Re: VACUUM delay (was Re: What's planned for 7.5?)

Tom Lane wrote:
> Christopher Browne <cbbrowne@libertyrms.info> writes:
>> "Stephen" <jleelim@xxxxxxx.com> writes:
>>> Any chance we'll see the VACUUM delay patch (throttle) get into 7.5?
> 
>> The hope, in 7.5, is to have ARC, which is the "super-duper-duper"
>> version, working.
> 
> Actually, I'm not sure that ARC should be considered to supersede the
> usefulness of a per-page delay in VACUUM.  ARC should prevent VACUUM
> from trashing the contents of Postgres' shared buffer arena, but it
> won't do much of anything to prevent VACUUM from trashing the kernel
> buffer contents.  And it definitely won't do anything to help if the
> real problem is that you're short of disk bandwidth and VACUUM's extra
> I/O demand pushes your total load over the knee of the response-time
> curve.  What you need then is a throttle.
> 
> The original patch I posted was incomplete for a number of reasons,
> but I think it may still be worth working on.  Jan, any comments?

I agree that there is considerable value in IO distribution. As such I 
already have the basics of the Background Writer in there.

I left out the vacuum delay since I thought it was good enough to proove 
that there is low hanging fruit, but that it was far from what I'd call 
a solution. Ideally Vacuum would coordinate it's IO not only against 
some GUC variables, but also against the BGWriter+BufStrategy combo.


Jan

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