[Pgcluster-general] Questions on PGCluster

[G Perry]

Hello,

I am currently evaluating Postgresql to replace a MySQL implementation,
and I happened across PGCluster during my research.  It seems that
PGCluster is ranked the best clustering/HA/load balancing solution out
there for Postgresql, I have a few questions about implementation that
hopefully someone can answer here.

The current project we are working on is a mapping application that
will eventually be used to navigate many terabytes worth of imagery and
GIS data.  The backbone of the project is running on Amazon EC2 and S3,
and I am investigation Postgresql as opposed to MySQL based on WAL (EC2
is non-persistent so WAL is a huge benefit).

We will eventually have several EC2 instances, each running a
Postgresql instance that is replicated from a single master.  The idea
is that for each web server, there will be a local Postgresql server
running which is replicated from a single master.  I would like to
support both read and write applications on each individual web server
(I guess this would be a master-master replication scenario?), and have
writes propagated up to the single master then replicated back out
across the cloud.

Is this type of replication possible, if we were to address any issues
with autoincrement using our application?  How large could such a
replication scenario scale to?  Master master replication using MySQL
is possible in this scenario using master-slave-master-slave ring
replication, but it breaks after about 10 hosts total (the db hosts end
up spending more time on replication than servicing requests).

If this is not possible, and we must have a single dedicated host that
handles all of the write operations, are there any limits to the amount
of slaves that can be replicated?  Would a single master support say
100 Postgresql slaves?

What form of load balancing does PGCluster support?  Right now we are
using round robin DNS for each service cluster; EC2's VM environment
doesn't really provide for standard layer-2 based load balancing.

Thanks in advance.