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From: Craig Ringer <craig@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Heikki Linnakangas <hlinnakangas@vmware.com>
Cc: Greg Stark <stark@mit.edu>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Andres Freund <andres@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: Wed, 18 Jun 2014 21:30:26 +0800
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On 06/18/2014 09:12 PM, Robert Haas wrote:
> No.  Otherwise, one of those bits could get changed after a backend
> takes a snapshot and before it finishes using it - so that the
> transaction snapshot is in effect changing underneath it.  You could
> avoid that by memorizing the contents of CLOG when taking a snapshot,
> but that would defeat the whole purpose of CSN-based snapshots, which
> is to make the small and fixed-size.

Ah.

Thankyou. I appreciate the explanation.

-- 
 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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