Re: patch for new feature: Buffer Cache Hibernation

Alvaro Herrera wrote:
> As for gain, I have heard of test setups requiring hours of runtime in
> order to prime the buffer cache.
>   

And production ones too.  I have multiple customers where a server 
restart is almost a planned multi-hour downtime.  The system may be back 
up, but for a couple of hours performance is so terrible it's barely 
usable.  You can watch the MB/s ramp up as the more random data fills in 
over time; getting that taken care of in a larger block more amenable to 
elevator sorting would be a huge help.

I never bothered with this particular idea though because shared_buffers 
is only a portion of the important data.  Cedric's pgfincore code digs 
into the OS cache, too, which can then save enough to be really useful 
here.  And that's already got a snapshot/restore feature.  The slides at 
http://www.pgcon.org/2010/schedule/events/261.en.html have a useful into 
to that, pages 30 through 34 are the neat ones.  That provides some 
other neat APIs for preloading popular data into cache too.  I'd rather 
work on getting something like that into core, rather than adding 
something that only is targeting just shared_buffers.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us
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