Re: pg_receivexlog --status-interval add fsync feedback

From: <furuyao(at)pm(dot)nttdata(dot)co(dot)jp>
To: <hlinnakangas(at)vmware(dot)com>, <simon(at)2ndQuadrant(dot)com>, <masao(dot)fujii(at)gmail(dot)com>
Cc: <sawada(dot)mshk(at)gmail(dot)com>, <pgsql-hackers(at)postgresql(dot)org>, <teranishih(at)nttdata(dot)co(dot)jp>
Subject: Re: pg_receivexlog --status-interval add fsync feedback
Date: 2014-10-24 10:24:59
Message-ID: A9C510524E235E44AE909CD4027AE196BF7D6FB25F@MBX-MSG-SV03.msg.nttdata.co.jp
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> >> Sorry, I'm going around in the circle. But I'd like to say again, I
> >> don't think this is good idea. It prevents asynchronous
> >> pg_receivexlog from fsyncing WAL data and sending feedbacks more
> >> frequently at all. They are useful, for example, when we want to
> >> monitor the write location of asynchronous pg_receivexlog in almost
> >> realtime. But if we adopt the idea, since feedback cannot be sent
> >> soon in async mode, pg_stat_replication always returns the
> not-up-to-date location.
> >
> > Why not send a message every 10 seconds when its not sync rep?
>
> Or even after every write(). It's a tiny amount of network traffic anyway.

I understand that send feedback message frequently will keep pg_stat_replication up-to-date state.

Are there really no needs who wants to fsync even in async mode ?
I think the people who dislike Data lost will like that idea.
Thought?

Nevertheless in sync or async, returning feedback and executing fsync() same as like walreceiver is such a problem?

--
Furuya Osamu

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