Kinerja fungsi analitik mungkin bergantung pada urutan kolom indeks. Mengubah indeks dari (ACCTNUM,DEPT_NUM) ke (DEPT_NUM,ACCTNUM) dapat menurunkan biaya dan menghilangkan kebutuhan untuk tablespace sementara.
partition by COL_2 order by COL_1 => INDEX FAST FULL SCAN|WINDOW SORT PUSHED RANK
partition by COL_1 order by COL_2 => INDEX FULL SCAN|WINDOW NOSORT
INDEX FAST FULL SCAN menggunakan IO multi-blok yang lebih cepat tetapi juga memerlukan pengurutan data dan kemungkinan tablespace sementara untuk area pengurutan.
INDEX FULL SCAN menggunakan IO blok tunggal yang lebih lambat tetapi mengembalikan data secara berurutan dan menghindari penyortiran.
Contoh skema dan data
--drop table mytable;
create table mytable(dept_num number not null, acctnum number not null
,a number, b number, c number, d number, e number);
insert into mytable
select 1 dept_num, 1 acctnum, 0,0,0,0,0 from dual union all
select 1 dept_num, 2 acctnum, 0,0,0,0,0 from dual union all
select 1 dept_num, 3 acctnum, 0,0,0,0,0 from dual union all
select 2 dept_num, 1 acctnum, 0,0,0,0,0 from dual union all
select 2 dept_num, 2 acctnum, 0,0,0,0,0 from dual union all
select 3 dept_num, 1 acctnum, 0,0,0,0,0 from dual;
--Create 600K similar rows.
insert into mytable
select dept_num + rownumber*3, acctnum, a,b,c,d,e
from mytable
cross join (select level rownumber from dual connect by level <= 100000);
begin
dbms_stats.gather_table_stats(user, 'mytable');
end;
/
(ACCTNUM,DEPT_NUM) =JENDELA URUTKAN PERINGKAT URUT
create index mytable_idx on mytable(acctnum, dept_num);
explain plan for
select dept_num, acctnum from
(
select dept_num, acctnum
,row_number() over (partition by dept_num order by acctnum) as row_identifier
from mytable
)
where row_identifier between 1 and 10;
select * from table(dbms_xplan.display);
Plan hash value: 952182109
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 600K| 22M| | 1625 (3)| 00:00:23 |
|* 1 | VIEW | | 600K| 22M| | 1625 (3)| 00:00:23 |
|* 2 | WINDOW SORT PUSHED RANK| | 600K| 4687K| 9424K| 1625 (3)| 00:00:23 |
| 3 | INDEX FAST FULL SCAN | MYTABLE_IDX | 600K| 4687K| | 239 (3)| 00:00:04 |
------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("ROW_IDENTIFIER">=1 AND "ROW_IDENTIFIER"<=10)
2 - filter(ROW_NUMBER() OVER ( PARTITION BY "DEPT_NUM" ORDER BY "ACCTNUM")<=10)
(DEPT_NUM,ACCTNUM) =JENDELA NOSORT
drop index mytable_idx;
create index mytable_idx on mytable(dept_num, acctnum);
explain plan for
select dept_num, acctnum from
(
select dept_num, acctnum
,row_number() over (partition by dept_num order by acctnum) as row_identifier
from mytable
)
where row_identifier between 1 and 10;
select * from table(dbms_xplan.display);
Plan hash value: 1773829932
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 600K| 22M| 792 (2)| 00:00:12 |
|* 1 | VIEW | | 600K| 22M| 792 (2)| 00:00:12 |
|* 2 | WINDOW NOSORT | | 600K| 4687K| 792 (2)| 00:00:12 |
| 3 | INDEX FULL SCAN| MYTABLE_IDX | 600K| 4687K| 792 (2)| 00:00:12 |
---------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("ROW_IDENTIFIER">=1 AND "ROW_IDENTIFIER"<=10)
2 - filter(ROW_NUMBER() OVER ( PARTITION BY "DEPT_NUM" ORDER BY
"ACCTNUM")<=10)
