help getting cost down in plan table?
- From: bbulsara23@xxxxxxxxxxx
- Date: 28 Feb 2006 09:17:03 -0800
Hello everyone. I think I need some guidance to get my query to use an
index. When I look at a plan table for a query I see "TABLE ACCESS
FULL" with bytes 186M.
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost
(%CPU)| Time |
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1172K| 72M| 2775
(5)| 00:00:34 |
|* 1 | HASH JOIN | | 1172K| 72M| 2775
(5)| 00:00:34 |
| 2 | TABLE ACCESS FULL| TBL_FVALJOIN | 3 | 78 | 3
(0)| 00:00:01 |
| 3 | TABLE ACCESS FULL| TBL_FVAL | 5007K| 186M| 2725
(3)| 00:00:33 |
-----------------------------------------------------------------------------------
The query performance is okay but I expected to see some index use
rather than "TABLE ACCESS FULL". Alternatively I don't understand what
the plan table is telling me so I would appreciate you telling too if
this is the case.
Table tbl_fval contains about 5million rows and table tbl_fvaljoin
contains a lot less (only contains 3 rows in the sample data below but
in our production system is contains a lot more). We are using Oracle
10.1.0.4 on Windows 2000 SP2. I have included the ddl to create the
tables, indexes etc, and the SQL to use the plan table. Am I missing
something to get the cost down (and reduce the 186M above)?
Thank you
Barry
create table tbl_fval(b_id number,b_fid number,b_fval number);
--
--and now insert lots and lots of data
--
create index idx_fval_id
on tbl_fval(b_id);
create index idx_fval_fid
on tbl_fval(b_fid);
create index idx_fval_fval
on tbl_fval(b_fval);
create table tbl_fvaljoin(b_fid number,b_fval number);
insert into tbl_fvaljoin values(100,10);
insert into tbl_fvaljoin values(101,12);
insert into tbl_fvaljoin values(103,150);
create index idx_fvaljoin_fid
on tbl_fvaljoin(b_fid);
create index idx_fvaljoin_fval
on tbl_fvaljoin(b_fval);
explain plan for
select t1.b_id
from tbl_fval t1,tbl_fvaljoin t2
where t1.b_fid=t2.b_fid
and t1.b_fval=t2.b_fval;
--
--this is the plan table shown at the start of the message
select plan_table_output from table(dbms_xplan.display);
.
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