Re: BUG #18238: Cross-partitition MERGE/UPDATE with delete-preventing trigger leads to incorrect memory access

On Sun, Dec 10, 2023 at 1:10 AM PG Bug reporting form
<noreply(at)postgresql(dot)org> wrote:
>
> The following bug has been logged on the website:
>
> Bug reference: 18238
> Logged by: Alexander Lakhin
> Email address: exclusion(at)gmail(dot)com
> PostgreSQL version: 16.1
> Operating system: Ubuntu 22.04
> Description:
>
> When the following query:
> CREATE TABLE t (a int) PARTITION BY LIST (a);
> CREATE TABLE tp1 PARTITION OF t FOR VALUES IN (1);
> CREATE TABLE tp2 PARTITION OF t FOR VALUES IN (2);
> INSERT INTO t VALUES (1);
>
> CREATE FUNCTION tf() RETURNS TRIGGER LANGUAGE plpgsql AS
> $$ BEGIN RETURN NULL; END; $$;
>
> CREATE TRIGGER tr BEFORE DELETE ON t
> FOR EACH ROW EXECUTE PROCEDURE tf();
>
> MERGE INTO t USING t st ON TRUE WHEN MATCHED THEN UPDATE SET a = 2;
>

--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -1828,10 +1828,10 @@ ExecCrossPartitionUpdate(ModifyTableContext *context,
* additional rechecking, and might end up executing a different
* action entirely).
*/
- if (context->relaction != NULL)
- return false;
- else if (TupIsNull(epqslot))
+ if (TupIsNull(epqslot))
return true;
+ else if (context->relaction != NULL)
+ return false;
else
{
/* Fetch the most recent version of old tuple. */

seems to work.
but now the new command tag is MERGE 1. should be MERGE 0.