Re: delta relations in AFTER triggers

On 08/28/2014 12:03 AM, Kevin Grittner wrote:
> Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> wrote:
>> I suggest adding a new hook to the ParseState struct, (p_rangevar_hook
>> ?). The planner calls it whenever it sees a reference to a table, and
>> the hook function returns back some sort of placeholder reference to the
>> tuplestore. With variables, the hook returns a Param node, and at
>> execution time, the executor calls the paramFetch hook to fetch the
>> value of the param. For relations/tuplestores, I guess we'll need to
>> invent something like a Param node, but for holding information about
>> the relation. Like your TsrData struct, but without the pointer to the
>> tuplestore. At execution time, in the SPI_execute call, you pass the
>> pointer to the tuplestore in the ParamListInfo struct, like you pass
>> parameter values.
>>
>> Does this make sense?
>
> I see your point, but SPI first has to be made aware of the
> tuplestores and their corresponding names and TupleDesc structures.
> Does it make sense to keep the SPI_register_tuplestore() and
> SPI_unregister_tuplestore() functions for the client side of the
> API, and pass things along to the parse analysis through execution
> phases using the techniques you describe?

Sorry, I didn't understand that. What do you mean by "first", and the
"client side of the API"? I don't see any need for the
SPI_register_tuplestore() and and SPI_unregister_tuplestore() functions
if you use the hooks.

>> In essence, make the relations work like PL/pgSQL
>> variables do. If you squint a little, the new/old relation is a variable
>> from the function's point of view, and a parameter from the
>> planner/executor's point of view. It's just a variable/parameter that
>> holds a set of tuples, instead of a single Datum.
>
> I don't have to squint that hard -- I've always been comfortable
> with the definition of a table as a relation variable, and it's not
> too big a stretch to expand that to a tuplestore. ;-) In fact, I
> will be surprised if someone doesn't latch onto this to create a
> new "declared temporary table" that only exists within the scope of
> a compound statement (i.e., a BEGIN/END block). You would DECLARE
> them just like you would a scalar variable in a PL, and they would
> have the same scope.

Yeah, that would be cool :-).

- Heikki