What is the "Data partitioned, Shared-Nothing, Parallel Database" solution for PostgreSQL ? I was looking for a open source parallel database solution. It seems Postgres-XC is a viable solution. However, I don't need the replication. In this case, is there any better solution towards read optimized parallel architecture ?
There is pl/proxy, which provides a basic federation capability, but it's not an engine optimised for this sort of work.  Greenplum is a commercial product that does have a shared nothing engine that might do what you want.  However, it's not cheap - less expensive than Oracle but more expensive than SQL Server.

There are no pure open-source engines of that type for PostgreSQL.  However, you might get what you want from PL/Proxy.