Re: AW: [HACKERS] Re: PL/PgSQL discussion

I wrote:
>
>
> Andreas Zeugswetter wrote:
> >
> > >From my experience, it *** is *** impossible. I would be glad if somebody
> > told me different, but to my understanding the doc is wrong here.
> >
> > Andreas
> >
> > >> Currently only 'null' and 'single value'. The executor
> > >> doesn't accept anything else for non-sql language functions.
> > >> PL functions are treated by the executor like 'C' functions.
> > >
> > >Actually what I understood from the docs was thatit is 'terribly complicated' and 'beyond the
> > >scope of this tutorial', but not impossible ;)
>
> The executor could check in ExecMakeFunctionResult() that the
> function is a PL function (simply by looking at
> fcache->func.fn_plhandler). So it is possible that the
> Executor treats PL functions somewhat like
> postquel_function().

That way it might be possible. The call interface to the PL
handler must be extended and the PL handler cannot use SPI
any more. The memory management of SPI makes it impossible
to return from the function and resume later. Leaving the
function while connected to SPI would possibly corrupt the
SPI stack.

And the handling of functions returning tuples is really a
mess. The executor calls postquel_function() first to get a
tuple table slot, and then again for each attribute used via
nested dot expression. It's up to the function itself then to
create the correct projection from the functions targetlist.

And there must be something in the parser/optimizer too. For
an 'sql' function, the fcache has a prepared tuple table slot
on the actual call. But for 'C' or 'PL' functions, it is NULL
on the call to ExecMakeFunctionResult().

For now, I'll let the PL interface as is and try to finish
PL/pgSQL in the trigger area. Someday I'll get back to here
and give it a real try to enable tuples and sets as return
from functions. That all is far too much work for me right
now cause the next 4 weeks I have to do some homework (bought
a new house and that's built now).

Jan

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