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From: Jeff Davis <pgsql@j-davis.com>
To: Greg Stark <stark@mit.edu>
Cc: Heikki Linnakangas <hlinnakangas@vmware.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@2ndquadrant.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Rajeev rastogi <rajeev.rastogi@huawei.com>
Cc: Ants Aasma <ants@cybertec.at>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Markus Wanner <markus@bluegap.ch>
Subject: Re: Proposal for CSN based snapshots
Date: Tue, 26 Aug 2014 13:12:07 -0700
Message-ID: <1409083927.2335.401.camel@jeff-desktop> (raw)
In-Reply-To: <CAM-w4HPa8hFr6SJDndAg4UXEB6cUbQLco-p9O6Mx2Fbr2KpjZw@mail.gmail.com>
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	<BF2827DCCE55594C8D7A8F7FFD3AB7713DDBC758@SZXEML508-MBX.china.huawei.com>
	<5370D323.1070606@vmware.com>
	<20140512144112.GB9619@awork2.anarazel.de>
	<5370E267.2020904@vmware.com>
	<20140515183436.GD25053@momjian.us>
	<CA+TgmoYiqga4KWz_1=O8D6ivmTAJfY=-fxO6Nk+D-o3M0M60=Q@mail.gmail.com>
	<20140515200632.GB16014@awork2.anarazel.de>
	<20140515213714.GB7857@eldon.alvh.no-ip.org>
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	<1409081570.2335.391.camel@jeff-desktop>
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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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