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
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