Jan Wieck <JanWieck at Yahoo.com> writes:
> On 11/23/2010 11:53 AM, Christopher Browne wrote:
>> A different suggestion, that doesn't involve any changes to Slony...
>>
>> Initially, it might be a good idea to set up the new subscriber with
>> FORWARD=no...
>
> I don't think it is actually the new subscriber, that is having a
> problem, but rather the fact that the origin and all forwarders keep
> the log and event data until every subscriber has confirmed it.

Yes, that seems the root of the problem, and I don't expect it to be
worthwhile to try to twist our way around it if we're not really getting
at the root of it.

> Let me ignore the problem of the initial COPY and catch up of the
> first replica for now.

Sure.  That may be unsolvable, and if so, there's little point fighting
it futilely.

> This fully redundant log and event keeping until everyone has
> confirmed everything is done so that any subscriber can be
> reconfigured to use another data provider at any point in time, willy
> nilly. It also keeps things simple for failover. But it does hurt in
> the cases described, like taking a leaf node down for a few days.
>
> The cure for this would be to add configuration information so that
> certain nodes will be allowed to "assume" confirmation from another
> node and go ahead with their cleanup. This certainly complicates the
> configuration, but I "assume" power users are fine with that.

That all sounds pretty plausible, and worth adding as a possible
enhancement.

[mulling for a while...]

So, would this suggest setting up a "shunned nodes" table, where a node
would ignore the specified set of nodes for the purposes of
confirmations?  That sounds not *too* tough to implement.  It's a bit of
a footgun, notably as it enables losing more nodes at FAIL OVER time.

I'll add a "shunned node" idea to the list.
-- 
let name="cbbrowne" and tld="ca.afilias.info" in String.concat "@" [name;tld];;
Christopher Browne
"Bother,"  said Pooh,  "Eeyore, ready  two photon  torpedoes  and lock
phasers on the Heffalump, Piglet, meet me in transporter room three"