Re: Re: [COMMITTERS] pgsql: Efficient transaction-controlled synchronous replication.

On Sat, Mar 19, 2011 at 4:29 AM, Simon Riggs  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  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.

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 problem can
be solved by making the data visible on the master before the standby. If we
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,

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