On 08.10.2010 11:25, Simon Riggs wrote:
> On Fri, 2010-10-08 at 10:56 +0300, Heikki Linnakangas wrote:
>>>
>>> Or what kind of customers do you think really need a no-lag solution for
>>> read-only queries? In the LAN case, the lag of async rep is negligible
>>> and in the WAN case the latencies of sync rep are prohibitive.
>>
>> There is a very good use case for that particular set up, actually. If
>> your hot standby is guaranteed to be up-to-date with any transaction
>> that has been committed in the master, you can use the standby
>> interchangeably with the master for read-only queries.
>
> This is an important point. It is desirable, but there is no such thing.
> We must not take any project decisions based upon that false premise.
>
> Hot Standby is never guaranteed to be up-to-date with master. There is
> no such thing as certainty that you have the same data as the master.
Synchronous replication in the 'replay' mode is supposed to guarantee
exactly that, no?
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com