Re: Some thoughts about i/o priorities and throttling vacuum

Tom Lane wrote:

> Shridhar Daithankar <shridhar_daithankar(at)persistent(dot)co(dot)in> writes:
>
>>What part of plain vacuum takes disk bandwidth?
>
>
> Reading (and possibly rewriting) all the pages.

I was under impression that was for shared memory pages only and not for disk pages.

OK. I can see difference of understanding here.

Plain Vacuum goes around the table/database and makes space, shared buffers and
disks, reusable whenever possible but *does not* free any space.

Would it be possible to have a vacuum variant that would just shuffle thr.
shared buffers and not touch disk at all? pg_autovacuum could probably be ulra
agressive with such a shared-buffers only scan? Is it possible or feasible?

IMO that could be a clever solution rather than throttling IO for vacuum. For
one thing, getting that throttiling right, would be extremely difficult and
varying from site to site. If it is going to be tough to tune, then it will be
underutilised and will lose it's value rather rapidly.

Just a thought..

Shridhar