Re: Sub-millisecond [autovacuum_]vacuum_cost_delay broken - Mailing list pgsql-hackers

Thomas Munro <thomas.munro@gmail.com> writes:
> On Fri, Mar 10, 2023 at 10:26 AM Melanie Plageman
> <melanieplageman@gmail.com> wrote:
>> I think that 4753ef37e0ed undid the work caf626b2c did to support
>> sub-millisecond delays for vacuum and autovacuum.

> Given that some of the clunkier underlying kernel primitives have
> milliseconds in their interface, I don't think it would be possible to
> make a usec-based variant of WaitEventSetWait() that works everywhere.
> Could it possibly make sense to do something that accumulates the
> error, so if you're using 0.5 then every second vacuum_delay_point()
> waits for 1ms?

Yeah ... using float math there was cute, but it'd only get us so far.
The caf626b2c code would only work well on platforms that have
microsecond-based sleep primitives, so it was already not too portable.

Can we fix this by making VacuumCostBalance carry the extra fractional
delay, or would a separate variable be better?

            regards, tom lane