Re: postgres_fdw vs data formatting GUCs (was Re: [v9.3] writable foreign tables)

On Tue, Mar 19, 2013 at 2:41 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Daniel Farina <daniel(at)heroku(dot)com> writes:
>> On Tue, Mar 19, 2013 at 1:16 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> I'd be inclined to eat the cost of calling PQparameterStatus every time
>>> (which won't be that much) and instead try to optimize by avoiding the
>>> GUC-setting overhead if the current value matches the local setting.
>>> But even that might be premature optimization. Did you do any
>>> performance testing to see if there was a problem worth avoiding?
>
>> Nope; should I invent a new way to do that, or would it be up to
>> commit standard based on inspection alone? I'm okay either way, let
>> me know.
>
> Doesn't seem that hard to test: run a dblink query that pulls back a
> bunch of data under best-case conditions (ie, local not remote server),
> and time it with and without the proposed fix. If the difference
> is marginal then it's not worth working hard to optimize.

Okay, will do, and here's the shorter and less mechanically intensive
naive version that I think is the baseline: it doesn't try to optimize
out any GUC settings and sets up the GUCs before the two
materialization paths in dblink.

Something I forgot to ask about is about if an strangely-minded type
input function could whack around the GUC as records are being
remitted, which would necessitate per-tuple polling of
pqParameterStatus (e.g. in the inner loop of a materialization) .
That seemed pretty "out there," but I'm broaching it for completeness.

I'll see how much of a penalty it is vs. not applying any patch at all next.

--
fdr