Subject: Re: Sync Rep for 2011CF1
From: Simon Riggs <simon@2ndQuadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Fujii Masao <masao.fujii@gmail.com>,
	Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>,
	pgsql-hackers@postgresql.org
In-Reply-To: <AANLkTi=boSWVHgjS6EQSOV9K0y_7gokPzS5vj965NT_A@mail.gmail.com>
References: <1295127631.3282.100.camel@ebony>
	<AANLkTikbV8afeeC6-iESC4myeR5BUzg-YnTqCvKJ3qcO@mail.gmail.com>
	<AANLkTikUxTM+6EaZ8S_OteDzCXaccsPVsd1U_ZUzM5i0@mail.gmail.com>
	<4D543723.9050101@enterprisedb.com>
	<AANLkTinF=DLP20ZJ57mkVa4ofTVLBMYn+pcRsqFMXK-=@mail.gmail.com>
	<AANLkTi=boSWVHgjS6EQSOV9K0y_7gokPzS5vj965NT_A@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
Date: Wed, 16 Feb 2011 15:36:40 +0000
Message-ID: <1297870600.1747.30144.camel@ebony>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit

On Tue, 2011-02-15 at 12:08 -0500, Robert Haas wrote:
> On Mon, Feb 14, 2011 at 12:25 AM, Fujii Masao <masao.fujii@gmail.com> wrote:
> > On Fri, Feb 11, 2011 at 4:06 AM, Heikki Linnakangas
> > <heikki.linnakangas@enterprisedb.com> wrote:
> >> I added a XLogWalRcvSendReply() call into XLogWalRcvFlush() so that it also
> >> sends a status update every time the WAL is flushed. If the walreceiver is
> >> busy receiving and flushing, that would happen once per WAL segment, which
> >> seems sensible.
> >
> > This change can make the callback function "WalRcvDie()" call ereport(ERROR)
> > via XLogWalRcvFlush(). This looks unsafe.
> 
> Good catch.  Is the cleanest solution to pass a boolean parameter to
> XLogWalRcvFlush() indicating whether we're in the midst of dying?

Surely if you do this then sync rep will fail to respond correctly if
WalReceiver dies.

Why is it OK to write to disk, but not OK to reply?

-- 
 Simon Riggs           http://www.2ndQuadrant.com/books/
 PostgreSQL Development, 24x7 Support, Training and Services