Re: Sync Rep v19

From: "Ross J(dot) Reedstrom" <reedstrm(at)rice(dot)edu>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Dimitri Fontaine <dimitri(at)2ndquadrant(dot)fr>, Bruce Momjian <bruce(at)momjian(dot)us>, Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Sync Rep v19
Date: 2011-03-11 19:42:59
Message-ID: 20110311194258.GB12106@rice.edu
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On Fri, Mar 11, 2011 at 09:03:33AM -0500, Robert Haas wrote:
> On Fri, Mar 11, 2011 at 8:21 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> >
> > In that case, the last write WAL timestamp would become equal to the
> > last replay WAL timestamp. So we can see that there is no lag.
>
> Oh, I see (I think). You're talking about write/replay lag, but I was
> thinking of master/slave transmission lag.
>

Which are both useful numbers to know: the first tells you how "stale"
queries from a Hot Standby will be, the second tells you the maximum
data loss from a "meteor hits the master" scenario where that slave is
promoted, if I understand all the interactions correctly.

Ross
--
Ross Reedstrom, Ph.D. reedstrm(at)rice(dot)edu
Systems Engineer & Admin, Research Scientist phone: 713-348-6166
Connexions http://cnx.org fax: 713-348-3665
Rice University MS-375, Houston, TX 77005
GPG Key fingerprint = F023 82C8 9B0E 2CC6 0D8E F888 D3AE 810E 88F0 BEDE

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