From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Jan Wieck <JanWieck(at)Yahoo(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrew Sullivan <andrew(at)libertyrms(dot)info>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: Buglist |
Date: | 2003-08-27 01:05:56 |
Message-ID: | 200308270105.h7R15u913130@candle.pha.pa.us |
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Lists: | pgsql-general pgsql-hackers |
Jan Wieck wrote:
> Tom Lane wrote:
> > Jan Wieck <JanWieck(at)Yahoo(dot)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(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
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