Message-ID: <529E92DC.4010708@lab.ntt.co.jp>
Date: Wed, 04 Dec 2013 11:26:36 +0900
From: KONDO Mitsumasa <kondo.mitsumasa@lab.ntt.co.jp>
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To: Andres Freund <andres@2ndquadrant.com>,
 Robert Haas <robertmhaas@gmail.com>
CC: =?ISO-8859-1?Q?Fabr=EDzio_Mello?= <fabriziomello@gmail.com>,
 Christian Kruse <christian@2ndquadrant.com>,
 Pgsql Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Time-Delayed Standbys
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 <20131203163302.GA18669@achilles.fritz.box>
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 <CA+TgmoapcHW_z6aJ_rxmf8MDxxrp+Yn6c3OTeXoEEstw7v+w8g@mail.gmail.com>
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(2013/12/04 4:00), Andres Freund wrote:
> On 2013-12-03 13:46:28 -0500, Robert Haas wrote:
>> On Tue, Dec 3, 2013 at 12:36 PM, Fabrízio de Royes Mello
>> <fabriziomello@gmail.com> wrote:
>>> On Tue, Dec 3, 2013 at 2:33 PM, Christian Kruse <christian@2ndquadrant.com>
>>> wrote:
>>>>
>>>> Hi Fabrizio,
>>>>
>>>> looks good to me. I did some testing on 9.2.4, 9.2.5 and HEAD. It
>>>> applies and compiles w/o errors or warnings. I set up a master and two
>>>> hot standbys replicating from the master, one with 5 minutes delay and
>>>> one without delay. After that I created a new database and generated
>>>> some test data:
>>>>
>>>> CREATE TABLE test (val INTEGER);
>>>> INSERT INTO test (val) (SELECT * FROM generate_series(0, 1000000));
>>>>
>>>> The non-delayed standby nearly instantly had the data replicated, the
>>>> delayed standby was replicated after exactly 5 minutes. I did not
>>>> notice any problems, errors or warnings.
>>>>
>>>
>>> Thanks for your review Christian...
>>
>> So, I proposed this patch previously and I still think it's a good
>> idea, but it got voted down on the grounds that it didn't deal with
>> clock drift.  I view that as insufficient reason to reject the
>> feature, but others disagreed.
>
> I really fail to see why clock drift should be this patch's
> responsibility.  It's not like the world would go under^W data corruption
> would ensue if the clocks drift. Your standby would get delayed
> imprecisely. Big deal. From what I know of potential users of this
> feature, they would set it to at the very least 30min - that's WAY above
> the range for acceptable clock-drift on servers.
Yes. I think that purpose of this patch is long time delay in standby server,
and not for little bit careful timing delay.

Regards,
-- 
Mitsumasa KONDO
NTT Open Source Software Center


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