Optimizer sees index, but ignores it in access path decision process

From: Baumgartel, Paul <paul.baumgartel_at_credit-suisse.com>
Date: Fri, 28 Sep 2007 16:35:53 -0400
Message-ID: <21469B88E0EA11498818517F21033531596FCC@EPRI17P32001A.csfb.cs-group.com>

Oracle 10.2.0.3 on Solaris.

Table is range-partitioned on TCONTRACT_TRADE_DATE. Query is

select
min(TCONTRACT_TRADE_DATE)
from ods.ods_tcontract;

A single-column partitioned index (NUK_TCONTRACT_TRD_DT) exists on TCONTRACT_TRADE_DATE. Another (composite) index contains that column in position 2. Optimizer chooses the second index every time, even when a hint specifies the first one.

Optimizer (event 10053) trace shows awareness of the preferred index:

Index Stats::
  Index: NUK_TCONTRACT_BUSDATE_CUSIP Col#: 52 20     USING COMPOSITE STATS
    LVLS: 3 #LB: 713238 #DK: 384265 LB/K: 1.00 DB/K: 86.00 CLUF: 33203958.00
  Index: NUK_TCONTRACT_CUSIP Col#: 20 35 57 1     USING COMPOSITE STATS
    LVLS: 3 #LB: 955919 #DK: 112199564 LB/K: 1.00 DB/K: 1.00 CLUF: 43217198.00
  Index: NUK_TCONTRACT_TRD_DT Col#: 35
    USING COMPOSITE STATS
    LVLS: 3 #LB: 402118 #DK: 80 LB/K: 5026.00 DB/K: 52071.00 CLUF: 4165752.00

But, in next section of trace, in which access paths are considered, NUK_TCONTRACT_TRD_DT does not appear at all (see below). How can that be?

Paul Baumgartel
CREDIT SUISSE
Information Technology
Securities Processing Databases Americas One Madison Avenue
New York, NY 10010
USA
Phone 212.538.1143
paul.baumgartel_at_credit-suisse.com
www.credit-suisse.com

SINGLE TABLE ACCESS PATH
Table: ODS_TCONTRACT Alias: ODS_TCONTRACT Card: Original: 115569516 Rounded: 115569516 Computed: 115569516.00 Non Adjusted: 115569516.00 Access Path: TableScan
Cost: 7280284.59 Resp: 7280284.59 Degree: 0

      Cost_io: 7028169.00  Cost_cpu: 193577124940
      Resp_io: 7028169.00  Resp_cpu: 193577124940
  Access Path: index (index (FFS))

    Index: NUK_TCONTRACT_CUSIP
    resc_io: 489938.00 resc_cpu: 20271467483     ix_sel: 0.0000e+00 ix_sel_with_filters: 1   Access Path: index (FFS)
    Cost: 516339.64 Resp: 516339.64 Degree: 1

      Cost_io: 489938.00  Cost_cpu: 20271467483
      Resp_io: 489938.00  Resp_cpu: 20271467483
  Access Path: index (index (FFS))

    Index: UK_TCONTRACT_TICKER
    resc_io: 364308.00 resc_cpu: 18525881475     ix_sel: 0.0000e+00 ix_sel_with_filters: 1   Access Path: index (FFS)
    Cost: 388436.18 Resp: 388436.18 Degree: 1

      Cost_io: 364308.00  Cost_cpu: 18525881475
      Resp_io: 364308.00  Resp_cpu: 18525881475
  Access Path: index (FullScan)

    Index: NUK_TCONTRACT_CUSIP
    resc_io: 955985.00 resc_cpu: 29247902618     ix_sel: 1 ix_sel_with_filters: 1
    Cost: 864847.50 Resp: 864847.50 Degree: 1   Access Path: index (FullScan)
    Index: UK_TCONTRACT_TICKER
    resc_io: 710868.00 resc_cpu: 27502316610     ix_sel: 1 ix_sel_with_filters: 1
    Cost: 649617.80 Resp: 649617.80 Degree: 1

trying bitmap/domain indexes ****** Access Path: index (FullScan) Index: NUK_TCONTRACT_CUSIP resc_io: 955985.00 resc_cpu: 29247902618 ix_sel: 1 ix_sel_with_filters: 1 Cost: 864847.50 Resp: 864847.50 Degree: 0 Access Path: index (FullScan) Index: UK_TCONTRACT_TICKER resc_io: 710868.00 resc_cpu: 27502316610 ix_sel: 1 ix_sel_with_filters: 1 Cost: 649617.80 Resp: 649617.80 Degree: 0 ******** Begin index join costing ********
trying bitmap/domain indexes ****** Access Path: index (FullScan) Index: NUK_TCONTRACT_CUSIP resc_io: 955985.00 resc_cpu: 29247902618 ix_sel: 1 ix_sel_with_filters: 1 Cost: 864847.50 Resp: 864847.50 Degree: 0 Access Path: index (FullScan) Index: UK_TCONTRACT_TICKER resc_io: 710868.00 resc_cpu: 27502316610 ix_sel: 1 ix_sel_with_filters: 1 Cost: 649617.80 Resp: 649617.80 Degree: 0 Access Path: index (FullScan) Index: UK_TCONTRACT_TICKER resc_io: 710868.00 resc_cpu: 27502316610 ix_sel: 1 ix_sel_with_filters: 1 Cost: 649617.80 Resp: 649617.80 Degree: 0 ******** End index join costing ******** Best:: AccessPath: IndexFFS Index: UK_TCONTRACT_TICKER Cost: 388436.18 Degree: 1 Resp: 388436.18 Card: 115569516.00 Bytes: 0

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Received on Fri Sep 28 2007 - 15:35:53 CDT