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 -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers