Re: Reduced power consumption in WAL Writer process

On Jul 15, 2011, at 8:55 AM, Simon Riggs <simon(at)2ndQuadrant(dot)com> wrote:
> On Fri, Jul 15, 2011 at 2:29 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
>> If the primary goal here is to reduce power consumption, another option
>> would be to keep the regular wake-ups most of the time but have some
>> mechanism for putting the process to sleep until wakened when no activity
>> happens for a certain period of time - say, 10 cycles. I'm not at all sure
>> that's better, but it would be less of a change to the existing behavior.
>
> Now we have them, latches seem the best approach because they (mostly)
> avoid heuristics.

That's my feeling as well.

> This proposal works same or better for async transactions.

Right. I would say probably better. The potential for a reduction in latency here is very appealing.

> The only difference is how bulk write operations are handled. As long
> as we wake WALWriter before wal_buffers fills then we'll be good.
> Wakeup once per wal buffer is too much. I agree we should measure this
> to check how frequently wakeups are required for bulk ops.

Yeah. The trick is to get the wake-ups to be frequent enough without adding too much latency to the backends that have to perform them. Off-hand, I don't have a good feeling for how hard that will be.

...Robert