| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, 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: | 2014-05-15 18:34:36 |
| Message-ID: | 20140515183436.GD25053@momjian.us |
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| Lists: | pgsql-hackers |
On Mon, May 12, 2014 at 06:01:59PM +0300, Heikki Linnakangas wrote:
> >Some of the stuff in here will be influence whether your freezing
> >replacement patch gets in. Do you plan to further pursue that one?
>
> Not sure. I got to the point where it seemed to work, but I got a
> bit of a cold feet proceeding with it. I used the page header's LSN
> field to define the "epoch" of the page, but I started to feel
> uneasy about it. I would be much more comfortable with an extra
> field in the page header, even though that uses more disk space. And
> requires dealing with pg_upgrade.
FYI, pg_upgrade copies pg_clog from the old cluster, so there will be a
pg_upgrade issue anyway.
I am not excited about a 32x increase in clog size, especially since we
already do freezing at 200M transactions to allow for more aggressive
clog trimming. Extrapolating that out, it means we would freeze every
6.25M transactions.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +
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