Re: Measuring replay lag

From: Craig Ringer <craig(at)2ndquadrant(dot)com>
To: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, David Steele <david(at)pgmasters(dot)net>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Measuring replay lag
Date: 2017-03-24 01:27:23
Message-ID: CAMsr+YGEqcR6mLkGUZWvqaQ2MXXv1FtpW-fLQKfL6Vuo-L9Xig@mail.gmail.com
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On 24 March 2017 at 05:39, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> wrote:

> Fujii-san for the idea of tracking write and flush lag too

You mentioned wishing that logical replication would update sent lag
as the decoding position.

It appears to do just that already; see the references to restart_lsn
in StartLogicalReplication, and the update of sentPtr in
XLogSendLogical .

It's a bit misleading, since it hasn't *sent* anything, it buffers it
until commit. But it's useful.

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

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