What an odd behavior I have come across when the the value is left for auto tune (on 10gR2), I have observed that the value goes to a higher value and it was causing optimize to favor FTS. 2009/1/25 Greg Rahn <greg@xxxxxxxxxxxxxxxxxx> > 10gR2 introduced Self-Tuning Multiblock Read Count > > http://download.oracle.com/docs/cd/B19306_01/server.102/b14214/chapter1.htm#FEATURENO05506 > > The basic premise is to allow large I/Os for MBRC operations w/o > giving the Optimizer too much preference to FTS. By default it uses a > MBRC of 8 for costing, or the system stats MBRC if it is set. > > On Sat, Jan 24, 2009 at 4:18 PM, Nuno Souto <dbvision@xxxxxxxxxxxx> wrote: > > 조동욱 wrote,on my timestamp of 25/01/2009 1:44 AM: > >> > >> This is called autotuned MBRC - literally, Oracle autotunes the value of > >> MBRC. > > > > > > I don't think this is the case in 10g. Maybe in 11, but not 10gr2. > > See this: > > > http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/initparams047.htm#CHDFAFHE > > There is a world of difference between a "default value" and "auto-tune". > > Nowhere in that doco is it said it is auto-tuned. I do recall reading > > something from Jonathan about it being so in 11g but I won't be using 11g > > anytime soon so I can't say for sure. > > -- > Regards, > Greg Rahn > http://structureddata.org > -- > //www.freelists.org/webpage/oracle-l > > > -- Best Regards, Syed Jaffar Hussain Oracle Certified Master (10g) http://www.oracle.com/technology/ocm/shussain.html Oracle ACE http://apex.oracle.com/pls/otn/f?p=19297:4:1579866181463918::NO:4:P4_ID:126 OCP 8i,9i & 10g DBA RAC Certified Expert Official Oracle RAC SIG Representative for Saudi Arabian region ( http://www.oracleracsig.org/) I blog at http://jaffardba.blogspot.com/ -------------------- "Winners don't do different things. They do things differently."