On February 8, 2005 08:28 am, David Parker wrote:
> A few weeks ago I was looking for a way to get around slony scalability
> issues for a large network of machines that need a replication
> relationship. The log shipping approach Christopher mentioned sounds
> promising, but I have to deliver something, hmmm, a couple of weeks from
> now....(sigh)
>
> The approach I'm thinking of involves leveraging the existing slony
> infrastructure I have, but implementing my own "push" process. This process
> maintains its own little schema to manage subscribers, etc., but it listens
> on sync events and uses the slony sl_log table(s) to capture the updates.
> Then it pushes these updates out to wherever it needs to. The requirements
> for synchronization here are somewhat looser, so I'm just tracking the
> lastest transaction id on every subscriber node.
>
> The main reason for this approach is to avoid the overhead of the n-1
> connections to every node in the system, and also to avoid de-stabilizing
> our existing slony-based clustering/failover infrastructure, which is
> working fine as it is.
>
> One thing I'm wondering about is the logic in the cleanup thread that
> cleans out the sl_log_1 table: the logic appears to be keying off of the
> min(ev_seqno) in the sl_event table to determine what the floor on the xid
> is should be in the log table, but it's not clear to me where the events
> get managed.  

The event cleanup themself get mannaged through the CleanupEvent  plpgsql 
function. see http://www.dbitech.ca/slony/book/function.cleanupevent.html

Also, in -HEAD the sl_log cleanup has been made a bit more aggressive, to help 
acomidate large transactional volume servers.

> Obviously it's all right there in front of me in SQL or C 
> code, but I keep getting confused by what's happening in what thread....
>
> Also, at what point does the switch get made from sl_log_1 to sl_log_2?

Currently there is no switch happening.  The mechanics and process for this 
are still under debate.

>
> TIA for any suggestions.
>
>
> - DAP
> ---------------------------------------------------------------------------
>------- David Parker    Tazz Networks    (401) 709-5130
> ?
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Darcy Buskermolen
Wavefire Technologies Corp.
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