RE: db_file_multiblock_read_count causing full scans to takelonger?

  • To: <Rich.Jesse@xxxxxx>, <oracle-l@xxxxxxxxxxxxx>, "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
  • Date: Wed, 20 Dec 2006 14:21:18 -0700

Also, I'm not clear on whether it uses the value of the SESSIONS
parameter, or rather a dynamic count, e.g. "select count(*) from
v$session", in order to adjust the value of dbfmbrc dynamically.  Chris,
can you please elaborate?

Thanks

-----Original Message-----
From: Allen, Brandon 
Sent: Wednesday, December 20, 2006 2:14 PM
To: 'Rich.Jesse@xxxxxx'; oracle-l@xxxxxxxxxxxxx
Subject: RE: db_file_multiblock_read_count causing full scans to
takelonger?

Do you have sga_target set?  If so, then db_cache_size is just a
minimum.  What are the results if you run this instead:

SELECT LEAST(dcs/(ses*dbs), 1048576/dbs) "CALC", dfmbrc FROM (
        SELECT b.value "SES", c.value "DBS", d.value "DFMBRC"
        FROM v$parameter a, v$parameter b, v$parameter c, v$parameter d
        WHERE a.name = 'db_cache_size'
                AND b.name = 'sessions'
                AND c.name = 'db_block_size'
                AND d.name = 'db_file_multiblock_read_count'),
        (SELECT bytes "DCS" from v$sgastat where name = 'buffer_cache');


Thanks,
Brandon


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