Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.
One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.
If you aren't licensed for it use the statspack.
(Oracle 10g and later) AWR reports, see:
http://docs.oracle.com/cd/B19306_01/server.102/b14211/autostat.htm#PFGRF027
(to start a snashot for the AWR report you need:
with execute privilege on package dbms_workload_repository.
execute dbms_workload_repository.c
parameter (default) is ‘TYPICAL’ - can be ‘ALL’)
For earlier Oracle versions, or without performance pack, use statspack
http://docs.oracle.com/cd/B19306_01/server.102/b14211/autostat.htm#PFGRF027
Other potentially useful resources:
http://www.oraperf.com/ (Upload your utlbstat/utlestat or STATSPACK file and get the performance recommendations on your screen)
http://ondataperf.com/ (provides ORACLE database performance analysis using your STATSPACK or AWR METRICS that is generated from your database. All that is required are simple text files that are uploaded to the OnDataperf performance analysis engine.)
http://community.dbapool.com/dbanalyzer.php
Also: Don't forget that although some queries may be costly they might not be run frequently, so you also need to consider frequency of use.
{edit, added the following}
and: regarding the AWR you might find this helpful:
http://prezi.com/glqm9zemzhup/interpreting-awr-report-straight-to-the-goal/