Re: Reducing bgwriter wakeups

On Sun, Feb 19, 2012 at 8:15 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> 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.

Then you misunderstand, since I am advocating waking it when needed.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
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