Performance issues on replication with materialized views

Hello,

We have several remote sites (Oracle Standard Edition 10.2.0.3.0), which are replicated to a central server (Oracle Standard Edition 12.1.0.1.0). Each remote site has the same schema (named as the city in which is located) and the central server replicates the entire schema for every site using read-only materialized views.

On the materialized view site, every hour many jobs are executed to refresh the groups of the MVs. Every group refreshes a different schema.

Problem is, only one refresh at a time can happen. All the other refreshes waits in line until the first is done, causing bottlenecks and performance issues.