Tenha certeza que o portal esta coletando as estatisticas.

Faça o login como PORTAL e execute:

SQL> exec dbms_stats.delete_schema_stats (ownname=>’PORTAL’); — analyzing PORTAL schema statistics is *NOT* supported
SQL> exec wwsbr_stats.delete_stats; — delete Portal statistics
SQL> exec wwsbr_stats.gather_stats; — create Portal statistics
SQL> exec wwsbr_stats.enable_monitoring; — Habilitar o DML sobre as tabelas se for necessário
SQL> exec wwsbr_stats.gather_stale;
SQL> commit;

Nota:
+ Para desabilitar Portal DML monitoring : exec wwsbr_stats.disable_monitoring
+ Para configurar o JOB: $ORACLE_HOME/portal/admin/plsql/wws/statsjsub.sql ‘START’ ‘NOW’ ’24’ => a cada 24 horas.