Flush shared_pool & buffer_cache

 Manually flush  buffer cache & shared pool cache without bouncing the database:-

For Standalone Databases 

alter system flush buffer_cache;

alter system flush shared_pool;

For RAC Databases 

alter system flush buffer_cache global;

alter system flush shared_pool global;

------- only do in case of system performance issue or maintenance issue ----

Flush shared pool meaning flushing cached execution plan and sql Quries from memory.

Flush buffer cache meaning flushing cached data from memory.

Database restart which internally flush both