Re: postgres_fdw: Emit message when batch_size is reduced

Hi,
I reviewed v5, applied it to the current master, and ran the postgres_fdw
regression tests. The patch applies cleanly and the tests pass.

Would it also make sense to emit a NOTICE or WARNING from
postgres_fdw_validator() in option.c when batch_size is set to a value
greater than PQ_QUERY_PARAM_MAX_LIMIT?

That would notify the user immediately during CREATE or ALTER, while still
accepting the value and preserving the existing behavior.

The existing tests cover cases where the messages are emitted, but I think
it may also be useful to cover the exact boundaries and the cases where no
message should be emitted.

For a two-parameter foreign insert, batch_size = 32767 should not produce a
DEBUG1 message, while batch_size = 32768 should be reduced to 32767.
Similarly, for a single parameter, batch_size = 65535 should not produce a
warning, while 65536 should.

Regards,
Nurlan

сб, 11 июл. 2026 г. в 21:13, Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com>:

>
>
> 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
>

--
Regards,
Nurlan