Flushing Database Buffer Cache

Question

I am trying out variants of a SQL statement in an attempt to tune it. Each variant involves joins across a different combination of tables, although some tables are common across all variants. In order to be able to do a valid comparison of the TKPROF outputs for the variants, I believe I need to flush the database buffer cache between variants so that the db block gets, consistent gets and physical reads parameters are true for each variant. By doing this, data retrieved for one variant is not already in the buffer cache for the next variant, thus not influencing the above parameters for the next variant.
Is it possible to flush the buffer cache? The shared pool can be flushed with the ALTER SYSTEM FLUSH SHARED_POOL command. I've searched but have not been able to find an equivalent for the buffer cache. The NOCACHE option to the ALTER TABLE command only pushes retrieved data to the LRU list in the buffer cache, but does not remove it from the buffer cache.
I'm hoping to be able to do this without bouncing the database between variants. It is a development instance, and I have it to myself after hours.

Answer 1

Hi,
I never tried this before, but if you want make a test you can try corrupt the block ID's returned by one of these queries below:
Try corrupt the ID of the block containing the segment header
select dbms_rowid.rowid_block_number(rowid) from hr.regions;
Try corrupt one of the blocks returned by the query, which shows the ID of the block where each row is located
select s.owner,t.ts#,s.header_file,s.header_block
from
v$tablespace t, dba_segments s
where
s.segment_name='REGIONS' and
owner='HR' and
t.name = s.tablespace_name;Legatti
Cheers