On Thu, Dec 02, 2010 at 03:15:21PM +0100, Matthias Leopold wrote:
> hi,
> 
> is it possible for a node to be subscriber and origin for the same set 
> at the same time so it "forwards" changes to its subscribers?

I think the terminology you have isn't quite right, but yes.  This is
a major feature of Slony.  The word you want is "provider".  Have a
look at the concepts documentation at
http://slony.info/documentation/2.0/concepts.html.

Something Slony does well here that, last I checked, nobody else does
well is to handle complicated intermediate failures.  For instance,
suppose you have a four-node-deep replication chain:
origin->subscriber/provider->subscriber/provider->subscriber.  If you
had simultaneous failure of any two of the provider nodes (including
the origin), you would still be able to reshape all this so that the
final subscriber wouldn't be an orphan.  Managing this is complicated,
however, and it's part of where Slony gets its (somewhat deserved)
reputation for being tricky to operate.

> i'm looking for a solution like this to reduce the number of slon 
> daemons (currently 11) on my origin server. are there other solutions 
> when you have "a lot of" nodes?

Note that there's no reason the slon has to run on the origin.  You're
not going to get a huge advantage in terms of query load from moving
around providers.  You might want to look at log shipping.

A

-- 
Andrew Sullivan
ajs at crankycanuck.ca