Simple is Best

after the tunning on Oracle9.2.0.6 under Rhel3 u4, the all system performance tunning was finished last week.
total architecture includes cache,web,application,database, tunning on all the part began at july last year, finished at april this year.
now the system can have about 10k-20k concurrent online user with the same hardware, the on bottle is database, though now we have oracle,mysql and sql server,maybe postgresql later, but none db is clustered.the expensive oracle rac-.
performance now become about 5-20 times than last year.
next step is the dirtributed architecture.maybe MQ,JMS & EJB.