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Message-ID: <1409083927.2335.401.camel@jeff-desktop>
Subject: Re: Proposal for CSN based snapshots
From: Jeff Davis <pgsql@j-davis.com>
To: Greg Stark <stark@mit.edu>
Cc: Heikki Linnakangas <hlinnakangas@vmware.com>, Robert Haas
 <robertmhaas@gmail.com>, Andres Freund <andres@2ndquadrant.com>, Alvaro
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Date: Tue, 26 Aug 2014 13:12:07 -0700
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On Tue, 2014-08-26 at 21:00 +0100, Greg Stark wrote:
> Well fundamentally the reason the visibility information is with the
> user data is so that we don't need to do two i/os to access the data.
> The whole point of hint bits is to guarantee that after some amount of
> time you can read data directly out of the heap page and use it
> without doing any additional I/O.

If the data is that static, then the visibility information would be
highly compressible, and surely in shared_buffers already.

(Yes, it would need to be pinned, which has a cost.)

Regards,
	Jeff Davis




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