Re: Buglist

Jan Wieck wrote:
> Tom Lane wrote:
> > Jan Wieck  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
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073