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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Anyway to optimize the optimizer
Hi Waleed,
> Oracle does not substitute the value of C2 in the expression.
this could be achieved with two nested views using an expression e.g. (c2 - 10) in the inner view and referencing this new column in query of the outer. But this is apparently not the desired solution.
I'd see a possible solution of this problem in a combination of partitioned views and partitioned tables (Jonathan mentioned it in his book, if I recall it correctly).
Something like this:
create or replace view v3
as
select c1,c2,c3
from test_p_v
where c2 >= 210 and c2 <= 309 and c1 >= 200
union all
select c1,c2,c3
from test_p_v
where c2 between 110 and 209 and c1 between 100 and 209
union all
select c1,c2,c3
from test_p_v
where c2 < 110 and c1 <= 99
;
So each UNION ALL subquery access at most 2 partitions. Note that this is only simplified solution to demonstrate the principle.
select * from v3
where c2 = 150;
Explaining this simple query you get following execution plan (10.1.0.2.0):
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
Time | Pstart| Pstop |
| 0 | SELECT STATEMENT | | 483 | 14490 | 342 (21)|
00:00:01 | | |
| 1 | VIEW | V3 | 483 | 14490 | 342 (21)|
00:00:01 | | |
| 2 | UNION-ALL PARTITION | | | | |
| | |
|* 3 | FILTER | | | | |
| | |
| 4 | PARTITION RANGE SINGLE | | 1 | 27 | 7622 (6)|
00:00:07 | 3 | 3 | |* 5 | TABLE ACCESS FULL | TEST_P_V | 1 | 27 | 7622 (6)| 00:00:07 | 3 | 3 |
| 6 | PARTITION RANGE ITERATOR| | 60 | 1740 | 18148 (21)|
00:00:17 | 2 | 3 | |* 7 | TABLE ACCESS FULL | TEST_P_V | 60 | 1740 | 18148 (21)| 00:00:17 | 2 | 3 | |* 8 | FILTER | | | | |
| | |
| 9 | PARTITION RANGE SINGLE | | 1 | 26 | 7193 (6)|
00:00:07 | 1 | 1 | |* 10 | TABLE ACCESS FULL | TEST_P_V | 1 | 26 | 7193 (6)| 00:00:07 | 1 | 1 | -------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
3 - filter(210<=150)
5 - filter("C2"=150 AND "C2">=210 AND "C2"<=309)
7 - filter("C2"=150 AND "C2">=110 AND "C2"<=209 AND "C1"<=209)
8 - filter(110>150)
10 - filter("C2"=150 AND "C2"<110 AND "C1"<=99)
A good question is if the obviously false filter (e.g. 210<=150) does prohibit the underlying table access. Some simple tests shows that this is OK and at most one union branch is executed if a equi-predicate on c2 is defined. See below.
You may wont to verify some more complex queries on this view, usage of bind variables etc.
HTH Jaromir D.B. Nemec
1 select count(*) from v3
2* where c2 = 550
SQL> / Elapsed: 00:00:00.01
2) test partition pruning, only the 1st partition should be accessed -- > OK, consistent gets corresponds to blocks of the partition
1 select count(*) from v3
2* where c2 = 109
SQL> / Elapsed: 00:00:04.32
Statistics
8 recursive calls
0 db block gets
18778 consistent gets
18758 physical reads
0 redo size
392 bytes sent via SQL*Net to client
512 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> set autotrace off
SQL> select partition_name,
2 blocks
3 from user_tab_partitions a
4 where
5 table_name = upper('test_p_v');
PARTITION_NAME BLOCKS ------------------------------ ---------- P1 18765 P2 19785 P3 19913
Elapsed: 00:00:03.34
-- http://www.freelists.org/webpage/oracle-lReceived on Thu Mar 03 2005 - 17:32:12 CST
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