| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Greg Stark <stark(at)mit(dot)edu> |
| Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Rajeev rastogi <rajeev(dot)rastogi(at)huawei(dot)com>, Ants Aasma <ants(at)cybertec(dot)at>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Markus Wanner <markus(at)bluegap(dot)ch> |
| Subject: | Re: Proposal for CSN based snapshots |
| Date: | 2014-08-26 20:12:07 |
| Message-ID: | 1409083927.2335.401.camel@jeff-desktop |
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| Lists: | pgsql-hackers |
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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