Message-ID: <4D83B02A.5090105@bluegap.ch>
Date: Fri, 18 Mar 2011 20:19:06 +0100
From: Markus Wanner <markus@bluegap.ch>
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To: Simon Riggs <simon@2ndQuadrant.com>
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>
Subject: Re: Re: [COMMITTERS] pgsql: Efficient transaction-controlled
	synchronous replication.
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>
In-Reply-To: <1300465171.18619.15193.camel@ebony>
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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?

> 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