Re: Simplify some codes in pgoutput - Mailing list pgsql-hackers

Hi Hou-san,

I tried to compare the logic of patch v3-0001 versus the original HEAD code.

IMO this patch logic is not exactly the same as before -- there are
some subtle differences. I am not sure if these differences represent
real problems or not.

Below are all my review comments:

======

1.
/* Switch relation if publishing via root. */
if (relentry->publish_as_relid != RelationGetRelid(relation))
{
    Assert(relation->rd_rel->relispartition);
    ancestor = RelationIdGetRelation(relentry->publish_as_relid);
    targetrel = ancestor;
}

~

The "switch relation if publishing via root" logic is now happening
first, whereas the original code was doing this after the slot
assignments. AFAIK it does not matter, it's just a small point of
difference.

======

2.
/* Convert tuple if needed. */
if (relentry->attrmap)
{
    ...
}

The "Convert tuple if needed." logic looks the same, but when it is
executed is NOT the same. It could be a problem.

Previously, the conversion would only happen within the "Switch
relation if publishing via root." condition. But the patch no longer
has that extra condition -- now I think it attempts conversion every
time regardless of "publishing via root".

I would expect the "publish via root" case to be less common, so even
if the current code works, by omitting that check won't this patch
have an unnecessary performance hit due to the extra conversions?

~~

3.
if (old_slot)
    old_slot = execute_attr_map_slot(relentry->attrmap,old_slot,MakeTupleTableSlot(tupdesc,
&TTSOpsVirtual));

~

The previous conversion code for UPDATE (shown above) was checking
"if (old_slot)". Actually, I don't know why that check was even
necessary before but it seems to have been accounting for a
possibility that UPDATE might not have "oldtuple".

But this combination (if indeed it was possible) is not handled
anymore with the patch code because the old_slot is unconditionally
assigned in the same block doing this conversion. Perhaps that
original HEAD extra check was just overkill?  TAP tests obviously
still are passing with the patch, but anyway, this is yet another
small point of difference for the refactored patch code.

======

4.
AFAIK, the "if (change->data.tp.newtuple)" can only be true for INSERT
or UPDATE, so the code would be better to include a sanity Assert.

SUGGESTION
if (change->data.tp.newtuple)
{
    Assert(action == REORDER_BUFFER_CHANGE_INSERT || action ==
REORDER_BUFFER_CHANGE_UPDATE);
...
}

======

5.
AFAIK, the "if (change->data.tp.oldtuple)" can only be true for UPDATE
or DELETE, so the code would be better to include a sanity Assert.

SUGGESTION
if (change->data.tp.oldtuple)
{
    Assert(action == REORDER_BUFFER_CHANGE_UPDATE || action ==
REORDER_BUFFER_CHANGE_DELETE);
...
}

======

6.
I suggest moving the "change->data.tp.oldtuple" check before the
"change->data.tp.newtuple" check. I don't think it makes any
difference, but it seems more natural IMO to have old before new.


------
Kind Regards,
Peter Smith