Re: Add SPLIT PARTITION/MERGE PARTITIONS commands

On Tue, Oct 28, 2025 at 1:12 AM Dmitry Koval <d(dot)koval(at)postgrespro(dot)ru> wrote:
> 1.
> > The second CommandCounterIncrement() is needed to make the renamed
> > relation visible within our transaction. Why do we need the first
> >one? I see tests pass without it.
>
> It's strange. If I comment the first "CommandCounterIncrement();", in block
> -----------------------------------------------------------------------
> /*
> * We must bump the command counter to make the split partition tuple
> * visible for renaming.
> */
> CommandCounterIncrement();
> /* Rename partition. */
> sprintf(tmpRelName, "split-%u-%X-tmp", RelationGetRelid(rel), ...);
> RenameRelationInternal(splitRelOid, tmpRelName, true, false);
> /*
> * We must bump the command counter to make the split partition tuple
> * visible after renaming.
> */
> CommandCounterIncrement();
> -----------------------------------------------------------------------
> , I got the error "ERROR: tuple already updated by self" in the
> partition_split.sql test (Ubuntu). If I comment the second
> "CommandCounterIncrement();", I got the error "ERROR: relation
> "sales_others" already exists" in the same test.

Sorry, actually it fails. It appears that the first
CommandCounterIncrement() is needed to see the result of
detachPartitionTable().

> 2.
> >The branch handling null value in the outer loop, uses null2 flag from
> >the inner loop. I think for the null value of the outer loop we still
> >need to run inner loop to search for the matching null value.
>
> This code looks a little confusing, but it probably works correctly.
> This can be verified using two typical examples:
> -----------------------------------------------------------------------
> list1: (NULL, 1)
> list2: (2, NULL)
>
> (1) isnull1 = true, (2) "if (isnull1) lappend(NULL)"
> -----------------------------------------------------------------------
> list1: (1, NULL)
> list2: (NULL, 2)
>
> (1) isnull2 = true, (2) "if (isnull2) lappend(NULL)"
> -----------------------------------------------------------------------
> In both cases, we return from the function immediately after lappend.
> This works because we need to find exactly one repeating value.

How this function could handle this case?

list1: (NULL)
list2: whatever containing NULL

The outer loop will just quit after iterating the only element of
list1 without even iterating list2.

------
Regards,
Alexander Korotkov
Supabase