Slow Query Using index. Fast with full table Scan.

Question

Hi;
(Thanks for the links)
Here's my question correctly formated.
The query:
SELECT count(1)
from ehgeoconstru  ec
where ec.TYPE='BAR' 
AND ( ec.birthDate <= TO_DATE('2009-10-06 11:52:12', 'YYYY-MM-DD HH24:MI:SS') )  
and deathdate is null
and substr(ec.strgfd, 1, length('[CIMText')) <> '[CIMText'Runs on 32 seconds!
Same query, but with one extra where clause:
SELECT count(1)
from ehgeoconstru  ec
where ec.TYPE='BAR' 
and  ( (ec.contextVersion = 'REALWORLD')     --- ADDED HERE
AND ( ec.birthDate <= TO_DATE('2009-10-06 11:52:12', 'YYYY-MM-DD HH24:MI:SS') ) ) 
and deathdate is null
and substr(ec.strgfd, 1, length('[CIMText')) <> '[CIMText'This runs in 400 seconds.
It should return data from one table, given the conditions.
The version of the database is Oracle9i Release 9.2.0.7.0
These are the parameters relevant to the optimizer:
SQL> show parameter optimizer
NAME                                 TYPE        VALUE
optimizer_dynamic_sampling           integer     1
optimizer_features_enable            string      9.2.0
optimizer_index_caching              integer     99
optimizer_index_cost_adj             integer     10
optimizer_max_permutations           integer     2000
optimizer_mode                       string      CHOOSE
SQL> Here is the output of EXPLAIN PLAN for the first fast query:
PLAN_TABLE_OUTPUT
| Id  | Operation                     |  Name               | Rows  | Bytes | Cost  |
|   0 | SELECT STATEMENT     |                         |           |       |       |
|   1 |  SORT AGGREGATE       |                         |           |       |       |
|*  2 |   TABLE ACCESS FULL   | EHCONS            |       |       |       |
Predicate Information (identified by operation id):
PLAN_TABLE_OUTPUT
   2 - filter(SUBSTR("EC"."strgfd",1,8)<>'[CIMText' AND "EC"."DEATHDATE"
              IS NULL AND "EC"."BIRTHDATE"<=TO_DATE('2009-10-06 11:52:12', 'yyyy
-mm-dd
              hh24:mi:ss') AND "EC"."TYPE"='BAR')
Note: rule based optimizationHere is the output of EXPLAIN PLAN for the slow query:
PLAN_TABLE_OUTPUT
   |       |
|   1 |  SORT AGGREGATE              |                             |       |
   |       |
|*  2 |   TABLE ACCESS BY INDEX ROWID| ehgeoconstru      |       |
   |       |
|*  3 |    INDEX RANGE SCAN          | ehgeoconstru_VSN  |       |
   |       |
PLAN_TABLE_OUTPUT
Predicate Information (identified by operation id):
2 - filter(SUBSTR("EC"."strgfd",1,8)<>'[CIMText' AND "EC"."DEATHDATE" IS
NULL AND "EC"."TYPE"='BAR')
PLAN_TABLE_OUTPUT
   3 - access("EC"."CONTEXTVERSION"='REALWORLD' AND "EC"."BIRTHDATE"<=TO_DATE('2
009-10-06
              11:52:12', 'yyyy-mm-dd hh24:mi:ss'))
       filter("EC"."BIRTHDATE"<=TO_DATE('2009-10-06 11:52:12', 'yyyy-mm-dd hh24:
mi:ss'))
Note: rule based optimizationThe TKPROF output for this slow statement is:
TKPROF: Release 9.2.0.7.0 - Production on Tue Nov 17 14:46:32 2009
Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.
Trace file: gen_ora_3120.trc
Sort options: prsela  exeela  fchela 
count    = number of times OCI procedure was executed
cpu      = cpu time in seconds executing
elapsed  = elapsed time in seconds executing
disk     = number of physical reads of buffers from disk
query    = number of buffers gotten for consistent read
current  = number of buffers gotten in current mode (usually for update)
rows     = number of rows processed by the fetch or execute call
SELECT count(1)
from ehgeoconstru  ec
where ec.TYPE='BAR'
and  ( (ec.contextVersion = 'REALWORLD')
AND ( ec.birthDate <= TO_DATE('2009-10-06 11:52:12', 'YYYY-MM-DD HH24:MI:SS') ) )
and deathdate is null
and substr(ec.strgfd, 1, length('[CIMText')) <> '[CIMText'
call     count       cpu    elapsed       disk      query    current        rows
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        2      0.00     538.12     162221    1355323          0           1
total        4      0.00     538.12     162221    1355323          0           1
Misses in library cache during parse: 0
Optimizer goal: CHOOSE
Parsing user id: 153 
Rows     Row Source Operation
      1  SORT AGGREGATE
  27747   TABLE ACCESS BY INDEX ROWID OBJ#(73959)
2134955    INDEX RANGE SCAN OBJ#(73962) (object id 73962)
alter session set sql_trace=true
call     count       cpu    elapsed       disk      query    current        rows
Parse        0      0.00       0.00          0          0          0           0
Execute      1      0.00       0.02          0          0          0           0
Fetch        0      0.00       0.00          0          0          0           0
total        1      0.00       0.02          0          0          0           0
Misses in library cache during parse: 0
Misses in library cache during execute: 1
Optimizer goal: CHOOSE
Parsing user id: 153 
OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS
call     count       cpu    elapsed       disk      query    current        rows
Parse        1      0.00       0.00          0          0          0           0
Execute      2      0.00       0.02          0          0          0           0
Fetch        2      0.00     538.12     162221    1355323          0           1
total        5      0.00     538.15     162221    1355323          0           1
Misses in library cache during parse: 0
Misses in library cache during execute: 1
OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS
call     count       cpu    elapsed       disk      query    current        rows
Parse        0      0.00       0.00          0          0          0           0
Execute      0      0.00       0.00          0          0          0           0
Fetch        0      0.00       0.00          0          0          0           0
total        0      0.00       0.00          0          0          0           0
Misses in library cache during parse: 0
    2  user  SQL statements in session.
    0  internal SQL statements in session.
    2  SQL statements in session.
Trace file: gen_ora_3120.trc
Trace file compatibility: 9.02.00
Sort options: prsela  exeela  fchela 
       2  sessions in tracefile.
       2  user  SQL statements in trace file.
       0  internal SQL statements in trace file.
       2  SQL statements in trace file.
       2  unique SQL statements in trace file.
      94  lines in trace file.Edited by: PauloSMO on 17/Nov/2009 4:21
Edited by: PauloSMO on 17/Nov/2009 7:07
Edited by: PauloSMO on 17/Nov/2009 7:38 - Changed title to be more correct.

Answer 1

Although your optimizer_mode is choose, it appears that there are no statistics gathered on ehgeoconstru. The lack of cost estimate and estimated row counts from each step of the plan, and the "Note: rule based optimization" at the end of both plans would tend to confirm this.
Optimizer_mode choose means that if statistics are gathered then it will use the CBO, but if no statistics are present in any of the tables in the query, then the Rule Based Optimizer will be used. The RBO tends to be index happy at the best of times. I'm guessing that the index ehgeoconstru_VSN has contextversion as the leading column and also includes birthdate.
You can either gather statistics on the table (if all of the other tables have statistics) using dbms_stats.gather_table_stats, or hint the query to use a full scan instead of the index. Another alternative would be to apply a function or operation against the contextversion to preclude the use of the index. something like this:
SELECT COUNT(*)
FROM ehgeoconstru  ec
WHERE ec.type='BAR' and 
      ec.contextVersion||'' = 'REALWORLD'
      ec.birthDate <= TO_DATE('2009-10-06 11:52:12', 'YYYY-MM-DD HH24:MI:SS') and
      deathdate is null and
      SUBSTR(ec.strgfd, 1, LENGTH('[CIMText')) <> '[CIMText'or perhaps UPPER(ec.contextVersion) if that would not change the rows returned.
John