Oracle resolves issues by using various types of locks and a multiversion consistency model. These features are based on the concept of a      

    transaction

The simplest way to think of Oracle's implementation of read consistency is to imagine each user operating a private copy of the database, hence    

    the multiversion consisten-

             cy model

Oracle also uses locks to control concurrent access to data. When updating information, the data server holds that information with a lock until the update is

     submitted or committed

One way to provide  from concurrent non-database administrator isolation is to shut down the database and reopen it in restricted mode. You could also put the system into quiesced state without disrupting users

​RAC comprises several Oracle instances running on multiple clustered computers, which communicate with each other by means of a so-called interconnect

​Oracle provides unique portability across all major platforms and ensures that your applications run without modification after changing platforms