On 2017/08/01 1:03, Robert Haas wrote:
On Fri, Jul 28, 2017 at 8:12 AM, Etsuro Fujita
<fujita.ets...@lab.ntt.co.jp> wrote:
On 2017/07/26 22:39, Robert Haas wrote:
So the first part of the change weakens the assertion that a 'ctid' or
'wholerow' attribute will always be present by saying that an FDW may
instead have other attributes sufficient to identify the row.
That's right.
But
then the additional sentence says that there will be a 'wholerow'
attribute after all. So this whole change seems to me to be going
around in a circle.
What I mean by the additional one is: if the result table that is a foreign
table has a row-level UPDATE/DELETE trigger, a 'wholerow' will also be
present. So, if the result table didn't have the trigger, there wouldn't be
'whole-row', so in that case it could be possible that there would be only
attributes other than 'ctid' and 'wholerow'.
I think maybe something like this would be clearer, then:
/*
* Initialize the junk filter(s) if needed. INSERT queries need a filter
* if there are any junk attrs in the tlist. UPDATE and DELETE always
- * need a filter, since there's always a junk 'ctid' or 'wholerow'
- * attribute present --- no need to look first.
+ * need a filter, since there's always at least one junk attribute present
+ * --- no need to look first. Typically, this will be a 'ctid'
+ * attribute, but in the case of a foreign data wrapper it might be a
+ * 'wholerow' attribute or some other set of junk attributes sufficient to
+ * identify the remote row.
*
* If there are multiple result relations, each one needs its own junk
* filter. Note multiple rels are only possible for UPDATE/DELETE, so we
Maybe I'm missing something, but I'm not sure that's a good idea because
the change says like we might have 'wholerow' only for the FDW case, but
that isn't correct because we would have 'wholerow' for a view as well.
ISTM that views should be one of the typical cases, so I'd like to
propose to modify the sentence starting with 'Typically' to something
like this: "Typically, this will be a 'ctid' or 'wholerow' attribute,
but in the case of a foreign data wrapper it might be a set of junk
attributes sufficient to identify the remote row." What do you think
about that?
Best regards,
Etsuro Fujita
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