On 5/29/08, David Fetter <david@fetter.org> wrote:
> On Thu, May 29, 2008 at 10:12:55AM -0400, Tom Lane wrote:
> > Ideally this would be coupled with the ability to execute read-only
> > queries on the slave servers, but we see technical difficulties that
> > might prevent that from being completed before 8.5 or even further
> > out. (The big problem is that long-running slave-side queries might
> > still need tuples that are vacuumable on the master, and so
> > replication of vacuuming actions would cause the slave's queries to
> > deliver wrong answers.)
>
> This part is a deal-killer. It's a giant up-hill slog to sell warm
> standby to those in charge of making resources available because the
> warm standby machine consumes SA time, bandwidth, power, rack space,
> etc., but provides no tangible benefit, and this feature would have
> exactly the same problem.
>
> IMHO, without the ability to do read-only queries on slaves, it's not
> worth doing this feature at all.
I would not be so harsh - I'd like to have the lossless standby even
without read-only slaves.
But Tom's mail gave me impression core wants to wait until we get "perfect"
read-only slave implementation so we wait with it until 8.6, which does
not seem sensible. If we can do slightly inefficient (but simple)
implementation
right now, I see no reason to reject it, we can always improve it later.
Especially as it can be switchable. And we could also have
transaction_timeout paramenter on slaves so the hit on master is limited.
--
marko
