I read from somewhere that issuing harmless DDL, for examples comment and grant statements could be a good way to invalidate a cursor. I have not got chance to verify it until today. I set up a test and find that the following method can invalidate a cursor.

- flush the shared_pool
- grant: i.e. grant select on t to system;
- comment: i.e. comment on table t is 'I am a table';
- dbms_stats.gather_table_stats (no_invalidate should not be true);

test case see: http://oracle-study-notes.blogspot.com/2009/04/how-to-invalidate-curosr.html