Poor performance

Hi, we've a problem in one of our databases and we cannot find the root of the problem.

The problem is that one of our schemas is giving very poor performance where calculating the execution plan for any query, however, same database just another schema and performance is ok.

To reproduce the problem...

set timing on;

explain plan for select * from <any_table>;

plan FOR correcto.

Elapsed: 00:00:03.484

plan FOR correcto.

Elapsed: 00:00:00.074

plan FOR correcto.

Elapsed: 00:00:06.511

plan FOR correcto.

Elapsed: 00:00:00.476

plan FOR correcto.

Elapsed: 00:00:07.058

plan FOR correcto.

Elapsed: 00:00:06.990

As you can see each execution of the explain plan is giving different time consuming in some cases, a simple query, 3 seconds, 6 seconds and so on... this behaviour is affecting to the performance of the application.