单项选择题 You work as a database administrator for Certkiller .com. Users complain that their query is taking a long time to complete. You suspect the database buffer cache size to be the reason， and you define an alert to be generated when the buffer cache hit metric goes below 85%. When you observe the dynamic performance views， you find that the buffer cache hit ratio is 81% but no alerts are being generated.  What could be the reason for this problem？（）

多项选择题 YouworkasadatabaseadministratoratCertkiller.com.Inyourproductiondatabase，youobservethatusers’transactionsareconsumingalotofresourceandyouplantoimposeresourcerestrictionsbyusingResourceManager.ForwhichthreeresourcescanyouenableusagerestrictionsbyusingResourceManager？（）

单项选择题 View the Exhibit and examine the attributes of an undo tablespace.    In an OLTP system, the user SCOTT has started a query on a large table in the peak transactional hourthat performs bulk inserts. The query runs for more than 15 minutes and then SCOTT receives thefollowing error:  ORA-01555: snapshot too old  What could be the reason for this error（）