Re: Bgwriter strategies

Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> Tom Lane wrote:
>> buffers_to_clean = Max(buffers_used * 1.1,
>> buffers_to_clean * 0.999);

> That would be overly aggressive on a workload that's steady on average,
> but consists of small bursts. Like this: 0 0 0 0 100 0 0 0 0 100 0 0 0 0
> 100. You'd end up writing ~100 pages on every bgwriter round, but you
> only need an average of 20 pages per round.

No, you wouldn't be *writing* that many, you'd only be keeping that many
*clean*; which only costs more work if any of them get re-dirtied
between writing and use. Which is a fairly small probability if we're
talking about a small difference in the number of buffers to keep clean.
So I think the average number of writes is hardly different, it's just
that the backends are far less likely to have to do any of them.

regards, tom lane