Re: Reducing power consumption on idle servers

On 2/21/22 10:11 AM, Simon Riggs wrote:

>>> * autovac launcher - autovacuum_naptime
>> On production systems autovacuum_naptime often can't be a large value,
>> otherwise it's easy to not keep up on small busy tables. That's fine for
>> actually busy servers, but with the increase in hosted PG offerings, the
>> defaults in those offerings needs to cater to a broader audience.
> Autovac varies its wakeup cycle according to how much work is done. It
> is OK to set autovacuum_naptime without affecting power consumption
> when idle.
I'm wondering how many people understand that. I've seen a number of 
servers running very low values of autovacuum_naptime in order to make 
things more responsive.
> Idle for autovac is defined slightly differently, since if all user
> work completes then there may still be a lot of vacuuming to do before
> it goes fully idle. But my observation is that there are many servers
> that go idle for more than 50% of each week, when operating 8-12 hours
> per day, 5 days per week, so we can still save a lot of power.
>
> This patch doesn't change how autovac works, it just uses a common
> setting for the hibernation that eventually occurs.
I'm wondering if it'd be worth linking autovac wakeup from a truly idle 
state to the stats collector. If there's no stats messages coming in 
clearly there's nothing new for autovac.