Re: Measuring replay lag

From: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>
To: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: 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: 2017-01-03 01:02:11
Message-ID: CAEepm=0VQ_fPbe3wHFC4fuHTWLMjJXvLpF8JBJhty4Q7CojZcg@mail.gmail.com
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On Thu, Dec 29, 2016 at 1:28 AM, Thomas Munro
<thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> On Thu, Dec 22, 2016 at 10:14 AM, Thomas Munro
> <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
>> On Thu, Dec 22, 2016 at 2:14 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>>> I agree that the capability to measure the remote_apply lag is very useful.
>>> Also I want to measure the remote_write and remote_flush lags, for example,
>>> in order to diagnose the cause of replication lag.
>>
>> Good idea. I will think about how to make that work.
>
> Here is an experimental version that reports the write, flush and
> apply lag separately as requested. This is done with three separate
> (lsn, timestamp) buffers on the standby side. The GUC is now called
> replication_lag_sample_interval. Not tested much yet.

Here is a new version that is slightly refactored and fixes a problem
with stale samples after periods of idleness.

--
Thomas Munro
http://www.enterprisedb.com

Attachment Content-Type Size
replay-lag-v16.patch application/octet-stream 37.7 KB

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