On Thursday 29 May 2008 20:31:31 Greg Smith wrote:
> On Thu, 29 May 2008, Tom Lane wrote:
> > There's no point in having read-only slave queries if you don't have a
> > trustworthy method of getting the data to them.
>
> This is a key statement that highlights the difference in how you're
> thinking about this compared to some other people here. As far as some
> are concerned, the already working log shipping *is* a trustworthy method
> of getting data to the read-only slaves. There are plenty of applications
> (web oriented ones in particular) where if you could direct read-only
> queries against a slave, the resulting combination would be a giant
> improvement over the status quo even if that slave was as much as
> archive_timeout behind the master. That quantity of lag is perfectly fine
> for a lot of the same apps that have read scalability issues.
>
> If you're someone who falls into that camp, the idea of putting the sync
> replication job before the read-only slave one seems really backwards.
>
Just looking at it from an overall market perspective, synchronous log
shipping pretty much only addresses failover needs, where as read-only slaves
address both failover and scaling issues. (Note I say address, not solve).
--
Robert Treat
Build A Brighter LAMP :: Linux Apache {middleware} PostgreSQL