Re: Sync Rep v19

On Fri, Mar 4, 2011 at 3:04 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> The "wait-forever" might be a straightforward approach against (B). But
> this option prevents transactions from running not only when the
> synchronous standby goes away, but also when the primary is invoked
> first or when the standby is promoted at failover. Since the availability
> of the database service decreases very much, I don't want to use that.

I continue to think that wait-forever is the most sensible option. If
you want all of your data on the disks of two machines before the
commit is ack'd, I think you probably want that all the time. The
second scenario you mentioned ("when the standby is promoted at
failover") is quite easy to handle. If you don't want synchronous
replication after a standby promotion, then configure the master to do
synchronous replication and the slave not to do synchronous
replication. Similarly, if you've got an existing machine that is not
doing synchronous replication and you want to start, fire up the
standby in asynchronous mode and switch to synchronous replication
after it has fully caught up. It seems to me that we're bent on
providing a service that does synchronous replication except when it
first starts up or when the timeout expires or when the phase of the
moon is waxing gibbons, and I don't get the point of that. If I ask
for synchronous replication, I want it to be synchronous until I
explicitly turn it off. Otherwise, when I fail over, how do I know if
I've got all my transactions, or not?

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company