Re: Vacuum rate limit in KBps

Excerpts from Simon Riggs's message of jue ene 19 16:05:36 -0300 2012:
> On Sun, Jan 15, 2012 at 9:17 PM, Heikki Linnakangas
> <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>
> > I think it makes more sense to use the max read rate as the main knob,
> > rather than write rate. That's because the max read rate is higher than the
> > write rate, when you don't need to dirty pages. Or do you think saturating
> > the I/O system with writes is so much bigger a problem than read I/O that it
> > makes more sense to emphasize the writes?
>
> Yes, the writes are more important of the two.
>
> Too many writes at one time can overflow hardware caches, so things
> tend to get much worse beyond a certain point.
>
> Also, rate limiting writes means we rate limit WAL rate also which is
> very important.
>
> I'd like this to apply to large DDL, not just VACUUMs.

More generally, this can sometimes be useful in general queries as well.

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