— compile public synonym that are invalid
Select ‘alter public synonym ‘||object_name||’ compile;’
From dba_objects
Where status <> ‘VALID’
And owner = ‘PUBLIC’
And object_type = ‘SYNONYM’;

— drop public synonym that are invalid
Select ‘drop  public synonym ‘||object_name||’;’
From dba_objects
Where status <> ‘VALID’
And owner = ‘PUBLIC’
And object_type = ‘SYNONYM’;