Re: delta relations in AFTER triggers

On 15 August 2014 04:04, Kevin Grittner <kgrittn(at)ymail(dot)com> wrote:
> Amit Khandekar <amit(dot)khandekar(at)enterprisedb(dot)com> wrote:
>
>>>> The execution level itself was almost trivial; it's getting the
>>>> tuplestore reference through the parse analysis and planning
>>>> phases that is painful for me.
>>> I am not sure why you think we would need to refer the
>>> tuplestore in the parse analysis and planner phases. It seems
>>> that we would need them only in execution phase. Or may be I
>>> didn't understand your point.
>> Ah I think I understand now. That might be because you are
>> thinking of having an infrastructure common to triggers and
>> materialized views, right ?
>
> Well, it's more immediate than that. The identifiers in the
> trigger function are not resolved to particular objects until there
> is a request to fire the trigger.
Ah ok, you are talking about changes specific to the PL language
handlers. Yes, I agree that in the plpgsql parser (and in any PL
handler), we need to parse such table references in the SQL construct,
and transform it into something else.
> At that time the parse analysis
> needs to find the name defined somewhere. It's not defined in the
> catalogs like a table or view, and it's not defined in the query
> itself like a CTE or VALUES clause. The names specified in trigger
> creation must be recognized as needing to resolve to the new
> TuplestoreScan, and it needs to match those to the tuplestores
> themselves.
One approach that comes to my mind is by transforming such transition
table references into a RangeFunction reference while in plpgsql
parser/lexer. This RangeFunction would point to a set-returning
catalog function that would return rows from the delta tuplestore. So
the tuplestore itself would remain a blackbox. Once we have such a
function, any language handler can re-use the same interface.

> Row counts, costing, etc. needs to be provided so the
> optimizer can pick a good plan in what might be a complex query
> with many options.
I am also not sure about the costing, but I guess it may be possible
to supply some costs to the FunctionScan plan node.