Re: Unexpected behavior when setting "idle_replication_slot_timeout"

On Saturday, July 5, 2025, Fujii Masao <masao.fujii@oss.nttdata.com> wrote:

>
>
> On 2025/07/05 15:16, David G. Johnston wrote:
>
>> On Fri, Jul 4, 2025 at 10:35 PM Laurenz Albe <laurenz.albe@cybertec.at
>> <mailto:laurenz.albe@cybertec.at>> wrote:
>>
>>     On the other hand, if the behavior is clearly documented, as I have
>>     tried to do with my patch, it should be fine.  So I'll rest my case if
>>     you apply my patch.
>>
>>
>> We should clearly document how rounding works in section 19.1.1 (which we
>> mostly do; "If the parameter is of integer type, a final rounding to
>> integer occurs after any unit conversion.") and not in every time-related
>> setting that chooses to use something larger than microseconds.  So, 30s is
>> 'unit converted' up to 0.5 minutes (not explicitly explained...) then
>> rounded to zero (which is odd, half normally rounds up...).
>>
>
> This happens because in this case rounding is done using rint(3),
> which uses banker's rounding by default. While the rint(3)'s rounding
> method
> can be changed with fesetround(), PostgreSQL doesn't seem to change it.
> So 0.5 rounds to 0, 1.5 and 2.5 round to 2, 3.5 and 4.5 round to 4, and so
> on.
>

Right, a.k.a., half-even rounding.  So, not odd.

David J.