Re: delta relations in AFTER triggers

Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> writes:
> On 10/22/2014 11:10 PM, Robert Haas wrote:
>> Studying this proposed design a bit further, I am a little fuzzy on
>> what is supposed to happen in this design during parse analysis. In
>> Kevin's current code, after checking whether a RangeVar might be a CTE
>> reference and before deciding that it must be a table reference,
>> scanNameSpaceForTsr() is used to check whether there's a tuplestore by
>> that name and, if so, then we insert a RTE with type RTE_TUPLESTORE
>> which references the tuplestore by name. To me, the obvious thing to
>> do here seems to be to instead call p_tableref_hook and let it return
>> a suitable RangeTblRef (or NULL if it wishes to take no action). In
>> the case where the hook wants to redirect the use of that name to a
>> tuplestore, it can add a range-table entry of type RTE_TUPLESTORE, and
>> that entry can store a parameter-index rather than, as in the current
>> design, a name. But then where does Heikki's notion of a
>> RelationParam get used?

> I was thinking that the hook would return a RelationParam. When parse
> analysis sees the returned RelationParam, it adds an entry for that to
> the range table, and creates the RangeTblRef for it. The way you
> describe it works too, but manipulating the range table directly in the
> hook seems a bit too low-level.

The problem with that idea is that then the API for the hook has to cover
every possible sort of RTE that hooks might wish to create; I see no
reason to restrict them to creating just one kind. I agree that the hook
should avoid *physically* manipulating the rangetable, but it seems
reasonable to expect that it can call one of the addRangeTableEntryXXX
functions provided by parse_relation.c, and then return a RangeTblEntry*
gotten that way. So hooks would have an API more or less equivalent
to, eg, transformRangeFunction().

regards, tom lane