Re: postgres_fdw: Emit message when batch_size is reduced

On Mon, 22 Jun 2026 at 22:40, Corey Huinker <corey(dot)huinker(at)gmail(dot)com> wrote:

> On Fri, Jun 19, 2026 at 8:38 AM Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com>
> wrote:
>
>>
>>
>> On Tue, 16 Jun 2026 at 22:20, Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
>> wrote:
>>
>>> On Wed, Jun 10, 2026 at 5:09 AM Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com>
>>> wrote:
>>>
>>>>
>>>>
>>>> On Tue, 9 Jun 2026 at 22:22, Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
>>>> wrote:
>>>>
>>>>>
>>>>>> Thanks for your inputs. Reworked patch is attached.
>>>>>> --
>>>>>> Regards,
>>>>>> Rafia Sabih
>>>>>> CYBERTEC PostgreSQL International GmbH
>>>>>>
>>>>>
>>>>> You've addressed all my concerns, aside from the desire for the check
>>>>> on the set/update of the value. Do you have a commitfest entry? I didn't
>>>>> find one.
>>>>>
>>>> There is commitfest entry now -->
>>>> https://commitfest.postgresql.org/patch/6873/
>>>>
>>>>
>>>>
>>> I've added myself as a reviewer. Did you want to try adding the check at
>>> time of the option being set? If not, I can make an attempt at that.
>>>
>> Please find the attached file for the patch with the warning message at
>> the time of batch_size option addition. Looking forward to your inputs.
>>
>> --
>> Regards,
>> Rafia Sabih
>> CYBERTEC PostgreSQL International GmbH
>>
>
> Applies clean, passes.
>
> I think we need to tweak the elog() below:
>
> + if (batch_size > PQ_QUERY_PARAM_MAX_LIMIT)
> + elog(WARNING, "postgres_fdw: batch_size %d is at or above the libpq "
> + "%d-parameter limit; the effective per-batch ceiling is "
> + "limit / number_of_columns and may be lower",
> + batch_size, PQ_QUERY_PARAM_MAX_LIMIT);
>
> I think this should be an ereport() because it's the sort of error we'd
> want the caller to see, and that means we need the message to conform the
> guidelines at
> https://www.postgresql.org/docs/current/error-style-guide.html, and I'm
> going to suggest this as a starting point:
>
> ereport(WARNING,
> errmsg("%s of %d exceeds protocol limit of %d", "batch_size",
> batch_size, PQ_QUERY_PARAM_MAX_LIMIT),
> errdetail("The %s for a query will be reduced to protocol limit
> divided by the number of columns in the query.", "batch_size"));
>
> Done.

> I'd like to hear other people's opinions on what the proper conforming
> error message would be.
>

--
Regards,
Rafia Sabih
CYBERTEC PostgreSQL International GmbH