How does changing the system time affect Oracle (for example, when daylight saving time is switched to standard time, and vice versa)?
Internally, Oracle works with System Change Numbers (SCN) and not with real time stamps. Therefore, a system time change does not have any impact on Oracle, which means that – from a database point of view – you do not need to stop Oracle to carry out a time change. However, you should bear the following restrictions in mind: If a time interval occurs twice as the result of a time change, the system cannot determine at which of the two identical points of time it should stop when you perform a point-in-time recovery with an end time in the duplicate interval. However, in this scenario, you can carry out the recovery with a target SCN instead of a target time. If you carry out an RMAN backup during a time change, so that the start time of the backup is after the end time, subsequent “list backup” commands may terminate with errors such as ORA-01455 because the RMAN function cannot handle this constellation. You can solve this problem by recreating the control files that contain the back
