Performance issue, same range scan different execution times

Question

Oracle 11gR1, queries run within seconds of each other.
I have 2 queries that are logically the same. Even the explain plans are very similar, except the second one reports an index range scan doing much more work than the first. The table is an IOT with deal_bucket_id and datetime as PK (in that order).
TKPROF output below:
select count(*) from deal_bucket_detail where deal_bucket_id
in
(815
,     816
,     817
,     818
,     997)
and datetime between to_date('01-JUL-08','dd-MON-rr') and to_date('01-JAN-09','dd-MON-rr')
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      0.79       2.24       2936       3551          0           1
total        4      0.79       2.24       2936       3551          0           1
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 43 
Rows     Row Source Operation
      1  SORT AGGREGATE (cr=3551 pr=2936 pw=2936 time=0 us)
1430928   FILTER  (cr=3551 pr=2936 pw=2936 time=380920 us)
1430928    INLIST ITERATOR  (cr=3551 pr=2936 pw=2936 time=372057 us)
1430928     INDEX RANGE SCAN PK_DEAL_BUCKET_DETAIL (cr=3551 pr=2936 pw=2936 time=8782 us cost=1203 size=4069596 card=339133)(object id 14199)
Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                       2        0.00          0.00
  db file sequential read                      2936        0.02          1.49
  SQL*Net message from client                     2        0.00          0.00
select count(*) from deal_bucket_detail where deal_bucket_id
between 815 and 997
and datetime between to_date('01-JUL-08','dd-MON-rr') and to_date('01-JAN-09','dd-MON-rr')
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      3.70       8.86      29199      26986          0           1
total        4      3.70       8.86      29199      26986          0           1
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 43 
Rows     Row Source Operation
      1  SORT AGGREGATE (cr=26986 pr=29199 pw=29199 time=0 us)
1430928   FILTER  (cr=26986 pr=29199 pw=29199 time=6986078 us)
1430928    INDEX RANGE SCAN PK_DEAL_BUCKET_DETAIL (cr=26986 pr=29199 pw=29199 time=6977063 us cost=45208 size=5195748 card=432979)(object id 14199)
Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                       2        0.00          0.00
  db file sequential read                       219        0.04          0.08
  db file parallel read                          35        0.04          0.32
  db file scattered read                        211        0.10          5.02
  SQL*Net message from client                     2        0.00          0.00
********************************************************************************How can I work out why the second query is doing much more work than the first?
Edited by: SamB on Aug 5, 2009 6:09 PM

Answer 1

Both are doing an index range scan, however a different index range scan.
query 1: inlist iterator with <n> index range scan for 1 value, due to hard-coded values.
query 2: index range scan for all values, starting at the lowest, due to between.
Sybrand Bakker
Senior Oracle DBA