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Date: Fri, 25 Mar 2011 21:12:05 +0900
Message-ID: <AANLkTinC2+OuVQdHWVRfDLOTA7Z1n2JZdbUsrgCmvmJN@mail.gmail.com>
Subject: Re: Re: [COMMITTERS] pgsql: Efficient transaction-controlled
	synchronous replication.
From: Fujii Masao <masao.fujii@gmail.com>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Markus Wanner <markus@bluegap.ch>,
	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>
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On Sat, Mar 19, 2011 at 4:29 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
> 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> =A0wrote:
>> >>>> In PostgreSQL other users cannot observe the commit until an
>> >>>> acknowledgement has been received.
>>
>> On other nodes as well? =A0To me that means the standby needs to hold ba=
ck
>> COMMIT of an ACKed transaction, until receives a re-ACK from the master,
>> that it committed the transaction there. =A0How else could the slave kno=
w
>> when to commit its ACKed transactions?
>
> We could do that easily enough, actually, if we wished.
>
> Do we wish?

No.

I'm not sure what's the problem with seeing from the standby the data which=
 is
not visible on the master yet? And, I'm really not sure whether that proble=
m can
be solved by making the data visible on the master before the standby. If w=
e
really want to see the consistent data from each node, we should implement
and use a cluster-wide snapshot as well as Postgres-XC does.

Regards,

--=20
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center