Dunno about the "one execution as an input to the next plan" but there is the SQL tuning sets, which is the basically the: "Mr CBO, I don't care how long as it takes, go and know yourself out finding a the best plan - get some more stats if you have to, do some dynamic sampling if needed, but make sure the information that comes out gives me a damn close to optimal plan" option...It would be really really cool if you use this facility on a standby database (then again, maybe you can? I've never really looked into it). Cheers Connor --- Cary Millsap <cary.millsap@xxxxxxxxxx> wrote: > People seem to cloud the concepts of the pre-run estimated runtime of a > query (officially its "estimated cost") and the post-run operationally > measured runtime of a query. The problem with a CBO is that before a = > query > runs, it can only estimate a cost using a model. The model is not = > perfect > (although it's usually more perfect than the input--db and schema > statistics--than DBAs feed the model). > > Now, AFTER a query runs, it's easy to see whether the estimated cost was = > any > good or not. But who wants the CBO to run a query six ways before = > choosing a > plan?! > > If I recall correctly, 10g has some operational memory built into the = > CBO > that allows the CBO to use operationally measured response times for a = > given > query as an input into computing the next plan. > > Mr. Sharman, care to comment? (And by the way, will I be seeing you in = > M=E5l=F8v > next week?) > > > Cary Millsap > Hotsos Enterprises, Ltd. > http://www.hotsos.com > * Nullius in verba * > > Upcoming events: > - Performance Diagnosis 101: 2/23 Houston, 3/16 Salt Lake City > - SQL Optimization 101: 2/7 Dallas > - Hotsos Symposium 2005: March 6-10 Dallas > - Visit www.hotsos.com for schedule details... > > > -----Original Message----- > From: oracle-l-bounce@xxxxxxxxxxxxx = > [mailto:oracle-l-bounce@xxxxxxxxxxxxx] > On Behalf Of Jaffar_DBA > Sent: Thursday, January 13, 2005 3:01 AM > To: premj@xxxxxxxxxxxxxx > Cc: oracle-l@xxxxxxxxxxxxx > Subject: Re: Which plan is better - what COST really means ? > > I definately agree with about what toms is saying. I had expereince > where higher COST queries much father than lower COST queries in the > CBO. Taking consideration of response time would be more better than > COST of the query. > > > > On 13 Jan 2005 08:57:11 -0000, Prem Khanna J <premj@xxxxxxxxxxxxxx> = > wrote: > > Friends, > > when i have got two plans , how do i decide > > which one is the best ? > >=20 > > just read in asktom , that COST of a plan , > > does not have any correspondence with response > > time of a query. > >=20 > > i.e.,a query with higher COST than another > > can be faster. > >=20 > > if so , what in the execution plan does help > > me to decide about a good (faster) plan ? > >=20 > > unless i execute it , can't i know it ? > > is that the only way !!! > >=20 > > Can someone throw light on this ? > > The environment is oracle 9.2.0.4/AIX5.2L. > >=20 > > Thanks in advance. > >=20 > > Regards, > > Prem. > > -- > > //www.freelists.org/webpage/oracle-l > >=20 > > > --=20 > Best Regards, > Jaffar, OCP DBA > Banque Saudi Fransi > Saudi Arabia > -- > //www.freelists.org/webpage/oracle-l > > -- > //www.freelists.org/webpage/oracle-l > ===== Connor McDonald Co-author: "Mastering Oracle PL/SQL - Practical Solutions" ISBN: 1590592174 web: http://www.oracledba.co.uk web: http://www.oaktable.net email: connor_mcdonald@xxxxxxxxx Coming Soon! "Oracle Insight - Tales of the OakTable" "GIVE a man a fish and he will eat for a day. But TEACH him how to fish, and...he will sit in a boat and drink beer all day" ------------------------------------------------------------ __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com -- //www.freelists.org/webpage/oracle-l