Re: generic plans and "initial" pruning

Hi Amit,

On Sat, Feb 15, 2025 at 3:51 PM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
>
> Hi Alexander,
>
> On Sat, Feb 15, 2025 at 6:00 AM Alexander Lakhin <exclusion(at)gmail(dot)com> wrote:
> >
> > Hello Amit,
> >
> > 06.02.2025 04:35, Amit Langote wrote:
> >
> > I plan to push 0001 tomorrow, barring any objections.
> >
> >
> > Please try the following script:
> > CREATE TABLE pt (a int, b int) PARTITION BY range (a);
> > CREATE TABLE tp1 PARTITION OF pt FOR VALUES FROM (1) TO (2);
> > CREATE TABLE tp2 PARTITION OF pt FOR VALUES FROM (2) TO (3);
> >
> > MERGE INTO pt
> > USING (SELECT pg_backend_pid() AS pid) AS q JOIN tp1 ON (q.pid = tp1.a)
> > ON pt.a = tp1.a
> > WHEN MATCHED THEN DELETE;
> >
> > which fails for me with segfault:
> > Program terminated with signal SIGSEGV, Segmentation fault.
> > #0 ExecInitMerge (mtstate=0x5a9b9fbccae0, estate=0x5a9b9fbcbe20) at nodeModifyTable.c:3680
> > 3680 relationDesc = RelationGetDescr(resultRelInfo->ri_RelationDesc);
> > (gdb) bt
> > #0 ExecInitMerge (mtstate=0x5a9b9fbccae0, estate=0x5a9b9fbcbe20) at nodeModifyTable.c:3680
> > #1 0x00005a9b67e6dfb5 in ExecInitModifyTable (node=0x5a9b9fbd5858, estate=0x5a9b9fbcbe20, eflags=0) at nodeModifyTable.c:4906
> > #2 0x00005a9b67e273f7 in ExecInitNode (node=0x5a9b9fbd5858, estate=0x5a9b9fbcbe20, eflags=0) at execProcnode.c:177
> > #3 0x00005a9b67e1b9d2 in InitPlan (queryDesc=0x5a9b9fbb9970, eflags=0) at execMain.c:1092
> > #4 0x00005a9b67e1a524 in standard_ExecutorStart (queryDesc=0x5a9b9fbb9970, eflags=0) at execMain.c:268
> > #5 0x00005a9b67e1a223 in ExecutorStart (queryDesc=0x5a9b9fbb9970, eflags=0) at execMain.c:142
> > ...
> >
> > starting from cbc127917.
> >
> > (I've discovered this anomaly with SQLsmith.)
>
> Thanks! It looks like I missed updating the MERGE-related lists in ModifyTable.
>
> I've attached a fix with a test added based on your example. I plan to
> push this on Monday.
>

I applied the patch and the problem solved, I have a small question that
should the following line

```
if (node->mergeActionLists == NIL)
```

be changed to

```
if (mtstate->mt_mergeActionLists == NIL)
```

ISTM that if we have pruned all the merge actions, there is no harm we
omit setting mtstate->mt_merge_subcommands to 0.

> --
> Thanks, Amit Langote

--
Regards
Junwang Zhao