About remove the statement from cache

Question

Hi Guys,
I am tuning a statement and it is slower in biginning and then faster after been cached. So I couldn't get reproduce the slower case. Is there any way to remove the statement from cache so that I can continue to test. Thanks.

Answer 1

As Billy has already answered, the first time you run the query, it's probably doing far more physical I/O than logical and this can make it run slower than on subsequent executions. To remove the data from the buffer cache, this has also been answered already. In 10g you can flush the buffer cache and in earlier versions you could "offline-online" a tablespace for tables in your query.
If you are trying to invalidate an execution plan in the shared pool (i.e. not the data blocks), you can do one of the following:
a) flush the shared pool using ALTER SYSTEM
b) invalid your plan with dbms_stats.gather_table_stats for one of the tables in the query with NO_INVALIDATE=>FALSE
c) invalidate your plan with dbms_stats.export/import_table_stats for one of the tables in the query (i.e. don't change the stats, just invalidate the plans with NO_INVALIDATE=>FALSE)
d) invalidate your plan with a "no-change" ALTER TABLE for one of the tables in your query. e.g. ALTER TABLE x LOGGING (if it is already logging).
Note that options b) to d) will affect potentially more cursors than just the one you are testing (i.e. any that reference the table you use).
Regards