Subject: Re: Re: [COMMITTERS] pgsql: Efficient
	transaction-controlled synchronous replication.
From: Simon Riggs <simon@2ndQuadrant.com>
To: Markus Wanner <markus@bluegap.ch>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>,
	Kevin Grittner <Kevin.Grittner@wicourts.gov>,
	MARK CALLAGHAN <mdcallag@gmail.com>,
	Alvaro Herrera <alvherre@commandprompt.com>,
	Andrew Dunstan <andrew@dunslane.net>, Aidan Van Dyk <aidan@highrise.ca>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
In-Reply-To: <4D83B02A.5090105@bluegap.ch>
References: <E1PwMns-00047O-UU@gemulon.postgresql.org>
	<4D741441.2090704@dunslane.net> <1299454125.1696.6138.camel@ebony>
	<4D74896C.5030402@enterprisedb.com> <4D74DDFA.70800@dunslane.net>
	<4D74E584.7080409@enterprisedb.com> <4D74E9FA.7070202@dunslane.net>
	<AANLkTinkzJ=UrLbThZy2KeQg+SjwYqj2r0mDomMwirB7@mail.gmail.com>
	<4D74F3AE.9000802@dunslane.net> <4D74FDEC.5040406@enterprisedb.com>
	<4D74FF15.1070804@dunslane.net> <1299513979-sup-1987@alvh.no-ip.org>
	<4D832571.5030808@bluegap.ch>
	<AANLkTi=B+cWE-pQJQM=zoA9=Zr25W7zPPMFvvBe11O4E@mail.gmail.com>
	<1300457958.18619.13780.camel@ebony>
	<4D832B4D020000250003BA98@gw.wicourts.gov>
	<4D837EA2.2070205@enterprisedb.com>
	<1300465171.18619.15193.camel@ebony> <4D83B02A.5090105@bluegap.ch>
Content-Type: text/plain; charset="UTF-8"
Date: Fri, 18 Mar 2011 19:29:50 +0000
Message-ID: <1300476590.18619.18115.camel@ebony>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit

On Fri, 2011-03-18 at 20:19 +0100, Markus Wanner wrote:
> Simon,
> 
> On 03/18/2011 05:19 PM, Simon Riggs wrote:
> >>> Simon Riggs<simon@2ndQuadrant.com>  wrote:
> >>>> In PostgreSQL other users cannot observe the commit until an
> >>>> acknowledgement has been received.
> 
> On other nodes as well?  To me that means the standby needs to hold back
> COMMIT of an ACKed transaction, until receives a re-ACK from the master,
> that it committed the transaction there.  How else could the slave know
> when to commit its ACKed transactions?

We could do that easily enough, actually, if we wished.

Do we wish?

> > No, only in the case where you choose not to failover to the standby
> > when you crash, which would be a fairly strange choice after the effort
> > to set up the standby. In a correctly configured and operated cluster
> > what I say above is fully correct and needs no addendum.
> 
> If you don't failover, how can the standby be ahead of the master, given
> it takes measures not to be during normal operation?
> 
> Eager to understand... ;-)
> 
> Regards
> 
> Markus

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