Lists: | pgsql-performance |
---|
From: | "Merlin Moncure" <merlin(dot)moncure(at)rcsonline(dot)com> |
---|---|
To: | <pgsql-performance(at)postgresql(dot)org> |
Subject: | improvise callbacks in plpgsql |
Date: | 2005-11-01 19:00:00 |
Message-ID: | 6EE64EF3AB31D5448D0007DD34EEB3417DD754@Herge.rcsinc.local |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Lists: | pgsql-performance |
hello performance minded administrators:
We have recently converted a number of routines that walk a bill of
materials (which is a nested structure) from the application side to the
server side via recursive plpgsql functions. The performance is
absolutely fantastic but I have to maintain a specialized 'walker' for
each specific task that I have to do. It would be very nice and elegant
if I could pass in the function for the walker to execute while it is
iterating through the bill of materials. I have been beating my head
against the wall for the best way to do this so here I am shopping for
ideas.
A simplified idealized version of what I would like to do is
begin
select (callback_routine)(record_type)
end;
from within a plpgsql function. I am borrowing the C syntax for a
function pointer here. The problem I am running into is the only way to
do callbacks is via dynamic sql...however you can use higher level types
such as row/record type in dynamic sql (at least not efficiently). I
could of course make a full dynamic sql call by expanding the record
type into a large parameter list but this is unwieldy and brittle.
Any thoughts?
Merlin
From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | "Merlin Moncure" <merlin(dot)moncure(at)rcsonline(dot)com> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: improvise callbacks in plpgsql |
Date: | 2005-11-01 21:29:22 |
Message-ID: | 28343.1130880562@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Lists: | pgsql-performance |
"Merlin Moncure" <merlin(dot)moncure(at)rcsonline(dot)com> writes:
> A simplified idealized version of what I would like to do is
> begin
> select (callback_routine)(record_type)
> end;
> from within a plpgsql function. I am borrowing the C syntax for a
> function pointer here.
Well, there's no function pointer type in SQL :-(. I don't see any way
to do what you want in pure plpgsql. If you're willing to implement an
auxiliary C function you could probably make it go:
create function callit(oid, record) returns void ...
where the OID has to be the OID of a function taking a record-type
argument. The regprocedure pseudotype would allow you not to need
to write any numeric OIDs in your code:
select callit('myfunc(record)'::regprocedure, recordvar);
The body of callit() need be little more than OidFunctionCall1()
plus whatever error checking and security checking you want to
include.
regards, tom lane