Yes, this is exactly my observation. I dont understand why Oracle did this ! They will never have this right, it seems. actually, i tried mread =3D 1.00000001 and sread =3D 1 -> cost =3D ~650 So basically, this makes using a very high value for mbrc (so that your mread > sread) almost mandatory in 10g, otherwise your FTS costs would use the old formula. On 5/17/05, Wolfgang Breitling <breitliw@xxxxxxxxxxxxx> wrote: > I found that Oracle does not use the new costing formula id mreadtm is > not larger than sreadtm. If sreadtm >=3D mreadtm it reverts back to the > the cost formula which uses the adjusted dfmrc value rather than the > system statistics mbrc value to estimate the cost of an FTS. That was > true for Oracle9i. I have not done extensive work with 10g and things > like that can change by patch release. >=20 > What you describe would be consistnt with that observation >=20 > mreadtm =3D sreadtm =3D 1 =3D=3D> cost(FTS) =3D #blocks/adjustedDFMRC =3D= ~1400 >=20 > mreadtm =3D 2, sreadtm =3D 1 =3D=3D> cost(fts) =3D #blocks/mbrc =3D ~1050 >=20 > mreadtm =3D 2, sreadtm =3D 3 =3D=3D> cost(FTS) =3D #blocks/adjustedDFMRC = =3D ~1400 >=20 > Christo Kutrovsky wrote: > > Hello, > > > > What i've discovered was something very strange. When I had both > > values to 1, my cost of a FTS would be ~1400. When I set multi to 2, > > the cost would go DOWN to ~1050. When I set it to 3, it would go back > > to ~1400. > > > > What I've discovered is that when SINGLE >=3D3D MULTI, then oracle uses= N > > * SINGLE for full table scans some formula independant from the value > > of MULTI. > > > > In a way, this makes sense, as it is not possible to have 1 read to be > > slower then MANY reads. But, this is an average value, thus it is > > quite possible (and likelly on many systems) that multi-block reads > > are faster then single block reads. > > > > However Oracle doesn't handle this case at all. I find this to be a > > severe limitation. What do you think ? > > >=20 > -- > Regards >=20 > Wolfgang Breitling > Centrex Consulting Corporation > www.centrexcc.com >=20 --=20 Christo Kutrovsky Database/System Administrator The Pythian Group -- //www.freelists.org/webpage/oracle-l