Thread: Incorrect command tag row count for MERGE with a cross-partition update

Playing around with MERGE some more, I noticed that the command tag
row count is wrong if it does a cross-partition update:

CREATE TABLE target (a int, b int) PARTITION BY LIST (b);
CREATE TABLE target_p1 PARTITION OF target FOR VALUES IN (1);
CREATE TABLE target_p2 PARTITION OF target FOR VALUES IN (2);
INSERT INTO target VALUES (1,1);

MERGE INTO target t USING (VALUES (1)) v(a) ON t.a = v.a
  WHEN MATCHED THEN UPDATE SET b = 2;

which returns "MERGE 2" when only 1 row was updated, because
ExecUpdateAct() will update estate->es_processed for a cross-partition
update (but not for a normal update), and then ExecMergeMatched() will
update it again.

I think the best fix is to have ExecMergeMatched() pass canSetTag =
false to ExecUpdateAct(), so that ExecMergeMatched() takes
responsibility for updating estate->es_processed in all cases.

Regards,
Dean

On 2023-Feb-20, Dean Rasheed wrote:

> Playing around with MERGE some more, I noticed that the command tag
> row count is wrong if it does a cross-partition update:
> 
> CREATE TABLE target (a int, b int) PARTITION BY LIST (b);
> CREATE TABLE target_p1 PARTITION OF target FOR VALUES IN (1);
> CREATE TABLE target_p2 PARTITION OF target FOR VALUES IN (2);
> INSERT INTO target VALUES (1,1);
> 
> MERGE INTO target t USING (VALUES (1)) v(a) ON t.a = v.a
>   WHEN MATCHED THEN UPDATE SET b = 2;
> 
> which returns "MERGE 2" when only 1 row was updated, because
> ExecUpdateAct() will update estate->es_processed for a cross-partition
> update (but not for a normal update), and then ExecMergeMatched() will
> update it again.

Hah.

> I think the best fix is to have ExecMergeMatched() pass canSetTag =
> false to ExecUpdateAct(), so that ExecMergeMatched() takes
> responsibility for updating estate->es_processed in all cases.

Sounds sensible.


-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"Las mujeres son como hondas:  mientras más resistencia tienen,
 más lejos puedes llegar con ellas"  (Jonas Nightingale, Leap of Faith)

On Tue, 21 Feb 2023 at 09:34, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> > I think the best fix is to have ExecMergeMatched() pass canSetTag =
> > false to ExecUpdateAct(), so that ExecMergeMatched() takes
> > responsibility for updating estate->es_processed in all cases.
>
> Sounds sensible.
>

I decided it was also probably worth having a regression test covering
this, since it would be quite easy to break if the code is ever
refactored.

Pushed and back-patched.

Regards,
Dean