Re: Core team statement on replication in PostgreSQL

* Dave Page <dpage(at)pgadmin(dot)org> [080529 12:03]:
> On Thu, May 29, 2008 at 4:48 PM, Douglas McNaught <doug(at)mcnaught(dot)org> wrote:

> > I think the idea is that WAL records would be shipped (possibly via
> > socket) and applied as they're generated, rather than on a
> > file-by-file basis. At least that's what "real-time" implies to me...
>
> Yes, we're talking real-time streaming (synchronous) log shipping.

But synchronous streaming doesn't mean the WAL has to be *applied* on
the salve yet. Just that it has to be "safely" on the slave (i.e on
disk, not just in kernel buffers).

The whole single-threaded WAL replay problem is going to rear it's ugly
head here too, and mean that a slave *won't* be able to keep up with a
busy master if it's actually trying to apply all the changes in
real-time. Well, actually, if it's synchronous, it will keep up, but it
just means that now your master is IO capabilities is limited to the
speed of the slaves single-threaded WAL application.

a.
--
Aidan Van Dyk Create like a god,
aidan(at)highrise(dot)ca command like a king,
http://www.highrise.ca/ work like a slave.