On 4/21/14, 6:07 PM, David G Johnston wrote:
Jim Nasby-2 wrote
>>I feel that if there is no memory pressure, frankly it doesnt matter much
>>about what gets out and what not. The case I am specifically targeting is
>>when the clocksweep gets to move about a lot i.e. high memory pressure
>>workloads. Of course,  I may be totally wrong here.
>
>Well, there's either memory pressure or there isn't. If there isn't then
>it's all moot*because we're not evicting anything*.
The trade-off I'm seeing here is between measuring when there is no memory
pressure - and thus eating at performance while not actually evicting
buffers - and not measuring but then encountering memory pressure and not
having a clue as to what should be evicted.


Right. OSes handle this by keeping a certain ratio of active vs inactive pages, 
regardless of pressure for free pages. That way when you need more pages in the 
free list you can pull them from the inactive list knowing that you're making a 
good decision.

One of the really nice things about this approach is that if memory pressure is 
low enough that you don't need more pages on the inactive list you don't even 
need to run that clock.
--
Jim C. Nasby, Data Architect                       j...@nasby.net
512.569.9461 (cell)                         http://jim.nasby.net


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