[KLUG Members] Postgres Cluster

[awilliam at whitemice.org]

> > Slony is "Slony-I is a "master to multiple slaves" replication system
> > with cascading and failover."
> > Still not what I'd call a cluster, but it gives you redundancy.  
> > 
> 
> adequate locking.  That would mean that each "peer" would have to get an
> acknowledgment from each of the other peers that that it has received a
> "record 53 of table mytable" is locked. 

Yes, and implement START/STOP operation notificaiton with timeouts, 
post-fault resyncronization, and multi-host rollback.  Yep.  And you 
wonder why almost no one support this? :)  Of course, almost no one needs 
it.

>  Then the record would be
> modified on the update querried against machine and then all of the
> other peers would have to get that update before the unlock could occur.
> How does true multimastering servers accomplish thist.  Seems like evan
> trivial updates could take quite a while and create possible cascading
> locks from hell as multiple users update multiple things.

You run the databases on high-end machines, most likely with fiber-channel 
interconnects. $$$,$$$.99 at a minumum.  I know of an Informix 
cluster instance of two geographically distant servers interconnected by 
an OC-3.  (Informix supports clusting, but since it isn't a 'current' 
product I wouldn't recommend any buy it - hence Oracle and DB2).  I think 
their monthly connect fee is probably higher than my entire annual IT 
budget.