Re: Reducing bgwriter wakeups

On Sun, Feb 19, 2012 at 1:53 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> Recent changes for power reduction mean that we now issue a wakeup
> call to the bgwriter every time we set a hint bit.
>
> However cheap that is, its still overkill.
>
> My proposal is that we wakeup the bgwriter whenever a backend is
> forced to write a dirty buffer, a job the bgwriter should have been
> doing.
>
> This significantly reduces the number of wakeup calls and allows the
> bgwriter to stay asleep even when very light traffic happens, which is
> good because the bgwriter is often the last process to sleep.
>
> Seems useful to have an explicit discussion on this point, especially
> in view of recent performance results.

I don't see what this has to do with recent performance results, so
please elaborate. Off-hand, I don't see any point in getting cheap.
It seems far more important to me that the background writer become
active when needed than that we save some trivial amount of power by
waiting longer before activating it. If we're concerned about saving
power, then IMHO what we should be worried about is that the wal
writer is still waking up 5x/s.

--
Robert Haas
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