Shared pool / buffer cache flush

Command

-- Clear the SQL plan/cursor cache:
ALTER SYSTEM FLUSH SHARED_POOL;

-- Clear the buffer cache (usually only for test/benchmark):
ALTER SYSTEM FLUSH BUFFER_CACHE;

What it does

Flushing the shared pool evicts all cached SQL/PL-SQL and dictionary information from memory; flushing the buffer cache evicts all data blocks.

When to use it

To test plan problems, after a one-off large operation, or for a consistent benchmark start.

Caution

Be careful IN PRODUCTION! After a flush all SQL is re-parsed (hard parse storm) and blocks are read from disk; a serious temporary performance drop follows.