J?r?mie LOPEZ <jlo at mgn.net> writes:
> Thanks a lot Christopher, a complete example is sure pleasant.
>
> However, my case is different, so I'll be indeed more specific:
> Let's say I have 2 PostgreSQL servers - PGSRV_1 and PGSRV_2 - and 3 different databases - DB_CLIENT, DB_PRODUCT and
> DB_ORDER.

If there are three databases, then the answer is clear: you need three
clusters, and hence six slon processes.

> DB_CLIENT is hosted on PGSRV_1. DB_PRODUCT and DB_ORDER are hosted
> on PGSRV_2.  I want to set up replication of the databases for
> backup purpose.  DB_CLIENT should be replicated on
> PGSRV_2. DB_PRODUCT and DB_ORDER should be replicated on PGSRV_1.
>
> So, I would have DB_CLIENT master, DB_PRODUCT slave and DB_ORDER
> slave on PGSRV_1 and DB_PRODUCT master, DB_ORDER master and
> DB_CLIENT slave on PGSRV_2.
>
> So for this replication system, I suppose that I must have 6 nodes,
> hence I certainly must have 6 slons too (in the real project, I have
> 10 databases and not only 3, so I suppose that would give me 20
> slons running), but how many clusters must/should/could I have?

If there are three differently-named databases, then you must have
three clusters.

> One possible configuration - and certainly the simplest - is to
> define 3 clusters (of 2 nodes each): one for each database to
> replicate. But couldn't it be possible to manage less clusters and
> shouldn't it be more practical?

The SET PATH entries have to reference _a database_; they cannot
express "get tables from one of these three databases."  

If you set up one database on each node, and set up three schemas,
db_client, db_product, and db_order, then THAT would allow you to cut
down to one Slony-I cluster.  That would have the further merit that
you could build queries that access data from multiple of those
schemas.

> (I in fact tried to define an unique cluster of 6 nodes, but maybe
> have did it wrong because I get the following error at the INIT
> CLUSTER command: loading of file /pgsql/share/xxid.v73.sql:
> PGRES_FATAL_ERROR ERROR:? current transaction is aborted, queries
> ignored until end of transaction block)

Something went wrong; I'm not sure what to point to offhand.

You might find some relevant info at...
<http://cbbrowne.dyndns.info:8741/cgi-bin/twiki/view/Sandbox/SlonyIAdministration>

If you find things that are unclear, feel free to add questions to the
wiki...
-- 
"cbbrowne","@","ca.afilias.info"
<http://dev6.int.libertyrms.com/>
Christopher Browne
(416) 673-4124 (land)