>> The problems with two stage commit type approches to replication are
IMHO the biggest problem with two phased commit is it doesn't scale.
The more servers
you add to the replica the slower it goes. Also there's the potential
for dead locks across
server boundaries.
>> 2) All of the databases must be able to communicate with each other at> all times in order for any edits to work.
Ifthe servers are> connected over some sort of WAN that periodically has short outages this> is a problem. Also if
yourusing replication because you want to be
able> to take down one of the databases for short periods of time without> bringing down the others your in trouble.
All true for two phased commit protocol. To have multi master
replication, you must have all
systems communicating, but you can use a multicast group communication
system instead of
2PC. Using total order messaging, you can ensure all changes are
delivered to all servers in the
replica in the same order. This group communication system also allows
failures to be detected
while other servers in the replica continue processing.
A few of us are working with this theory, and trying to integrate with
7.2. There is a working
model for 6.4, but its very limited. (insert, update, and deletes) We
are currently hosted at
http://gborg.postgresql.org/project/pgreplication/projdisplay.php
But the site has been down the last 2 days. I've contacted the web
master, but haven't seen
any results yet. If any one knows what going on with gborg, I'd
appreciate a status.
Darren