Jan Wieck wrote:
> Tom Lane wrote:
> > Jan Wieck <JanWieck@Yahoo.com> writes:
> >
> >>What about a little hint to the buffer management that if it has to
> >>evict another buffer to physically read this one (meaning the buffer
> >>pool was full already) then it will not put this buffer at the top of
> >>the LRU chain but rather at it's end? This way a vacuum on a large table
> >>will not cause a complete cache eviction.
> >
> >
> > I think what we really need is a way to schedule VACUUM's I/O at a lower
> > priority than normal I/Os. Wouldn't be very portable :-( ... but if the
> > OS offers a facility for requesting this, it'd be worth experimenting
> > with.
>
> Whatever priority it has, I think the fact that a VACUUM is kicking
> everything out of a carefully populated buffer cache and possibly
> replacing it with data of low to no interest at all should have some
> space for improvement. And that one single optimizer mistake choosing a
> seqscan over an index scan for a huge table does the same doesn't strike
> me as smart either.
I am hoping a smarter cache replacement policy, hopefully for 7.5, will
prevent VACUUM from pushing out frequently accessed pages.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
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