Re: Re: [COMMITTERS] pgsql: Add --synchronous option to pg_receivexlog, for more reliable WA

From: Peter Eisentraut <peter_e(at)gmx(dot)net>
To: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Re: [COMMITTERS] pgsql: Add --synchronous option to pg_receivexlog, for more reliable WA
Date: 2015-11-19 19:39:41
Message-ID: 564E257D.5000307@gmx.net
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On 9/15/15 11:04 PM, Fujii Masao wrote:
> If --slot option is specified, pg_receivexlog reports a flush position to
> the server even though --synchronous is not specified. So users might think
> that --synchrnous option is not necessary for synchronous pg_receivexlog
> setting. But that's not true. If --synchronous option is not specified, the
> received WAL data is flushed to the disk only when WAL segment is switched.
> So the transactions on the master need to wait for a long time, i.e.,
> we can think that synchronous pg_receivexlog doesn't work smoothly.
> To avoid such situation, --synchronous option also needs to be specified and
> which makes pg_receivexlog flush WAL data immediately after receiving it.

Thank you for this information. I hope to have clarified this in the
documentation now.

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