In the last couple of days I have noticed several alerts were created with following message Metrics "Database Time Spent Waiting (%)" is at n for event class "Commit". The n value is varying between 32 and 65. Default Threshold is at 30. I haven't done any modifications to the db. Can someone please help me in finding out the reason for these alerts. Thanks in advance.
Have a look at the OracleŽ Enterprise Manager Oracle Database and Database-Related Metric Reference Manual, which you can get if you download the Grid Control documentation from OTN.
There is no 'correct' value for the metric, it depends entirely on your environment. You may find the default settings do not apply to your application. Have you experienced issues with your application? If not you may want to adjust the thresholds.