You should almost always index foreign keys. The only exception is when the matching unique or primary key is never updated or deleted. For more information take a look on Concurrency Control, Indexes, and Foreign Keys.
The sql file which will generate these indexes is created for you
Invalid object does not mean a problem sometimes. Sometimes will fix itself as is is executed or accessed. But if there is an error in USER_ERRORS table, you are in trouble then...
The sql file which will compile these objects is created for you.
| Object name | Type | Error | At line |
|---|---|---|---|
| COMMAND_PARAMETER_THRESHOLD | SYNONYM | No error. It will be fixed itself later. |