PROBLEM:

While starting the database, got below error.

SQL> startup
ORACLE instance started.

Total System Global Area 1.2549E+10 bytes
Fixed Size 12155024 bytes
Variable Size 6744442736 bytes
Database Buffers 5771362304 bytes
Redo Buffers 21397504 bytes
Database mounted.
ORA-38760: This database instance failed to turn on flashback database.

SOLUTION:

1. Check the alert log:

2. Check the flashback_mode of the database.

From the alert log, it is clear that flashback mode is enabled in the database and someone has mistakenly deleted flashback log physically.

So, to fix this issue, the only solution is to disable the flashback mode and open the database.