BITMAP index cost 10053 trace

  • From: "Barr, Stephen" <Stephen.Barr@xxxxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Tue, 24 May 2005 09:33:35 +0100

I'm trying to resolve how the CBO has come up with the cost of 9131 in the
10053 extract below.
 

If the formula is blevel + FF*leaf_blocks + FF*clustering_factor then the
cost comes out as 11 - how does it then jump to 9131? I'm assuming the cost
calculationfor bitmap indexes is very different?

 

 

***************************************

BASE STATISTICAL INFORMATION

***********************

Table stats    Table: AF_TEST   Alias: AF_TEST

  TOTAL ::  CDN: 962324  NBLKS:  21041  AVG_ROW_LEN:  100

-- Index stats

  INDEX NAME: BI_AF_TEST  COL#: 3 

    TOTAL ::  LVLS: 1   #LB: 14  #DK: 4  LB/K: 3  DB/K: 7  CLUF: 28

_OPTIMIZER_PERCENT_PARALLEL = 0

***************************************

SINGLE TABLE ACCESS PATH

Column:          C  Col#: 3      Table: AF_TEST   Alias: AF_TEST

    NDV: 4         NULLS: 0         DENS: 2.5000e-01

    NO HISTOGRAM: #BKT: 1 #VAL: 2

  TABLE: AF_TEST     ORIG CDN: 962324  ROUNDED CDN: 240581  CMPTD CDN:
240581

  Access path: tsc  Resc:  3195  Resp:  3195

  Access path: index (equal)

      Index: BI_AF_TEST

  TABLE: AF_TEST

      RSC_CPU: 0   RSC_IO: 4

  IX_SEL:  2.5000e-01  TB_SEL:  2.5000e-01

******** Bitmap access path accepted ********

Cost: 9131 Cost_io: 9131 Cost_cpu: 0.000000 Selectivity: 0.250000

Not believed to be index-only.

  BEST_CST: 9130.56  PATH: 20  Degree:  1




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