On 24/09/10 13:57, Simon Riggs wrote:
> If you want high availability you need N+1 redundancy. If you want a
> standby server that is N=1. If you want a highly available standby
> configuration then N+1 = 2.
Yep. Synchronous replication with one standby gives you zero data loss.
When you add a 2nd standby as you described, then you have a reasonable
level of high availability as well, as you can continue processing
transactions in the master even if one slave dies.
> Show me the textbook that describes what happens with 2 standbys. If one
> exists, I'm certain it would agree with my analysis.
I don't disagree with your analysis about multiple standbys and high
availability. What I'm saying is that in a two standby situation, if
you're willing to continue operation as usual in the master even if the
standby is down, you're not doing synchronous replication. Extending
that to a two standby situation, my claim is that if you're willing to
continue operation as usual in the master when both standbys are down,
you're not doing synchronous replication.
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
