postgres-xc-general Mailing List for Postgres-XC

> I'm a post-graduation student 

Hm.

> and my conclusion work is about Postgres-XC. I've read a lot about
> the project and I really think this is a powerful tool.
> Unfortunately, I couldn't achieve the performance I had expected.
> 
> I've configured a cluster with 4 virtualized servers (all of them on
> the same hardware using Virtual Box):

You're running several RDBMS server instances on one physical computer
and you expect to get more throughput from that than with one single
instance running on the same physical computer?

Errr, huh?

> I used pgbench to compare the number of transactions per second in
> Postgres-XC and in a standalone PostgreSQL server. Postgres-XC
> achieved only half TPS compared to PostgreSQL. The test was basically
> consisted of inserts into distributed tables (I used a custom script
> in pgbench) simulating many clients simultaneously.

That's what is to be expected. The same hardware minus the additional
overhead for virtualisation and replication *has to* give you less
throughput than one single RDBMS server instance.

And if you emulate the clients by running scripts on the same hardware
as the servers...
 
> - How many servers would be enough to have a write/read scalability
> compared to a single PostgreSQL?

More than one. *Hardware* servers.

> - Would it be a problem to have all servers on the same hardware?

That's not just "a problem", that's the whole point.

If you want more throughput, you need more hardware*. That's what
replication is made for in the first place.
 
Sincerely,

Wolfgang

*Of course you also must optimise your configuration to get the maximum
out of the hardware.