Andres Freund <andres@2ndquadrant.com> wrote:
> On 2014-01-08 13:34:08 -0800, Kevin Grittner wrote:
>
>> On the other hand, we keep getting people saying they want the
>> database to make the promise of synchronous replication, and
>> tell applications that it has been successful even when it
>> hasn't been, as long as there's a line in the server log to
>> record the lie.
>
> Most people having such a position I've talked to have held that
> position because they thought synchronous replication would mean
> that apply (and thus visibility) would also be synchronous. Is
> that different from your experience?
I haven't pursued it that far because we don't have
maybe-synchronous mode yet and seem unlikely to ever support it.
I'm not sure why that use-case is any better than any other. You
still would never really know whether the data read is current. If
we were to implement this, the supposedly synchronous replica could
be out-of-date by any arbitrary amount of time (from milliseconds
to months). (Consider what could happen if the replication
connection authorizations got messed up while application
connections to the replica were fine.)
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company