Re: Clock sweep not caching enough B-Tree leaf pages?

From: Stephen Frost <sfrost(at)snowman(dot)net>
To: Merlin Moncure <mmoncure(at)gmail(dot)com>
Cc: Andres Freund <andres(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Robert Haas <robertmhaas(at)gmail(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Clock sweep not caching enough B-Tree leaf pages?
Date: 2014-04-17 19:00:07
Message-ID: 20140417190007.GO2556@tamriel.snowman.net
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* Merlin Moncure (mmoncure(at)gmail(dot)com) wrote:
> I doubt that's necessary though -- if the postgres caching algorithm
> improves such that there is a better tendency for hot pages to stay in
> s_b, Eventually the O/S will deschedule the page for something else
> that needs it. In other words, otherwise preventable double
> buffering is really a measurement of bad eviction policy because it
> manifests in volatility of frequency accessed pages.

I wonder if it would help to actually tell the OS to read in buffers
that we're *evicting*... On the general notion that if the OS already
has them buffered then it's almost a no-op, and if it doesn't and it's
actually a 'hot' buffer that we're gonna need again shortly, the OS will
have it.

In other words, try to make the OS more like a secondary cache to ours
by encouraging it to cache things we're evicting.

Thanks,

Stephen

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