| From: | Craig Ringer <craig(at)2ndquadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Andres Freund <andres(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: | 2014-06-18 13:30:26 |
| Message-ID: | 53A19472.8020206@2ndquadrant.com |
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| Lists: | pgsql-hackers |
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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