HACKERS] backend/utils/adt/float.c uses non-existent NAN value
@ 1999-01-16 05:40  Bruce Momjian <[email protected]>
  parent: Taral <[email protected]>
  1 sibling, 0 replies; 822+ messages in thread

From: Bruce Momjian @ 1999-01-16 05:40 UTC (permalink / raw)
  To: Taral <[email protected]>; +Cc: [email protected]

> Seems at some point someone decided not to be machine-independent in
> backend/utils/adt/float.c
> 
> Redhat 5.2 system with gcc 2.8.1 doesn't define NAN unless _GNU_SOURCE is
> defined first. Although include/utils/dt.h *does* check for NAN (and HUGE_VAL)
> before using them, the float.c doesn't.
> 
> What happened?

I don't see NAN used in any file except numberic.c.  I don't see it in
float.c, at least in 6.5.

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  [email protected]            |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026



^ permalink  raw  reply  [nested|flat] 822+ messages in thread

* Re: [HACKERS] backend/utils/adt/float.c uses non-existent NAN value
@ 1999-01-18 08:36  Jan Wieck <[email protected]>
  parent: Taral <[email protected]>
  1 sibling, 2 replies; 822+ messages in thread

From: Jan Wieck @ 1999-01-18 08:36 UTC (permalink / raw)
  To: Taral <[email protected]>; +Cc: [email protected]

>
> Seems at some point someone decided not to be machine-independent in
> backend/utils/adt/float.c
>
> Redhat 5.2 system with gcc 2.8.1 doesn't define NAN unless _GNU_SOURCE is
> defined first. Although include/utils/dt.h *does* check for NAN (and HUGE_VAL)
> before using them, the float.c doesn't.
>
> What happened?

    Don't know exactly - but

    the new NUMERIC data type started recently a discussion about
    NAN, because I tried  to  be  able  to  convert  NAN  from/to
    float's, and that started some trouble. I'm not sure how this
    went into adt/float.c. At least I think we should fix all the
    NAN handling for v6.5.


Jan

--

#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me.                                  #
#======================================== [email protected] (Jan Wieck) #





^ permalink  raw  reply  [nested|flat] 822+ messages in thread

* Re: [HACKERS] backend/utils/adt/float.c uses non-existent NAN value
@ 1999-01-18 12:27  Bruce Momjian <[email protected]>
  parent: Jan Wieck <[email protected]>
  1 sibling, 0 replies; 822+ messages in thread

From: Bruce Momjian @ 1999-01-18 12:27 UTC (permalink / raw)
  To: [email protected]; +Cc: [email protected]; [email protected]

> >
> > Seems at some point someone decided not to be machine-independent in
> > backend/utils/adt/float.c
> >
> > Redhat 5.2 system with gcc 2.8.1 doesn't define NAN unless _GNU_SOURCE is
> > defined first. Although include/utils/dt.h *does* check for NAN (and HUGE_VAL)
> > before using them, the float.c doesn't.
> >
> > What happened?
> 
>     Don't know exactly - but
> 
>     the new NUMERIC data type started recently a discussion about
>     NAN, because I tried  to  be  able  to  convert  NAN  from/to
>     float's, and that started some trouble. I'm not sure how this
>     went into adt/float.c. At least I think we should fix all the
>     NAN handling for v6.5.
> 

I fixed that.  Added the NAN define from numeric.c.

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  [email protected]            |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026



^ permalink  raw  reply  [nested|flat] 822+ messages in thread

* Re: [HACKERS] backend/utils/adt/float.c uses non-existent NAN value
@ 1999-01-18 14:33  Thomas G. Lockhart <[email protected]>
  parent: Jan Wieck <[email protected]>
  1 sibling, 2 replies; 822+ messages in thread

From: Thomas G. Lockhart @ 1999-01-18 14:33 UTC (permalink / raw)
  To: Jan Wieck <[email protected]>; +Cc: Taral <[email protected]>; [email protected]

> > Seems at some point someone decided not to be machine-independent in
> > backend/utils/adt/float.c

That was me.

> > Redhat 5.2 system with gcc 2.8.1 doesn't define NAN unless 
> > _GNU_SOURCE is defined first. Although include/utils/dt.h *does* 
> > check for NAN (and HUGE_VAL) before using them, the float.c doesn't.
> > What happened?
>     the new NUMERIC data type started recently a discussion about
>     NAN, because I tried  to  be  able  to  convert  NAN  from/to
>     float's, and that started some trouble. I'm not sure how this
>     went into adt/float.c. At least I think we should fix all the
>     NAN handling for v6.5.

Jan started with NAN handling for numeric, and I'd already done the same
thing for the date/time types quite a while ago. We also had a
discussion recently that we should be handling 'NaN' and 'Infinity' on
float8 input values so that dump/reload is more robust and symmetric, so
I added that in ('-Infinity' still needs to be done).

I added in the new code, knowing that there was some fixup and
consolidation which needs to be done. Unless someone has worked out
another scheme, I'd suggest using the date/time code in dt.h as an
example to work from. We might want to use PG_NAN and PG_INFINITY, which
we can then define in one central place.

If someone want to work this out, I'd be happy to use the result. Or I
can do something directly. I'd like a solution with the equivalent of
NAN and HUGE_VAL (and -HUGE_VAL). Jan? Taral?

                    - Tom



^ permalink  raw  reply  [nested|flat] 822+ messages in thread

* Re: [HACKERS] backend/utils/adt/float.c uses non-existent NAN value
@ 1999-01-18 19:26  Taral <[email protected]>
  parent: Thomas G. Lockhart <[email protected]>
  1 sibling, 0 replies; 822+ messages in thread

From: Taral @ 1999-01-18 19:26 UTC (permalink / raw)
  To: Thomas G. Lockhart <[email protected]>; +Cc: [email protected]

On Mon, 18 Jan 1999, you wrote:
>If someone want to work this out, I'd be happy to use the result. Or I
>can do something directly. I'd like a solution with the equivalent of
>NAN and HUGE_VAL (and -HUGE_VAL). Jan? Taral?

Doesn't dt.h have some replacements for NAN and HUGE_VAL? Something like that?
Couldn't we use those?

Aha... DT_INVALID is the generic NAN, and DT_NOBEGIN/DT_NOEND are the generic
HUGE_VAL and -HUGE_VAL...

Taral



^ permalink  raw  reply  [nested|flat] 822+ messages in thread

* (no subject)
@ 1999-01-19 02:41  Puchong <[email protected]>
  parent: Thomas G. Lockhart <[email protected]>
  1 sibling, 0 replies; 822+ messages in thread

From: Puchong @ 1999-01-19 02:41 UTC (permalink / raw)
  To: [email protected]

unsubscribe




^ permalink  raw  reply  [nested|flat] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ 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; 822+ 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] 822+ messages in thread