Well, almost. Here's what I get on 10.2.0.2.0 on AIX 5.3: SELECT LEAST(dcs/(ses*dbs), 1048576/dbs) "CALC", dfmbrc FROM ( SELECT a.value "DCS", 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' ); CALC DFMBRC ---------- ------- 68.2666667 66 At some point, I'll find out *why* this comes up this way. Sorry for coming in late on the thread...just catching up... Rich p.s. I know I didn't need to do the subquery. I did it that way for clarity. :) -----Original Message----- From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] Sent: Tuesday, December 19, 2006 2:52 PM To: Allen, Brandon Cc: oracle-l@xxxxxxxxxxxxx Subject: RE: db_file_multiblock_read_count causing full scans to takelonger? Brandon > Am I missing something, or isn't it best to just leave this parameter > unset (default) in 10.2, in which case Oracle will automatically adjust > it to the max io size of your OS? Mhmm... I don't like that for the simplest reason that the maximum is not the best value for performance! As the OP noticed... > Along with computing system stats on a typical workload so you have an > accurate mbrc, you should get the best of both worlds - accurate costing > and optimized sequential scans, right? In some situations, as I just wrote, no. > I have it unset on my 10.2 AIX 5.3 system and it has defaulted to 128 > with an 8k block size (1MB). Notice that there are some limits... According to my tests the value of db_file_multiblock_read_count is calculated with the following formula: min( DbCacheSize/(Sessions*DbBlockSize) , 1048576/DbBlockSize ) Regards, Chris -- //www.freelists.org/webpage/oracle-l -- //www.freelists.org/webpage/oracle-l